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1 SYNTHESIS AND PHOTOPHYSICAL CHARACTERIZATION OF CONJUGATED NONLINEAR ABSORBING ORGANOMETALLIC PLATINUM COMPLEXES By ABIGAIL HOBBS SHELTON A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 2011
2 2011 Abigail Hobbs Shelton
3 To Phillip, my sweet heart and sunshine
4 ACKNOWLEDGMENTS I must first acknowledge my advisor, Dr. Kirk Schanze His support, advice, and knowledge have provided me the opportunity to work in an environment where I could tinker with instrumentation and explore physical inorganic chemistry. I would also like to thank my committee members, Dr. Stephen Hage n Dr. Lisa McElwee White, Dr. Michael Scott, and Dr. Dan Talham, for their time and support. Large portions of my projects could not have been completed without the NMR help of Dr. Ion Ghiviriga, the X Ray crystallographic guidance of Dr Khalil Abboud and his team, the instrumentation help of Dr. Ben Smith, and the creative skills of Joe Shalosky, Brian Smith, and Todd Prox i n the machine shop and Steve Miles and Larry Hartley in the electronic shop. I would also like to thank Dr. Schan ze and the United States Air Force for project funding during my graduate career. Additionally, I am grateful for funding provided by the CLAS dissertation fellowship. My family has provided a stable and supportive network for me. Though I travelled a bit far from home to attend graduate school, they have constantly been here for me with encouragement, advice, and faith. I thank them for their moral support and prayers. I am eternally grateful for Phillip, for his unceasing love and support. I am al so grateful for the many friendships I made while here for Seth and Molly Dumbris, Sarah Stefans, Brad House, Julia and Jonathan Keller, David Snead and Stephanie Elder for keeping the friendships going even when we all became stressed with work. Speci al thanks go to Jenny Johns for literally helping me survive the last several months, and for tolerating the many adventures I subjected her to. I also thank the McElwee White group members, for adopting me as an honorary member and letting me invade thei r space. I am also grateful for Ann Moore for working her magic
5 I am much indebted to the numerous past and present Schanze group researchers who helped pave the way for me. I would like to thank Julia Keller, Emine Demir, and Anand Parthasarthy for the many, many conversations on synthetic options and additionally for Randi Price, Rett Vella, Dongping Xie, and Yongjun Li for also letting me make messes and take up their space. I am especially grateful for my lab mates who selflessly gave of their time to introduce me to the laboratory and teach me instruments, specificall y Richard Farley, John Peak, and Kye Young Kim for teaching me the wonders that are the laser lab. Special thanks go to Randi Price for not only teaching me instruments, but designing and fabricating instruments and software programs that I needed! Addition ally, thanks go to Luisa Brokmann and Barbara Dettlaff, who synthesized portions of the chromophores used in many of my projects
6 TABLE OF CONTENTS page ACKNOWLEDGMENTS ................................ ................................ ................................ .. 4 LIST OF TABLES ................................ ................................ ................................ ............ 9 LIST OF FIGURES ................................ ................................ ................................ ........ 10 ABSTRACT ................................ ................................ ................................ ................... 13 CHAPTER 1 INTRODUCTION ................................ ................................ ................................ .... 15 Basic Principles of Photophysics ................................ ................................ ............ 15 Linear Absorption of Light ................................ ................................ ................. 16 Emission of Light ................................ ................................ .............................. 19 Nonlinear Abso rption ................................ ................................ ........................ 23 Two photon absorption ................................ ................................ .............. 23 Excited state absorption ................................ ................................ ............. 24 Combined two photon absorption and excited state absorption ................. 24 Design Paradigms ................................ ................................ ............................ 26 Platinum Acetylide Materials ................................ ................................ ................... 28 Synthesis of Platinum Acetylides ................................ ................................ ...... 29 Photophysics ................................ ................................ ................................ .... 30 Linear Optical Properties ................................ ................................ .................. 33 Nonlinear Optical Properties ................................ ................................ ............. 34 Phenylethynyl based platinum acetylides ................................ .................. 34 Platinum acetylides with heteroatomic ligands ................................ ........... 37 Platinum acetylides with TPA chromophores ................................ ............. 39 Objective of Present Study ................................ ................................ ..................... 41 2 OPEN APERTURE Z SCAN APPERATUS AND RESPONSE ............................... 44 Background ................................ ................................ ................................ ............. 44 Techniques ................................ ................................ ................................ ............. 45 Open Aperture Z Scan Apparatus ................................ ................................ .......... 49 Hardware ................................ ................................ ................................ .......... 49 Software and Data Co llection ................................ ................................ ........... 51 NLA Test Series ................................ ................................ ................................ ...... 53 Platinum and Iridium Cyclometalated Complexes ................................ ............ 53 Design ................................ ................................ ................................ ........ 54 Characterization ................................ ................................ ......................... 55 Platinum End Capped Phenylene Ethynylene Oligomers ................................ 58 Introduction ................................ ................................ ................................ 58 Characterization ................................ ................................ ......................... 59
7 Results and Discussion ................................ ................................ ........................... 60 NLA Response ................................ ................................ ................................ 60 Limitations of C urrent System ................................ ................................ .......... 64 Experimental ................................ ................................ ................................ ........... 66 Materials and Instrumentation ................................ ................................ .......... 66 Synthesis ................................ ................................ ................................ .......... 68 3 STEREOCHEMICAL EFFECTS OF PLATINUM ACETYLIDES ............................. 72 Background ................................ ................................ ................................ ............. 72 Synthesis ................................ ................................ ................................ ................ 78 Results and Discussion ................................ ................................ ........................... 79 NMR Characterization ................................ ................................ ...................... 79 1 H NMR characterization. ................................ ................................ ........... 79 31 P NMR characterization. ................................ ................................ ......... 80 X Ray Crystallography ................................ ................................ ...................... 81 cis PE2 ................................ ................................ ................................ ...... 81 cis BTF ................................ ................................ ................................ ....... 85 Ground State Absorpt ion Spectroscopy ................................ ........................... 89 Steady State Photoluminescence Spectroscopy ................................ .............. 92 Transient Absorption Spectroscopy and Triplet Excited State Lifetimes .......... 96 Nonlinear Absorption ................................ ................................ ........................ 98 Summary ................................ ................................ ................................ .............. 100 Experimental ................................ ................................ ................................ ......... 103 Instrumentation ................................ ................................ ............................... 103 Materials and Synthesis ................................ ................................ ................. 106 4 PLATINUM ACETYLIDE MONOMERS AND POLYMERS ................................ ... 119 Background ................................ ................................ ................................ ........... 119 Synthesis ................................ ................................ ................................ .............. 122 Platinum Acetylides ................................ ................................ ........................ 122 Polymerization ................................ ................................ ................................ 123 Film Preparation ................................ ................................ ............................. 125 Results an d Discussion ................................ ................................ ......................... 125 Ground State Absorption Spectroscopy ................................ ......................... 127 Steady State Photoluminescence Spectroscopy ................................ ............ 129 Triplet Triplet Transient Absorption ................................ ................................ 132 Nonlinear Absorption Response ................................ ................................ ..... 136 Summary ................................ ................................ ................................ .............. 139 Experimental ................................ ................................ ................................ ......... 141 Instrumentation ................................ ................................ ............................... 141 Materials and Synthesis ................................ ................................ ................. 144
8 APPENDIX A USER MANUAL FOR OPEN APERTURE Z SCAN APPARATUS ....................... 154 B X RAY CRYSTAL STRUCTURE PARAMETERS ................................ ................. 162 LIST OF REFERENCES ................................ ................................ ............................. 172 BIOGRAPHICAL SKETCH ................................ ................................ .......................... 182
9 LIST OF TABLES Table page 2 1 Linear optical properties of Pt(II) and Ir(III) complexes in THF. .......................... 56 2 2 Summary of photophysical properties of Ph n Pt 2 series in THF. .......................... 59 3 1 31 P NMR signals of the cis and trans plat inum acetylide complexes .................. 81 3 2 Selected bond distances () and bond angles (degrees) observed in cis PE2 and trans PE2. ................................ ................................ ................................ .... 82 3 3 Selected bond distances () observed in trans BTF and cis BTF. ..................... 87 3 4 Selected bond angles (degrees) observed in trans BTF and c is BTF. ............... 87 3 5 One photon photophysical properties of the cis and trans platinum acetylide series in THF. ................................ ................................ ................................ ..... 92 3 6 Triplet excited state properties of cis and trans platinum acetylide series in THF. ................................ ................................ ................................ ................... 95 4 1 Polymer molecular weights and PDIs ................................ ............................... 126 4 2 Summary of photophysical properties of the polymer series in THF ................. 129
10 LIST OF FIGURES Figure page 1 1 Franck Condon principle. ................................ ................................ ................... 18 1 2 Electrons of ground and excited states. ................................ .............................. 19 1 3 Jablonski diagram illustrating radiative and nonradiative transitions. ................. 20 1 4 A simplified Jablonski diagram of a molecule that exhibits NLA via TPA and triplet triplet ESA. ................................ ................................ ................................ 26 1 5 Cartoons illustrating the design principles behind organometallic TPA/ESA complexes. ................................ ................................ ................................ ......... 27 1 6 Structure units of a platinum acetylide oli gomer and polymer ........................... 28 1 7 Synthetic routes for generation of platinum acetylides ................................ ....... 29 1 8 Ligand field splitting diagram for metal d orbitals in a square planar complex. ... 30 1 9 Potential energy surface for the d d excited state in a square pla nar d 8 complex, formed by population of the d x2 y2 orbital. ................................ ............. 31 1 10 Potential energy surface and ligand field splitting diagram o f square planar Pt(II) complexes with ligand excited states and metal d 8 states. ........................ 32 1 11 Structure of trans PE2. ................................ ................................ ....................... 35 1 12 Butadiyne platinum acetylide oligomers structures. ................................ ............ 36 1 13 Platinum acetylide polymers examined by Wilson ................................ .............. 38 1 14 Thiophene containing platinum acetylides, as examined by Glimsdal. ............... 38 1 15 Platinum acetylides with TPA chromophores ................................ ..................... 39 1 16 DPAF endcapped di platinum acetylides with various core aryl units. ................ 40 2 1 Linear and nonlinear absorption response as a function of transmittance versus input energy. ................................ ................................ ........................... 45 2 2 Components of the z scan apparatus ................................ ................................ 46 2 3 Z scan plots of C60 in toluene at an excitation wavelength of 1064 nm ............. 48 2 4 Nanosecond open aperture z scan apparatus instrument schematic. ................ 50
11 2 5 Structur es of the Pt(II) and Ir(III) cyclometalated complexes and chromophore precursors. ................................ ................................ ................... 54 2 6 T 1 T n absorption spectra of Pt(bt)acac, Ir(bt) 2 acac, Pt(AF240)acac, and Ir(AF240) 2 acac ................................ ................................ ................................ ... 57 2 7 Structures of the Ph n Pt 2 s eries, where n = 1, 2, 4, and 9 ................................ .... 58 2 8 Normalized transient absorption spectra of the Ph n Pt 2 series. ........................... 60 2 9 Nanosecond NLA response of 1 mM cyclometalated Pt(II) and Ir(III) complexes in THF after 628 nm excitation. ................................ ........................ 61 2 10 NLA response dependency on solution concentration of T2 in benzene u nder 600 nm excitation. ................................ ................................ .............................. 63 2 11 NLA response via ns z scan measurements of 1 mM Ph n Pt 2 solution in THF under 600 nm excitation. ................................ ................................ .................... 64 2 12 Formation of the dimer precursor and subsequent reaction to form the target Pt(II) cyclometalated complex. ................................ ................................ ............ 69 3 1 Stilbene containing platinum acetylides ................................ .............................. 73 3 2 Diimine platinum acetylide complexes ................................ ................................ 75 3 3 Cis platinum acetylides examined by Castellano. ................................ ............... 75 3 4 Structures of the target cis and trans platinum acetylide complexes .................. 77 3 5 Synthetic pathway for generation of the three trans platinum acetylide complexes. ................................ ................................ ................................ ......... 78 3 6 Synthetic pathway for generation of the three cis platinum acetylide complexes. ................................ ................................ ................................ ......... 79 3 7 Molecular structure with atomic numbering scheme for cis PE2. ....................... 82 3 8 Molecular structure with atomic numbering scheme for trans PE2. .................... 82 3 9 Vinylidene tautomer ................................ ................................ ............................ 85 3 10 Molecular structure with atomic numbering scheme for cis BTF. ....................... 86 3 11 Molecular structure with atomic numbering scheme for trans BTF. .................... 86 3 12 Ground state absorption of the cis and trans platinum acetylide series in THF .. 90
12 3 13 Emission spectra of the cis and trans platinum acetylide series via excitation at the ground state absorption maxima ................................ ............................. 93 3 14 Triplet triplet transient absorption spectra of the cis and trans complexes ........ 96 3 15 NLA response of 1 mM platinum acetylides.. ................................ ................... 100 3 16 Synthetic scheme for formation of PE2 chromophore. ................................ ..... 107 3 17 Synthetic scheme for formation of DPAF chromophore ................................ .... 108 3 18 Synthetic scheme for formation of BTF chromophore ................................ ...... 111 4 1 Platinum acetylide oligomers and polymers. ................................ .................... 120 4 2 Chemical structures investigated by Wong and Malmstrom ............................. 121 4 3 Platinum acetylide monomers prior to modification of the aniline group. .......... 122 4 4 Synthetic sche me for 4 ethynylaniline and platinum acetylide precursor. ......... 123 4 5 Formation of Pt PE2, Pt DPAF, and Pt BTF platinum acetylide monomers. .... 123 4 6 General modification and polymerization of platinum acetylide monomers. ..... 124 4 7 Ground state absorption spectra of the monomers and polymers in THF, and the polymer films by chromophore type. ................................ ........................... 128 4 8 Ground state absorption spectra and fluorescence emission in THF of the PE2 DPAF, and BTF chromophores and ethynylaniline ligand. ....................... 128 4 9 Photoluminescence spectra of monomer and polymer series. ......................... 130 4 10 Luminescence of doctor bladed polymer films under 365 nm excitation. ......... 131 4 11 Transient absorption spectra of the monomers and polymers .......................... 132 4 12 Transient absorption of Pt BTF, acrylamide Pt BTF, and Pt BTF(PMMA) soln .. 133 4 13 Film transient absorption instrumentation. ................................ ........................ 134 4 14 Transient absorption spectra of polymer films ................................ ................ 135 4 15 NLA response of 1 mM polymer solutions via excitation at 6 00 nm .................. 136 4 16 Nonlinear response of concentration matched polymer monoliths ................... 138 4 17 Nonlinear response at 600 nm excitation of Pt BTF(PMMA) monoliths of varying percent incorporation. ................................ ................................ .......... 139
13 Abstract of Dissertation Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy SYNTHESIS AND PHOTOPHYSICAL CHARACTERIZATION OF CONJUGATED NONLINEAR ABSORBING ORGANOMETALLIC PLATINUM COMPLEXES By Abigail Hobbs Shelton May 2011 Chair: Kirk S. Schanze Major: Chemistry M y research focuses on the design, synthesis, and photophysica l characterization of organometallic platinum and iridium complexes. By incorporation of heavy metals into conjugated systems of efficient two photon absorbing chromophores t hese new families of complexes are designed to feature strong nonlinear absorption with respect to nanosecond laser pulses. First, in order to partially characterize the nonlinear absorption properties of these materials, an open aperture z scan appar atus was constructed that integrates a nanosecond laser and a series of opti cs A series of cyclometal ating platinum and iridium complexes was generated to characterize both the apparatus and the photophysical properties of the complexes. An additional series of platinum end capped phenylene ethynylene oligomers was examined to further characterize the nonlinear absorption response upon exten sion of the conjugat ed linker between the plat inum end caps. Observed in both series is the attenuation of transmittance as the laser fluence is increased, indicating that the designed compl exes are able to undergo absorption via nonlinear pathways.
14 Second, a series of platinum acetylides was generated to quantify the effect of stereochemistry on the magnitude of the excited state properties and nonlinear absorption response. Two geometries, cis and trans were examined to investigate the extent of conjuga tion through the platinum metal center with the three known two photon absorbing chromophores. The results of this study indicate that complexes in either geometry can exhibit strong triplet triplet transient absorption and nanosecond nonlinear absorption response. Third, a series wa s synthesized that incorporated platinum acetylid e monomer s with known strong two photon absorbing chromophores into polymer backbones. The photophysical properties of the polymer s in solution and on film were compared to the monomers The polymer solution s display ed strong triplet tr iplet transient absorption and longer triplet excited state lifetimes. T he polymer films exhibit ed stronger phosphorescence than observed in the solution form, indicating less lo ss of energy through triplet nonradiative decay pathways and suggesting stronger nonlinear absorption response in the film. The results of this work provide insight regarding the introduction of platinum acetylides into polymers for optical applications.
15 CHAPTER 1 INTRODUCTION Organometallic conjugated materials that exhibit nonlinear absorption (NLA) properties have attracted much attention over recent years. 1 3 Specifically, synthetic and photophysical studies have sought to improve how these materials are generated and to better understand the structure property relationships and the unique absorption and emission features of the materials. 4 7 The focus of much of this organometallic work has centered on platinum acetylide complexes, with specific interest in well defined polymers and small oligomers. 8 9 To better underst and these materials and their properties, this introductory chapter has been divided into two sections. The first section present s the concepts involved in the interaction of light with matter. The second section is an overview of platinum acetylide mate rials, including synthetic processes, photophysical expectations, and current applications. The photophysical foundations will be used to characterize the discussed platinum acetylides. Basic Principles of Photophysics Examination of the world on an atomic level has occurred almost simultaneously with the examination and understanding of light. 10 11 With the study of light a controversy regarding the nature of the light was born Sir Isaac Newton is credited wit h laying the foundation of spectroscopy with his studies of light in the 1660s, followed by his corpuscular theory that light consisted of small particles. 12 13 Conversely, light was theorized to behave as a wave by Huygens in 1678 ; this theory was further supported by the diffraction patterns observed within the double slit experiments of Young in the early 1800s. 14 Despite these works, the wave theory of light was largely overshadowed
16 developed the theory of electromagnetism in 1860. This theory, which linked the fields of electricity, magnetism, and optics, defined an electromagnetic wave that should transmit at the speed of light, 3 x 10 8 m s 1 However, also accepted at this time was the thought that light emission was the result of energy changes in atomic and molecular electrons, which behaved as particles. These views were both drastically altered in the early 20 th theoretical calculations on blackbody ex periments, which postulated that the dis tribution of blackbody energy i s not continuous but rather, i s limited to specific, finite values. quantization to explain the phot oelectric effect, and developed his theory of light wave particle duality, which posited ; de Broglie further expanded this theory to encompass all matter to behave as waves. His work, relating wavele ngth and momentum, was confirmed for electrons by the electron diffraction experiments of Thomson and Germer. 13 Soon after, Schr dinger developed the mathematical equations that describe the wave functions of electr ons in atomic structures. This development of quantum theory has defined how the structure of atoms and molecules are currently described ultimately characterizing the nature of light as having wave particle duality which was largely understood by studying the interaction of electromagnetic radiation with matter or electromagneti c radiation emitted from matter 14 15 Linear Absorption of Light The interaction of light with matter can provide insight into molecula r electronic structure. When an atom or molecule absorbs light, a valence electron is promoted to a lev el of higher energy. For this to occur, since the electronic energy levels are discrete
17 rather than continuous, the light frequency must match the resonant frequency of the molecule. The relationship between the photon energy and its frequency is given b y Eq uation 1 1: E = h (1 1) where E is the energy of the photon, h 34 J s), is the frequency c is the speed of light, and is the wavelength. The difference in the energy levels of the molecule is equal to the energy of the photon absorbed. The relationship between molecular absorbance versus concentration for a specific wavelength is expressed by the Beer Lambert Law, Equa tion 1 2: A = log (I/I o ) = log T = bc (1 2) where A is the absorbance, I o is the intensity of initial incident light, I is the final intensity of light, T is the transmittance, is the molar absorptivity of the molecule (L mol 1. cm 1 ), b is the pathlength of the light (cm) and c is the concentration of the absorbing species (mol L 1 ). The molar absorptivity is a measure of the probability that the electronic transition will occur; it is proportional to the transition dipole moment betwee n the two states. The Beer Lambert Law indicates a linear relationship between the concentration of an absorbing species and its resulting absorbance. By definition of Equation 1 1, and since the electronic energy levels of molecules are discrete absorpt ion spectra should appear as sharp lines. However, t he absorption often appears as broad bands. The interpretation for this phenomenon is given by the observation that electronic excitation is usually accompanied by vibrational transitions. This is desc ribed by the Franck Condon principle, which states that electronic transitions, such as the absorption of light, occur very rapidly (10 15 s) compared to
18 equilibration of nuclei (10 13 s). 16 17 This indicates th at the adjustment of the nuclear geometry takes place after the electronic transitions have occurred To illustrate this occurrence, the ground and excited electronic states of a molecule are represented by potential energy curves as a function of their r elative equilibrium geometry, Figure 1 1. Vertical transitions occur from the lowest vibrational level of the ground state to vibrational levels of the excited electronic state. The molecule then relaxes to the lowest vibrational level of the excited ele ctronic state. The ground state absorption spectrum of a complex will thus appear as a series of vibrational bands. However, the vibrational bands are not always well resolved, especially in polar solvent solutions, due to solvation interactions with th e excited state molecules. As such, ground state absorption spectra, though depicting the vibrational structure characteristic of the upper excited state, often appear as broad bands. Figure 1 1. Franck Condon principle. The figure was adopted from At kins. 10
19 Emission of Light Per the Pauli exclusion principle, paired electrons in a single atomic or molecular orbital are of opposite spin The absorpti on of light causes the excitation of an electron from a low energy orbital to a higher energy orbital electronic state. The spin of the electron does not change upon excitation due to the spin restrictions effect by quantum mechanics. As such, the ground state and initial excited state are called singlet states, S 0 and S 1 respectively, and exist as molecular electronic states where all electrons spins are pairs. Following absorpt ion of a photon, t he excited molecule typically relaxes to the lowest vibrational level of the singlet excited state via thermal or collisional relaxation without changing spin states. However, the excited electron can spin flip under certain conditions This resulting state is termed a triplet state, T 1 and is characterized by a molecule with electrons with parallel spins, as depicted in Figure 1 2. Th e nonradiative transition from a singlet state to a triplet state (or vice versa) is known as intersy stem crossing (ISC). While this process is forbidden by quantum rules, it can occur readily when the vibrational levels of the excited singlet and excited triplet states are of the same energy. The rate of ISC is Figure 1 2. Electrons of ground and excited states.
20 greatly increased when strong spin orbit coupling (SOC) is present. Most organic mo ieties for example, would exhibit ISC at a slow rate and would thus generate a low triplet excited state yield. However SOC occurs when the spin angular momentum and orbital angular momentum can interact such that the total orbital momentum is conserved, as is more often observed within heavy atom containing molecules such as in organometallic and inorganic molecules. ISC of organometallic complexes typi cally occurs on a time scale of 10 8 to 10 3 s. 18 A molecule can follow many pathways to return to the ground state once absorption and population of an excited electronic state have occurred. The absorption and relaxation processes of a molecule can be depicted in a Jablonski diagram, as shown in Figure 1 3. The radiative decay from the singlet excited state to the singlet ground state is termed fluorescence (F); as a quantum mechanically allo wed transition from states of the same spin, fluorescence is a quick process (10 8 s 1 ). Because the emissive transition occurs after vibrational relaxation to the lowest excited state, Figure 1 3. Jablonski diagram illustrating radiative and non radiati ve transitions. S 0 = Singlet ground state; S 1 = Singlet excited state; T 1 = Triplet excited state; A = Absorption; IC = Internal conversion; F = Fluorescence ; ISC = Intersystem crossing; P = Phosphorescence.
21 fluorescence typically occurs at a lower freque ncy than the incident radiation. The difference between the absorption and emission peak maxima is termed the Stokes shift. This shift can be the result of solvent effects, excited state reactions, complex formation, or energy transfer in addition to the rmalization to the lowest energy level. 19 Radiative e mission of a ph oton from the triplet excited state is termed phosphorescence (P) ; as a forbidden transition, phosphorescence occurs much slower than fluorescence on the order of 10 5 10 2 s 1 Note that the triplet excited state is lower in energy than the singlet excited state. Consequently, if a molecule crosses into the triplet state, it can vibrational excited triplet state. The radiation of energy from the trip let excited state to the single t ground state is spin forbidden. However, the SOC that aided in ISC to the triplet excited state breaks the selection rule, allowing the slow phosphorescence transition to occur. 20 Phosphorescence occur s at a lower frequency than the incident radiation and fluorescent emission be cause the emissive transition occurs after vibrational energy has been lost in both the singlet and triplet excited states. An additional type of radiative decay is delay fluorescence, which involves populating the singlet excited state through an i ndirect route. This can include such pathways as a thermally assisted T 1 S 1 process or triplet triplet annihilation. Triplet triplet annihilation occurs when two molecules in the triplet state collide to create a singlet excited state and a singlet gro und state molecule T* + T* S* + S, where T* and S* are the triplet and singlet excited states, respectively, and S is the singlet ground state This pathway allows the repopulation of the singlet excited state after ISC to the triplet excited state has occurred.
22 Nonradi ative processes also occur during excited state rela xa tion ; these transitions do not involve the absorption or emission of photons but result in the loss of energy through collisions or the dissipation of heat 15 Such transitions only occur when the potential energy curves of two electronic states are of the same energy. When a radiationless transition occurs between states of the same spin, the process is referred to as internal conversion (IC) A radiationless transition between states of differe nt spin is referred to as ISC. Two additional properties of the excited state are the p hotoluminescence quantum yield, and the excited state lifetime, Th e efficiency of a particular process is defined as the quant um yield: for fluorescence or phosphorescence, the quantum yield is the ratio of the number of photons emitted to the number of photons absorbed. 19 Substances with large quantum yields (approaching unity) exhibit the brightest emissions. The excited state lifetime is the amount of time available for the excited state to int eract with its environment before undergoing a radiative or nonradi ative decay process. Thus the lifetime is equal to the inverse sum of all decay p rocesses from the excited state. A general quantum yield expression is given by Equation 1 3 15 : e = e k e (1 3) where e is the emission quantum yield, e* is the formation of the emitting state, k e is the emission rate constant, and is the lifetime. The lifetime is defined by Equation 1 4: = 1/(k e + k i ) (1 4) where k i is the sum of all deactivating rate constants.
23 Nonlinear Absorption The field of nonlinear optics was initiated soon after the demonstration of the first laser; irradiation of a quartz crystal with a ruby laser produced the second harmonic generat ed by the crystal. 21 Since then, many s econd and third order processes have been examined. The nonlinear phenomena relevant to the research presented will be two photon absorption (TPA) and excited state absorption ( E SA), as will be discussed in the following sections. Two photon a bsorption TPA is the simultaneous and instantaneous absorption by a chromophore or complex of two photons from one state to a higher energy electronic state. The energy difference between the lower and upper states is equal to the sum of the energies of the two pho tons. This NLA process is advantageous for multiple reasons. Primarily, simultaneous TPA has an instantaneous response time and the quadratic dependency on light intensity causes the photophysical or photochemical processes to occur in a small focal region. Further, the material is often protected from photodegradation effects through the use of two lower energy photons instead of the one higher energy photon utilized in linear one photon abs orption pathways. In much the same way, t wo photon absorbe rs are advantageous for many applications because the high energy photophysical properties are often activated by near infrared low energy excitation, which can result in greater penetration than can be provided by visible or UV light. Chromophores that e xhibit such TPA and the ensuing fundamental properties and application possibilities have been extensively studied and reviewed in recent years. 2 22 25 Often examined are dyes, benzene derivatives, naphthalenes, indoles,
24 xanthenes, and porphyrins. These TPA moieties are frequently l ong conjugat ed systems with stron g donor and/or acceptor groups incorporated into the system. Excited state a bsorption Excited state absorption ( E SA) is an additional pathway fo r NLA to occur. This process is exhibited when light is absorbed in an excited electronic state rather than in the electronic ground state. E SA can occur through the absorption of either a singlet or a triplet excited state ; however, within metal organic complexes, the absorbing exci ted state is usually the triplet state This is largely due to short lived singlet excited states and efficient population of the triplet excited state through ISC facilitated by the heavy atom effect. Combined t w o photon absorption and excited state a b sorption Recent developments in enhanced NLA have focused on the combination of TPA and triplet E SA within transition metal organometallic systems. Platinum, and other h eavy t ransition metals, can mix the singlet and triplet excited states via spin orbit coupling, resulting in rapid and efficient s inglet to triplet intersystem crossing (ISC) and population of the triplet excited state manifold. Additionally, incorporation of heavy metals into conjugated organic moieties can elicit large effects on the re dox, electronic, and optical properties of the molecule; the careful combination of metal centers and organic structures can allow for systematical vari ation of these properties. The strength of a material to undergo NLA is typically characterized by the s ize of the relevant cross section. NLA via TPA from the singlet ground state to the singlet 2 2 includes contributions from triplet excited state absorption, and is thu s typically much
25 2 2 upon the pulse length and excitation conditions of the NLA experiment. Changes in the measured cross sections can be observed by variation of the p ulse frequency lower pulse frequencies are more purely TPA processes. The molecular cross sections are usually quoted in units of Goeppert Mayer (GM), honoring its discoverer, Nobel laureate Maria Goeppert Mayer, where 1 GM = 10 50 cm 4 s photon 1 This unit is the result of the effective photon capture area in cm 2 for two photons and the time required for the photons to arrive in order to act together. The cross sections can be determined by several techniques, to include nonlinear transmission methods (i.e. open aperture z scan), and luminescence measurements (i.e. two photon induced luminescence or relative fluorescence). Intrinsic TPA chromophores exhibit NLA in the short time domain (fs ps) and become less efficient in longer pulse duratio n s. Opportunely, triplet E S A processes operate via long pulse attenuation (e.g., ns or longer). The triplet E SA also benefits from the combination with a TPA chromophore the TPA pathway is efficient at instantaneously producing the T 1 excited state with in an organometallic framework with high ISC rates T he two photon absorption response strength is wavelength dependent. Moderately strong TPA response is often observed near the double of the one photon absorption (O PA ) ex O PA ), which gradua lly decreases toward longer wavelengths. When successfully paired, the incorporation of TPA and E SA processes with heavy transition metals can provide strong NLA in a broad range of pulse durations, from the femtosecond to microsecond time domain 26 29 O rganometallic
26 comp lexes are thus designed that incorporate the TPA chromophore into a framework that will further promote longer nonlinear time response via E SA. 27 36 Design Paradigms TPA chromophores with large cross sections typically exhibit several features that make them useful in optical applications. L ong, fully conjugated ligands that display strong donor or acceptor properties are typical. I ncreases in the molecular two photon cross section have been observed with extension of conjugation length, enhancement in donor or acceptor strength, introduction of more polarizable double bonds or of more planar chromophores, and variation of c onjug ation bridge identity. 30 31 Specifically within organometallic complexes this enhanced nonlinear process uses a TPA chromophore to populate the singlet excited state, at which time the metal center can promote the single triplet intersystem crossing (ISC) transition to quickly and efficiently populate the triplet excited state. If the chromophore has a large triplet t riplet cross section, further NLA via E SA within the triplet manifold i s possible, as shown in Figure 1 4. 4 24 37 Since such E SA involves long lived triplet excited states and triplet triple t absorptions the overall nonlinear response is often in the ns s time regime. 38 Figure 1 4. A simplified Jablonski diagram of a molecule that exhibits NLA via TPA and triplet triplet ESA.
27 Additionally, NLA via organometallic TPA /ESA complexes are often achieve d through one of a few well defined structural des igns, as ill ustrated in Figure 1 5 One design strategy is to incorporate chromophores with large changes in polarization upon excitation. 39 Such polarization changes can occur through donor conjugated linker acceptor (D A), D D, or A A structural motifs The platinum acts as a coordination ce nter, as observed in Figure 1 5 A and B, with a lin ear two dimensional or three dimensional scaffold, or as an end cap functionalization unit, as seen in Figure 1 5 C. These motifs employ similar design parameters as would enhance TPA but additionally depend upon the incorporation of strong donor and acc eptor groups. Figure 1 5 Cartoons illustrating the design principles behind organometallic TPA/ESA complexes. Desired are complexes that show large TPA cross sections, efficient singlet to triplet intersystem crossing, and large triplet triplet ES A cross sections while minimi zing the one photon absorption cross sections from the ground state SS NLA via this pathway has no need for ground state absorption, i.e., the material is transparent at low fluence. Additionally, limiting response to short ( TPA ) and long ( E SA) pulses gives rise, in principle, to broad temporal timescale limiting materials. Both experimental and
28 theoretical investigations of platinum acetylide TPA materials have been examined, leading to the development of a variety of appli cations, including (but not limited to) optical power limiting devices 36 40 3 D microfabrication, 41 42 high efficiency electroluminescent devices, 43 photodynamic therapy, 44 two photon micro scopy, 45 and optical data storage. 46 47 These applications depend on linear visible transparency, fast NLA response time, reasonable processibility, and a high damage threshold of the material. 48 50 Platinum Acetylide Materials Platinum acetylide complexes have generated much attention in recent years due to their linear and nonlinear optical properties These materials are typically air stable, conjugated organometallic complexes. The general structure of platinum acetylide monomers and polymers is given in Figure 1 6 Figure 1 6 S tructure units o f a platinum acetylide oligomer (left) and polymer (right) Platinum acetylides are square planar by nature of the platinum (II) metal center T hough organic moieties have been incorporated onto the platinum metal center in the cis conformation most platinum acetylid e s ha ve the general formula trans Pt(PR 3 ) 2 (C 2 where t he R groups are typically non chrom ophoric alkyl groups that contribute to the crystallinity and solubility of the complex, s uch as methyl, ethyl, or butyl groups group is a conjugated aromatic group that dominates the photophysica l properties ; common are phenyl, 51 thienyl, 52 and fluorenyl 25 groups Incorporation of the platinum transition metal into organic moieties can change the
29 redox, electronic, and opti cal properties of the molecule the careful combination of metal centers and organic structures can allow for systematic variation and tuning of these properties. Synthesis of Platinum Acetylides There are a number of synthetic methods for generating platinum acetylide complexes, dendrimers and polymers. The first series of platinum acetylides was prepared by a copper(I) halide catalyzed dehydrohalogenation reaction between dichlorobis(trialkylphosphine) platinum and terminal alkynes in alkylamine, as developed by Hagihara S onogashira an d co workers 53 54 The reactions proceeded under mild conditions, generating dialkynyl Pt(II) complexes, w ith yields above 80%, Figure 1 7 route A Efficien t synthesis of monoalkynyl platinum(II) complexes can be achieved by reaction of cis Pt(PPh 3 ) 2 Cl 2 and acetylene without cupr ous halides, route B Figure 1 7 55 56 The starting Pt(PR 3 ) 2 Cl 2 can be in either the cis or trans geometry, since an isomerization to the trans form will occur in the presence of tertiary amine. The two isomers can be distinguished by 31 P NMR by observation of the coupling between the phosphorus and an NMR active isotope; the magnitude of the coupling constant is dependent on the ligands present on the platinum metal center. 57 61 Figure 1 7 Synthetic routes for generation of platinum acetylides where route A is reacted in diethylamine in the presence of CuI, 54 and where route B is reacted in refluxing diethylamine. 55 56
30 Several variations on these synthetic protocols have been explor ed. Efficient one pot synthesis of trans mono or dialkynyl platinum(II) complexes can be obtained by heating PtCl 2 alkyne, and trialkylphosphine in tetrahydrofuran and triethylamin e. 6 2 Organo tin alkynylating agents ha ve been reported by Lewis and co workers to make dialkynyl platinum complexes via a transmetallation reaction of platinum halides. 63 64 Oligomers and polymers can also be synthesized by dehydrohalogenation reaction between equivalent amounts of Pt(PBu 3 ) 2 Cl 2 and terminal a lkynes in the presence of CuI and amine. 53 65 Selection of orthogonal protecting groups that can be indi vidually deprotected, and step wise coupling has allowe d for the generation of structurally well defined platinum acetylide oligomers. 56 66 67 Photophysics A ligand field splitting diagram reveals why d 8 metal ions, such as Pt(II), form square planar complexes Figure 1 8 By convention, the z axis is perpendicular to the plane of the complex and the M L bonds l ie along the x and y axes. In the presence of Figure 1 8. Ligand field splitting diagram for metal d orbitals in a square planar complex.
31 strong field ligands, d 8 metal ions have a thermodynamic preference for the square planar geometry due to the substantial stabilization of three of the occupied orbitals while pushing a single unoccupied orbi tal to a high er energy 68 For Pt(II), the ligand field is almost always sufficiently large to ensure a square planar geometry; however, the exact ordering of the lower energy levels is dependent upon the ligand set. 68 The d 8 electronic configuration of Pt(II) within the square planar geometry leads to the d xy orbital acting as the highest occupied molecular orbital (HOMO), while the lowest unoccupied molecular orbital (LUMO) originates from the d x2 y2 orbital. The d x2 y2 orbital is strongly antibonding; population of this orbital via absorption of light will result in significant distortion upon formation of the excited state. 68 This phenomenon can be observed within the non emissive cis a nd trans Pt(PEt 3 ) 2 Cl 2 complexes, as examined by Demas and co workers, 69 and visualized with a d d ex cited state potential energy surface wher e the energy minimum is largely displaced f rom the ground state, Figure 1 9 68 The thermally accessible isoenergetic crossing point leads to deactivation of the excited state via nonr adiative internal conversion or ISC to the ground state rather than Figure 1 9 Potential energy surface for the d d excited state in a square planar d 8 complex, formed by population of the d x2 y2 orbital.
32 luminescent pathways. As such, platinum acetylides with simple inorganic ligands, such as cis and trans Pt(PEt 3 ) 2 Cl 2 are less likely to be strongly luminescent. However, the excited state properties within platinum complexes can be modified by the introduction o f conjugated organic ligands, resulting in mixing of the metal d orbitals with the ligand system via metal to ligand charge transfer (MLCT, d *) or ligand centered (LC, or n *) transitions As such, the MLCT or LC states can l ie at lower energies than the d x2 y2 orbital Figure 1 10 The HOMO orbital in such complexes would still originate from the d xy orbital, but the LUMO could or i ginate from the orbital of the ligand. Such complexes are often emissive. Figure 1 10 Potential energy surface (left) and ligand field splitting diagram (right) of square planar Pt(II) complexes with ligand excited states and metal d 8 states. Additionally, the introduction of strong field ligands onto the platinum metal center can elicit effects on the splitting and arrangement of the d metal orbitals in relation to the p orbitals. The use of ligands such as hydrides and acetylides can result in higher d orbital splitting such that the energy of the 6p z orbital is lower than the 5d x2 y2 orbital. A combined experimental and theoretical investigation of the electronic excitations in
33 nickel, palladium, and platinum phenylene ethynylene complexes suggests that the HOMO orbital of platinum acetylides originate from the hybridization of the d x z and d yz platinum orbitals with the system of the alkynyl ligands, whereas the LUMO orbital arises from the overlap of the 6p z metal orbitals with the orbitals of the ligand. Taken together, thes e ligand field splitting diagrams and resulting potential energy diagrams can show how the most emissive platinum complexes are typically those where the state is separated from the d x2 y2 orbital, either as a result of the emissive state being low in e nergy or the d d transition being at an inaccessible energ y 68 70 Linear Optical Properties The metal d orbital arrangement and resulting square planar geometry are responsible for many of the features that characteriz e the absorption, luminescence, and other excited state transitions of Pt(II) complexes. Much of the initial characterization of platinum acetylides was carried out by Lewis, Friend, and co workers. 64 71 77 Platinum acetylides typically display ground state absorption in the UV incorporation of the platinum meta l into the conjugated organic framework induces phosphorescence, usually observed in the 500 650 nm region, while fluorescence is characteristically exhibited near the ground state absorption bands with relatively small Stokes shifts. Though luminescence of some platinum acetylide complexes must be measured at low temperatures, many exhibit strong phosphorescence at room temperature, suggesting that the rate of ISC between the singlet and triplet manifolds is efficient and rapid. Variation of conjugation length, ligand choice, metal placement, and overall complex design can generate changes in the observed absorption and emission
34 properties, allowing for systematic modification and tuning of the photophysical properties of the platinum acetylide. Addition ally, the highly tunable functional properties of platinum acetylide polymers have been demonstrated via the variatio n of low band gap organic spacer and the resulting photovoltaic properties. 34 78 In general, the emission spectra of platinum acetylides show significant vibronic structur e. As suggested above, the structured p rogression is common for MLCT or excited s tates Conversely, d d transitions are usually sharp and structureless. The phosphorescent lifetimes of platinum acetylides also tend to fall between lifetimes that ar e common for 3 and 3 MLCT, indicating again that hybridization of the orbitals is occurring. Nonlinear Optical Properties The large spin orbit coupling constant of the platinum atom creates well populated and highly emissive triplet excited states within platinum acetylides. Platinum acetylides often display high linear transmission through most of the visible region and NLA over a wide spectral region. Such platinum acetylide species provide the opportunity for examination of spin forbidden S 0 1 state absorption, ISC, triplet state emission (T 1 S 0 ), and triplet triplet excited state absorption (T 1 n ). These features mak e the complexes ideal candidates for examining the triplet ESA properties. Phenylethynyl based platinum acetylides McKay and co workers were the first to report the nonlinear optical properties of platinum acetylide complexes ; m uch of their initial work centered on the optical properties of a plat i num ethynyl complex, Figure 1 11 38 77 79 84
35 Figure 1 11 Structure of trans PE2 The bis ((4 (phenylethynyl)phenyl)ethynyl)bis (tributylphosphine) platinum(II) abbreviated trans PE2 or PE2 has become a benchmark for measuring the NLA of pl atinum acetylides, partially ow ing to the near unity ISC efficien cy to the triplet manifold and strong triplet triplet ESA that are exhibited. 8 Additionally, OPA and TPA processes can be used to generate th e triplet excited state. The effective TPA cross section of trans PE2 was reported at 235 GM at 595 nm, using picosecond pulses, which allowed for ESA from both the singlet and triplet excited states. 77 81 The intrinsic f emto s econd TPA cross section of trans PE2 is 7 GM at 720 nm. 52 85 D istinct regions typically emerge in the NLA spectral response of platinum acetylides. 38 81 T he triplet excited state is highly absorbing throughout the visible region of most platinum acetylides and can be accessed through various excitation methods. ex < 500 nm) consists of one photon excitation to the singlet excited state and rapid ISC to the tripl ex = 500 540 nm) exhibits direct spin forbidden excitation of the triplet excited state from the singlet ex = 540 700 nm) is dominated by TPA to populate the singlet excited s tate, followed by rapid ISC to the triplet excited state. The triplet E SA cross section is independent of the OPA or TPA excitation pathway. 82 Several series based on trans PE2 have been synthesized, including platinum acetylides with varying numbers of phenyl ethynyl repeat units (PEn, n = 1, 2, 3); 51 chloroplatinum complexes with one phenyl ethynyl unit mimicking half of PEn (Half
36 PEn); 86 platinum phenyl ethynyls with sydnones on the peripheral phenyl rings (Syd PEn); 87 and asymmetric platinum phenyl ethynyl complexes where the conjugation lengths are different on either side (PE a b ), 7 Figure 1 12 Figure 1 12 Butadiyne platinum acetylide oligomers structures The P E n series illustrates the effect of platinum on the photophysical properties as the degree of conjugation is increased 6 Conjugation through the platinum center occurs in the singlet state. The S 1 excited state of PE1 has the most MLCT character, but PE2 and PE3 display increasi ng character due to the increased ligand size. As expected, the addition of the platinum metal decreases the fluorescence quantum yield and increases the ISC yield. However, platinum decreases the triplet lifetime when compared to a purely butadiyne species. 88 The platinum effects are largest in the PE 1 complexes and the influence of the metal decrease s as ligand size increases. The lowest triplet excited state, T 1 also shows MLCT character suggestion the T 1 exciton is
37 most likely confined t o one ligand. The T n e xciton, conversely, shows LMCT character. 6 The ground singlet state and triplet excited state within the examined platinum acetylide molecules are more sensitive to molecular size. That is, the ground singlet and first triplet excited states ar e more confined than are the more delocalized excited singlet and higher excited triplet states. An additional study by the same group investigated the incorporation of butadiyne ligands to generate the unsymmetrical mononuclear platinum acetylide oligome rs, PE 1 2 PE 1 3 and PE 2 3 Figure 1 12 7 T hese oligomers allowed examination of the localization of singlet and triplet excited states and their ISC mechanisms. Computational calculations generated the geometry optimizations and energies for the ground and T 1 states. The combination of the computational results with the observed spectroscopic properties gave evidence that the singlet exciton is delocalized through the central platinum, whereas the triplet exciton is confined to the lowest energy, and largest, organic ligand. Platinum acetylides with heteroatomic ligands Introduction of heteroatoms into conjugated frameworks can change the electronic and optical properties and chemical stability of the structures A series of platinum acetylide complexes have been examined that varied a core ar y l group, as s tudied by Wilson and co workers and s hown in Figure 1 13 The photophysical characterization of these complexes revealed that as the energy of the triplet excited state decreased, the nonradi ative decay rates increased. 89 This observation correlated well with the energy gap law : an increase in nonradi ative decay processes resulted in a decrease in bot h triplet excited state lifetimes and emission intensities. 76
38 Figure 1 13 P latinum acetylide polymers examined by Wilson and co workers. 89 A series of t hiophenyl Pt( II) ethynyl derivatives Figure 1 14, have also been examined relative to trans PE2 52 The structures incorporate thiophene rings into the organic ligands, generating variations of trans PE2. The TPA cross sections around 720 740 nm of the thiophenyl Pt(II) complexes are 17 and 9.5 GM, respectively, under 1 MHz pulse fs measurements. These complexes show similar, but larger NLA cross sections via TPA than trans PE2. Figure 1 14 Thiophene containing p latinum acetylides as examined by Glimsdal. 52 A large portion of NLA platinum acetylide research and their applications has also focused on the de velopment of chromophores with large TPA cross sections. Many reviews exist that specifically cover NLA, TPA and third order NLA via metal alkynyls. 23 62 63 As such, the design, synthesis and fabrication, and structure properties
39 within platinum acetylides relationships have been examined so as to better understand the TPA process. Platinum acetylides with TPA chromophores As discussed previously, enhanced NLA is possible in platinum complexes. A TPA chromophore is incorporated into the complex to populate the singlet excited state upon excitation at which time the Pt metal center can induce the single triplet ISC transition to quickly and efficiently populate the triplet ex cited state. If the chromophore has a large triplet triplet cross section, further NLA via E SA within the triplet manifold i s possible. The two photon cross section of a simple phenylethynyl based platinum acetylide, such as trans PE2, is small. As such much research has focused on improving the 2 of platinum acetylides by incorporation of strong TPA chromophores. A series that examined the electronic localization of the triplet excited state and the strong NLA of platinum acetylides is shown in Figure 1 15 The complexes include p latinum acetylide s that incorporated two alkynyl benzothiazolylfluorene ligands ( trans BTF ) and two alkynyl diphenylaminofluorene ligands ( trans DPAF). 90 These complexes Figure 1 15 P latinum acetylides with TPA chromophores 90
40 show similar or larger effective trans PE2 and improved response with 780 GM at maxima TPA wavelengths via 100 fs relative fluorescence technique. A n additional series of platinum acetylide oligomers have been studied that contained the large cross section two photon absorbing chromophore, DPAF, combined with various central conjugated units, Figure 1 16 35 The complexes consisted of two TPA chromophores based on the DPAF moiety, end capped to the core aryl unit via Pt acetylide linkages. Because the lowest triplet excited state was localized on the central arylene unit, the triplet triplet absorption of the long lived excited state was largely determined by the structure of the arylene chromophore. Nanose cond transient absorption spectroscopy revealed that the series displayed intense and broad triplet triplet absorption across the visible and near infrared regions and significant NLA to Figure 1 16 DPAF endcapped di platinum acetylides with various c ore aryl units. 35
41 nanosecond pulses in the 600 800 nm region. The NLA response was postulated to be the result of dual mode TPA and triplet ESA absorption. Femtosecond TPA response was observed for the series in the near infrared region (600 1,000 nm) with peak cross section values in the range of 2 = 88 230 GM. 90 The TPA response was large ly attributed to the DPAF chromophores. Objective of Present Study Platinum acetylide complexes provide a unique platform for examining triplet excited state properties These complexes typically display strong phosphorescence and enhanced triplet quantum yields as a result of the spin orbit coupling of the platinum metal. Further, incorporation of select chromophores can elicit strong effects on the linear and NLA response of the materials. The strength of the NLA response is pa ramount to the development of these organometallic systems for applications in nonlinear optics, optical and chemical sensors, and molecular electronic devices. As such, an open aperture z scan apparatus wa s designed and constructed that integrate d a nano second laser to examine the NLA response of generated complexes. A series of platinum and iridium cyclometalated complexe s with varying chromophores was synthesized and examined by z scan. Additionally, a series of platinum phenylene ethylene oligomers w as investigated. Modifications and arrangements of optical components, in additional to developed software, are discussed. This characterization of the photophysical properties can help determine which structural features relate to effective materials fo r optical applications and thus broaden the understanding of the nonlinear absorption pathway.
42 From previous investigations, our group has concluded that platinum acetylides can be designed and generated that exhibit NLA via a combined TPA and triplet ESA pathway. These complexes can provide efficient NLA response over a b road range of pulse durations from femtosecond to nano and microsecond time scales. In a continuation of our investigation into these materials, we seek to further define the structure property relationships of the complexes and the resulting photophysical responses so as to design organometallic conjugated complexes that exhibit e nhance d efficiencies of singlet to triplet ISC, strong phosphorescence and long lived triplet excited st ates With regards to NLA, we seek to generate complexes that exhibit a large TPA cross section, a large triplet ESA cross section, high ISC efficiency, and minimal one photo n absorption cross section from the singlet ground state. Most previously examined platinum acetylides have been in a trans geometry at the platinum metal center. The effect of stereochemistry on the photophysical response of platinum acetylides is crucial to the incorporation of these complexes into optical applications. As such, a series of cis and trans platinum acetylides were synthesized and examined to quantify the effect of platinum stereochemistry on the magnitude of the excited state properties and NLA response. The extent of conjugation ac ross the platinum center was also examined as a function of platinum stereochemistry ; t his was examined within the X ray crystal structures and luminescent properties of the complexes. An additional series of complexes incorporate three known strong TPA c hromophores onto platinum acetylide monomer s These monomer s were then integrated into polymethylmethacrylate polymer backbones. The photophysical
43 properties of the resulting polymers were examined in solution and solid state and compa red to the platinum acetylide monomers The polymerization of the monomers also allowed for examination of the mechanics and engineering of the complexes into thin films and monoliths. The results of this work provide insight regarding the introduction of platinum acetylid es into polymers and examination of nonlinear active polymers in films for optical applications.
44 CHAPTER 2 OPEN APERTURE Z SCAN APPERATUS AND R ESPONSE Background Laser technology has witnessed drastic advancement in the past few decades, leading to the in corporation of lasers into a variety of applications ranging from surgical i nstrumentation and fiber optic communications to compact disc players and printers Unfortunately, the integration of lasers into these applications also introduces m ajor safety concerns that must be addressed. Primarily, the need for protection from laser pulses has become important to prevent damage to the user or the optical components within and near the application. This safety concern is largely due to the sensitivity of t he components and the susceptibility to irreversible laser damag e. Protection from laser damag e is most straightforward if both the laser power and wavelength are known; such protection can be achieved with optical filters. 91 However, protection is also desired within applications that integrate a laser source of multiple frequencies and energies. An optical power limiter is a device which allows the transmittance of lig ht at low intensities, but which strongly attenuates the incident laser energy at high intensities Figure 2 1 31 92 Optical power limiters often operate via nonlinear absorption ( NLA ) pathways. Two photon absorption ( TPA ) is a desirable pathway for optical protection due to the high linear transparen cy at low light intensities a nd fas t temporal response. The further NLA enhancement via excited state absorption ( ESA ) through incorporation of a strongly absorbing and long lived excited state is also an attractive feature. The synergistic combination o f TPA and ESA, which provides instantaneous response and long lived NLA, is ideal for optical power limiting. Many of the complexes generated in
45 the Schanze Group are designed to feature NLA. As such, instrumentation has been developed in house to charac terize the NLA response. Figure 2 1. Linear (a) and nonlinear (b) absorption response as a function of transmittance versus input energy. Techniques The transmitt ance attenuation observed by nonlinear absorbing materials in Figure 2 1 is dependent on increasing the laser energy during the experiment A tra ditional method of obtaining such NLA response i s via a nonlinear transmission (NLT) measurement which r equires that the laser energy be increased duri ng the course of the experiment T his increase is achieved by either modification of the q switch delay setting of the laser or of the filters used prior to the sample cuvette. However, adjustments of the q switch delay settings can lead to changes in the beam profile that are detrimental to the reproducibility and accuracy of the observed NLA response. A more common method of measuring the NLA is the z scan technique. This technique addresses the issue of beam profile distortion by holding the laser energy settings constant. Crucial to the z scan technique is the ability to move the sample along the z axis, or the direction of the laser beam, through a tight focal plane; this differs from the NLT technique where the sample remains stationary with respect t o the
46 laser focus. As such, the laser energy remains constant throughout the z scan measurement, but the laser fluence (or laser energy over beam size) changes throughout the focus of the laser path. The z scan technique was first reported in 1989 by Va n Stryland and co workers 93 94 This technique can measure the nonlinear refract ion and absorption of a sample. The nonlinear refraction measurement employs an aperture in the far field, as depicted in schematic shown in Figur e 2 2. The NLA measurement utilizes the same system but with the aperture open to collect all the incident laser energy Fi gu re 2 2. Components of the z s can apparatus BS: beam splitter, D1 and D2: detector 1 and 2 The ability to move the sample along the z axis is achieved through a one directional translation stage positioned directly behind a focusing lens. A beam splitte r (BS) divides the single beam prior to the focusing lens so that the effect on transmittance through the focus can be m easured as a ratio of detector 1 (D1 ) over detector 2 (D2 ). A short pathlength qua rtz cuvette is used during the z scan measurement to ensure that the thickness of the sample is smaller than the diffraction length of the focused beam. Since the light travelling to D 2 undergoes no changes, the incoming intensity should remain constant throughout the sc an. The light transmitted to D1 i n contrast,
47 will be affected by the sample and its position along the z axis. If the sample displays nonline ar characteristics, the transmitted intensity will change with respect to the position along the optical axis. The closed aperture z scan begins while the sample is positioned at a negative z axis position prior to the laser beam focus. The intensity and effect of self focusing should be small. The transmittance ratio (D 1/D2 ) should remain constant, displaying negligible nonlinear response As t he sample is moved towards and through the focus along the z axis, the sample will self lens (beam irradiance increases) or self defocus (beam divergence increases). 95 Self lensing in the sample should increase the transmittance measured at D1 because the beam has narrowed. Self defocusing should lead to beam broadening at the aperture and a decrease in transmit tance at D1 As the sample is moved further from the focal plane, nonlinear transmittance should become negligible since the irradiance is again low. A prefocus transmittance maximum (peak) followed by a postfocus transmittance minimum (valley) is charac teristic of a negative value refractive nonlinearity whereas a valley peak transmittance profile is characteristic of a positive refractive nonlinearity value. The change in the transmittance ratio of D1/D2 is monitored in relation to the z position ; a plot of the normalized transmittance ratio versus the z position generates the expected closed aperture z scan response, as shown in Figure 2 3 for C60 in toluene under 1024 nm excitation. With the aperture removed, the transmittance is insensitive to beam distortion and will thus show nonlinear absorption. When the sample is positioned at la rge negative or positive z axis positions, no NLA response should be observed because the intensity
48 should be small; the transmittance ratio (D 1/D2 ) should remain cons tant. As the sample is moved closer to the focal point, the energy density of the laser will increase. This increase is analogous to increasing the laser energy, but is achieved without manipulation of the laser settings. If the sample undergoes NLA th e transmittance ratio will decrease. The lowest ratio observed during the open aperture z scan should be when the sample is at the position of tightest laser focus. As the sample then travels out of the focus, the NLA will lessen and the transmittance ra tio should increase until no NLA occurs. Negligible NLA should be observed in the far field that is equal to the transmittance ratio detected at the onset of the scan. The expected profile for a sample that does not display NLA would be a straight horizo ntal line since a steady transmittance ratio across all z positions would be ob served. A sample that displays NLA should show negligible change in response initially, followed by data that would be parabolic in shape as the transmittance ratio initially d ecreases and then increases as the sample is moved through the focal plane Figure 2 3 Negligible NLA response should again be observed at the large positive z axis positions. Figure 2 3. Z scan plots of C60 in toluene at an excitation wavelength of 1 064 nm, a) closed aperture, b) open aperture. 96
49 Open Aperture Z Scan Apparatus Hardware The z scan apparatus has been modified several times; an electronically driven one directional translation stage and different optics, sample holders, and filters have been incorporated at various stages of the development. A diagram of the final apparatu s is shown in Figure 2 4 The laser is created by using an optical parametric oscillator (Continuum Surelite OPO PLUS) pumped by the t hird harmonic of a Nd:YAG laser (355 nm, Continuum Surelite II, 5 ns fwhm). The OPO provides visible laser light in the 420 670 nm region and near infrared light in the 800 25 00 nm region. The laser energy is adjusted b y modification of the q switch delay of the flashlamp Typical laser energies for the z scan system are 150 J 1.5 mJ. Energies above this level can thermally excite the sample to the point of damaging the quartz cuvette whereas lower energies become difficult to measure because of detection limits of the optical components. The laser beam is directed to the sample using conventional laser optics. As shown in Figure 2 4 the beam is passed through an iris and an option al neutral density filter (NDF) before being divided by a 50/5 0 beam splitter. The reflected beam serves as the experimental reference, and is focused wi th a 15 cm focal length plano convex lens into d etector 2 without interacting with the sample. The transmitted beam is tightly focused by a 50.8 mm focal length pl ano convex lens. The sample is inserted into this focused beam and moved along the optical path The transmitted beam is then re focused with a 50 mm focal length plano convex lens and collected at d etector 1
50 Figure 2 4 Nanosecond open aperture z sc an apparatus instrument schematic. The sample is moved along the z axis with an electronic actuator (Thorlabs Z825B Motorized DC Servo Actuator) attache d to the translation stage. The actuator is driven by a servomotor (Thorlabs TDC001 T Cube DC Servo Con troller ) to move the stage with high precision (minimum resolution of 29 nm). The Z825 has a travel length of 25 mm. There is an automatic power cutoff when the actuator reaches its maximum and minimum mechanical limits. The Z825 can be operated at var ying speeds, however the speed is constant in this application The load capacity of the entire stage and sample on the actuator is 9 kg. The T Cube controll er powers the actuator with 12 volts and provides an interface to the computer for use in softwar e applications. Manual control of the actuator is available by toggling the switch to move the actuator forward and backward. The sample and reference beam energies are collected with matched 9 mJ capacity Ophir e nergy m eter h eads that connect to an Ophir Laserstar energy display The energy meter heads are used to monitor the change in energy as the sample is subjected through the focus of the laser beam ; the energy display shows shot by shot energy changes of both meter heads during the experiment The heads have a
51 sensitivity range of 10 J 9 mJ The energy d isplay is configured to calculate the e nergy ratio of the sample head over the reference head. The distance between the OPO signal output port and the NDF is 145 mm. The NDF is positioned 213 mm prior to the beam splitter. The 50.8 mm focal length lens in the sample path is positioned 60 mm past the beam splitter. A distance of 103 mm exists between the 50.8 mm and 50.0 mm focal length lenses, and a distance of 112 mm is between the 50.0 mm focal length lens and detector 1 The 150 mm focal length plano convex lens in the reference path is positioned 44 mm from the beam splitter and 92 mm before d etector 2 This arrangement of optics allows for the creation of a tight focus along the z axis and full collection of the sample and reference beams. The longer distances prior to the beam splitter are only necessary in this system to allow the option of the OPO signal beam to be steered to other optical configurations without interfering with the z scan apparatus. Software and Data Collection A Labview based virtual instrument (VI) program has been developed in house by Randi Price to provide a computer interface for the motorized actuator and data collection. This program also allows the u ser to specify several parameters that determine the quality and speed at which the z scan measurement is made. The most important factor in collecting the NLA response is the step feature. This feature controls the relative step size through the z axis as well as the starting and stopping positions. The motorized DC servo actuator is specified at nm resolution; however this degree of resolution is not needed for the z scan experiment. The values in the program are in mm. The maximum values for the sta rt and stop positions are 12.5 mm. A position of
52 0.0 mm is assumed to be the approximate focal point of the laser beam. A r easonable step size should be selected to allow an adequate, but not excessive, number of data points ; a step size of 0.5 mm is ty pically sufficient. It is also important to have a sufficient number of data points before and after the focus for generation of a good baseline Recommended step values for most samples would be a 21 mm scan (start at 10 mm, stop at 10 mm) with a step size of 0.5 mm. The z scan.vi program also allows for control of the number of laser pulses m easured at each position. Each pulse is given approximately 0.1 sec ond to be read by the program ; 1 00 measurements sh ould take an average of 10 seconds of laser pulses at each position. Z scan experiments have shown that a setting of 10 measurements /position led to incorrect data not enough values were collected to obtain accurate averages or acceptable standard deviation values. Little change was observed between 25 and 50 measurements /position. However, a setting of 100 measurements /position occasionally led to sample degradation at the focus of the laser beam. As such, i t is recommended to use a setting of 25 measurem ents /position An additional option provided by the z scan.vi program is the data reject feature. When enabled, this feature allow s t he option of individually accepting or redoing each data point along the scan Occasionally an extraneous point might be obtained Such a point can be corrected during the experiment by re peating the measurement at the specific position before the translation stage is moved. T he program also provides the energy ratio and standard deviation of each shot which are evaluated by the user to determine the validity of the data. A standard deviation of approximately 0.004 is common near the baseline, and a standard deviation of approximately 0.02 is common
53 near the peak. The hardware and software involved in the z scan apparatu s are further described in the instrument instruction manual (Appendix A). NLA T est Series Two series of complexes were investigated to evaluate the open aperture z s can apparatus. The platinum and iridium cyclometalated complexes were examined by the sys tem prior to the use of the electronic, motorized translation stage and Lab view based software program. As described in the experimental, these complexes were also investigated with a different series of optics to generate the focus needed for the z scan The platinum acetylide oligomeric series was used to evaluate the z scan system after all modifications to the system were complete. However, the NLA responses of both series were compared against T2 (shown in Figure 1 16 ) a platinum acetylide that ha s previously be en investigated under nanosecond NLA conditions. 35 The one photon photophysical characteristics of both series are briefly described before discussion of their NLA responses. Platinum and Iridium Cyclometalated Complexes Cyclometalated complexes have exhibited photophysical properties suitable for applications as dopants in organic light emitting diodes, 97 98 biological labeling reagents, 99 and singlet oxygen sensitizers. 100 102 The square planar Pt(II) complexes ha ve the general structure Pt(C^N)(O^O), where C^N is a monoanionic cyclometalating ligand such as 2 thienyl)pyridyl, 2 phenylpyridyl, 2,4 diphenyloxazolate, etc., and O^O is a diketonato ligand such as acetyl acetonate. The octahedral Ir(III) complexes contain two cyclometalating ligands ; as a result, these complexes are abbreviated Ir(C^N) 2 (O^O). The nitrogens of the cyclometalating complexes are of a trans geometry within the Ir(III) complexes.
54 Design Expanding on what has been learned fr om organometallic conjugated oligomers, two photon absorbing chromophores, and efficient nonlinear response to long time domain laser pulses, cyclometalated platinum (II) and iridium (III) complexes have been developed to undergo enhanced NLA. The cyclo metalated Pt(II) and Ir(III) complexes are typically stable; this is due largely to the influence of the aromatic carbon and the donation from the metal center. 103 The asymmetric TPA chromophore, AF240, features a D A (electron donor conjugated spacer electron acceptor) structure which is achieved by incorporating a diphenylamine fluorine electron donor chromophore with an electron acceptor 2 benzothiazole Figure 2 5 This asymmetric chromophore design and use of strong donors and acceptors have been shown to produce effective TPA chromophores. 104 105 AF240 is an efficient, linear ligand that displays enanced TPA from both singlet and triplet excited states ; it features an effective two photon cross section of 50 GM 8 in Figure 2 5 Str uctures of the Pt(II) and Ir(III) cyclometalated complexes and chromophore precursors.
55 the nanosecond regime. 24 As such, introduction of the AF240 ch romophore into the Ir(III) and Pt(II) frameworks should elicit large TPA/ESA dual mode NLA response. Presented are organometallic Pt(II) and Ir(III) complexes in which either AF240 or phenylbenzothiazole (bt) is strongly coupled to the metal center Figu re 2 5 Ir(bt) 2 acac and Pt(bt )acac are designed to establish the metal organic framework and are used for comparison against the complexes that contain the TPA chromophores Characterization The ground state absorption and photoluminescent properties of the pla tinum and iridium cyclometalated complexes are reported elsewhere ; a summary of the one photon photophysical properties is shown in Table 2 1 106 The organometallic complexes exhibit strong linear absorption bands in the region of 255 487 nm, but no absorption is observed in the spectra range of 500 800 nm. As such, there should be no linear absorption induced e mission in the 600 nm region where the z scan instrumentation will be used to probe the NLA properties. Cyclometalated Pt(II) and Ir(III) complexes are characteristically luminescent If the emitting triplet state (whether intraligand, MLCT, or an admixtu re) and the metal centered states are close in energy, the excited state can thermally equilibrate via nonradiat ive decay pathways through the metal centered state. The phosphorescence is often directly related to the selection of the cyclometalated ligan d ; t he luminescence originates from a predominantly ligand centered ( 3 LC) transition with some contribution from a 1 MLCT transition 103 107 110 The phosphorescence of the AF240 containing complexes is red shifted approximately 60 nm from that of the benzothiazole derivatives. The bathochromic shift observed in the organometallic complexes is similar to the shift observed in the free chromophores. However, t he phosphorescent quantum
56 yields are similar between complexes of the same metal center regardless of the chromophore selection Table 2 1 The 1 MLCT contribution within Ir(III) complexes has been shown to decrease the triplet excited state lifetimes and causes the appearance of metal ligand vibrational bands in the ground state absorption and photoluminescence spectra. 111 112 As shown in Table 2 1, both Ir(bt) 2 acac and Ir(AF240) 2 acac exhibit more ground state absorption bands and short er triplet excited state lifetimes than the platinum analogs. Table 2 1 Linear optical properties of Pt(II) and Ir(III) complexes in THF Complex Abs a ( nm) (M 1 cm 1 ) Ph max b (nm) Ph c T1 Tn (nm) d TA ( s) AF240 306 393 25,119 33,884 474 0.65 -e -e Pt(bt)acac 252 318 394 33,113 25,704 11,482 540 584 634 0.13 417 4.08 Pt(AF240)acac 307 407 446 471 33,113 30,903 30,903 31,623 610 665 0.12 750 9.71 Ir(bt) 2 acac 271 328 358 408 448 31,295 27,883 8,198 5,680 5,230 546 594 0.26 535 1.54 Ir(AF240) 2 acac 405 441 487 38,019 30,903 7,762 610 667 0.23 713 2.54 a Ground state absorption maxima b Phosphorescence spectra, obtained by excitation at ground state absorption maxima c Quantum yields relative to Ru(bpy) 3 in air saturated DI water, = 0.0379 113 d Triplet triplet transient absorption maxima e The triplet triplet transient absorption spectrum and triplet lifetime of AF240 were not measured. The triplet triplet excited state absorption properties of the complexes are key to the NLA re sponse of the complexes. As such, the nanosecond triplet triplet transient absorption spectra of the cyclometalated complexes are measured, as presented in Figure 2 6. Near UV excitation at 355 nm generates strongly absorbing transients. In
57 the transien t absorption spectra of Pt(bt)acac and Ir(bt)2acac, the UV ground state absorption bands assigned to the (S 0 S 1 ) transition have been corrected for with an emission correction scan. The spectra of Pt(AF240)acac and Ir(AF240) 2 acac still show the bleaching due to the ground state absorption bands, which appear as the negative bands below 450 nm. F igure 2 6 T 1 T n absorption spectra of Pt(bt)acac, Ir(bt) 2 acac, Pt(AF240)acac, and Ir(AF240) 2 a cac following n anosecond pulsed 355 nm excitation in deoxygenated THF Molar extinction coefficients were obtained by relative actinometry. The positive and moderately intense visible absorptions indicate that the complexes exhibit population of the triplet excited state. The AF240 con taining complexes exhibit much stronger and broader triplet transient absorption, postulated to be due to the contribution of the TPA chr omophore. As shown in Table 2 1 introduction of the TPA chromophore into the organometallic complexes also nearly dou bles the triplet excited lifetime. Additionally, the introduction of the AF240 chromophore produces a strong bathochromic shift in the triple t triplet transient absorption.
58 P t(bt)acac has a triplet absorption maximum at 417 nm, whereas Pt(AF240)acac is s trongly red shifted to 750 nm. A similar trend is observed in the Ir(III) complexes, where Ir(bt) 2 acac exhibits a maximum at 535 nm while Ir(AF240) 2 acac complex is red shifted 188 nm. Platinum End Capped Phenylene Ethynylene O ligomers Introduction A series of dinuclear platinum capped oligomers are presented in Figure 2 7 The effect of extending the length of the phenylene ethynylene conjugated spacer ( Ph n ) is examined with regards to delocalization of the singlet and triplet states. The platinum acetylides should feature NLA that can be investigated via the z scan apparatus. The series works well for characterizing the z scan system since the change in organic spacer length should result in notable changes in the NLA response. Figure 2 7 Structures of the Ph n Pt 2 series, where n = 1, 2, 4, and 9
59 Characterization The ground state absorption and photoluminescent properties of the Ph n Pt 2 series have been reported elsewhere though the res ults are summ arized in Table 2 2 114 A photophysical investigation of the oligomers indicated that the singlet ground and excited states were delocalized throughout the com plexes. The phosphorescence of the longer oligomers was red shifted from that of Ph 1 Pt 2 though the shift is small between Ph 4 Pt 2 and Ph 9 Pt 2 Additionally, the phosphorescent quantum yields decreased across the series. Taken together, these phosphorescent emission observations indicate that the triplet excited state is more localized than the singlet excited state the extent of triplet delocalization appears to have been reached by n=4. Table 2 2 Summary of p hotophysical properties of Ph n Pt 2 series in THF n Abs (nm) a 1 cm 1 ) Fl max (nm) b Ph max (nm) c T1 Tn (nm) d TA ( s) e 1 352 67,500 391 517 660 6.0 2 360 92,000 403 561 637 15.1 4 382 115,000 423 584 748 26.0 9 391 161,000 424 585 748 32.9 a Ground state absorption maxima b Fluorescence spectra, obtained by excitation at ground state absorption maxima c Phosphorescence spectra, obtained by excitation at ground state absorption maxima d Triplet triplet transient absorption maxima e Triplet excited state lifetime, calculated from the decay profile of the transient absorption spectra The triplet triplet transient absorption spectra and triplet excited state lifetimes are important for characterization of the observed NLA response. As such, the transient absorption spectra are shown in Figure 2 8 and summarized in Table 2 2. The transient absorption spectra for the Ph n Pt 2 series were measured in deoxygenated THF solutions after excitat ion at 355 nm. Strong, broad signals are exhibited across much of the visible region for the series. Interestingly, Ph 2 Pt 2 exhibits the most blue shifted absorbance, with a maximum at 637 nm, a 23 nm shift from Ph 1 Pt 2 Both Ph 4 Pt 2 and Ph 9 Pt 2 display a t ransient absorption maximum at 748 nm.
60 Figure 2 8 Normalized transient absorption spectra of the Ph n Pt 2 series in deoxygenated THF following n anosecond pulsed 355 nm excitation 10 ns camera delay, 8 mJ energy,100 averages The oligomers are sensitive to light and oxygen. Despite care in deoxygenating the solutions, the samples show decomposition after multiple transient absorption measurements. As such, the triplet excited state lifetimes are calculated from transient abso rption decays measured at three wavelengths rather than a global analysis approach. Noted is the trend that the triplet excited state lifetimes increase as the organic space lengthens and the contribution of the metal dec reases Results and Discussion NLA Response The structures and one photon photophysical properties of the cyclometalated and Ph n Pt 2 complexes have been introduced so that the complexes can be used to characterize and evaluate the open aperture z scan apparatus. Important to the nanosec ond measurements is excitation of the complexes at a wavelength that is much longer than the cut
61 As such, the cyclometalated complexes are excited at 628 nm. Solutions of 1 mM were prep ared in HPLC grade THF from an in house solvent system. The solutions were not deoxygenated prior to measurements. The laser q switch delay was adjusted to 260 s, which provided approximately 360 J input energy to detector 1. The NLA response of the P t(II) and Ir(III) cyclometalated complexes in solution under these conditions is shown in Figure 2 9 The qualitative data show a marked difference in response intensities among the series where Ir(AF240) 2 acac exhibits the largest TPA response. As expec ted from their structural designs, AF240, Pt(bt)acac, and Ir(bt) 2 acac do not display any NLA response. While AF240 is a TPA chromophore, the excitation at 628 nm does not generate the triplet excited state. Since the cyclometalated complexes do not exhib it ground state absorption at 628 nm, population of the triplet excited state is proposed via T PA to the singlet excited state followed by ISC to the triplet manifold. H owever the contribution from TPA and triplet ESA cannot easily be separated quantita tively Figure 2 9 Nanosecond NLA response of 1 mM cyclometalated Pt(II) and Ir(III) complexes in THF after 628 nm excitation, 260 s q switch delay ( 1.2 mJ input energy ).
62 Pt(AF240) 2 acac exhibits a markedly smaller change in transmittance than does Ir(AF240) 2 acac despite the intersystem quantum efficiencies of nearly 100 % in both complexes One plausible explanation for this observation is a synergistic effect of the TPA chromophores since Ir(AF240) 2 acac contains two chromophores compared to the one chromophore in Pt(AF240) 2 acac, Ir(AF240) 2 acac should exhibit stronger overall NLA response. Surprising is the large difference between the complexes. However, Ir(AF240) 2 acac is also an octahedral, iridium complex. The iridium metal and the change in geometry could have a large effect on the observed NLA response. However Pt(AF240) 2 acac and Ir(AF240) 2 acac suffered from oxygen and light sensitivity problems and could only be obtained pure in small yields. As such, the NLA response of Pt(AF240) 2 acac and Ir(AF240) 2 acac were only probed at one wavelength and energy. Additional tests would be needed to characterize the effect of the geometry and chromophore concentration. Ideal tests would probe the NLA response at higher and varying laser energies. Despite the stability issues of the AF240 complexes, the open aperture nanosecond z scan apparatus can be used to probe the NLA response of these compl exes. The T2 platinum acetylide, however, is robust and stable under laser excitation. As such, T2 was used to investigate the effect of increasing sample concentration on the observed NLA response Figure 2 10 The response of T2 in benzene was measured at concentrations of 20, 6.7, and 3.3 mM under 600 nm excitation conditions and a q switch delay settin g of 280 s (input energy of 230 J to detector 1). Increasing the solution concentration directly and positively affects the degree of transmittance
63 attenuation observed by the z scan system. The T2 solutions were compared to benzene, which exhibits no NLA response. Figure 2 10 NLA response dependency on solution concentration of T2 i n benzene under 600 nm excitation, 280 s q switch delay (230 J input energy ). T he z scan system was modified to include a motorized translation stage and Labview bas ed z scan.vi program Additionally, two plano convex lenses were added to ensure complete capture of the beam at the detectors, as shown in the final instrument schematic in Figure 2 4 After the modifications were complete the system was used to charac terize the NLA response of the Ph n Pt 2 series under 600 nm excitation. Matched solution concentrations of 1 mM were prepared in HPCL grade THF from an in house solvent system. The solutions were not deoxygenated prior to measurements. The laser q switch delay was adjusted to 280 s, which provided approximatel y 75 0 900 J input energy to detector 1 (A full pump beam and OPO optical alignment was performed on the Surelite Continuum laser and OPO between measuring the cyclometalated and Ph n Pt 2 series The alignment provided more stable laser output and required lower q switch delay settings.) A 0.5 mm translation stage step size was used. The response of the series was compared to T2. The z scan NLA
64 response is shown in Figure 2 11 T2 and Ph 9 Pt 2 we re both measured twice to verify response reproducibility; no change in transmittance was observed. The oligomer complexes exhibit NLA response intensity that is related to the organic spacer length the strongest response is observed from Ph 9 Pt 2 with a marked decrease in response as the spacer is shortened. Figure 2 11 NLA response via ns z scan measurements of 1 mM Ph n Pt 2 solution in THF under 600 nm excitation, 280 s q switch delay (750 900 J) L imitations of C urrent S ystem As illustrated with the cyclometalated and Ph n Pt 2 series, the new open aperture z scan apparatus can be used to measure nanosecond NLA responses exhibited via TPA and triplet ESA. While the s ystem does provide the ability to s tudy many materials, there are some limitations. The first restriction, as will b e further described in Chapter 4 limits the z scan to solution measurements. Attempts at measuring polymer films on glass and monoliths have not resulted in consistent, re peatable z scan response. The films contained materials known to exhibit NLA response. However, the films were very thin and were not of a high enough concentration to observe NLA response via z scan. The glass
65 backing on the films also caused slight re flection and refraction problems ; however, this could be addressed by adjustment of the sample and reference beam focus prior to collection at the detectors. Monoliths were generated from the same polymer to further investigate the concentration problem o f the films. The monoliths were approximately 500 micrometers thick, closer to the solution measurements that are 1 millimeter in pathlength. Howev er, the monoliths tended to obtain optical damage at the focal point of the z scan. Additionally, the mono liths caused strong refraction of the laser light in the f ar field z positions. A ttempts at capturing the laser light through modification of the optics have proved unsuccessful. The apparatus is being optimized currently to address these issues. An additional limitation of the system arises from the Nd:YAG laser used. The OPO provides visible excitation in the region of 420 670 nm. However, the types of NLA materials studied in our laboratory are designed to exhibit single photon ground state abs orption in the UV and blue region; the TPA properties can typically be investigated in the excitation region of the OPO. If necessary, the OPO can be used for excitation in the 780 1200 nm region. Needed would be introduction of properly coated optics and energy meter heads that can accommodate such excitation wavelengths. A n additional limitation arising from the laser used was observed in a study that investigated the effect of laser excitation wavelength on the NLA response The study compared two m arkedly different platinum acetylides, as will b e further discussed in Chapter 3 The complexes contained different TPA chromophores and exhibited triplet triplet transient absorption m axima that were separated by 20 nm. Expected were
66 regions where the N LA response would be dominated by either two photon or excited state absorption pathways, depending on the excitation wavelength. However, the results were nearly identical for the two complexes, indicating that the OPO laser source provided an inconsiste nt laser profile at the varying wavelengths. The ability to measure the NLA response at different wavelengths via z scan is beyond the scope of the Surelite Continuum II laser and OPO. Despite the discussed limitations, the current z scan apparatus has ma ny advantages. S olutions are not needed in high concentration or large volume. The samples typically do not exhibit decomposition during the experiment despite being subjected to a tight focused, high laser fluence beam which is largely due to the low l aser energies that are needed in measuring the NLA response. The current system does not suffer from changes in the beam profile or energy due to q switch delay modification. The addition of the electronically controlled translation stage and Labview z s can.vi program allow for quick examination of samples (less than 10 minutes/sample). Modifications are under development to address the problems of measuring films and monoliths. Experimental Materials and Instrumentation 1 H, 13 C, and 31 P NMR spectra were recorded on a 300 MHz Varian Gemini, VXR, or Mercury spectrometer in deuterated chloroform; chemical shifts ( ) are reported in ppm and referenced to tetramethylsilane or protonated solvent signals. Elemental analyses were performed by the University of Florida Spectroscopic Services. Photophysical measurements were conducted with dry HPLC grade THF as a solvent in 1 x 1 cm quartz cu vettes unless otherwise noted. Triplet triplet transient
67 absorption measurements were conducted on a ho me built apparatus consisting of a fwhm). 115 Typical excitation energies were 7 mJ/pulse. Triplet excited state lifetime measurements of the Ph n Pt 2 series were conducted on a previously described home built apparatus 116 though the laser source has been changed to the third harmonic output (355 nm) of a Surelite Continuum I Nd:YAG laser. Samples for transient absorption and triplet excited state lifetimes were contained in a 1 cm pathlength cell with a total volume of 10 mL and the contents were continuously ci rculated through the pump probe region of the cell. Solutions were deoxygenated by argon purging a nd concentrations adjusted so that A 355 ~0.7. Transient absorption spectra and triplet excited state lifetimes of the cyclometalating series were generated by using software programs developed in house. 115 The open aperture nanosecond time domain z scan techniq ue was measured on a system which utilizes the third harmonic output of a Continuum Surelite II Nd:YAG laser coupled to a Continuum Surelite OPO PLUS for excitation at 600 and 628 nm. For the platinum and iridium cyclometalated complexes, t he 628 nm excit ation light was directed through a 50/50 beam splitter A 50.8 mm focus length, 38.1 mm diameter plano convex lens focused the beam. The samples were contained in a 1 mm pathlength quartz cuvette and moved along the focused beam via a manual one directio nal translation stage positioned directly behind the focusing lens. The energy of the laser light was detected with Ophir pyroelectric heads ( 10 J 9 mJ) and an Ophir Laserstar power/energy monitor, and collected using StarCom32 software.
68 For the Ph n Pt 2 series, an iris was inserted into the z scan laser system prior to the beam splitter. A 50.8 mm focus length, 38.1 mm diameter plano convex lens focused the beam. The sample beam was focused onto detector 1 with a 50 mm, 12.7 mm plano convex lens. The reference beam was focused onto detector 2 with a 15 cm, 12.7 mm plano convex lens. The samples were contained in a 1 mm pathlength quartz cuvette and mov ed along the focused beam via an electronic motorized actuator manual attached to a one directional t ranslation stage positioned directly behind the focusing lens. The energy of the laser light was detected with Ophir pyroelectric heads (10 J 9 mJ) and an Ophir Laserstar power/energy monitor The data were collected using the LabView z scan.vi progra m developed in house Synthesis Potassium tetrachloroplatinate This known complex, if not purchased from Strem Chemicals, was synthesized by a modification of literature methods. 117 118 Potassium hexachloroplatinate (7.294 g, 15.00 1mmol) and deionized water (75 mL) were added to a beaker. To the bright yellow suspension was added hydrazine dihydrochloride (753 mg, 7.173 mmol) in small portions. The yellow mixture was stirred while the temperature was slowly raised to 50 65 C over a period of ten minutes. The temperature was maintained until only a small amount of the yellow potassium hexachloroplatinate remained undissolved in a deep red solution. The temperature was then raised to 85 C to ensure completion of the reaction. Th e reaction was then cooled and filtered to remove unreacted K 2 Pt Cl 6 (588 mg). The yellow solid was washed with several portions of cold DI water. To the red filtrate and water washings was added a 1:1 acetone/diethyl ether solution. The resulting pale p ink powder was collected via
69 suction filtration and recrystallized with hot dilute aqueous hydrochloric acid, yielding fine, dark red needle like crystals, 4.514 g, 79%. ESI mass spectrometry taken in water indicated the expected K 3 PtCl 4 + isotope pattern. T he cyclometalated complexes we re obtained through synthesis of a dichloride bridged dimer via modifications of methods described by Nonoyama, 119 Lewis 120 and Thompson. 103 110 The dimer precursor wa s cleaved along the chloride bridges to form the target compounds by reaction of the dimer with excess acetylacetone and sodium carbonate in ethoxyethanol. The two step reaction was used, with slight modifications in stoichiometry to generate the similar unsymmetrical cyclome talating iridium (III) complexes. As an example, F igure 2 12 shows the formation of the dimer precursor and subsequent reaction to form the Pt(bt)acac complex. Figure 2 12 Formation of the dimer precursor and subsequent reaction to form the target Pt(II) cyclometalated complex. The platinum dimer wa s prepared by a modified method of Lewis 120 and Thompson 103 by the reaction of potassium tet rachloroplatinate (239 mg, 0.576 mmol) with the protonated cyclometal ating precursor, 2 phenolbenzothiazole (255 mg, 1.207 mmol) in 7.5 mL 2 et hoxyethanol and 2.5 mL deionized water The resulting solution wa s sparged with argon, then heated to 80 C und er argon for 16 hours. The product wa s precipitated out of solution with deionized water, then purified via flash
70 chromatography (1:1 DCM/hexanes), 148 mg, 59 % yield. Observed 1 H NMR spectrum (DMSO d 6 ) i s in accord with known literature values. Platin um(II) (2 phenylbenzothiozolato N,C )(2,4 pentanedionato O O ) The platinum dimer (150 mg, 0 .170 mmol) was r eacted with 3.0 equivalents of actylacetone (54 mg) and 188 mg (1.77 mmol) sodium bicarbonate in 15 mL 2 ethoxyethanol a t 100 C for 16 hours The initial olive green solution color change d to a dark brown color upon several hours of heating. The solvent wa s removed by reduced pressure, and Pt(bt)acac wa s isolated by flash chromatography using dichloromethane as eluent, 58 % yield 1 H NMR (CD Cl 3 H), 7.50 (td, 1 H), 7.42 (td, 1 H), 7.21 (td, 1 H), 7.11 (td, 1 H), 5.57 (s, 1 H), 2.09 (s, 3 H), 2.03 (s, 3 H). Elemental analysis for C 18 H 15 NO 2 PtS: found C 43.02, H 2.87, N 2.62, calc ulated C 42.85, H 3.00, N 2.78. The chloride bridged iridium dimer precursor of Ir(bt) 2 acac wa s synthesized according to a modification of a literature procedure. 110 A 50 mL round bottom flask wa s charged with i ridium trichloride hydrate (300 mg, 1.01 mmol) and 2 phenolbenzothiazole (507 mg, 2.40 mmol). To the solids wa s added 10 mL 2 ethoxyethanol. The resulting dark brown solution wa s argon purged with stirring before heated to a reflux under argon for 24 hou rs. Upon heating to reflux, the solution immediately turn ed from a dark brown solution to a milky yellow brown color. A 24 hour reflux result ed in a bright ora nge solution. The formation of the iridium dimer wa s monitored by thin layer chromatography. The dimer precipitated out of solution upon slow addition 20 mL of 1 M HCl. The product wa s filtered and washed with an additional 100 mL of 1 M HCl and small washes with ethoxyethanol. Unreacted
71 cyclo metalating ligand wa s removed with hexane s Flash ch romatography using dichloromethane isolates the dimer compound. Recrystallization with benzen e produced pure orange crystals, 457 mg, 70.3 % yield. Observed 1 H NMR spectrum (DMSO d 6 ) i s in accord with known literature values. Iridium (III) bis(2 phenyl benzothiozolato N C ) 2 (2,4 pentanedionato O O ) The target complex was synthesized according to literature procedure. 110 Observed 1 H NMR spectrum (DMSO d 6 ) i s in accord with known literature values. AF240, Pt(AF240)acac, an d Ir(AF240) 2 acac were provided by Dr. Chen Liao; the synthesis is reported elsewhere. 106 The Ph n Pt 2 oligomeric series was provided by Dr. Julia Keller; the synthesis is reported elsewhere. 114 T2 was provided by Dr. Kye Young Kim; the synthesis is reported el sewhere. 35
72 CHAPTER 3 STEREOCHEMICAL EFFEC TS OF PLATINUM ACETY LIDES Background The introduction of different chromophoric ligands of varying chain lengths ha s yielded monomeric platinum acetylides with a wide range of properties. Most of the platinum acetylid es investigated have been linear complexes in trans geometric configurations. A s illustrated in the previous chapters, introduction of select two photon absorption ( TPA ) chromophores into platinum acetylide moieties can elicit advantageous effects on the photophysical properties, in terms of both one and two photon processes. Interest in such two photon absorbing materials has led to many investigations into design stra tegy. The majority of the photophysical investigations of these TPA chromophores, however, ha ve focused on platinum acetylides in the trans configuration. This focus is parti all y due to the thermodynamic instability of the cis isomer with respect to the trans isomer in solution, specifically when the platinum auxiliary ligands are monophosphine groups such as PBu 3 and PEt 3 For example, when butadiyne is reacted in the presence of CuI with cis Pt(PBu 3 ) 2 Cl 2 at temperatures at or below 20 C, the cis Pt( PBu 3 ) 2 (C CC C ) 2 product can be obtained 54 However, when the reaction of cis Pt(PBu 3 ) 2 Cl 2 and butadiyne was carried out at 20 C, a mixtur e of the cis and trans isomers was obtained. Additionally, the isolated cis isomers were less stable than the trans analogs the cis isomers slowly decomposed at room temperature and were less solubl e in common organic solvents 54 However, this thermodynamic instability within the cis isomers can be overcome by the incorporation of chelating auxiliary groups such as bidentate phosphines ( e.g. 1,2 bis( diphenylphosphino ) ethane (dppe) or 1,3
73 bis( diphenylphosphino ) propane (dppp)) 121 122 or diimine groups such bipyridine 121 123 A previous investigation by Schanze and co workers examined four platinum acetylides that contained 4 ethynylstilbene c hromophores, Figure 3 1 121 This study investigated the reactivity of the lowest excited states through both variation of the auxiliary bidentate ligand and the geometry at the platinum center U bipyridine ligand in platinum complexes introduced an energetically low lying d (Pt) (bpy) metal to ligand charge transfer (MLCT) excited state. This excited state c ould be tuned by alteration of the substituents on the diimine ligand. Electron with drawing substituents, for example, lower the energy of the MLCT state while electron donating groups increase the energy. 123 124 Like most platinum acetylide seri es, the platinum center promoted delocalization of the chromophores, and the lowest energy absor ption s for the cis dppe and trans ethynylstilbene analog wer e the result of a transition between HOMO and LUMO levels that wer e substantially delocalized over the molecule. This observation is confirmed both by the ground state absorption spectra of the complexes 121 and by molecular orbital calculations. 88 Figure 3 1 Stilbene containing platinum acetylides 121
74 The triplet excited states of the four ethynylstilbene complexes, howev er, we re not delocalized over the molecular. Rather the triplet excited states we re confined on a single chromophore, as observed by the nearly identical low temperature phosphorescence spectra obtained regardless of the geometry or substituent effects. However, platinum acetylides that incorporate diimines often generate photophysical properties that are, in part, the result of the MLCT interactions of the diimine and platinum center. A dditional p hotophysical investigations have examined platinum compl exes of the type (diimine) PtL 2 where L = halide, nitrile, thiolate, isonitrile, and acetylide 124 130 The platinum(II) diimine complexes featured long lived excited states and photophysics that were predominately dependent on the energetically low lying Pt diimine 3 MLCT. 123 An examp le of the effect of MLCT excitation was observed in (diimine)Pt( C C Ar) 2 Examined was the effect o n ground state absorption, photo luminescence, and triplet triplet transient absorption as the electron demand was modified on the diimine ligand with a di( p tolylacetylene) platinum core ; bis( tert ( butyl)2, bipyridine) imine, Figure 3 2 has also been examined 123 A similar study of platinum complexes, where the diimine was a substituted 1,10 phenanthroline bipyridine, examined the effect of electron withdrawing groups on the acceptor diimines. 124 131 Consistent with the dominant MLCT o bserve d in the complexes in Figure 3 2 the absorption and emission energies decrease d by substitution of electron withdrawing group on the diimine. 124
75 Figure 3 2 Diimine platinum acetylide complexes 123 The large effect on the photophysical response of such diimine platinum acetylides encourages the use of the dppe auxiliary ligand. The replacement of the conjugated extended diimine chelating phosphine with the dppe diphosphine should result in less MLCT effects involving the auxiliary ligand A study by Castellano and co workers as shown in Figure 3 3, examine d the effect of the auxiliary ligand on the photophysical Figure 3 3 Cis platinum acetylides examined by Castellano and c o workers 132 A) Structures with varying auxiliary ligands. B) Absorption and emission spectra of 1 in benzene (blue dashed) and CH 2 Cl 2 (red dashed) and 2 in benzene (black) and CH 2 Cl 2 (gray). C) Absorption and emission spectra of 3 in benzene (blue) and CH 2 Cl 2 (red).
76 properties of platinum acetylides. 132 The ground state absorption spectra of complex 1 and 3 exhibited strong transitions from the phenylethynyl based chromophore, but 1 also possessed a lower energy charge transfer absorption originating from the diimine. Chromophore based fluorescence and phosphorescence were observed for 3 ; the emission was not solvatochromatic, suggesting that th e emission was from a ligand localized triplet ( 3 IL) state. In contrast, the luminescence of 1 was strongly solvent dependent to the extent that solvent selection dictated whether the observed emission wa s from a triplet charge transfer ( 3 CT) state, an 3 I L state, or a mixture. 132 Use of a dppe bidentate ligand ove r the hexyl ligand in Figure 3 3 seem ed to only affect the photophysical properties of platinum acetylides to a small extent. A series of dppe based cis platin um acetylides by Raithby and co workers exhibited acetylide chromophore dependent emission rather than luminescence from the 3 CT states 122 Stable cis platinum acetylide complexes have been studied for their intraligand and charge transfer properties and for use in white 97 133 and red 134 OLEDS neutral molecular square s, 61 135 137 and as molecular tweezers 138 139 applications which are aided by the locked geometry and the near 90 angles formed between the ligand arms. Most investigations within this research area have focused on 1,4 diethynylbenzene or 4,4 diethynylbiphenyl ancillary ligands, and variations, within monomeric or multi platinum species. Despite the growing amount of literature on cis platinum complexes, very few studies have reported the photophysical response (photol uminescen ce, transient absorption ) or nonlinear absorption ( NLA ) and m ost are not designed to exhibit TPA and excited state absorption ( ESA )
77 Reported herein are the cis and trans configured monomeric platinum acetylide s that incorporate three different chromophores onto the platinum core Figure 3 4 and their resulting photophysical and nonlinear characterization As discussed in Chapter 1, t he diphenylaminofluorene ( DPAF ) and benzothiazolefluorene ( BTF ) chromophores utilized are both large c ross section TPA chromophores; these donor and acceptor chromophores will be incorporated onto platinum metal cores by acetylide linkages in both cis and trans geometries. A s previously discussed, trans PE2 (bis ((4 (phenylethynyl)phenyl)ethynyl)bis (tri butylphosphine) platinum(II)) has become a common benchmark for platinum acetylide chemistry. Despite this complex not containing strong donor or acceptor character, it has been shown to display moderate NLA. As such, the cis and trans geometries of PE2 are additionally investigated. The series should allow elucidation of the effects of stereochemistry on the photophysical and nonlinear properties Figure 3 4. Structures of the target cis and trans platinum acetylide complexes
78 The cis and trans complexes are characterized via 1 H and 31 P NMR spectroscopy. The photophysical properties of the series are evaluated by ground state absorption s teady state emission spectroscop y, and triplet triplet transient absorption NLA response is characterized in the nanosecond regime. Synthesis In an effort towards understanding the effects of stereochemistry at the platinum core of platinum acetylides, three trans and three cis target complexes have been synthesized. The PE2, DPAF, and BTF chromophores were synthesized prior to attachment to the platinum metal core ; the chromophores were synthesized by modifications of literature methods, as further described in the experimental section Traditionally, the synthesis of trans platinum acetylides is achieved t hrough a Hagihara coupling reaction, which involves the condensation of the desired alkyne with a chloro platinum(II) complex in the presence of a copper(I) catalyst and an amine base in a polar solvent. It is in this fashion that the three known trans ta rget complexes were synthesized, Figure 3 5 Figure 3 5 Synthetic pathway for generat ion of the three trans platinum acetylide complexes Figure 3 6 shows the pathway for synthesizing the target cis complexes The first intermediate was synthesized by reaction of K 2 PtCl 4 with 1,5 cyclooctadiene in ethano l according to the method described by Baker and co workers. 140 The obtained COD product was then reacted with dppe to synthesize the Pt(dppe)Cl 2 precursor. 60 As has previously been examined with similar dppe bound platinum complexes, the
79 [Pt(dppe)Cl 2 ] precursor was utilized to generate the target cis complexes by reaction with the corresponding chromophores. 121 141 A diphosphine dppe chelating auxiliary group is incorporated into the cis complexes to increase the thermodynamic stability of the generated complexes in a ddition to locking the geometry into a cis coordination. Figure 3 6 Synthetic pathway for generation of the three cis platinum acetylide complexes Results and Discussion The known trans complexes have previously been examined in terms of photophysical and nonlinear characterization. Previously reported are the ground state absorption and molar absorptivities, photoluminescence and quantum yields, and intrinsic two photon absorption cross sections. 38 85 90 As formerly mentioned, t rans PE2 has also been examined under effective NLA 81 142 Transient absorption response s of t rans DPAF and t rans BTF have also been reported. 90 The generated trans complexes are in good agreement with previously reported photophysical characteriza tion. 90 As such, the trans complexes are examined as a comparison to the novel cis complexes. NMR Char acterization 1 H NMR c haracterization The expected 1 H NMR signals from the dppe and PBu 3 protons were observed and identified in the cis and trans complexes. Namely, the methylenic protons were observed at 2.3 2.5 ppm within th e dppe containing cis complexes, whereas the
80 expected PBu 3 protons were observed as an upfield triplet at approximately 0.38 ppm and three multiplets in the region of 0.98 1.8 ppm. In a similar fashion, the three chromophores utilized in the six complexes exhibited expec ted proton sig nals, as is further described in the experimental section. 31 P NMR c haracterization T he 31 P NMR spectra of the examined complex e s provide valuable information about the stereochemistry and influence of the chromophores and auxiliary ligands within the complexes. The phosphorus resonances of all six complexes appear as a singlet with two Pt P satellites resulting from the coupling of the 19 5 Pt nuclei. The trans complexes contained signals between P 1.4 and 4.2 ppm whereas the cis complexes were between P 42.1 and 42.4 ppm The PPt values as shown in Table 3 1, are consistent with previously reported cis and trans platinum acetylides; the trans complexes exhibit PPt values greater than 2300 Hz whereas the PPt for the cis complexes are below 2300 Hz. The platinum coupling constants of the cis complexes are compared to those observed for dppe boun d mononuclear plat inum complexes such as PtPh 2 (dppe) and PtCl 2 (dppe), which exhibit PPt values of 1687 and 3615 Hz, respectively. 60 The coupling constants of the target cis complexes a ppear to be the result of the trans influ ence of the specific ligands within the complexes; a much lower coupling constant is observed for the acetylides or phenyls relative to chlorides. The position of the cis signal s however, is more the effect of the conjugated dppe auxiliary ligand in comp arison to the PBu 3 ligands of the trans complexes This trend has been observed in cis and trans platinum chloride mixtures, where cis and trans PtCl 2 ((PC 2 H 5 ) 3 ) 2 displayed chemical shifts that were only 2.6 ppm apart. 59 Further
81 exemplifying the effect of the auxiliary ligands is the comparison of the complex Pt(C CH) 2 (dppp) where dppp is 1,3 bis( diphenylphosphino ) propane, which exhibited a PPt value of 2195 Hz a nd a singlet at P 6.4 ppm, against the analogous dppe complex, [Pt(C CH) 2 (dppe)], which exhibited a PPt value of 2288 Hz and a singlet at P 40.8 ppm. 61 The close proximity of the coupling constants aids in confirming that the cis platinum complexes were generated. No additional splitting of the central resonance was observed in the cis or trans complexes. Likewise, no resonances were observed in addi tion to the singlet with the platinum coupling satellites. Taken together, these suggest that symmetric complexes were formed where two chromophores were attached to the platinum metal center. This was further confirmed by the proton integration observed for the auxiliary ligands on the metal in comparison to those of the chromophores. Table 3 1. 31 P NMR signals of the cis and trans platinum acetylide complexes in CDCl 3 Chromophore Trans (ppm) Trans PtP (Hz) Cis (ppm) Cis PtP (Hz) PE2 4.16 2347 42.35 2280 DPAF 3.98 2359 42.08 2278 BTF 1.36 2303 42.43 2280 (dppe)PtCl 2 --42.24 3615 X Ray Crystallography Suitable single crystals of c is PE2 and cis BTF have been grown via vapor diffusion of diethyl ether into THF and diethyl ether into DCM, respectively. cis PE2 T he molecular structure of cis PE2 is shown in Figure 3 7 and select interatomic bond distances an d angles are reported in Table 3 2 The molecular structure of trans PE2, Figure 3 8 has been previously been examin ed 137 143 and is compared to cis PE2. The hydrogen atoms have been removed from both structures for clarity.
82 Figure 3 7 Molecular structure with atomic numbering scheme for cis PE2. Figure 3 8 Molecular structure with atomic numbering scheme for trans PE2. 143 Table 3 2. Select ed bond distances ( ) and bond angles (degrees) observed in cis PE2 and trans PE2 143 Distance cis PE2 trans PE2 Angle cis PE2 trans PE2 Pt P 2.271(2) 2.304(1) P Pt P 85.77(11) 180.000 P C29 1.846(5) --C1 Pt C1 94.0(5) 180.000 Pt C1 2.011(8) 1.981(6) P Pt C1 90.1(2) 86.4(1) C1 C2 1.195(9) 1.229(8) P Pt C1 175.8(3) 93.6(1) C2 C3 1.435(7) 1.422(8) Pt C1 C2 172.4(6) 176.7(5) C4 C5 1.388(9) 1.382(9) C1 C2 C3 176.4(6) 176.9(6) C7 C8 1.362(7) 1.380(8) C2 C3 C4 121.2(5) 121.0(5)
83 Table 3 2. Selected bond distances ( ) and bond angles (degrees) observed in cis PE2 and trans PE2 143 c ontinued Distance cis PE2 trans PE2 Angle cis PE2 trans PE2 C3 C4 1.396(8) 1.407(8) C2 C3 C8 121.5(4) 121.6(5) C3 C8 1.419(6) 1.385(8) C5 C6 C9 119.7(5) 121.3(5) C5 C6 1.410(8) 1.391(9) C7 C6 C9 121.6(4) 120.0(5) C6 C7 1.408(6) 1.393(8) C6 C9 C10 177.2(6) 179.5(7) C6 C9 1.434(7) 1.432(8) C9 C10 C11 175.8(8) 178.2(7) C9 C10 1.184(8) 1.191(9) C10 C11 C12 121.1(6) 119.3(6) C10 C11 1.449(8) 1.438(8) C10 C11 C16 118.8(6) 121.5(6) C12 C13 1.411(8) 1.37(1) C4 C3 C8 117.3(5) 117.3(5) C15 C16 1.402(8) 1.38(1) C5 C6 C7 118.5(4) 118.7(5) C11 C12 1.364(8) 1.395(1) C3 C4 C5 122.3(6) 121.0(5) C11 C16 1.422(1) 1.383(9) C4 C5 C6 119.5(5) 120.8(5) C13 C14 1.382(9) 1.37(1) C6 C7 C8 121.2(4) 121.3(5) C14 C15 1.367(9) 1.37(1) C7 C8 C3 121.3(4) 120.2(5) C29 C29 1.532(8) --C12 C11 C16 118.8(6) 119.1(6) C13 C14 C15 120.2(6) 119.9(7) C12 C11 C16 120.5(6) 119.6(7) C11 C12 C13 119.6(6) 121.0(8) C14 C15 C16 121.4(6) 120.4(7) C15 C16 C11 118.2(6) 120.0(6) C5 C6 C11 C12 9.054(710) 15.825(746) C7 C6 C11 C16 12.983(717) 13.975(738) The geometry around the platinum metal center in cis PE2 is approximately square planar, with a sum of the angles around the metal center being 359.97 The cis PE2 P Pt C1 and P Pt of 90.1 (2) and 175.3 (3) respectively, are similar to other known cis platinum acetylides. 61 The smallest angle around the platinum metal is that subtended by the dppe ligand, as is anticipated due to the expected bit e angle of the dppe ligand onto a platinum center. 61 144 ( Variation to a diphenylphosphinopropane auxiliary ligand as previously observed in a [Pt 4 (C CC C) 4 (dppp) 4 ] molecular square in comparison, has a P Pt P angle of 95.52(9) due to the larger bit e angle onto t he platinum center. 61 ) The Pt C 1 and Pt P bond lengths of cis PE2 are 2.011 (8) and 2.271 (2) respectively, which are also in good agreement with previously reported cis platinum
84 complexes. The observed Pt C 1 length is 0 .03 longer than that observed in the trans analogue, while the Pt P is 0.03 shorter This deviation is most likely the result of the dppe ancillary ligand and resulting geometry with in the cis complex. The platinum acetylide units deviate more strongly from the expected linear angle of 180 within the cis complex; the cis complex has a Pt C1 C2 angle of 172.4 (6) while the trans analogue exhibits an angle of 176.7 (5) However, the angle observed in cis PE2 is consi stent with other similar cis platinum acetylides such as 174.3 (5) in Pt(C CH) 2 (dppe) 61 168.0 (3) in Pt( C CC 6 H 4 p CH 3 ) 2 (dppe), 122 and 171.9 (4) in Pt(C CC 6 H 4 p C 6 H 4 p C CH) 2 (dppe) 122 The C C bond proximal to the platinum metal center in cis PE2 is longer than the distal C C bond 1.195 (9) versus 1.184 (8) This length is lon ger than those observed in Cl C C Cl systems of 1.183 but notably shorter than the C C bond length observed in trans PE2 of 1.229(8) 143 Davy and co workers suggest that the lengthening of the acet ylide bond observed in trans PE2 is the result of d backbonding i n the phenylethynyl chromophore, as is especially evident for the C C adjacent to the metal center. The shorter distal C C bond in trans PE2 (1.191(9) ) in addition to the average dihedral angle of 14.9 between the two phenyl groups, indicates that the conjugation does not extend throughout the PE2 chromophore. The observed lengths in cis PE2 suggest that d backbonding could occur in the chromophore, particularly near the plat inum center, but to a smaller extent than observed in trans PE2. Interestingly, the average dihedral angle in cis PE2 of 11.0 is smaller than the 14.9 angle observed in trans PE2, which would promote conjugation throughout the chromophore in the cis geo metry
85 Contribution from the vinylidene tautomer has been previously noted based on the (at C4 C5 and C7 C8) within the phenyl units and the resulting sma ller internal phenyl angles; t he internal angles in cis PE2 at C3 and C 6 are 117.3(5) and 118.5(4), respectively, which are significantly smaller than the surrounding internal phenyl angles of 119.5(5) 122.3(6) This sug gest s that the cis species also exhibits contribution from the valence isomer Figur e 3 9 and Table 3 2 The internal angles in cis PE2 at C11 and C14 are more consistent with the other angles present in the second phenyl unit, 118.8(6) and 120.2(6), respectively in a unit with internal angles of 118.2(6) 121.4(6). Figure 3 9 V inylidene tautomer cis BTF The molecular structure of cis BTF is shown in Figure 3 10 and select interatomic bond distances an d angles are reported in Table s 3 3 and 3 4 The benzothiazole portion of one chromophore displayed a small degree of disorder, with the nitrogen on the same side as the aliphatic chains of the fluorene unit 80% of the time; the disorder resulted in the two chromophores being similar, but not symmetr ically equivalent. As such, the bond lengths and angles are listed separately by chromophore within the cis BTF complex. Additionally, two DCM solvent molecules were observed in the cis BTF crystal structure. While at distances such that they do not in teract with the complex, the DCM molecules are also shown in Figure 3 10. The molecular structure of trans BTF,
86 Figure 3 11, has been previously been examined 90 and is compared to cis BTF. The hydrogen atoms have been removed from both structures for clarity. Figure 3 10 Molecular structure with atomic numbering scheme for cis BTF. Figure 3 11 Mole cular structure with atomic numbering scheme for trans BTF. 90
87 Table 3 3 Selected bond distances ( ) observed in trans BTF 90 and cis BTF. Distance trans BTF Distance cis BTF Distance cis BTF Pt P 2.2941(7) Pt P1 2.2649(7) Pt P2 2.2709(7) P1 C53 1.849(3) P2 C54 1.845(3) C53 C54 1.535(4) Pt C1 2.000(3) Pt C1 2.013(3) Pt C27 2.010(3) C1 C2 1.208(4) C1 C2 1.203(3) C27 C28 1.201(4) C2 C3 1.442(4) C2 C3 1.439(4) C28 C29 1.438(4) C4 C5 1.391(4) C4 C5 1.391(4) C30 C31 1.379(4) C7 C8 1.378(4) C7 C8 1.377(4) C33 C34 1.381(4) C3 C4 1.406(4) C3 C4 1.409(4) C29 C30 1.413(4) C3 C8 1.414(4) C3 C8 1.407(4) C29 C34 1.408(4) C5 C6 1.395(4) C5 C6 1.393(4) C31 C32 1.392(3) C6 C7 1.401(4) C6 C7 1.407(4) C32 C33 1.405(4) C6 C15 1.466(2) C6 C15 1.471(4) C32 C41 1.461(3) C7 C9 1.525(4) C7 C9 1.529(4) C33 C35 1.530(3) C9 C10 1.525(4) C9 C10 1.527(4) C35 C36 1.527(3) C10 C11 1.374(4) C10 C11 1.381(4) C36 C37 1.385(3) C13 C14 1.387(4) C13 C14 1.387(4) C39 C40 1.384(4) C10 C15 1.403(4) C10 C15 1.411(4) C36 C41 1.408(3) C14 C15 1.396(4) C14 C15 1.383(4) C40 C41 1.387(3) C11 C12 1.411(4) C11 C12 1.403(4) C37 C38 1.402(4) C12 C13 1.399(4) C12 C13 1.403(4) C38 C39 1.403(4) C12 C16 1.472(4) C12 C16 1.471(4) C38 C42 1.468(4) C16 S 1.775(3) C16 S1 1.761(3) C42 S2 1.761(3) C16 N 1.316(5) C16 N1 1.270(4) C42 N2 1.303(3) C17 S 1.734(3) C17 S1 1.755(4) C43 S2 1.727(3) C22 N 1.409(4) C22 N1 1.372(4) C48 N2 1.393(3) Table 3 4 Selected bond angles (degrees) observed in trans BTF 90 and cis BTF. Angle trans BTF Angle cis BTF Angle cis BTF P Pt C1 90.68(8) P1 Pt C1 90.82(7) P Pt 89.32(8) P1 Pt C27 177.53(7) P2 Pt C1 176.18(7) P2 Pt C27 91.42(7) P Pt 179.998(17) P1 Pt P2 86.33(2) C1 Pt 180.00(4) C1 Pt C27 91.38(10) Pt C1 C2 176.6(3) Pt C1 C2 170.8(2) Pt C27 C28 178.1(2) C1 C2 C3 174.4(3) C1 C2 C3 170.0(3) C27 C28 C29 176.9(3) C4 C3 C8 119.0(3) C4 C3 C8 119.0(2) C30 C29 C34 119.4(2) C5 C6 C7 120.4(3) C5 C6 C7 120.4(2) C31 C32 C33 120.8(2) C7 C9 C10 101.0(2) C7 C9 C10 100.7(2) C33 C35 C36 100.8(2) C10 C15 C14 120.6(3) C10 C15 C14 120.6(2) C36 C41 C40 120.8(2) C11 C12 C13 119.6(3) C11 C12 C13 119.6(2) C37 C38 C39 119.5(2) N C16 S 116.5(2) N1 C16 S1 115.2(2) N2 C42 S2 115.8(2)
88 Similar to cis PE2, the geometry around the platinum center of cis BTF is approximately square planar and the angle subtended by the dppe ligand is 86.33(2) the smallest of the four angles around the metal center. The P1 Pt C1 and P1 Pt C27 angl es of 90.82(7) and 177.53(7) respectively, are consistent with previousl y reported cis platinum acetylides. 61 The Pt C1 and Pt C27 bond lengths of 2.013(3) and 2.010(3) within the cis BTF complex are slightly longer than the comparative Pt C1 bonds of the tra ns BTF of 2.000(3) Similarly, the Pt P1 and Pt P2 bond lengths of 2.2649(7) and 2.2709(7) within the cis BTF complex are slightly shorter than the comparative Pt C1 bonds of the trans BTF of 2.2941(7) Common within platinum acetylides is the obse rvation that the Pt P bond lengths are 0.2 0.4 longer than the Pt C bond lengths, regardless of the geometry around the platinum center. 61 121 122 143 145 Taken together, the observed cis BTF and trans BTF platinum bond lengths further indicate that the dppe ligand and geometry around the platinum center affect the length deviat ion more so than the choi ce of chromophore. As previously indicated the cry stal structure of cis BTF displayed a small degree of disorder within one benzothiazole portion of one chromophore. The effect of this disorder is most apparent when examining the bond angles of the chromophores. The Pt C27 C28 bond angle of 178.1(2) i s much more linear than the Pt C1 C2 angle of 170.8(2) However, both angles are within the expected region for cis platinum acetylides. 122 61 The Pt C C bond angle of 176.6(3) observed in trans BTF also shows slight deviation from linearity. The acetylide bond lengths are nearly identical in both complexes : 1.203(3) for C1 C2 and 1.201(4) for C27 C28 within cis BTF, and
89 1.208(4) for trans BTF, suggesting similar conjugation across the platinum acetylide portions of the complexes. The two phenyl rings present within the chromophore are locked by the five membered ring. As such, the formed dihedral angle is small: 1.796(496) for C5 C6 C15 C14 and 0.235(465) for C31 C32 C41 C40 within cis BTF, and 0.153(511) for C5 C6 C15 C14 within trans BTF. However, the dihedral angle formed between the second phenyl and the benzothiazole displays mo re pronounced twist ing particularly within trans BTF: 8.787(353) for C13 C12 C16 S1 and 6.417(345) for C39 C38 C42 S2 within cis BTF, and 13.682(361) for C13 C12 C16 S within trans BTF. The internal phenyl angles within the fluorene portion of the chromophores deviate only slightly from the expected 120 The internal fluorene phenyl angles in cis BTF at C3 and C29 are 119.0(2) and 119.4(2) respectively, while the surround ing internal fluorene phenyl angles are between 118. 8 (2) and 121.4(3). Similarly, the internal angle in trans BTF at C3 is 119.0(3) while the surrounding internal fluorene phenyl angles are between 11 9.6(3) and 121. 1 (3) These angles are in contras t to those observed within the cis PE2 and trans PE2 complexes, where shortening of the phenyl es suggest contribut ion from the vinylidene valence isomer Such contribution is unlikely within th e BTF complexes, as confirmed by the lack of significantly smaller internal angles that resulted Ground State Absorption Spectroscopy The ground state absorption spectra for the cis and trans platinum acetylide series in THF s olutions are shown in Figure 3 12 The wavelength maxima and molar
90 Figure 3 12 Ground state absorption of the cis and trans platinum acetylide series in THF absorption coefficients for the platinum ac etylides are listed in Table 3 5 The S 0 S 1 absorption maxima for the complexes in the cis geometry are blue shifted relative to the absorption maxima observed for the trans complexes The PE2 platinum acetylides are th e most blue shifted of the series, with cis PE2 exhibiting a maximum at 330 nm and trans PE2 at 353 nm. The DPAF acetylides are red shifted to 377 nm and 384 nm for the cis and trans complexes, respectively. Similarly, the BTF acetylides exhibit S 0 S 1 absorption maxima at 375 nm and 402 nm for the cis and trans complexes, respectively.
91 Noted is the trend that the trans complexes are red shifted approximately 20 nm from that of the cis complexes. In addition to the observed shift in ground state absorpt ion maxima, the cis platinum acetylides exhibit more pronounced vibrational structure relative to the trans complexes examined. This observation has also been noted in similar 4 ethynylstilbene cis and trans platinum acetylide complexes. 121 The pronounced structure implies that electron vibrational coupling is stronger in the cis complexes The combination of the blue shift and the increase of vibrational structure suggests a weaker i nteraction between the chromophores in the cis complexes and indicates that the singlet excited state is more localized on a single ligand. In contrast, the trans platinum acetylides show a larger red shift from the free ligands and a lack of vibr onic structure, suggesting weaker electron vibrational coupling, which implies a larger degree of delocalization in the S 1 excited state due to the proximity and mixing of the Pt d orbitals. Noted also is the trend that the trans complexes exhibit higher extinction coefficients than do the cis complexes for both the DPAF and BTF series approximately 160,000 M 1 cm 1 for the trans BTF and DPAF complexes in comparison to approximately 130,000 M 1 cm 1 for the cis equivalents Additionally, the DPAF complexes both exhibit similar, but higher, coefficients than do the BTF equivalents. In comparison to the DPAF and BTF complexes, the cis and trans PE2 complexes display similar, but lower molar absorptivity values, 85,600 and 83,400 M 1 cm 1 respectiv ely. The observed red shifts and increases in extinction coefficients in the trans complexes relative to the cis complexes indicate larger conjugation conjugation that may extend through the platin um acetylide to a larger extent
92 Table 3 5 One ph oto n photophysical properties of the cis and trans platinum acetylide series in THF Complex Abs max a (nm) (M 1 cm 1 ) Fl max b (nm) F c F Ave (ps) Ph max d (nm) P c trans PE2 353 83,381 391 0.0005 < 200 e 527 0.0108 cis PE2 330 (345) 84,015 425 0.0003 528 f 522 0.0011 trans DPAF 384 159,892 401 0.0059 < 200 e 533 0.3552 cis DPAF 377 131,628 424 0.0061 1827 g 533 0.0039 trans BTF 402 154,574 436 0.0092 < 200 e 567 0.1752 cis BTF 375 (396) 128,024 439 0.0208 507 h 562 0.0102 a Ground state absorption maxima b Fluorescence s pectra obtained by excitation at ground state absorption maxima c Quantum yields relative to Ru(bpy) 3 in air saturated DI water, = 0.0379 113 d Phosphorescence spectra, obtained by excitation at ground stat e absorption maxima e Lifetime is shorter than lower threshold of PicoQuant instrument, 200 ps f 1 ( 1 ) = 739 ps (23.64%); 2 ( 2 ) = 318 ps ( 71.26%); 3 ( 3 ) = 2.48 ns (5.10%) g 1 ( 1 ) = 2.17 ns (80.60 %); 2 ( 2 ) = 408 p s ( 19.40 %) h 1 ( 1 ) = 685 ps (34.14%); 2 ( 2 ) = 414 ps (65.86%) Steady State Photoluminescence Spectroscopy Emission spectra of the cis and trans platinum acetylide series are shown i n Figure 3 13 The fluorescence and phosphorescence of the complexes can be distinguished by comparing the photoemission in air saturated and deoxygenated solutions the phosphorescence is largely quenched in the presence of oxygen. As such, the solid lines in Figure 3 13 represent the fluorescence and weak phosphorescen ce of the samples that are exhibited in air saturated solutions whereas the dashed lines represent the phosphorescence exhibited in deoxygenated solutions. All six complexes feature moderately intense photoluminescence at room temperature. The cis comple xes exh ibit fluorescence maxima that are red shifted from the similar trans complexes (425 nm 439 nm for cis complexes compared to 391nm 436 nm for trans complexes ) The phosphorescence, in contrast, exhibits only a small red shift when comparing the trans complexes to the ir cis counterparts Interestingly, the
93 Figure 3 13 Emission spectra of the cis and trans platinum acetylide series via excitation at the ground state absorption maxima in air saturated (solid line) and deoxygenated (dashed line ) THF. phosphorescence bands of each cis and trans pair are almost identical to each other. This finding suggests that the luminescent 3 state is the same within each set, which implies that the chromophore, not the coordination geometry, is dominating the transition the triplet excited state is possibly localized on a single chromophore. While the phosphorescence emission may originat e from the chromophore based triplet state, the population of T 1 occurs through efficient spin orbit coupling between the
94 excited chromophore and the heavy metal platinum atom. This phosphorescent observation is consistent with similar conjugated pla tinum acetylide systems that also show a localized triplet excited state. 88 90 146 148 The photoluminescent spectra of the cis complexes also show no evidence for MLCT emission involving the ancillary ligand, w hich would appear as a broad, structureless emission bands. 121 This lack of emission bipyridine. Addi tionally noted in the emission spectra are the large differences in phosphorescence quantum yields between the cis and trans complexes that contain the same chromophore. Specifically noted is the order of magnitude or greater increase in the phosphorescen ce quantum yields of the trans complexes versus the cis analogs. The fluorescent lifetime data are also summarized in Table 3 5. The trans complexes exhibit a very short fluorescent lifetime (< 200 ps), shorter than the lower threshold of the available instrumentation. Conversely, the cis complexes exhibit short but measureable lifetimes of 528 ps, 507 ps, and 2.01 ns for cis PE2, cis DPAF, and cis BTF, respectively. The phosphorescence lifeti mes and triplet decay rates are summarized in Table 3 6. Assuming that the triplet excited state is populated only through excitation of the ground state to form the singlet excited state, followed by ISC, then the rate of radiative decay of the triplet k P can be determined by Equation 3 1: k p = p / ( ISC P ) (3 1 ) where p and ISC are the quantum yields of phosphorescence and intersystem
95 c rossing, respectively, and P the phosphorescence decay lifetime is defined in Equation 3 2: P = 1 / ( k P + k nr ) (3 2) where k nr is the rate of all nonradiative processes from the triplet excited state. T he differences in lifetimes and phosphorescent quantum yields between the cis and trans complexes are most likely not the result of ISC efficiency, since platinum acetylides in both geometries have been shown to exhibit fast ISC rates and ISC near unity. 35 90 Rather, the large observed differences are proposed to be th e result of radiative and nonradiative decay rates of the triplet excited state. Table 3 6. Triplet excited state properties of cis and trans platinum acetylide series in THF Complex max (nm) T1 Tn ( s) a Phos ( s) b k Phos (s 1 ) c k nr (s 1 ) d trans PE2 577 15.4 48.9 2.21 x10 2 2.02 x10 4 cis PE2 556 17.8 35.9 0.31 x10 2 2.78 x10 4 trans DPAF 612 8.9 61.3 57.94 x10 2 1.05 x10 4 cis DPAF 597 3.3 36.7 1.06 x10 2 2.71 x10 4 trans BTF 507, 660 13.3 75.6 23.17 x10 2 1.09 x10 4 cis BTF 633 6.5 80.5 1.27 x10 2 1.23 x10 4 a Triplet excited state lifetime, calculated from the transient absorption spectra b Phosphorescent lifetime c Phosphorescent decay lifetime d Nonradiative decay lifetime The radiative decay rate of the triplet (k p ) is larger in trans DPAF and trans BTF than in the cis counterparts. For the cis complexes, the nonradiative decay pathways are more favorable, Table 3 6. Nonradiative decay processes also appear to compete strongly with the phosphorescent emission of the PE2 complexes. This is more lik ely within the PE2 complexes since the chromophore structure is not as rigid as the DPAF or BTF chromophores. Further, it is proposed that cis and trans PE2 may exhibit thermal bending in the form of an acetylene rearrangement in the excited state, allow ing these complexes to relax readily via nonradiative processes.
96 Transient Absorption Spectroscopy and Triplet Excited State Lifetimes Nanosecond transient absorption spectra of the six platinum acetylides were measured in deoxygenated THF to provide addit ional information about the triplet excited states Figure 3 14 Pulsed photoexcitation of the platinum acetylide complexes Figure 3 14 Triplet triplet transient absorption spectra under 355 nm excitation of the cis and trans complexes in deoxygenat ed THF 360 s q switch delay 8 mJ energy, 10 ns camera delay, 100 images averaged, 10 ns gate width.
97 with the third harmonic output (355 nm) of a Continuum Surelite II Q switched Nd:YAG laser affords transient absorption spectra that are strong and broad throughout most of the visible region. The absorption maxima are listed in Table 3 6. The negative differ ence absorption bands below 450 nm correspond to bleaching of the UV ground state absorption bands assigned to the (S 0 S 1 ) transition. The positive and moderately intense visible absorptions are due to the triplet triplet (T 1 T n ) absorption by the 3 triplet excited state. The absorption region displayed by the complexes is largely the result of the chromophore; the PE2 complexes exhibited absorption from approximately 450 600 nm, whereas the DPAF and BTF complexes exhibited broader absorption, from approximately 450 800 nm. These observations are consistent with previously examined transient absorption of t DPAF and t BTF, which exhibit broad and strong triplet signals with maxima absorptions at 612 and 660 nm in benzene 90 An additional observation in the triplet triplet transient absorption spectra is a blue shift of the cis complexes relat ive to their trans analogs. This is in contrast to the previously investigated stilbene containing platinum acetylides, in which virtually identical transient absorption spectra were observed for trans Pt(PBu 3 ) 2 (4 ES) 2 cis Pt(dppe)(4 ES) 2 and cis Pt( t Bu bpy)(4 ES) 2 (where 4 ethynylstilbene is abbreviated 4 di tert butyl bipryidine is abbreviated t Bu bpy). 121 However, the stilbene complexes also exhibited short lived tri plet excited state lifetimes (sub s) and triplet triplet absorption that extended from 400 to 600 nm and bore strong resemblance to that of stilbene. Taken together, these observations suggested that the transient within the 4 ethynylstilbene containing platinum complexes is localized on a single
98 stilbene ligand. The short lifetimes are proposed to be the result of rapid nonradiative decay of the triplet via twisting around the C=C bond in the stilbene ligand. The cis and trans complexes of this study a re unable to undergo such nonradiative decay as a result of twisting; as such, the triplet excited state lifetimes of the examined complexes are much longer than the stilbene derivatives approximately 3 to 18 s in length. Recent research by Sun has repor ted the photophysical characterization of a cis diimine platinum acetylide that contains two BTF chromophores. 149 150 Similar to the observed cis and trans complexes of this study, the cis diimine platinum complex also exhibited a transient absorption spectrum that was blue shifted approximately 50 nm from the T 1 T n absorption maximum of the trans BTF analog and a T 1 T n lifetime of 10.8 s. The superimposable nature of the phosphorescence bands within each cis and trans pair suggests that the emissive triplet excited state is the same within each set, which implyi ng that he chromophore, not the coordination geometry, is dominating the transition. This trend has been observed in similar platinum acetylide systems and is proposed to be the result of the triplet emissive state being localized on a single chromophore. 88 90 146 148 However, the observed shifts in the triplet triplet transient absorption between the cis and trans pairs suggest that the T n state is more delocalized in the trans isomers. Nonlinear Absorption Key to the design and generation of these platinum acetylide complexes is their NLA response. These materials are designed to undergo rapid TPA followed by intersystem crossing to populate the triplet excited state. The complexes should then
99 allow the ab sorption of an addition al photon to generate a higher triplet excited state. The photoluminescence and transient absorption data on the cis and trans complexes suggest that this dual mode pathway, which combines TPA with triplet ESA should be a viable excitation pathway for NLA Nonlinear measurements of the cis and trans complexes were conducted via an open aperture nanosecond z scan apparatus in 1 mM solutions in THF Figure 3 15 Cis DPAF was not readily soluble in THF at the co ncentrations needed for the ns z scan experiments; as such, the measurements of this sample were conducted in a 1:24 DCM/THF solution mixture. An excitation wavelength of 600 nm was selected due to the lack of appreciable ground state absorption at this w avelength for all complexes The platinum acetylide complexes are compared to T2, a diplatinum acetylide with a dithiophene core and endcapped with DPAF chromophores, Figure 1 16 that exhibits strong NLA response at 600 nm excitation. 35 Figure 3 15 A shows a representative ns z scan experiment of the transmittance of the six complexes. Negligible NLA was observed initially, as reflected in the consistent transmittance at the larger, negative z positions. As the flux of the laser increases, the samples displayed NLA response, seen in Figure 3 15 A as the attenuation of transmittance in response to the changing laser focus. As the samples travelled out of the focus, the NLA response lessened and the transmittance ratio increases until no NLA occu rs. Figure 3 15 B shows the average percen t absorptance (absorptance = 1 transmittance) at the laser focus z = 0 mm for the six cis and trans complexes from multiple trials. Trans DPAF exhibits the strongest overall NLA response, with an
100 average absorptance of 0.714, whereas cis DPAF exhibits weaker attenuation of 0.891. The cis and trans BTF pair exhibit similar responses of 0.805 and 0.788, respectively. Both PE2 complexes exhibit NLA response, but markedly less than the other complexes: tra ns PE2 exhibits absorptance of 0.934 while cis PE2 exhibits absorptance of 0.912. These results suggest that chromophore selection is more critical to the NLA response strength than is the geometry at the platinum center. However, trans DPAF exhibits not iceably stronger transmittance attenuation than its cis counterpart. Figure 3 15 NLA response of 1 mM platinum acetylides A: Ns open aperture z scan response in THF after 600 nm excitation and 750 J input energy B: Average nonlinear absorptanc e (1 T ransmittance ) Summary A series of platinum acetylides is studied to quantify the effect of stereochemistry on the excited state properties and nonlinear absorption response. Two geometries, cis and trans are examined to investigate the extent of conjugation through the platinum metal center with the three known chromophores. The known trans complexes are generated via Hagihara coupling reactions. The cis complexes are synthesized via a [Pt(COD)Cl 2 ] in termediate, which is locked into the desired geometry via a bidentate
101 dppe ligand before reaction with the TPA chromophore s to generate the target complexes. A detailed photophysical investigation has been conducted on the six cis and trans platinum acet ylides The ground stat e absorption spectra of the complexes are dominated by a 3 transition, which red shifts upon addition of the strong TPA chromophores. The cis complexes exhibit more pronounced vibronic structure than the trans analogs. Additio nally, a smaller red shift from the ground state absorption of the free chromophores is observed for the cis complexes. Taken together, these findings suggest less delocalization of the S 1 excited state in the cis platinum acetylide complexes. All six c omplexes exhibit moderately intense photoluminescence at room temperature indicating that the platinum center is able to induce intersystem crossing and population of the triplet excited state manifold The phosphorescent spectra of each chromophore set are nearly identical in peak position, suggesting that the emission is a localized, ligand centered transition However, the phosphorescent quantum yields are lower in the complexes of cis stereochemistry. The crystal structure comparison of cis and tra ns PE2 and BTF sh ows longer platinum C C bond lengths in the trans complexes, suggesting a higher degree of d backbonding Consistent with the observed photophysical characterization, the C C bond length in cis BTF is very similar to its trans analogue. It is proposed that the rigid nature of the BTF and DPAF chromophores and extent of backbonding aid in higher phosphorescent quantum yields observed in trans BTF and trans DPAF. The PE2 complexes, cis BTF, and cis DPAF exhibit lower
102 phosphore scent quantum yields that are proposed to be the result of strongly competing nonradi ative decay processe s; for the PE2 complexes, the nonradiative decay pathway may be the consequence of thermal bending of the acetylene in the excited state. T he tri plet excited state s were further probed via triplet triplet transient absorption. The six complexes exhibit relatively strong and broad transient absorpti on across most of the visible region. The tran sient absorption maxima appear to be dependent on chro mophore selection, whereas the delta absorption strength observed is more dependent on the stereochemistry of the platinum center. The NLA response s of the complexes were measured via a ns open aperture z scan apparatus against the diplatinum acetylide T2 Based on the z scan experiments, several trends are proposed. The trans complexes exhibit attenuation of transmittance in order of trans DPAF > trans BTF > trans PE2 while the cis complexes are in order of cis BTF > cis DPAF > cis PE2. The NLA respons e of cis PE2 is similar to, but stronger than trans PE2. Trans BTF and cis BTF exhibit comparable NLA response s As such, the overall ordering of the NLA response of the complexes is proposed to be trans DPAF > trans BTF ~ cis BTF > cis DPAF > cis PE2 > trans PE2. In summary, the platinum acetylide complexes in the cis geometry exhibit photoluminescent and nonlinear properties similar to their trans analogues. The broad and strong triplet triplet transient absorption spectra across most of the visible spectral region of the cis complexes, paired with the weak ground state absorption in the visible to near IR makes these complexes promising candidates for photonic and electronic devices that require NLA. The ease of synthesis and locked cis stereochemi stry make these complexes ideal materials within applications where incorporation of two
103 chromophores is desired without inhibiting the access to the platinum metal center; envisioned is the use of such complexes in platinum acetylide polymers, where the d ppe portion of the molecule is modified for incorporation into the polymer backbone, allowing for incorporation of two NLA chromophores onto the platinum center. Experimental Instrumentation 1 H, 13 C, and 31 P NMR spectra were recorded on a Varian Mercury 300 s pectrometer in deuterated chloroform; chemical shifts ( ) are reported in ppm and referenced to tetramethylsilane or protonated solvent signals. Elemental analyses were performed by the University of Fl orida Spectroscopic Services. X Ray Intensity data were collected at 100 K on a Bruker SMART diffractometer using MoK radiation ( = 0.71073 ) and an APEXII CCD area detector. Raw data frames were read by program SAINT and integrated using 3D profiling algorithms. 151 The resulting data were reduced to produce hkl reflections and their intensities and estimated standard deviations. The data were corrected for Lorentz and polarization effects and numerical absorption corrections were applied based on indexed and measur ed faces. The molecular structure was solved and refined in SHELXTL6.1, using full matrix least squares refinement. 152 The non H atoms were refined with anisotropic thermal parameters and all of the H atoms w ere calculated in idealized positions and refined riding on their parent atoms. For the x ray structure of cis PE2: The asymmetric unit consists of two half Pt complexes (each located on 2 fold rotational axis of symmetry), and two half THF solvent molecules. The latter were disordered and could not be modeled properly, thus program SQUEEZE, a part of the PLATON package of crystallographic software was
104 used to calculate the solvent disorder area and remove its contribution to the overall int ensity data. 153 In the final cycle of refinement, 10398 reflections (of which 9524 are observed with I > 2 (I)) were used to refine 552 parameters and the resulting R 1 wR 2 and S (goodness of fit) were 2.97 %, 6.72 % and 1.135 respectively. The refinement was carried out by minimizing the wR 2 function using F 2 rather than F values. R 1 is calculated to provide a reference to the conventional R value but its function i s not minimized. For the x ray structure of cis BTF: The asymmetric unit consists of the Pt comple x and two dichloromethane solvent molecules. There are two disordered regions in the ir site occupation factors dependently refined. The second disordered region involves atoms S1/N1 and C17 C22. The two parts were also refined with their site occupation factors fixed at 0.8/0.2 for the major and minor parts, respectively. In the final cycle of refinement, 1 5721 reflections (of which 12 308 are observed with I > 2 (I)) were used to refine 820 parameters and the resulting R 1 wR 2 and S (goodness of fit) were 2.4 3 %, 4. 98 % and 0.96 8 respectively. The refinement was carried out by minimizing the wR 2 function using F 2 rather than F values. R 1 is calculated to provide a reference to the conventional R value but its function is not minimized. Unless noted, one photon photophysical studies were carried out with samples contained in 1 x 1 cm quartz or glass spectroscopic cuvettes. Ground state absorption spectra were measured on a Varian Cary 100 dual beam spectrop hotometer. Corrected steady state emission measurements were performed on a Photon Technology International (PTI) photon c ounting fluorescence spectrometer; sample
105 concentrations were adjusted to produce optically dilute solutions, O.D. max < 0.20. Samples were argon purged for 20 minutes for phosphorescent measurements. Low temperature measurements were conducted in distil led HPCL grade 2 methyl THF and placed in a standard NMR tube. The tube was then inserted into a liquid nitrogen filled silvered finger dewar and placed into the PTI spectrometer sample holder. Quantum yields were calculated against Ru(bpy) 3 Cl 2 in air sa turated deionized water ( = 0.0379). 113 Fluorescent lifetimes were obtained with a PicoQuant FluoTime 100 Compact Fluorescence counting technique (TCSPC) with a PicoQuant FluoTime 100 Compact Fluorescence Lifetime Spectrophotometer. A UV pu lsed diode laser provided the excitation at 375 nm (P < 10 mW). The laser was pulsed using an external BK Precision 4011A 5MHz function generator. Decays were obtained using the biexponential fitting parameters within the PicoQuant PicoHarp software. Nanosecond triplet triplet transient absorption measurements were conducted using the third harmonic of a Continuum Surelite II an excitation pulse of E p = 8 mJ. Sample concentrations were adjusted to an optical density of 0.7 at the excitation wavelength. The sample solutions were placed in a continuously circulating 1 cm pathlength flow cell holding a volume of 10 mL. The sample solutions were prepared in THF and deoxygenated by bubbling with argon. Triplet excited state lifetimes were calculated from the tran sient absorption spectra with software developed in house using samples prepared identically to those used for nanosecond triplet triplet transient absorption measurements The software and instrumentation have been described previously, though the system has been modified
106 to incorporate a Surelite Continuum I Nd:YAG laser for excitation at 355 nm. 116 The lifetimes were such that the arc lamp pulser was not necessary. A 1 k termination was used at the scope on channel one. The software settings were adjusted to a 20 MHz bandwidth and 1 M termination. Nonlinear transmission measurements were performed via an open aperture z scan apparatus. The excitation wavelength w as generated by a Continuum Surelite OPO Plus pumped with the third harmonic (355 nm) of a Continuum Surelite II 10 Nd:YAG laser. The laser beam was split with a 50:50 beam splitter to two OPH PE10 SH V2 pyroelectric detectors, which measured the transmit ted pulse energy as a function of the input pulse energy using an Ophir Laserstar dual channel optical laser energy meter. The beam was focused with a 25.4 mm d iameter, 50.8 mm focal length concave lens. A ThorLabs motorized translation state (Z825B and TDC001) allow ed mm movement along the z axis. Materials and Synthesis All chemicals used for the synthesis of the cis and trans platinum acetylide complexes were reagent grade and used without purification unless otherwise noted. Potassium tetrachloropl atinate was purchased from Strem Chemicals; all other chemicals were purchased from Sigma Aldrich or Fisher Scientific. Solvents were of reagent grade unless otherwise noted. Flash chromatography was performed on Sili cycle Inc. silica gel, 230 400 mesh Dichlorobistriphenylphosphine platinum(II) This known complex was synthesized by a modification of literature methods. 154 To a 50 mL round bottom flask with a stir bar was added K 2 PtCl 4 ( 295 mg, 0.711 mmol) and 5 mL deionized water. The
107 r esulting red solution was argon purged for 30 minutes, followed by the addition of room temperature 350 L tributylphosphine ( 1.426 mmol) via syringe. The resulting solution was stirred under argon for f our hours, then left overnight without stirring. The pink mother liquor was decanted and the resulting solid washed three times with cold deionized water. The solid was then dried on a vacuum line for 24 hours resulting in an off white solid. Recrystal lization in minimum hot ethanol results in white crystals that were collected via suction filtration. Filtrate was reduced and recrystallized for multiple crystal crops. Yield 437 mg, 91% The PE2 chromophore was synthesized as outlined in Figure 3 1 6 : Figure 3 1 6 Synthetic scheme for formation of PE2 chromophore. 3 (4 ( P henylethynyl)phenyl)prop 2 yn 1 ol ( 4 ) To a 250 mL round bottom flask were added 35 mL each of THF and triethylamine. The solution was purged with argon p rior to the addition of CuI (118 mg, 0.620 mmol) and PdCl 2 (PPh 3 ) 2 (182 mg, 0. 259 mmol). The solution wa s further argon purged before the addition of 1,4 diiodobenzene (4.95 g, 15.014 mmol) and room temperature phenyl acetylene (98%, 1.48 mL, 13.475 mmol). The resulting amber br own solution wa s stirred at room temperature for 1.25 hours and monitored by TLC. Propargl alcohol (0.87 mL, 14.945 mmol) wa s added via syringe, then the reaction wa s stirred for 8 hours. The salt wa s removed via filtration and the solvent removed in vac uo. The resulting orange brown liquid wa s dissolved in DCM and washed with aqueous NH 4 Cl and NaCl solutions. The organic layer wa s reduced in vacuo and the crude product purified via flash chromatography (gradient shift
108 3:2 hexanes/DCM to DCM), 1.381 g s hiny tan powder isolated, 40% yield. 1 H NMR (300 MHz, CDCl 3 ) 7.52 (m, 2H), 7.44 (m, 4H), 7.35 (m, 3H), 4.52 (d, 2H), 1.66 (t, 1H). 1 E thynyl 4 (phenylethynyl) benzene ( PE2 ) To an argon purged 250 mL round bottom flask wa s added 3 (4 (phenylethynyl )phenyl)prop 2 yn 1 ol (1.238 g, 5.33 mmol) and 100 mL diethylether. The resulting pale orange solution wa s argon purged and wrapped in foil prior to addition of KOH (748 mg, 13.31 mmol) and activated MnO 2 (2.328 g, 26.78 mmol). The resulting solution wa s stirred at room temperature in the dark for one hour intervals before the second and third additions of KOH and activated MnO 2 (2.25 g, 40.15 mmol KOH and 6.99 g, 80.35 mmol MnO 2 total). The MnO 2 wa s removed by flash chromatography through a plug of sil ica. The solvent wa s removed in vacuo and the isolated tan crystalline solid purified via flash chromatography with hexanes as the eluent, 794 g white crystalline solid isolated, 74% yield. 1 H NMR (300 MHz, CDCl 3 ) 7.54 (m, 2H), 7.48 (s, 4H), 7.36 (t, 3 H), 3.17 (s, 1H). The synthesis of th e DPAF chromophore was generated by a modification of a literature method, 90 as shown in Figure 3 1 7 : Figure 3 1 7 Synthetic scheme for formation of DPAF chromophore 9,9 D iethylfluorene ( 5 ) Fluorene ( 6.80 g, 40.9 mmol), potassium hydroxide (11.21 g, 200 mmol) and potassium iodide (0.69 g, 4.2 mmol ) were dissolved in DMSO
109 (40 mL) and cooled to 10 C. Bromoethane (8 mL, 107 mmol) was added drop wise over 45 minutes. The reactions was then remov ed from the ice bath and stirred at room temperature for 2 0 hour s during which the reaction mixture turned from orange brown to dark blue The reaction was quenched with deionized water (200 mL), followed by an extraction with toluene (5 x 50 mL). The organic phase was washed with deionized w ater (1 x 100 mL) and dried over Na 2 SO 4 The solvent was removed in vacu o to yield a dark red oil The crude product was purified via column chromatography (hexane/CH 2 Cl 2 99:1), resulting in a colorless oil. Yield 7.52 g (83%). 1 H NMR (3 00 MHz CDCl 3 ) 0.31 (t, 6H), 2.01 (q, 4H), 7. 31 7. 36 (m, 4 H ), 7.69 7.72 (m, 2H). 2 B romo 9,9 diethylfluorene ( 6 ) A mixture of 9,9 diethylfluorene (0.88 g, 4.0 mmol) and propylene carbonate (5 mL) was heated to 60 C, NBS (0.71 g, 4.0 mmol) was added and the reaction mixture was stirred for 1 h at 60 C. After cooling to room temperature, the mixture was quenched with deionized water and extracted with toluene (5 x 50 mL). The collected organic phase was washed with deionized water (2 x 100 mL) and dried over Na 2 SO 4 The solvent was removed in vacuo, resulting in a yellow oil The crude product was filtered over silica gel with hexanes as eluent to remove residual propylene carbonate, resulting in a colorless oil. Yield 1.09g (90%). 1 H NMR (300 MHz, CDCl 3 ) 0.31 (t, 6H), 2.01 (q, 4H), 7.31 7.34 (m, 3H), 7.4 4 7.46 (m, 2 H), 7.54 7.57 (m, 1H), 7.65 7.69 (m, 1H). 2 B romo 9,9 diethyl 7 iodofluorene ( 7 ) A mixture of 2 bromo 9,9 diethylfluorene (1.09 g, 3.6 mmol), iodine (0.37 g, 1.5 mmol), iodic acid (0.15 g, 0.8 mmol), concentrated sulfuric acid (0.6 mL), deionized wate r (0.5 mL) and carbon tetrachloride (0.3 mL) was heated for 2.5 h our to 85 C, during which a red solid
110 precipitated The solid was separated by filtration and washed with 1:1 acetic acid/ deionized water and deionized water before reslurri ng in hot metha nol for 30 minutes The resulting colorless, fine solid contained a mixture of 2 b romo 9,9 diethyl 7 iodofluorene and 2,7 diiodo 9,9 diethylfluorene which was used in subsequent steps without further purification. Yield 0.52 g (34%). (7 B romo 9,9 diethylfluoren 2 yl) N,N diphenylamine ( 8 ) The mixture of 2 bromo 9,9 diethyl 7 iodofluorene and 2,7 diiodo 9,9 diethylfluorene (10.03 g, 23.6 mmol), diphenylamine (4.39 g, 25.9 mmol), copper (3.01 g, 47.4 mmol) and potassium carbonate (6.52 g, 47.2 mmo l) were suspended in DMSO (100 mL) and heated to 180 C under argon for 20 h ours To remove DMSO and copper, the reaction mixture was filtrated over silica gel with a 10:1 hexanes/CH 2 Cl 2 eluent. The removal of the solvent in vacuo resulted in a yellow oi l as crude product, which was purified via column chromatography 10:1 hexanes/CH 2 Cl 2 ) to result in a light yellow, shiny solid. Yield 1.29 g (12%). 1 H NMR (300 MHz CDCl 3 ) 0.35 (t, 6H), 1.90 (q, 4H), 6.99 7.66 (m, 16H). 9,9 D iethyl 7 (2 trimethylsilyl)ethynyl) N,N diphenyl 9H fluoren 2 amine ( 9 ) This complex was s ynthesized by a modification of a lite rature method 90 (7 b romo 9,9 diethylfluoren 2 yl)diphenylamine (200 mg, 0.406 mmol) was dissolved in triethylamine (5 mL) in a sealing tube. T he resulting solution was argon purged for 30 minutes before trimethylacetylene (90 L, 0.637 mmol) was added via syringe, followed by triphenylphosphine (4.5 mg, 0.017 mmol), CuI (3.1 mg (0.016 mmol), and Pd(dba) 2 (5.2 mg, 0.006 mmol). The mixture was further argon purged for 15 minutes before the tube was sealed and heated t o 85 C for 25 hours. The solvent was then removed with nitrogen. The resulting orange oil with black powder was purified by flash
111 chromatography (1:1 hexanes/DCM) to yield an orange oil. Further flash chromatography (5:1 hexanes/DCM) yielded the desired product as a pale yellow solid. Yield 138 mg (70%). 1 H NMR agrees with known literature values. 9,9 D iethyl 7 ethynyl N N diphenyl 9 H fluoren 2 amine ( DPAF ) This complex was synthesized by a modifica tion of a known literature method 90 THF (10 mL) and methanol (10 mL) were charged to a 100 mL round bottom flask and purged with argon, to which was added 9,9 diethyl 7 (2 trimethylsilyl)ethynyl) N,N diphenyl 9H fluoren 2 amine (300 mg, 0.618 mmol), resulting in a pale yellow, clear solution. The solution wa s further argon purged for 15 minutes before potassium hydroxide (181 mg, 3.235 mmol) was added. The reaction was stirred under argon at room temperature for 2.5 hours. To the flask was added 20 mL DCM, followed by 30 mL deionized water. The organic layer was extracted and dried over Na 2 SO 4 The solvent was removed in vacuo. The resul ting yellow oil was purified via flash chromatography (1:4 DCM/hexanes gradient shifted to DCM). Yield 249 mg (98%). 1 H NMR agrees with known literature values. The synthesis of the BTF chromophore was generated by a modification of a literature method, 90 as outlin ed in Figure 3 1 8 : Figure 3 1 8 Synthetic scheme for formation of BTF chromophore
112 2,7 D ibromo 9,9 diethylfluorene ( 10 ). A mixture of 2,7 dibromofluorene (16.02 g, 49.4 mmol), powdered potassium hydroxide (13.85 g, 246.9 mmol), potassium iodide (0.825 g, 4.9 mmol) and DMSO (55 mL) was stirred in a round bottom flask at 0 C Ethylbromide (9 .6 mL, 128.4 mmol) was added drop wise over 45 minutes, during which the solution turned from orange to lilac. The reaction mixture was stirred overnight at room temperature, then poured into deionized water. Vacuum filtration yielded a green solution an d a pale yellow solid. Recrystallization from hexanes and hot gravity filtration afforded the desired product as shiny yellow crystals, which were washed with cold hexanes. Yield 14.5 g (76%). 1 H NMR (300 MHz, CDCl 3 7.25 7 .54 (m, 6H). 9,9 D iethyl 7 bromo fluorene 2 carboxaldehyde ( 11 ). To a stirred and degassed solution of 2,7 dibromo 9,9 diethylfluorene (15.0 g, 39 mmol) in THF (86 mL) at 72 C, n butyllithium (18 mL, 43.4 mmol) was added drop wise over 10 minutes. The solution turned from orange to dark red. After 20 minutes, DMF (4.2 mL, 53.2 mmol) was added and the mixture was stirred for 1.5 hours in and 1 hour outside the cooling bath. The reaction was cooled to 5 C and treated with HCl (3.7 5 mL concentrated HCl in 15 mL water) and diluted with toluene (50 mL). After the extraction with toluene, the combined organic phase was washed with sodium bicarbonate solution, dried over MgSO 4 and the solvent removed under reduced pressure. The yello w solid was purified by flash chromatography (1:1 toluene:hexanes) to result in the desired product as a pale yellow solid. Yield 9.41 g (73%). 1 H NMR (300 MHz, CDCl 3 2.07 (m, 4H), 7.52 7.50 (m, 2H), 7.66 7.63 (m, 2H), 7.86 7.82 (m, 3H), 10.06 (s, 1H).
113 2 (9,9 D iethyl 7 bromo 2) fluorenyl benzothiazole ( 12 ) DMSO (68 mL), 9,9 diethyl 7 bromo fluorene 2 carboxaldehyde (9.4 g, 28.6 mmol), and 2 aminothiophenol (3.8 mL, 35.7 mmol) were heated in a round bottom flask to 190 C for 60 minutes. After cooling to room temperature, the reaction mixture was poured into deionized water. Extraction of the aqueous phase with DCM gave a yellow solid. Purification by reslurry in cold hexanes gave the desired product as a pale yellow solid. Yield 7.99 g, (6 4 %). 1 H NMR ( 300 MHz, CDCl 3 7.38 (m, 1H), 7.52 7.50 (m, 3H), 7.70 (d, 1H), 7.78 (d, 1H), 7.93 (d, 1H), 8.09 (m, 1H), 8.12 (d, 1H), 8.13 (d, 1H). 2 (9,9 D iethyl 2 (2 (trimethylsilyl)ethynyl) fluoren 7 yl)benzothiazole ( 13 ). To a sealing tube was charged 2 (9,9 diethyl 7 bromo 2) fluorenyl benzothiazole (1 g, 2.3 mmol) and triethylamine (24 mL). The resulting solution was argon purged for 60 minutes before addition of TMS acetylene (1.4 mL, 9.2 mmol), CuI (11 mg, 0.058 mmol), PPh 3 (25 mg, 0.095 mmol) and Pd(dba) 2 (45.8 mg, 0.05 mmol). The tube was sealed and heated to 85 C for 26 hours. The solvent was removed under reduced pressure. Purification by fla sh chromatography (3:2 DCM:hexanes) gave the desired product as a yellow solid. Yield 981 mg (95%). 1 H NMR (300 MHz, CDCl 3 9H), 0.36 (t, 6H), 2.15 (m, 4H), 7.40 7.38 (m, 1H), 7.52 7.49 (m, 3H), 7.70 (d, 1H), 7.79 (d, 1H), 7.93 (d, 1H), 8.09 ( m, 1H), 8.12 (d, 1H), 8.13 (d, 1H). 2 (9,9 D iethyl 9 H fluoren 7 yl)benzo[ d ]thiazole ( BTF ) To a round bottom was charged 2 (9,9 diethyl 2 (2 (trimethylsilyl)ethynyl) fluoren 7 yl)benzothiazole (600 mg, 1.33 mmol), THF (11.5 mL) and MeOH (1.9 mL), then purging with argon for 30 minutes. TBAF (1.65 mL of a 1M solution in THF, 1.65 mmol) was added to the
114 resulting yellow solution vi a a glass precision syringe. The reaction mixture was stirred at room temperature for 8.5 hours under argon. The solvent was removed in vacuo. Purification of the dark orange oil by flash chromatography (hexanes:DCM 4:1) gave the target product as a pal e yellow, fluffy solid. Yield 474 mg (94%). 1 H NMR (300 MHz, CDCl 3 ) 8.13 (d, 1H), 8.12 (d, 1H), 8.09 (m, 1H), 7.93 (d, 1H), 7.78 (d, 1H), 7.73 (d, 1H), 7.54 7.49 (m, 3H), 7.40 7.38 (m, 1H), 3.18 (s, 1H), 2.15 (m, 4H), 0.35 (t, 6H) 1,5 C yclooctadiene platinum (II) dichloride This complex was synthesized by literature methods. 140 K 2 PtCl 4 (500 mg, 1.205 mmol) was dissolved in 20 mL deionized water, argon purged, and heated to 55 C with stirring. To this solution was slowly added a solution of 1,5 c yclooctadiene (500 L, 4.077 mmol) in ethanol (234 mL) over 10 minutes. Stirring and heating was continued until the pale pinkish color of the solution faded, 40 minutes. The reaction was removed from heat, allowed to cool to room temperature, and cooled in an ice bath. The resulting mixture was vacuum filtered and washed with four 5 mL aliquots of both cold deionized water and diethyl ether. The resulting slight tan powder was air dried. Yield 328 mg (73%) 1 H NMR (300 MHz, CDCl 3 ) 2.29 (4H, m), 2.7 2 (4H, m), 5.63 (4H, m). 13 C NMR (75 MHz, CDCl 3 ) 100.06, 30.26. cis D iphenylphosphineethane platinum (II) dichloride This complex was synthesized by literature methods. 60 In a 100 mL round bottom flask wa s dissolved 1,5 cyclooctadieneplatinum(II) dichloride (300 mg, 0.802 mmol) in 28 mL deuterated chloroform. To the clear, colorless solution was added diphenylphosphinoethane (320 mg, 0.803 mmol), resulting in immediate precipitation. The reaction was sti rred for 1 hour at room temperature. The solvent was removed in v acuo; the product was
115 collected as a white solid. Yield 512 mg (96%). 1 H NMR (300 MHz, CDCl 3 ) 7.86 (m, 8H), 7.51 (m, 12 H), 2.32 2.38 ( dt, 4H). 31 P NMR (121 MHz, CDCl 3 ) 42.25 with 195 Pt satellites PtP = 3615 Hz. cis D iphenylphosphinoethane bis((4 p henylethynyl)phenyl)ethynyl ) platinum(II) ( cis PE2) This complex was synthesized by modification of similar literature methods. 121 141 Cis diphenylphosphineethane platinum(II) dichloride (125.5 mg, 0.189 mmol) and (4 phenylethynyl)phenyl ethynylene (114.5 mg, 0.5 66 mmol) were added to an argon purged 50 mL round bottom flask, followed by 2. 2 mL diisoproplyamine and 14 mL dichloromethane. The resulting cloudy white solution was further purged with argon for 30 minutes, followed by the addition of CuI (1.1 mg, 0.006 mmol). The resulting pale yellow and clear solution was stirred under argon for 27 hours. The solvent was removed in vacuo to yield a yellow white crystalline solid. The solid was dried on a vacuum line for 24 hours and then purified by flash chromatography (2:3 DCM/hexanes gradient shifted to DCM with 5% MeOH by volume). Pale yellow white crystals we re collected and dried. Yield 154.5 mg (82 %). 1 H NMR (300 MHz, CDCl 3 ) 7.96 (m, 8H), 7.45 (m, 18H), 7.31 (m, 8H), 7.12 (d, 4H), 2.46 (dt, 4H). 31 P (121 MHz, CDCl 3 ) 42.35 with 195 Pt satellites PtP = 2280 Hz. EA calculated C 66.8 H 4.44 Found C 65.8 8, H 3.9 6 cis D iphenylphosphinoethane bis (2 (9,9 diethyl 9 H fluoren 7 yl)benzo [ d ]thiazole) platinum (II) ( cis BTF) This complex was synthesized by modification of similar literature methods. 121 141 To a 50 mL round bottom flask was added cis diphenylphosphineethaneplatinum(II) dichloride (50 mg, 0.075 mmol), 2 (9,9 diethyl 9H fluoren 7 yl)benzo[d]thiazole (84 mg 0.221 mmol), 5.6 mL dichloromethane and 0.84
116 mL diisopropylamine. The resulting yellow solution was argon purged for 30 minutes prior to the addition of 99.999% CuI (0.5 mg, 0.0026 mmol). The reaction stirred at room temperature under argon for 24 hours. The solve nt wa s then removed in vacuo to give a crude yellow powder, which was purified by flash chromatography with a 1:1 DCM/hexanes eluent. The resulting yellow powder was further purified by recrystallization by dissolving in minimum DCM and precipitat ing with hex anes. The resulting off white crystals were collected via vacuum filtration and washed with cold hexanes. Yield 90 mg (88%). 1 H NMR (300 MHz, CDCl 3 ) 7.98 (m, 8H), 7.92 (m, 8H), 7.83 (d, 2H), 7.61 (m, 2H), 7.38 (m, 18H), 7.30 (d, 2H), 2.46 2.52 (dt, 4H), 2.06 (two sets of diastereotopic quart., 8H), 0.31 (t, 12H). 31 P (121 MHz, CDCl 3 ) 42. 43 with 195 Pt satellites PtP = 2280 Hz. EA calculated C 66.37, H 4. 78, N 2.07 Found C 66.98, H 4.82, N 1.81. MP 177.8 182.8 C. cis D iphenyl phosphinoethane bis(9,9 diethyl 7 ethynyl N,N diphenyl 9H fluoren 2 amine) platinum(II) ( cis DPAF) This complex was synthesized by modification of similar literature methods. 121 141 To a 50 mL round bottom flask was added 11.2 mL chloroform and 1.8 mL diisopropylamine. The solut ion was argon purged for 20 minutes, then cis diphenylphosphineethane platinum(II) dichloride ( 100 mg, 0. 151 mmol) and 9,9 diethyl 7 ethynyl N,N diphenyl 9H fluoren 2 amine ( 189 mg, 0. 357 mmol) were added, resulting in a cloudy pale yellow solution. The resulting s olution was argon purged f or 30 minutes prior to the addition of 99.999% CuI (0.5 mg, 0.0026 mmol). The reac t ion was stirred at room temperature under argon for 24 hours. The solvent was then removed in vacuo to give a crude yellow crystalline solid which was purified by flash chromatography with a 2 : 3 DCM/hexanes eluent. The resulting
117 white powder was furthe r purified by recrystallization by dissolving in minimum DCM and precipitating with hexanes. The resulting white crystals were collected via vacuum filtration and washed wit h cold hexanes. Yield 168 mg (78.5 %). 1 H NMR (300 MHz, CDCl 3 ) 8.02 (m, 8H), 7. 43 ( m, 18H), 7.22 (m, 12 H), 7.10 (m, 14H), 7.04 (d, 2H), 6.97 (dt, 8H), 2.43 2.49 (dt, 4H), 1.80 (two sets of diastereotopic quart., 8H), 0.30 (t, 12H). 31 P (121 MHz, CDCl 3 ) 42.08 with 195 Pt satellites PtP = 2278 Hz. EA calculated C 74.51 H 5.40 N 1.97 Found C 74.58 H 5.65 N 1.79. MP 238.7 241.7 C. trans bis((4 P henylethynyl)phenyl)ethynyl)bis (tributylphosphine) platinum(II) ( trans PE2) This known complex was synthesized via a modification of a literature procedure. 38 A n argon sparged 150 mL round bottom flask was charged with dichlorobistributyl phosphine platinum (II) ( 560 mg, 0.835 mmol) and (4 phenylethynyl) phenylethynylene ( 373 mg, 1.844 mmol). To the mixture was added triethylamine ( 19 mL) and pyridine ( 3 mL). Tributylphosphine (50 L) was then injected via syringe. The solution was further argon purged for 15 minutes before addition of CuI ( 6.4 mg, 0.034 mmol). The solution was stirred overnight at room temperature. The reaction solvent was removed in vacuo. The resulting yellow material was dissolved in DCM and washed with NH 4 Cl (aq). Most so lvent was removed in vacuo, yielding a concentrated yellow oil, which was precipitated with MeOH. The resulting white crystals were redissolved in DCM and reprecipitated in MeOH twice more, yielding pure white crystals, 430 mg ( 51% ). 1 H NMR is in accord with known literature values. trans bis ( T ributylphosphine) bis (2 (9,9 diethyl 9 H fluoren 7 yl)benzo[ d ] thiazole) platinum (II) ( trans BTF) This known complex was synthesized via a modification of a literature procedure. 90 To a 100 mL round bottom flask was added 2
118 (9,9 diethyl 9H fluoren 7 yl)benzo[d]thiazole (101 mg 0.266 mmol), dichlorobistributyl phosphine platinum (II) (81 mg, 0.121 mmol), and diethylamine (10 mL). The resulting pale yellow solution was argon purged prior to the addition of CuI (1.7 mg, 0.009 mmol) The round bottom flask was attached to a water cooled condenser, heated to reflux, and stirred overnight. The reaction mixture was reduced in vacuo. The resulting orange solid was purified via flash chromatography (1:1 DCM/hexanes). Yield 129 mg (79%). The 1 H NMR is in accord with known literature values
119 CHAPTER 4 PLATINUM ACETYLIDE M ONOMERS AND POLYMERS Backgrou n d Platinum acetylide polymers are of interest largely due to the potential ab ility for the intrinsic absorption and emi ssion properties (to include nonlinear absorption ( NLA ) response) to be maintained upon incorporation into the polymer. Additionally, the resulting bulk polymeric structure lends itself readily to molecular engineering for optical applications that would be difficult for platinum acetylide monomers or oligome rs th e polymers can be processed to form coatings or thin film s and can be characterized in solu tion and solid state Such platinum acetylide polymers have been incorporated into photovoltaic solar cells and light emitting devices. 78 155 156 However, t he photophysical characterization o f polymers can be complicated due to variation in polymer molecular weight distributions and backbone chain defects E xperimental and theoretical investigations on multiple platinum containing acetylide oligomers and polymers have explored the relationship between structure delocalization and migration of singlet and triplet excitons 157 158 159 Examples of two previously investigated platinum acetylide oligomers and polymer s eries ar e shown in Figure 4 1 For complex 1 the ground state absorption and fluorescence spectra indicate that the singlet excited state is delocalized over several repeat units. 56 The phosphorescence is less affected by conjugation length, signifying a more l ocalized triplet excited state, on one or two [ Pt(PBu 3 ) 2 Ph ] units In a similar fashion, the singlet exciton of complex 2 is delocalized over several repeat units along the platinum acetylide chain; however, the triplet excited state is spatially confined on one or two repeat units. 8 The triplet excited state quantum yields remain high within the
120 polymer series (> 0.4) despite t he decreasing effect of metal induced spin orbit coupling as the loading of the metal into the polymer backbone decreased. 8 Figure 4 1 Platinum acetylide oligomers and polymers 8 56 The characterization of the nonlinear response of platinum acetylide polymers is additionally of interest for platinum and polymer science. However, a limited number of platinum acetylide polymers for NLA applications have been investigated to date. 160 165 Wong and co workers have examined several series of platinum acetylide polymers based on diethynyl fluorene and carbazole based compl exes, Figure 4 2 complexes 3 10 ; NLA response via the nanosecond z scan technique with 532 nm excitation demonstrated strong optical power limiting for polymers 5 6 7 and 9 in solution. 162 A recent investigation by Malmstr m and co workers examined polymers in the solid state based on trans PE2, as depicted in Figure 4 2 160 The platinum acetylides were designed such that incorporation into the polymer was achieved by dispersion into or reaction with methyl methacrylate (MMA) Complex 1 2 was copolymerized with MMA through the methacrylate endgroup f unctionality, whereas complex 1 1 w as only mixed into the polymerization reaction. The characterization of the resulting solid state
121 polymethylmethacrylate (PMMA) based polymers showed that both methods resulted in p latinum acetylide polymers that exhibited NLA, with the dispersion method exhibiting stronger response than the covalently bound method. However, input energies above 120 J for complex 11 and above 90 J for complex 12 at 532 nm led to optical damage of the polymers. 160 Figure 4 2 Chemical structures investigated by Wong and co workers 162 163 (complexes 3 10 ) and Malmstrom and co workers 160 ( complexes 11 12 ). Complexes 11 a nd 12 were incorporated into PMMA. The aim of this project is to examine how the nonlinear absorbing properties of platinum acetylide complexes are affected by covalent incorporation into PMMA polymers. Unsymmetric platinum acetylides are generated that i ncorporate one
122 ( phenylethynyl)phenyl)ethynyl (PE2), diphenylaminofluorene (DPAF), or benzothiazolefl uorene (BTF) chromophore and one ethynylaniline group onto the platinum acetylide core, as shown in Figure 4 3 The amine functionality on the ethynylanili ne group is modified for incorporation into the polymer backbone via free radical polymerization with MMA Presented are the synthesis and photophysical characterization s of the platinum acetylide monomer s and resulting PMMA based polymers Additionally, the polymers are used to generate solid state films and monoliths; a comparison between the solution and the solid state properties of the polymers is examine d Figure 4 3 Platinum acetylide monomers prior to modification of the aniline group. Synthesis Platinum Acetylides The PE2, DPAF, and BTF chromophores were synthesized prior to attachment to the platinum metal center as described in Chapter 3 Synthesis of the target unsymmetric monomers was attempted via reaction of Pt(PBu 3 ) 2 Cl 2 with th e chromophores preceding attachment of 4 ethynylaniline; however higher yields were obtained when the ethynylaniline was reacted with Pt(PBu 3 ) 2 Cl 2 before reaction with the chromophore as shown in Figure 4 4. Figure 4 5 illustrates the overall synthetic route used to prepare the platinum acetylide monomers
123 Figure 4 4 Synthetic scheme for 4 ethynylaniline and platinum acetylide precursor Figure 4 5 Formation of Pt PE2, Pt DPAF, and Pt BTF platinum acetylide monomers Polymerization The platinum a cetylide monomers are modified at the amine to make the complexes suitably reactive for free radical polymerization. This is achieved by reaction of the monomers with acryloyl chloride to form the acrylami de Figure 4 6 Modification of th is functionality allows the monomers to be covalently bound into the polymer backbone; the alkene is sensitive towards polymerization and is incorporated into the polymer backbone via copolymerization with MMA, Figure 4 6. A range of monomer
124 concentration s were prepared, reaching concentrations up to 11 weight percent. Covalent incorporation of the monomer into the matrix reduces the mobility of the monomer in the polymer, which limits aggregation and promotes homogeneity. PMMA is advantageous as the hos t polymer material because of its good optical transparency, impact resistance, and low density. 166 Figure 4 6 General modific ation and polymerization of platinum acetylide monomers The PMMA based platinum acetylide polymers were prepared via free radical polymerization. The acrylamide modified platinum mon omer azobis (cyclohexanecarbonitrile) were dissolved in dimethylformamide in a 10 mL S chlenk flask. Purified MMA was injected into the reaction vessel and the resulting solution was deoxygenated via freeze pu mp thaw techniques, nitrogen purged a nd warmed to room temperature. The sealed vessel was then heated to 65 C until the polymerization reaction became viscous and unable to stir ( approximately 10 hours) resulting in a
125 clear, slight ly yellow solid. The resulting polymer was dissolved in DMF and re precipitated with methanol several times to yield fine, fluffy solid. Film Preparation Polymer films can be generated via several processing techniques. Two common techniques are spin coating and doctor blading. Spin coated films are formed by applying an excess amount of dissolved material in a volatile solvent onto the substrate, which is then rotated at a high speed. The rotation spreads the solvent across the substrate surface by centrifugal force. The film thickness can be adjusted by varying the rotation speed of the instrument the solvent, and the solution concentration. However, material loss is high via spin coating Doctor bladed films are made by applying high concentration solution s to the edge of the substrate, which is then pulled across the substrate surface prior to evaporation. The doctor blade technique has little or no material loss and can be employed to generate homogeneous films that are up to several micrometers thick. T he platinum acetylide based polymers we re used to make films on glass substrates via the doctor blade technique. The films were investigated by atomic force microscopy for film thickness and surface morphology The doctor bladed films, as expected, were strongly dependent upon the solution concentration used to form the films, with films in the range of 600 nm 3.6 m. The thickness decreased slightly across the film, with the area of deposition being the thick est and up to a 30% thickness variation acr oss the film Results and Discussion The purpos e of the polymer project was to incorporat e platinum acetylides that contained TPA chromophores into polymer backbones to be coated as films Central to
126 the characterization of the resulting polymers is the c omparison of the photophysical properties of the monomers to the resulting polymers, both in solution and on film. To investigate the photophysics of the platinum acetylides, platinum acetylide b ased polymers were synthesized that incorporated varying am ounts of the chromophore based monomers by weight percent of the monomer to MMA The molecular weights and polydispersity indexes (PDI) of the resulting polymers were determined via gel permeation chromatography against known molecular weights of linear polystyrene standards in THF The PDI is a useful measure of the distribution of molecular masses in a polymer. The PDI is the ratio of the weight average molecular weight (M w ) over the number average molecular weight (M n ); a M w /M n value of one would re present a perfectly monodisperse polymer. 166 As shown in T able 4 1, the PDIs were greater than unity for the generated polymers but were relatively low for radical polymerizations due largely to multiple, sequential precipitations of the polymers The gel permeation chromatography spectra showed small molecular weight distributions for the polymers. The obtained PDIs, M n and M w values were dependent on the amount of monomer incorporated into the PMMA polymer: the polymers that contain less platinum acetylide monomer exhibited larger M n and M w values and higher PDIs. Table 4 1. Polymer molecular weights and PDIs Chromophore Theoretical a monomer (% wt) Actual b monomer (% wt) M n M w PDI PE2 2.5 1.7 190,505 309,356 1.62 PE2 10 9.1 189,160 289,922 1.53 DPAF 5.6 3.5 207,143 351,377 1.70 DPAF 10 6.6 57,291 88,531 1.55 BTF 1.0 1.2 252,106 501,498 1.99 BTF 5.0 4.7 145,121 272,252 1.88 BTF 10 12.3 83,759 140,805 1.67 a Weight percent of monomer to MMA into polymerization reaction. b Calculated from ground state absorption of polymer and molar absorptivity of monomer.
127 As such, the polymerization reactions appeared to be inhibited upon addition of 10 or more weight percent platinum acetylide monomer Polymerization attempts that sough t to incorporate more than 12% monomer were not successful either low molecular weights or no polymer were obtained. This is consistent with the covalently bound PMMA polymers shown in Figure 4 2, which could only be obtained up to 13 weight percent. 160 Ground State Absorption Spectroscopy Figure 4 7 presents the ground state absorption of the platinum acetylide monomers and resulting polymers in solution and on film. The monomers are characterized prior to m odification of the aniline functionality due to the instability of the resulting acrylamide monomer. For comparison, the ground state absorption spectra of th e three chromophores and the ethynyaniline ligand prior to attachment to the platinum metal are shown in Figure 4 8. PMMA does not exhibit ground state absorption above 300 nm. The monomers and polymers display strong absorptions in the near UV region that are similar to the absorptions of the free chr omophores. The absorption spectra of the free ligands are slightly blue shifted from the monomers, Table 4 2. Additionally, the free chromophores exhibit more pronounced vibrational structure than the monomers and resulting polymers, indicating stronger electron vibrational coupling in the chromophores prior to attachment to the metal center. The ground state absorption spectra of the polymers in solution and on film are nearly identical to the spectra of the monomers. Pt PE2 and Pt PE2(PMMA) exhibit th e most blue shifted ground state absorption (345 349 nm), whereas the BTF and DPAF based monomers and polymers are red shifted to 375 397 nm. The absorption spectra are similar to those seen for other complexes that contain PE2, BTF, or DPAF chromoph ores. 38 90 105
128 Figure 4 7 Ground state absorption spectra of the monomers (black) and polymers (red ) in THF, and the polymer films (green) by chromophore type. Figure 4 8 Ground state absorption spectra (A) and fluorescence emission (B) in THF of the PE2 (black), DPAF (red), and BTF (green) chromophores and ethynylaniline ligand (blue). The emissio n spectra were obtained by excitation at the ground state absorption maxima.
129 Table 4 2 Summary of photophysical properties of the polymer series in THF Complex Abs (nm) a (M 1 cm 1 ) Fl max (nm) b Ph max (nm) c T1 Tn (nm) d TA ( s) e PE2 298 50,040 412 335 ---Pt PE2 3 49 65,500 408 526, 561 572 1.2 Pt PE2(PMMA) soln 347 -432 526, 561 596 2.3 Pt PE2(PMMA) film 347 -378 523, 558 560 31.3 DPAF 369 144,789 395, 412 ---Pt DPAF 3 80 152,000 397 531, 578 617 0.73 Pt DPAF(PMMA) soln 378 -398, 454 530, 578 638 6.8 Pt DPAF(PMMA) film 374 -422 530, 569 590 39.2 BTF 350 75,660 395 --Pt BTF 397 73,800 440 568 6 59 2.3 Pt BTF(PMMA) soln 382 -432 567 668 3.7 Pt BTF(PMMA) film 378 -431 565 590 36.5 a Ground state absorption maxima b Fluorescence s pectra obtained by excitation at ground state absorption maxima c Phosphorescence spectra, obtained by excitation at ground state absorption maxima d Triplet triplet transient absorption maxima e Triplet excited state lifetimes, calculated from the transient absorption spectra Steady State Photoluminescence Spectroscopy The photoluminescence emission of the platinum acetylide monomers and resulting polymers were examined via excitation at the gro und state absorption maxima. The room temperature solution measurements were conducted in deoxygenated THF. The polymer films were measured in air saturated conditions. The photoluminescence emission spectra are shown in Figure 4 9. Pt PE2 exhibits fluo rescence in the 350 450 nm region and a phosphorescence maximum at 527 nm, Figure 4 9 A. Pt PE2(PMMA) in solution exhibits nearly identical emission to the monomer. The Pt PE2(PMMA) polymer film exhibits fluorescence emission similar to the solution me asurements, but also exhibits strong, structured phosphorescence. The magnitude of the phosphorescence is such that the fluorescence appears weak, despite being of a similar strength as the solution
130 Figure 4 9. Photoluminescence spectra of monomer and polymer series A: Pt PE2 (black) and Pt PE2(PMMA) (red) solutions in argon purged THF and doctor bladed Pt PE2(PMMA) film (green) in air. B: Pt DPAF (black) and Pt DPAF(PMMA) (red) solutions in argon sparged methyl THF at 77 Kelvin, Pt DPAF (blue) in a rgon purged THF at room temperature, and doctor bladed Pt DPAF(PMMA) film (green) in air C: Pt BTF (black) and Pt BTF(PMMA) (red) solutions in argon purged THF and doctor bladed Pt BTF(PMMA) film (green) in air Samples were excited at the ground state absorption maxima.
131 measurements. Interestingly, the film was measured in an air saturated environment that was subject to oxygen quenching of the triplet excited state. The photoluminescent properties of the DPAF complexes are shown in Figure 4 9 B Pt DPAF and Pt DPAF(PMMA) in solution display fluorescence centered at 427 nm, but do not exhibit structured phosphorescence in argon purged THF, as is shown by the blue spectrum ; thus e mission from the triplet excited state was obtained by measuring the phot oluminescence in methyl THF at 77 Kelvin, as shown by the black and red spectra. However, the Pt DPAF(PMMA) polymer film exhibited strong phosphorescence at 530 nm in air saturated, room temperature measurements. In a similar fashion to the PE2 complexes, Pt BTF and Pt BTF(PMMA) exhibit fluorescence and phosphorescence in argon purged THF solutions, Figure 4 9 C As was observed in the Pt PE2 (PMMA) and Pt DPAF (PMMA) films, Pt BTF(PMMA) film exhibits phosphorescence that is stronger in intensity than the f luorescence emission, despite being measured in an air saturated environment. The emission of the polymer films can also be observed by 365 nm excitation light, as shown in the photograph in Figure 4 1 0 Figure 4 1 0 Luminescence of Pt PE2 (PMMA) (left) Pt DPAF (PMMA) (center), and Pt BTF (PMMA) (right) doctor bladed polymer films under 365 nm excitation.
132 Triplet Triplet Transient Absorption The triplet excited state is further studied via triplet triplet transient absorption Figure 4 11 Near UV excitation at 355 nm generates strongly absorbing transients for Figure 4 1 1 Transient absorption spectra of the monomers ( black solid) and polymers ( red dashed) in deoxygenated THF, 355 nm excitation, 360 s q switch delay 8 mJ energy, 10 ns gate width, 10 ns camera delay, 100 images averaged
133 the platinum acetylide monomers and polymers in THF. The negative bands from 350 400 nm correspond to bleaching of the ground state absorption. The positive and moderately intense bands are due to the triplet triplet (T 1 T n ) excited state absorption. A red shift occurs in the trans ient absorption maxima exhibited by the polymers versus the monomers of the same chromophore: 599 nm versus 572 nm for Pt PE2(PMMA) and Pt PE2, 638 nm versus 617 nm for Pt DPAF(PMMA) and Pt DPAF, and 669 nm versus 658 nm for Pt BTF(PMMA) and Pt BTF. Addi tionally, as shown in Table 4 2, the triplet excited state lifetimes of the polymer solutions are longer than the lifetimes of the monomers The observed red shift in the transient absorption spectra from the monomer to the polymer is proposed to be the result of functionality rather than from incorporation into the PMMA backbone; the red shift is exhibited in the normalized transient absorption spectra of the acrylamide functionalized monomer prior to polymer ization, as shown in Figure 4 12 The triplet triplet transient absorption of the acrylamide Pt BTF is nearly identical to that of Pt BTF(PMMA), supporting the hypothesis that the Figure 4 1 2 Transient absorption of Pt BTF (black), acrylamide Pt BTF (red), and Pt BTF(PMMA) soln (green) at 355 nm excitation in deoxygenated THF. 8 mJ energy, 10 ns gate width, 10 ns camera delay, 100 images averaged.
134 incorporation into the polymer backbone is not the cause for the observed red shift. However, the transient absorption spectra for the monomers and resulting polymers are similar, exhibiting strong and broad absorption across most of the visible region, with maxima in the 600 700 nm region. This makes these complexes ideal for NLA via triplet excited state absorption (ESA). The ins trument used for measuring the transient absorption of the monomers and polymers in solution is not designed to measure films, which is due largely to the need for a perpendicular arrangement of the laser light and the probe light for solution measurements As such, an instrument was designed in house to specifically measure the transient absorption and triplet excited state lifetimes of films. This instrument employs lower, less damaging laser energies for the measurement. Further, it is configured such that the laser light and probe light are nearly co linear which makes measuring thin films possible as shown in Figure 4 13 Figure 4 1 3 Film transient absorption instrumentation Components: A: Surelite I 10 Nd:YAG laser ; B: Second and Third Harmo nic Generator ; C: 250 W QTH Lamp ; D: Slow Shutter ; E: Fast Shutter ; F: 130/m Monochromator ; G : photomultiplier tube; H: photodiode Optics: 1 4 and 7:
135 Interestingly, the transient absorption spectra of the polymer films are strongly blue shifted from that of the solution measur ements, Figure 4 1 4 and Table 4 2 This Figure 4 14 Transient absorption spectra of polymer films 355 nm excitation, 390 s q switch delay, 1 k termination at scope 40 s time/division, 10 nm increments, 1,000 points at each wavelength, 450 nm band pass filter prior to sample, 380 nm band pass filter prior to monochromator
136 shift does not appear to be instrumental in nature, but rather the result of the solid state polymer incorporated with the platinum acetylide complexes. Additionally, the tr iplet excited state lifetimes exhibited by the polymer films are longer than the polymers in solution. This change is proposed to be the result of less accessible energy loss via nonradiative decay processes in the solid state. The increased lifetimes in the polymer films are consistent with the significant enhancement in the phosphorescence of the films. Nonlinear Absorption Response Because these polymers were designed to incorporate platinum acetylides that contained TPA chromophores into polymer backb ones their NLA response was investigated. As such, the polymers were examined in solution and on film by nanosecond open aperture z scan NLA measurements of the polymers were conducted in 1 mM solutions in benzene as shown in Figure 4 15. The polymer s in Figure 4 15 NLA response of 1 mM polymer solutions Pt PE2(PMMA) soln : red squares Pt BTF (PMMA) soln : blue up triangles Pt DPAF(PMMA) soln : green down triangles against T2 (black circles ) in THF via excitation at 600 nm, 850 J
137 solution were compared against the known DPAF capped diplatinum acetylide, T2 (Figure 1 16 ). 35 The solution concentration was based on the platinum content and took into account the amount of platinum acetylide monomer incorporated into the PMMA po lymer. An excitation wavelength of 600 nm was selected due to the lack of appreciable ground state absorption at this wavelength. The polymer solutions clearly display attenuation of the transmittance; Pt DPAF(PMMA) soln exhibited markedly stronger respon se than Pt PE2(PMMA) soln or Pt BTF(PMMA) soln The strong photoluminescence emission and transient absorption data of the polymer films, paired with the incorporation of strong TPA chromophores, suggest that the films should exhibit NLA. As such, the doc tor bladed polymer films were investigated via the z scan apparatus. The films however, did not exhibit signal that was strong enough to be detected by the current z scan system. This is proposed to be the result of the smaller pathlength of the doctor b laded polymer film s Thus, free standing polymer monoliths were generated using a one half inch circular Teflon mold. The resulting monoliths were thicker and did not require a glass substrate The monoliths exhibited the same photophysical properties as the films, though the longer pathlengths of the monoliths resulted in larger signal intensit y However, the monoliths caused strong divergence of the z scan beam in the far field (positive z positions), making the collection of the signal and reference energies inaccurate. As such, a nonlinear transmission (NLT) measurement was designed. As described in Chapter 2, this measurement does not involve the movement of the sample through the laser beam focus. The NLT instrument setup was achieved by modification
138 of the z scan apparatus the sample wa s placed in the focus of the laser beam and the laser energy wa s increased throughout the experiment with filters. A sample that displays linear absorption would exhibit equivalent amounts o f output and input energy ( i.e., a line with a slope of 1) whereas a sample that displays NLA would show decreased output energy as a function of input energy. The nonlinear responses of two monolith series were measured at an excitation wavelength of 600 nm. The first series consisted of three monoliths of the three monomer types (Pt PE2(PMMA), Pt DPAF(PMMA), and Pt BTF(PMMA)). As further described in the experimental section, the monoliths were concentration matched based on the specific weight perc entage of monomer in the polymer. Though the z scan was not effective for measuring the NLA response of the doctor bladed films or monoliths, the NLT measurement exhibited energy attenuation o f the monoliths, Figure 4 16. Figure 4 1 6 Nonlinear resp onse of concentration matched polymer monoliths at 600 nm excitation: 1.7% Pt PE2 (PMMA) = red triangles, 3.5% Pt DPAF (PMMA) = green squares, 1.2% Pt BTF(PMMA) = yellow diamonds blank = black circles.
139 The second series examined the effect of the monome r weight percent of incorporation into the PMMA polymer on the nonlinear response, Figure 4 17. The monoliths were formed by addition of the same amount of polymer, but used three Pt BTF(PMMA) polymers of different monomer weight percentages (7.4 mg of 1. 2, 4.7, and 12.3% Pt(BTF(PMMA)). The NLT measurements indicate that the solid state polymers exhibit NLA response However small changes were observed among the specific incorporated chromophores ; Pt DPAF(PMMA) exhibited slightly strong response The p olymers with higher monomer loading concentration s exhibited stronger response. Figure 4 17. Nonlinear response at 600 nm excitation of Pt BTF(PMMA) monoliths of varying percent incorporation: 1.2% Pt BTF(PMMA) = red triangles, 4.7% Pt BTF(PMMA) = gr een squares, 12.3% Pt BTF(PMMA) = yellow diamonds, blank = black circles. Summary Three unsymmetric platinum acetylide monomers have been synthe s i z ed that incorporate known TPA chromophores. Modificat ion of the aniline ligand to form an acrylamide allowed for co polymerization of the monomers with MMA to form platinum acetylide polymers in which the monomers were covalently attached into the polymer
140 backbone The photophysical properties of the platinum acetylide monomers and resulting polymers we re investigated to determine if the desirable TPA and triplet excited state properties were maintained upon polymerization. The resulting polymer s w ere studied in solution and solid state with minimum exhibited shifts in the ground state absorption and ph otoluminescence. However, the polymer films displayed markedly stronger phosphorescence than the polymer s in solution or the monomers even when measured in air saturated conditions. The intersystem crossing rates from the singlet to the triplet excited state is near unity for similar platinum acetylide monomers and oligomers. 35 90 As such, it is suggested that the polymer films exhibit stronger phosphorescence and longer triplet excited state lifetimes b ecause the nonradiat ive relaxation decay pathways are less accessible in the solid state polymer than in the polymer solution and monomer The mobility of the polymer film is more restricted making the loss of energy via nonradiat ive decay mor e difficult. The polymers exhibit ed strong triplet triplet transient absorption in the visible region both in solution and on film. T h e polym er films display ed a blue shift from the polymers in solution and the monomers While the film measurements were conducted on a separate instrument from the solution measurements, this shift is not proposed be instrumental in nature. Rather, the blue shift is postulated to be the result of the s olid state polymer. Other r eported p latinum acetylide PMMA based polymers in the solid state have not examined the complexes via triplet triplet transient absorption. 160 The NLA response s of the polymers suggest that the incorporation of platinum acetylide TPA chromophores into PMMA polymers c an be use ful for optical power limiting applicati ons The integration of PMMA allows for the materials to be used as
141 thin films or monoliths. Films up to 3.6 m in thickness have been prepared. The NLA response s of the polymers in solution were measured via nanosecond z scan and the solid state polyme r monolith s w ere measured via NLT. Both measurement types indicated that the polymers exhibited strong transmittance attenuation at high laser energies As expected from the nature of the chromophore, the PE2 based polymer exhibited weaker solution response than the BTF and DPAF based polymers. The NLA responses of the polymers were similar to the trends observed in the cis / trans project; Pt DPAF(PMMA) exhibited markedly stronger response in the open aperture z scan measurement. Experimental Instru mentation 1 H, 13 C, and 31 P NMR spectra were recorded on a 300 MHz Varian Gemini, VXR, or Mercury spectrometer in deuterated chloroform; chemical shifts ( ) are reported in ppm and referenced to tetramethylsilane or protonated solvent signals. Unless note d, one photon solution photophysical studies were carried out with samples contained in 1 x 1 cm quartz or glass spectroscopic cuvettes. Ground state absorption spectra in solution and on film were measured on a Varian Cary 100 dual beam spectrop hotometer with either the solution solvent or a clean blank glass slide as the instrument baseline blank. Corrected steady state solution emission measurements were performed on a Photon Technology International (PTI) photon counting fluorescence spectrometer; sa mple concentrations were adjusted to produce optically dilute solutions, O.D. max < 0.20. Samples were deoxygenated for phosphorescent measurements. Low temperature measurements were conducted in distilled HPCL
142 grade 2 methyl THF and placed in a standard NMR tube. The tube was then inserted into a liquid nitrogen filled silvered finger dewar and placed into the PTI spectrometer sample holder. Luminescence measurements of the polymer films were performed on a SPEX Fluorolog 3 spectrometer via front face alignment. The m olecular weights and polydispersity indexes of polymers were measured by gel permeation chromatograph y were employed. A Spectroflow 757 ultraviolet detector calibrated against linear polystyrene standards in THF Nanos econd triplet triplet transient absorption measurements of the monomers and polymers in solution were conducted using the third harmonic of a Continuum Surelite II E p = 8 mJ. Sample concentrations were adjusted to an optical density of 0.7 at the excitation wavelength. The sample solutions were placed in a continuously circulating 1 cm pathlength flow cell holding a volume of 10 mL. The sample solutions were prepare d in THF and deoxygenated by bubbling with argon. Triplet lifetimes were calculated by fitting the transient absorption decay data with a single exponential global fitting parameter in the SpecFit analysis software. A transient absorption system was buil t for th in film analysis. A Surelite I 10 Nd:YAG laser with second and third harmonic generator s deliver ed nanosecond pulses for excitation at 532 or 355 nm respectively. A Newport 250 watt quartz tungsten halogen lamp and radiometric power supply were used as the probe source. A Cornerstone 130/m motorized monochromator isolated the wavelength of detection. Two gratings were installed with in the monochromator: one for ultraviolet visible analysis (1200 l/mm blaze 500) and one for near infrared analysi s (800 l/mm blaze
143 1000). Output signal from the detector wa s collected on a Tektronics 3032B o scilloscope. Light exposure of the sample wa s controlled by a series of shutters. A BNC Model 575 8 channel pulse generator controlled the l aser flashlamp, q s witch delay slow shutter, fast shutter, and oscilloscope. A Hama matsu R928 PMT powered by 730 volts wa s mounted to the monochromator in a custom base modified in house using 5 of the 9 PMT stages for signal amplification. Solution NLA measurements were performed via an open aperture z scan apparatus. The excitation wavelength was generated by a Continuum Surelite OPO Plus pumped with the third harmonic (355 nm) of a Continuum Surelite II 10 Nd:YAG laser. The laser beam was split with a 50:50 beam spli tter to two OPH PE10 SH V2 pyroelectric detectors, which measured the transmitted pulse energy as a function of the input pulse energy using an Ophir Laserstar dual channel optical laser energy meter. The beam was focused with a 25.4 mm diameter, 50.8 mm focal length concave lens. A ThorLabs motorized translation state (Z825B and TDC001) allow ed mm movement along the z axis. The solution NLA measurements of the polymers were conducted in 1 mM (based on the weight percentage of monomer) THF solutions. Th e NLA response of the films was measured by modifying the z scan apparatus to measure NLT The sample holder on the translations stage was replaced with a film holder such that the film could be placed in the focus of the laser beam. A neutral density fi lter was placed directly passed the OPO signal port and used to modify the energies to detector 1 and 2. The StarCom32 software program was employed to control the output of the Laserstar energy meter heads and energy meter. The films
144 were excited at 600 nm with a q switch delay of 240 s, which corresponded to an energy variation to detector 1 of 60 J 1.6 mJ. Materials and Synthesis All chemicals used for the synthesis of the cis and trans platinum acetylide complexes were reagent grade and used without purification unless noted. T HF and DMF (Acros) were distilled over sodium/benzophenone prior to use. Methylmethacrylate (Sigma Aldrich 9 9 %, inhibited with 10 100 ppm hydroquinone monomethyl ether, flash chromatography thro ugh two disposable pasteur pipettes of Dynamic Adsorbents Inc. basic flash alumina (230 400 mesh) immediately prior to injection into polymerization reactions. Reaction products were purified via flash chromatography on Silicycle Inc. silica gel, 230 40 0 mesh. Potassium tetrachloroplatinate (unless synthesized), t etrakis(triphenyl phosphine)palladium, and tris(dibenylideneacetone)dipalladium were purchased from Strem Chemicals; all other chemicals were purchased from Sigma Aldrich or Fisher Scientific. Solvents were of HPLC grade unless otherwise noted. The three chromophores, 1 ethynyl 4 (phenylethynyl)benzene (PE2), 2 (9,9 diethyl 9 H fluoren 7 yl)benzo[ d ]thiazole (BTF), and 9,9 diethyl 7 ethynyl N N diphenyl 9 H fluoren 2 amine (DPAF) and d ichloro bistriphenylphosphine platinum(II) were synthesized as described in Chapter 3. 4 ((T rimethylsilyl)ethynyl)aniline Triethylamine (80 mL) and 4 iodoaniline (4.63 g, 21.1 mmol) were added to a 250 mL round bottom flask, stirred, and argon purged. To the resulting pale yellow solution was added CuI (80.5 mg, 0.423 mmol) and PdCl 2 (PPh 3 ) 2 (149.4 mg, 0.213 mmol). The solution was further argon purged for 45
145 minutes with stirring ; TMS acetylene (2.08 g, 21.1 mmol) was then added via syringe, resulting in a p ale orange to yellow green color change The reaction was monitored by TLC. After 2.5 hours, a second e quivalence of the catalysts was added, followed by 0.75 mL TMS acetylene. The reaction was stir red for an additional four hours before removing the solvent in vacuo. The crude solid was dissolved in DCM, washed with NH 4 Cl and NaOH, and precipitated wi th hexanes, 3.39 g, 85% yield. 1 H NMR (300 MHz, CDCl 3 7.27 (d, 2H), 6.56 (d, 2H), 3.79 (bs, 2H), 0.22 (s, 7H). 4 E thynylaniline To a 250 mL round bottom flask was added 35 mL each of methanol and DCM. The solvents were purged with argon before addition of 4 ((trimethylsilyl)ethynyl)aniline (1.90 g, 10.0 mmol). The vessel w as further argon purged ; crushed potassium carbonate was then added (7.06 g, 51.1 mmol). The react ion was stir red for 3 hours prior to quenching with deionized water. The organic layer was extracted, dried with sodium sulfate, and removed in vacuo to yie ld the crude product. The product was dissolved in minimal DCM and precipitated out of solution with hexanes, then purified via flash chromatography with DCM as an eluent to yield the desired product, 1.07 g, 91% yield. 1 H NMR (300 MHz CDCl 3 ) 7.30 (d, 2H), 6.59 (d, 2H), 3.81 (s, 2H), 2.95 (s, 1H). t rans bis ( T ributylphosphine) 4 ethynylaniline platinum(II) chloride PtCl 2 (PBu 3 ) 2 (787 mg, 1.17 mmol) and 4 ethynylaniline (125 mg, 1.07 mmol) were dissolved in minimum THF (2 mL) in a 200 mL roun d bottom flask and deoxygenated Reagent grade diethylamine (10.5 mL) was added, resulting in a pale yellow solution, to which an additional 2 mL of THF was added to fully dissolve all starting material. The resulting solution was furth er argon purged fo r 10 minutes, then allowed to stir at room
146 temperature under argon overnight. The clear, yellow solution became cloudy with salt precipitate. The solvent was removed in vacuo. The resulting yellow, cloudy oil was dissolved in DCM and washed with DI wate r. The yellow organic layer was dried over Na 2 SO 4 and solvent removed in vacuo, yielding a yellow oil that was vacuum dried before purification via flash chromatography (2:3 DCM/hexanes) to yield a yellow o il. Yield 605 mg (75%). 1 H NMR (300 MHz, CDCl 3 ) 7.05 (d, 2H), 6.54 (d, 2H), 3.61 (bs, 2H), 2.00 (m, 12H), 1.79 (m, 24H), 0.92 (t, 18H) 31 P NMR (121 MHz, CDCl 3 ) 7.7 5 with 195 Pt satellites PtP = 2387 Hz. t rans bis ( T ributylphosphine)(1 ethynyl 4 (phenylethynyl)benzene)(4 ethynylaniline) platinum (Pt PE2) Trans bis (tributylphosphine) 4 ethynylaniline platinum(II) chloride (108 mg, 0.129 mmol) was dissolved in diethylamine (5 mL) and THF (5 mL) in a 50 mL round bottom flask and argon purged. To the reaction were added 4 ethynylaniline (17.3 mg, 0.148 mmol) and CuI (2.4 mg, 0.13 0 mmol). The resulting clear solution was stirred at room temperature under argon overnight. The reaction was then attached to a water condenser and heated to 50 C under argon for two hours. The solvent was removed in vacuo. The resulting orange solid was purified via flash chromatography (1:1 DCM/hexanes) to yield a pale yellow solid, 77 mg, 61% yield. 1 H NMR (300 MHz CDCl 3 ) 7.52 (m, 2H) 7.36 (m, 5 H), 7.24 (d, 2H), 7.11 (d, 2H), 6.57 (d, 2H), 3.59 (bs, 2H), 2.15 (m, 12 H), 1.61 (m, 12 H), 1.46 (m, 12 H), 0.93 (t, 18 H ). t rans bis ( T ributylphosphine)(1 ethynyl 4 (phenylethynyl)benzene)( N (4 ethynylphenyl)acrylamide ) platinum Trans bis (tributylphosphine)(1 ethynyl 4 (phenylethynyl)benzene)(4 ethynylaniline) plat inum (47 mg, 0.051 mmol) was added to
147 7.5 mL DCM in a round bottom flask. The yellow orange solution was cooled to 0 C with stirring, to which acryloyl chloride (8 L, 0.101 mmol) was added via glass precision syringe, resulting in a darker orange soluti on. Triethylamine (14 L, 0.101 mmol) was added. The reaction was stir red for 5 minutes, then warmed t o room temperature. The resulting solution was washed twice with deionized water and the orange/yellow organic layer was extracted and dried over Na 2 SO 4 The organic solvent was removed in vacuo, resulting in an orange oil that was purified via flash chromatography (8:2 DCM/hexanes), yielding a yellow solid. Yield 36 mg (72%). 1 H NMR (300 MHz CDCl 3 ) 7.52 (m, 2H), 7.45 (d, 2H), 7.36 (m, 5H), 7.27 (dd, 4 H), 7.18 (s, 1H) 6.46 (d, 1H), 6.28 (dd, 1H), 5.78 (d, 1H), 2.13 (m, 12H), 1.60 (m, 12H), 1.46 (m, 12H), 0.93 (t, 18 H). t rans bis ( T ributylphosphine)(9,9 diethyl 7 ethynyl N,N diphenyl 9H fluoren 2 amine(4 ethynylaniline) platinum (Pt DPAF) Tra ns bis (tributylphosphine) 4 ethynylaniline platinum(II) chloride (140 mg 0.186 mmol) and 9,9 diethyl 7 ethynyl N N diphenyl 9 H fluoren 2 amine (70 mg, 0. 169 mmol) were dissolved in a 1:1 THF/diethylamine solution (16 mL) in a 100 mL round bottom flask. The resu lting yellow solution was argon purged prior to the addition of CuI (1.4 mg, 0.007 mmol). The reaction was stirred under argon at room temperature for 9.5 hours. The solvent was removed in vacuo and the resulting solid purified via flash chromato graphy (1:1 DCM/hexanes), 67 mg orange solid isolated, 41% yield. 1 H NMR (300 MHz, CDCl 3 ) 7.47 (d d 2H), 7.23 ( t 7H) 7.19 ( m 6 H), 6.99 ( t 3H ), 6.56 ( d 2 H), 3.57 ( bs 1H) 2.15 (m, 12H), 1.86 (two sets of diastereotopic q 4H), 1.62 (m, 12H), 1.43 (m, 12H), 0.90 (t, 18H), 0.34 (t, 6H)
148 t rans bis ( T ributylphosphine)(9,9 diethyl 7 ethynyl N,N diphenyl 9H fluoren 2 amine(N (4 ethynylphenyl)acrylamide) platinum Trans bis tributylphosphine)(9,9 diethyl 7 ethynyl N,N diphenyl 9H fluoren 2 amine(4 ethyn ylaniline) platinum (60 mg, 0.053 mmol) was dissolved in DCM (5 mL). The resulting orange solution was cooled to 0 C with stirring prior to the addition of acryloyl chloride (8.7 L, 0.107 mmol) and triethylamine (15 L, 0.108 mmol) via glass precision syringe. The solution was stirred for five minutes, then removed from the ice bath and further stirred for 20 minutes. The resulting brown orange solution was washed twice with deionized water. The organic layer was dried with Na 2 SO 4 before the solvent was removed in vacuo. The resulting dark orange oil was purified via flash chromatography (1:3 DCM/hexanes), 54.6 mg, 88% yield. 1 H NMR (300 MHz CDCl 3 ) 7.62 (d, 2H), 7.49 (dd, 2 H), 7.25 (M, 8H), 7.13 (m, 4H), 7.00 (d, 2H), 6.92 (m, 2H), 6.41 (d, 1H), 6.24 (dd, 1H), 5.78 (d, 1H), 2.17 (m, 12 H), 1.88 (two sets of diastereotopic q, 4H), 1.64 (m, 12 H), 1.47 (m, 12 H), 0.94 (t, 18 H), 0.35 (t, 6H). 31 P NMR (121 MHz, CDCl 3 ) 4 .00 with 195 Pt satellites PtP = 2358 Hz. t rans bis ( T ributylphosphine) bis (2 (9,9 diethyl 9H fluoren 7 yl)benzo [d]thiazole)(4 ethynylaniline) platinum (Pt BTF) Trans bis (tributylphosphine) 4 ethynylaniline platinum(II) chloride (605 mg, 0.805 mmol) and 2 (9,9 diethyl 9 H fluoren 7 yl)benzo[ d ]thiazole (33 6 mg, 0.885 mmol) were dissolved in minimum THF (1.5 mL), resulting in an orange yellow solution. Diethylamine (10 mL) was added and the resulting solution purged with argon prior to the addition of CuI (7.5 mg, 0.039 mmol). The solution rea cted at room temperature with stirring for 5.5 hours ; t he solvent was then removed in vacuo. The resulting orange brown oil was dissolved in DCM and w ashed with deionized water. The organic layer was dried over Na 2 SO 4 and the solvent
149 removed in vacuo. The resulting brown oil was purified via flash chromatography (1:1 DCM/hexanes) to yield the crystalline product, 461 mg, 52% yield. 1 H NMR (300 MHz CDCl 3 ) 8.09 (d, 2H), 8.07 (d, 1H), 7.88 (d, 1H), 7.72 (d, 1H), 7.58 (d, 1H), 7.48 (t, 1H), 7.36 (t, 1H), 7.28 (t, 2H) 7.10 (d, 2H), 6.55 (d, 2H), 3.42 (bs, 1H), 2.17 (m, 12H), 2.03 (two sets of diastereotopic q 4H), 1.63 (m, 12H), 1.44 (m, 12H), 0.94 (t, 18H), 0.35 (t, 6H) 31 P NMR (121 MHz, CDCl 3 ) 4.01 with 195 Pt satellites PtP = 2365 Hz. t rans bis ( T ributylphosphine) bis (2 (9,9 diethyl 9H fluoren 7 yl)benzo[d] thiazole)(N (4 ethynylphenyl)acrylamide) platinum Trans bis (tributylphosphine) bis (2 (9,9 diethyl 9H fluoren 7 yl)benzo[d]thiazole)(4 ethynylaniline) platinum (145 mg, 0.133 mmol) was disso lved in 3 mL chloroform, argon purged, and cooled to 0 C Acryloyl chloride (22 L, 0.271 mmol), then triethylamine (37 L, 0.266 mmol) were added via glass precision syringe. The solution was stirred for seven minutes, then warmed to room temperature. The solvent was removed in vacuo ; the solid was then washed twice with deionized water (extracted with DCM) and dried over Na 2 SO 4 The solvent was removed in vacuo. The resulting brown oil was purified via flash chromatography (2:1 DCM/hexanes), 101 mg yellow oil, 66% yield. 1 H NMR (300 MHz CDCl 3 ) 8.09 (d, 3H), 8.01 (d, 1H), 7.91 (d, 1H), 7.71 (d, 2 H), 7.61 (d, 1H), 7.47 (m, 3H), 7.38 ( d 1H), 7.27 ( d 2 H), 6.63 (d, 1H), 6.24 (dd, 1H), 5.75 (d, 1H), 2.14 (m, 12H), 2.03 (two sets of diastereotopic q 4H), 1.64 (m, 12H), 1.46 (m, 12H), 1.26 (s, 1H), 0.94 (t, 18H), 0.34 (t, 6H) 31 P NMR (121 MHz, CDCl 3 ) 4.14 with 195 Pt satellites PtP = 2354 Hz. azobis (cyclohexanecarbonitrile ) were dissolved in 99.8% anhydrous dimethylformamide in a
150 10 mL S chlenk flask. Methylmethacrylate was purified immediately prior to injection (via glass precision syringe) into polymerization reactions; MEHQ was removed via flash chromatography through b asic flash alumina. The resulting solution was deoxygenated via freeze pump thaw techniques, purged with nitrogen, and warmed to room temperature. The S chlenk flask was heated via oil bath to 65 C until the polymerization reaction became viscous and una ble to stir. The resulting polymer was dissolved in minimum DMF (20 mL) and precipitated with methanol (200 mL), resulting in fine, fluffy solid that aggregated upon removal of stirring. The mother liquor was decanted and the polymer re dissolved and re precipitated three additional times, then filtered and dried, yielding the platinum polymer. Equivalents for polymers of varying mass percentages of platinum starting material: 2.5 % by mass Pt PE2 monomer to MMA: 60 mg trans bis (tributylphosphine)(1 eth ynyl 4 (phenylethynyl) benzene)(N (4 ethynylphenyl)acrylamide) platinum (0.062 mmol), 2.49 mL MMA (23.4 mmol), 12.3 mg (0.0 50 azobis(cyclohexane carbonitrile), 2.4 mL DMF, stir for 6 hours with heating at 70 C. 10% by mass Pt PE2 monomer to MMA: 35 mg trans bis (tributylphosphine)(1 ethynyl 4 (phenylethynyl) benzene)(N (4 ethynylphenyl)acrylamide) platinum (0.038 mmol), 335 L MMA (3.15 mmol), 1.6 mg (0.01 azobis(cyclohexane carbonitrile), 300 L DMF, ~8 hours of heating at 65 C. 5.6% by mass Pt DPAF monomer to MMA: 23 mg (0.02 mmol) trans bis (tributylphosphine)( 9,9 diethyl 7 ethynyl N,N diphenyl 9H fluoren 2 amine(N (4
151 ethynylphenyl)acrylamide) platinum, 415 L (3.90 mmol) MMA, 2.1 mg (0.01 azobis (cyclohexanecarb onitrile), 400 L DMF, ~8 hours of heating at 65 C. 10% by mass Pt DPAF monomer to MMA: 15.5 mg (0.01 mmol) trans bis (tributylphosphine)( 9,9 diethyl 7 ethynyl N,N diphenyl 9H fluoren 2 amine(N (4 ethynylphenyl)acrylamide) platinum, 148 L (1.39 mmol) MM A, 0.7 mg (0.003 mmol) azobis (cyclohexanecarbonitrile), 140 L DMF, stir overnight at 65 C. 1% by mass Pt BTF monomer to MMA: 33.8 mg (0.03 mmol) trans bis (tributylphosphine) (2 (9, 9 diethyl 9H fluoren 7 yl)benzo [d]thiazole)( N (4 ethynylphenyl) acrylamide) platinum, 324 L (3.04 mmol) MMA, 1.5 mg ( 0.01 azobis (cyclohexanecarbonitrile), 310 L DMF, stir overnight at 65 C. 5% by mass Pt BTF monomer to MMA: 19 mg (0.017 mmol) trans bis (tributylphosphine) (2 (9, 9 diethyl 9H fluoren 7 yl)benzo [d]thiazole)( N (4 ethynylphenyl) acrylamide) platinum, 405 L (3.80 mmol) MMA, 1.9 mg (0.008 azobis (cyclohexanecarbonitrile), 390 L DMF, stir for 11.5 hours heating at 65 C. 10% by mass Pt BTF monomer to MMA: 4. 2 mg (0.004 mmol) trans bis (tributylphosphine) (2 (9, 9 diethyl 9H fluoren 7 yl)benzo [d]thiazole)( N (4 ethynylphenyl) acrylamide) platinum, 405 L (3.80 mmol) MMA, 1.9 mg (0.008 azobis (cyclohexanecarbonitrile), 390 L DMF, stir overnight at 65 C. The actual weight percentage of the platinum acetylide monomer incorporated into the PMMA polymer was calculated from the molar absorptivity of the monomer precursor and the ground state absorption of the resulting poly mer. This measurement can be used to determine the mass percentage of the monomer in the resulting polymer because the ground state absorption of the polymer in the ultra violet visible region is
152 only the result of the incorporation of the platinum acetylide monomer. As such, a plot of a bsorption versus concentration of the monomer was generated from the molar absorptivity measurements A known amount of polymer was then dissolved into a known volume of THF. The resulting ground state absorption of the polymer solution was fit onto the monomer absorption versus concentration plot to determine the concentration of the polymer solution, and resulting mass percentage of monomer that was incorporated into the PMMA polymer. General doctor blading procedure: Two layers of Scotch Magic Tape we re applied to two opposite edges of a clean glass slide. The polymer material was well dissolved in dry THF, then applied to the edge of a clean glass slide via a precision syringe or Eppendorf pipette. The polymer solution was bladed across the slide wi th a straight edge, then covered, and allowed to slowly dry. Small and large slides were made, of approximately 1 x 2.5 cm and 2.5 x 2.5 cm in size, respectively. Amounts of polymer onto films: 22 mg of 1.7% Pt PE2(PMMA) was dissolved in 160 L THF, of w hich 40 L were applied to a small slide and 80 L were applied to a large slide. 5.4 mg of 9.1% Pt PE2(PMMA) was dissolved in 160 L THF, of which 40 L were applied to three small slides. 5.4 mg of 3.5% Pt DPAF(PMMA) was dissolved into 30 L THF and ap plied to a small slide. 10.9 mg of 12.3% Pt BTF(PMMA) was dissolved in 200 L THF, of which 30 L were applied to three small slides and 60 L were applied to a large slide. 2 mg each of 1.7% and 9.1% Pt PE2(PMMA), 3.5% Pt DPAF(PMMA), 1.2%, 4.7%, and 12.3% Pt BTF(PMMA) were dissolved in 70 L THF, of which 10 L were applied to small slides.
153 General monolith procedure: The polymer was measured into a clean glass vial, to wh ich was added DCM by precision syringe. The vial was closed and the solution was sonocated for two minutes before being deposited via syringe into the Teflon mold. The solutions were covered and allowed to slowly dry. Amounts of polymer into monoliths: Pt BTF(PMMA) polymer weight percent comparison series: 7.4 mg each of the 1.2%, 4.7%, and 12.3% were dissolved in 200 L DCM. Chromophore comparison series : 11.7 mg of 1.7% Pt PE2(PMMA), 5.7 mg of 3.5% Pt DPAF(PMMA), and 16. 7 mg of 1.2% Pt BTF(PMMA) wer e dissolved in 200 L DCM. Polymer amount comparison series: 7.4 mg, 16.7, and 23.6 mg of 1.2% Pt BTF(PMMA) were dissolved in 200 L DCM. PMMA polymer monoliths were generated by dissolving 7.5 mg and 14.6 mg PMMA into 200 L DCM.
154 A PPENDIX A USER MANUAL FOR OPEN APERTURE Z SCAN APPARATUS Open Aperture Z Scan with Manual Translation Stage (Z Scan and CCDSystemControl programs) Abigail Shelton and Randi Price December 2010 This manual is designed to walk you through a z scan experiment, including sample preparation, setup, data collection, and data processing. Check with Dr. Schanze or the z s can m anager for further direction and training. Always wear proper eye protection while working with the lasers. Do not remove blackout material surrounding the laser table while operating the laser. Know the laser beam path and optics involved before turning on the laser. NEVER look directly into the laser beam or lean over the table into the path of the laser. Be aware of reflection and stray light, as eye damage may result. Lasers and optical alignment are very sensitive. Do not move or make adjustments to the optics or lasers without permissio n of Dr. Schanze or the z scan m anager. Instrument Schematic: Introduction This manual is designed to gui de you through the use of the equipment and software necessary to collect nanosecond nonlinear absorption response of solutions. For complete instructions on the laser, energy meters, or other components, please consult their respective ma nuals or the z s can manager.
155 Components: Continuum Surelite II Nd:YAG Laser: Provides 355 nm excitation source used to pump the OPO. Continuum Surelite OPO : An optical parametric oscillator that contains a nonlinear optics crystal that tunes the 355 nm laser output to wavelengths in the range of 420 670 nm and 800 2500 nm, which can be used for excitation of the sample. BNC 555 pulse/delay generator: The pulser controls the laser flashlamp and q switch delay timing. Thorlabs Z825B Motorized DC Servo Actuator: The Thorlabs Z825B Motorized DC Servo Actuator attaches to the movable stage on which the sample holder is mounted. It is driven by the servomotor to move the stage with high precision (minimum resolu tion of 29 nm). The Z825 has a travel length of 25 mm. There is an automatic power cutoff when the actuator reaches its maximum and minimum mechanical limits. The Z825 can be operated at varying speeds, however the speed is constant in this application Its load capacity is 9 kg. Thorlabs TDC001 T Cube DC Servo Controller : The Thorlabs TDC001 T Cube DC Servo Controller powers the actuator with 12 V and provides an interface to the computer for use in software applications. Manual control of the actua tor is available by toggling the switch to move the actuator forward and backward. Ophir Laserstar Energy Meter Heads, 9 mJ capacity : These matched energy meter heads are used to monitor the change in energy as your sample is subjected through the focu s of the laser beam. These heads can be used to measure the laser energy at 600 nm, but should not be used for measuring the pump beam at 355 nm. These heads have a sensitivity range of 10 J 9 mJ; laser energies in excess of 9 mJ will damage the meter heads. Ophir Laserstar Energy Display: The Ophir Laserstar energy meter heads are connected to the energy display to show you the shot to shot energy changes of both energy meter heads during the experiment. The energy display is configured to manua lly calculate the energy ratio of the sample head A over the reference head B. Computers: The z scan experiment will use the Surelite Continuum II laser desktop computer and the z scan laptop. The laptop and power cord are stored in the red toolbox. So ftware updates or changes should not be made on either computer without the permission of Dr. Schanze or the z scan manager. Software programs: The Surelite Continuum II laser will be controlled through the new CCDSystemControl.vi program on the laser de sktop. The Ocean Optics hardware is controlled through the OOIBase32 program on the laser desktop. The z scan translation stage and data collection will be controlled through the z scan.vi program on the z scan desktop.
156 Sample Preparation: This manual i s designed to guide you through the collection of nonlinear absorption response of solutions. The specific volume and concentration of the samples can be varied. A starting point would be 300 L of a 1 mM solution. A 1 mm narrow pathlength cuvette is ne cessary for accurate solution measurements. Start Up Turn on the z scan laptop and login to your chemnet account or the local user account. Plug the two matched 9 mJ PE10 V2 pyroelectric Ophir Laserstar energy meter heads into the Ophir Laserstar en ergy display. The sample meter should be plugged into slot A while the reference meter should be plugged into slot B. Plug in the power cord, and plug the Ophir energy display RS232 to USB converter cable into the bottom left hand USB slot in the laptop. Turn on the Ophir Laserstar energy meter. The energy meter should bring up all the settings for the z scan experiment; however the settings should be verified using the following steps: Adjust the energy settings for meter A and B to both read to 2.00 mJ. This setting represents the maximum energy to be read. The setting can be adjusted individually. Click Verify that the meter is reading in A/B mode. This can be adjusted by clicking reading in Plug in the power cord for the T horlabs m otor d river. Observe that the green power indicator light on the motor controller turns on. Plug the Thorlabs m otor d river USB cable into the top left hand USB slot in the laptop. Open the z s can.vi program on the lap top by double clicking the icon A warning message may ap pear, click ignore if it does. Verify that the Surelite Continuum II pump laser is directed through the OPO. A whit e magnetic arrow is used on top of the OPO housing to indicate the direction of the pump beam. The arrow should be pointing towards the front of the OPO housing. A steering optic needs to be removed from inside the OPO housing if the pump beam is directe d out the left side port of the OPO. Consult a laser manager for training on making this optical change. Turn on the pulser.
157 Power up the laser: Turn the key a quarter turn anticlockwise. The LCD display will cycle through its set up. It is ready whe Push the start/stop button. Push the shutter button. You should hear a click from the laser head when the shutter button is pressed. The laser flashlamps will not flash until initiated by the CCDS ystemControl Program. Open the New CCDSystemControl.vi by double clicking the icon on the laser desktop computer. Excitation Calibration **Please familiarize yourself with proper laser operation and laser safety prior to using the laser or adjusting th e laser path. This manual is not intended to provide full instruction of the laser or OPO.** The Surelite Continuum II pump beam can generate visible excitation wavelengths from approximately 420 670 nm by pumping through the OPO. The z scan experimen t operates best when excitation occurs at a wavelength that is much longer than the cut off wavelength of the linear (single photon) absorption. Strong, stable, and typically suitable excitation wavelengths are in the 580 620 nm region. The w avelength of the OPO modified beam can be measured with the Ocean Optics fiber optic cable and software. The blue fiber optic cable is located on the laser shelf by the PTG. The cable attaches to a gray control box that connects to the Surelite Continuum II laser computer via a USB port. The cable is correctly connected to the computer when the green indicator light o n the control box is illuminated. Check the connectivity. Open the OceanOptics32 program by double clicking the icon on the laser computer desktop. Position the fiber optic cable to point towards the z scan apparatus. Set up the white card block to reflect the laser light towards the cable head mount. A distance of at least two feet between the card block and the cabl e head mount is desirable; the fiber optic cable requires very little energy to obtain readings. Do not position the cable head mount in any direct laser path. Verify that the Surelite Continuum II pump beam is directed through the OPO. I n the CCDSys temControl program, click to initiate the program. The laser flashlamp will begin to flash (you will hear them clicking). This is the default initialization of the program. Allow the flashlamps to warm up for 15 minutes before continuing to the next s tep. Turn on the laser by toggling the q switch in the CCDSystemControl program. The laser should be set to a safe, low power ( q switch delay > 280 s) for wavelength
158 calibration. The delay can be changed by entering the desired value. A longer delay setting corresponds to lower laser intensity. Click Apply Changes after the values are set. Visible laser light should be observed out the signal output at the front of the OPO. The laser flashlamp and q switch should fire when the CCDSystemControl pr ogram looks like the following: Monitor the wavelength of the laser beam on the Ocean Optics software program. (Turning off the room lights will allow you to easily determine which peak on the program screen corresponds to the laser output.) The e xcitation wavelength can be adjusted by slowly rotating the micrometer on the top of the OPO housing. Do not turn the micrometer to wavelengths below 420 nm or above 670 nm. Once you have adjusted the output laser to the desired wavelength, r eturn the ca rd block and the ocean optics fiber optic cable to their positions off the laser table. Keep the laser flashlamp and q switch Alignment There is no reason the signal output should be out of alignment, but it is necessary to verify the alignment before beginning your experiment. Adjust the q switch delay setting to 270 s. Click Apply Changes. Allow the flashlamp and q switch to fire for 20 minutes before adjusting the laser beam alignment.
159 Examine the beam profile. Th e beam should be circular in shape, with no noticeable hotspots or donuts. The z scan manager can help you adjust the beam profile if it is not circular or consistent Check the alignment of the laser to the beam splitter, through the focusing optics, an d to both energy meter heads. Verify that the entire beam is being collected by the energy meter heads. The energy meter heads can be adjusted horizontally to ensure proper collection of the beam. Do not adjust the position of the lenses or beam split ter. Verify that the sample holder on the translation stage is positioned so that the laser would pass through the sample cuvette. The sample holder allows for one inch movement from left to right to ensure that the laser light will pass through the cu vette. The sample holder can also be adjusted vertically by raising or lowering the post in the post base. Adjusting the position of the cuvette post base on the translation stage, however, will change the zero position of the z scan. To maintain a cons tant beam profile, the laser should not be toggled off during the course of the experiment. Use the white card block to block the laser beam prior to the sample holder in order to safely insert or remove your sample. Data Collection Click the white arrow on the top menu bar in the z scan.vi program to initiate the program. The arrow will turn black when the program is running. Enter in the start, stop, and step relative positions for the stage. Values are in mm. A position of 0 is assumed to be t he approximate focal point of the laser beam. The maximum values for the start and stop positions are 12.5 mm. The motorized DC servo actuator is specified at nm resolution; however this degree of resolution is not needed for the z s can experiment. Choose a reasonable step size (0.5 1 mm is typically sufficient). It is important to have enough data points for a good baseline before and after the 10, Stop: 10, Step : 0.5 mm. Choose the number of shots at each position. This is roughly the number of laser pulses that will be averaged at each position. (Each shot is given approximately 0.1 sec, so 100 shots will take an average of 10 seconds of laser pulses at eac h position.) It is recommended to use 25 shots. Choose a filename. Files are saved to the desktop. You must choose a unique filename! The program appends each data point to your chosen filename. If you choose a filename that already exists, the da ta collected in the current run will be appended to the end of that file. The position information is NOT saved in the file, so be sure to make note of the starting/stopping/step positions you choose!
160 Choose whether or not to allow data reject. If data r eject is turned on, a box will pop up after each data point to allow the option of accepting or redoing that data point. Occasionally an extraneous point might be obtained (appears as an Inf or NaN in the data reject function. The energy ratio and standard deviation of the average value are shown and useful for determining data validity. A standard deviation of approximately 0.004 is common near the baseline, and a standard deviation of approximately 0.0 2 is common near the peak. With these features enabled, the z scan program should look like the following: Block the laser beam with the white card block. Insert your cuvette into the sample holder on the translation stage. Remove the card block. V erify that the beam is going to the energy meter head A without clipping at the cuvette. Click RUN. In the middle of the screen, there is a progress indicator (x of y), a relative position indicator, and the average energy value obtained at that position The program will manually move the translation stage according to the step settings you entered. When the experiment is complete, the experiment file will be saved to the desktop under the chosen filename. Block the laser beam with the beam block. Remove your sample cuvette. scan program to move the motor to its home position. Clean the sample cuvette and insert the new
161 solution into the cuvette. Insert the cuvette into the sam ple holder while the beam block is in place. Remove the card block and verify that the beam is going to the energy meter head A without clipping at the cuvette. Do not adjust the laser alignment or energy meter head positions between experiments. Click Run and monitor the experiment as before. Data Processing Files will be saved to the desktop under the chosen filename and can be imported into Excel and plotted in Excel or SigmaPlot. The position information (x axis) must be added manually according to the step settings entered for each run. Extraneous points can be manually removed. Adjust the z position in your data set if the lowest point of transmittance is not at the zero z position. Shut Down The laser flashlamps will continue to fire after the data collection has completed. Shut down the software programs before powering d own the hardware. To exit the z s can.vi program, press the red stop button on the top menu bar and go to Fil e Exit. When prompted, select Do Not Save. Close the CCDSystemControl and Ocean Optics32 programs by clicking the X in the top right hand corner of the programs. On the z scan laptop, eject the USB ports from the translation stage and energy meter. Tur n off and unplug the Ophir Laserstar energy meter. Remove the energy meter heads and RS 232 to USB converter from the energy meter. Unplug the power to the Thorlabs Motor Driver. Observe that the green power indicator light on the motor controller turns off. Power down the laser by pushing the shutter button, then the start/stop button (the yellow LED should turn off). Turn the key a quarter turn clockwise to the off position. Turn off the pulser. Return the z scan laptop, energy meter, and cables to their proper storage drawers. Cover all optics and clean up any samples from the laser bench. Return all tools and extra hardware to their storage drawers or containers. The equipment in the laser lab is expensive and sensitive to dust, so please kee p the laser lab clean and uncluttered.
162 A PPENDIX B X RAY CRYSTAL STRUCTUR E PARAMETERS cis PE2 Crystal Data and Structure R efinement for cis PE2 Identification code abby2 Empirical formula C58 H42 P2 Pt Formula weight 995.95 Temperature 100(2) K Wavelength 0.71073 Crystal system Monoclinic Space group P2 Unit cell dimensions a = 15.8357(11) = 90. b = 8.9008(7) = 113.033(3). c = 18.9781(14) = 90. Volume 2461.7(3) 3 Z 2 Density (calculated) 1.344 Mg/m 3 Absorption coefficient 2.950 mm 1 F(000) 996 Crystal size 0.42 x 0.14 x 0.05 mm 3 Theta range for data collection 2.14 to 27.50. Index ranges Reflections collected 23463 Independent reflections 10398 [R(int) = 0.0364]
163 Completeness to theta = 27.50 99.9 % Absorption correction Numerical Max. and min. transmission 0.8569 and 0.3726 Refinement method Full matrix least squares on F 2 Data / restraints / parameters 10398 / 1 / 552 Goodness of fit on F 2 1.135 Final R indices [I>2sigma(I)] R1 = 0.0297, wR2 = 0.0672  R indices (all data) R1 = 0.0341, wR2 = 0.0687 Absolute structure parameter 0.146(6) Largest diff. peak and hole 1.588 and 1.447 e. 3 R1 = (||F o | |F c ||) / |F o | wR2 = [ [ w(F o 2 F c 2 ) 2 ] / [w( o 2 ) 2 ]] 1/2 S = [ w(F o 2 F c 2 ) 2 ] / (n p)] 1/2 w= 1/[ 2 (F o 2 )+(m*p) 2 +n*p], p = [max(F o 2 ,0)+ 2* F c 2 ]/3, m & n are constants. Crystal Structure Bond Lengths an d Angles cis PE2 Table B 1. Bond l engths () for cis PE2 Bond Length ( ) Bond Length ( ) Bond Length ( ) Pt1 C1A#1 2.015(8) C20A C21A 1.385(8) C8B H8B 0.9500 Pt1 C1A 2.015(8) C18A C19A 1.400(8) C9B C10B 1.184(8) Pt1 P1#1 2.269(2) C20A H20A 0.9500 C10B C11B 1.449(8) Pt1 P1 2.269(2) C21A C22A 1.403(6) C11B C12B 1.364(8) P1 C23A 1.807(5) C21A H21A 0.9500 C11B C16B 1.422(10) P1 C17A 1.824(5) C22A H22A 0.9500 C12B C13B 1.411(8) P1 C29A 1.850(5) C23A C28A 1.399(7) C12B H12B 0.9500 C1A C2A 1.196(9) C23A C24A 1.400(7) C13B C14B 1.382(9) C2A C3A 1.434(7) C24A C25A 1.394(7) C13B H13B 0.9500 C3A C8A 1.396(7) C24A H24A 0.9500 C14B C15B 1.367(9) C3A C4A 1.418(7) C25A C26A 1.381(7) C14B H14B 0.9500 C4A C5A 1.363(10) C25A H25A 0.9500 C15B C16B 1.402(8) C4A H4A 0.9500 C26A C27A 1.379(8) C15B H15B 0.9500 C5A C6A 1.394(9) C26A H26A 0.9500 C16B H16B 0.9500
164 Table B 1. Bond lengths () for cis PE2, c ontinued Bond Length ( ) Bond Length ( ) Bond Length ( ) C5A H5A 0.9500 C27A C28A 1.382(8) C17B C22B 1.387(7) C6A C7A 1.406(6) C27A H27A 0.9500 C17B C18B 1.403(7) C6A C9A 1.426(7) C28A H28A 0.9500 C18B C19B 1.382(7) C7A C8A 1.374(7) C29A C29A#1 1.561(9) C18B H18B 0.9500 C7A H7A 0.9500 C29A H29A 0.9900 C19B C20B 1.381(8) C8A H8A 0.9500 C29A H29B 0.9900 C19B H19B 0.9500 C9A C10A 1.200(7) Pt2 C1B#2 2.011(8) C20B C21B 1.395(7) C10A C11A 1.436(8) Pt2 C1B 2.011(8) C20B H20B 0.9500 C11A C16A 1.394(9) Pt2 P2#2 2.271(2) C21B C22B 1.398(6) C11A C12A 1.411(8) Pt2 P2 2.271(2) C21B H21B 0.9500 C12A C13A 1.358(8) P2 C17B 1.810(5) C22B H22B 0.9500 C12A H12A 0.9500 P2 C23B 1.821(5) C23B C24B 1.381(7) C13A C14A 1.395(9) P2 C29B 1.846(5) C23B C28B 1.398(7) C13A H13A 0.9500 C1B C2B 1.195(9) C24B C25B 1.414(6) C14A C15A 1.353(9) C2B C3B 1.435(7) C24B H24B 0.9500 C14A H14A 0.9500 C3B C4B 1.396(8) C25B C26B 1.388(7) C15A C16A 1.412(8) C3B C8B 1.419(6) C25B H25B 0.9500 C15A H15A 0.9500 C4B C5B 1.388(9) C26B C27B 1.400(8) C16A H16A 0.9500 C4B H4B 0.9500 C26B H26B 0.9500 C17A C22A 1.380(8) C5B C6B 1.410(8) C27B C28B 1.378(7) C17A C18A 1.386(7) C5B H5B 0.9500 C27B H27B 0.9500 C18A C19A 1.400(8) C6B C7B 1.408(6) C28B H28B 0.9500 C18A H18A 0.9500 C6B C9B 1.434(7) C29B C29B#2 1.532(8) C19A C20A 1.38(1) C7B C8B 1.362(7) C29B H29A 0.9900 C19A H19A 0.9500 C7B H7B 0.9500 C29B H29D 0.9900 Table B 2. Bond angles (degrees) for cis PE2 Bond Angle ( ) Bond Angle ( ) Bond Angle ( ) C1A#1 Pt1 C1A 93.9(4) C17A C22A C21A 119.8(5) C12B C11B C10B 121.1(6) C1A#1 Pt1 P1#1 175.8(3) C17A C22A H22A 120.1 C16B C11B C10B 118.8(6) C1A Pt1 P1#1 89.9(2) C21A C22A H22A 120.1 C11B C12B C13B 120.5(6) C1A#1 Pt1 P1 89.9(2) C28A C23A C24A 118.0(5) C11B C12B H12B 119.7 C1A Pt1 P1 175.8(3) C28A C23A P1 120.3(4) C13B C12B H12B 119.7 P1#1 Pt1 P1 86.36(11) C24A C23A P1 121.3(4) C14B C13B C12B 119.6(6) C23A P1 C17A 106.0(2) C25A C24A C23A 120.6(4) C14B C13B H13B 120.2 C23A P1 C29A 106.5(2) C25A C24A H24A 119.7 C12B C13B H13B 120.2 C17A P1 C29A 105.0(3) C23A C24A H24A 119.7 C15B C14B C13B 120.2(6) C23A P1 Pt1 115.5(2) C26A C25A C24A 119.9(5) C15B C14B H14B 119.9 C17A P1 Pt1 115.3(2) C26A C25A H25A 120.1 C13B C14B H14B 119.9 C29A P1 Pt1 107.70(16) C24A C25A H25A 120.1 C14B C15B C16B 121.4(6) C2A C1A Pt1 171.7(6) C27A C26A C25A 120.4(5) C14B C15B H15B 119.3 C1A C2A C3A 174.2(6) C27A C26A H26A 119.8 C16B C15B H15B 119.3 C8A C3A C4A 117.6(5) C25A C26A H26A 119.8 C15B C16B C11B 118.2(6) C8A C3A C2A 121.0(4) C26A C27A C28A 119.9(5) C15B C16B H16B 120.9 C4A C3A C2A 121.4(5) C26A C27A H27A 120.1 C11B C16B H16B 120.9 C5A C4A C3A 120.4(6) C28A C27A H27A 120.1 C22B C17B C18B 119.7(5)
165 Table B 2. Bond angles (degrees) for cis PE2, c ontinued Bond Angle ( ) Bond Angle ( ) Bond Angle ( ) C5A C4A H4A 119.8 C27A C28A C23A 121.2(5) C22B C17B P2 120.6(4) C3A C4A H4A 119.8 C27A C28A H28A 119.4 C18B C17B P2 119.7(4) C4A C5A C6A 122.1(6) C23A C28A H28A 119.4 C19B C18B C17B 119.5(5) C4A C5A H5A 118.9 C29A#1 C29A P1 108.2(2) C19B C18B H18B 120.3 C6A C5A H5A 118.9 C29A#1 C29A H29A 110.1 C22B C17B C18B 119.7(5) C5A C6A C7A 117.5(5) P1 C29A H29A 110.1 C17B C18B H18B 120.3 C5A C6A C9A 122.0(5) C29A#1 C29A H29B 110.1 C20B C19B C18B 120.6(5) C7A C6A C9A 120.4(5) P1 C29A H29B 110.1 C20B C19B H19B 119.7 C8A C7A C6A 120.9(5) H29A C29A H29B 108.4 C18B C19B H19B 119.7 C8A C7A H7A 119.6 C1B#2 Pt2 C1B 94.0(5) C19B C20B C21B 120.8(5) C6A C7A H7A 119.6 C1B#2 Pt2 P2#2 175.8(3) C19B C20B H20B 119.6 C7A C8A C3A 121.4(4) C1B Pt2 P2#2 90.1(2) C21B C20B H20B 119.6 C7A C8A H8A 119.3 C1B#2 Pt2 P2 90.1(2) C20B C21B C22B 118.5(5) C3A C8A H8A 119.3 C1B Pt2 P2 175.8(3) C20B C21B H21B 120.7 C10A C9A C6A 178.4(7) P2#2 Pt2 P2 85.77(11) C22B C21B H21B 120.7 C9A C10A C11A 176.9(5) C17B P2 C23B 106.9(2) C17B C22B C21B 120.9(5) C16A C11A C12A 118.6(6) C17B P2 C29B 104.7(2) C17B C22B H22B 119.5 C12A C13A C14A 120.0(6) C23B P2 C29B 107.3(2) C21B C22B H22B 119.5 C12A C13A H13A 120.0 C17B P2 Pt2 114.30(18) C24B C23B C28B 119.9(4) C14A C13A H13A 120.0 C23B P2 Pt2 115.6(2) C24B C23B P2 119.9(3) C15A C14A C13A 120.2(6) C29B P2 Pt2 107.32(17) C28B C23B P2 119.7(4) C15A C14A H14A 119.9 C2B C1B Pt2 172.4(6) C23B C24B C25B 120.0(4) C13A C14A H14A 119.9 C1B C2B C3B 176.4(6) C23B C24B H24B 120.0 C14A C15A C16A 121.1(6) C4B C3B C8B 117.3(5) C25B C24B H24B 120.0 C14A C15A H15A 119.5 C4B C3B C2B 121.2(5) C26B C25B C24B 119.3(5) C16A C15A H15A 119.5 C8B C3B C2B 121.5(4) C26B C25B H25B 120.4 C11A C16A C15A 118.9(6) C5B C4B C3B 122.3(6) C24B C25B H25B 120.4 C11A C16A H16A 120.5 C5B C4B H4B 118.9 C25B C26B C27B 120.4(4) C15A C16A H16A 120.5 C3B C4B H4B 118.9 C25B C26B H26B 119.8 C22A C17A C18A 120.7(4) C4B C5B C6B 119.5(5) C27B C26B H26B 119.8 C22A C17A P1 120.7(4) C4B C5B H5B 120.3 C28B C27B C26B 119.7(5) C18A C17A P1 118.6(4) C6B C5B H5B 120.3 C28B C27B H27B 120.1 C17A C18A C19A 118.8(6) C7B C6B C5B 118.5(4) C26B C27B H27B 120.1 C17A C18A H18A 120.6 C7B C6B C9B 121.6(4) C27B C28B C23B 120.6(5) C19A C18A H18A 120.6 C5B C6B C9B 119.7(5) C27B C28B H28B 119.7 C20A C19A C18A 121.2(7) C8B C7B C6B 121.2(4) C28B C27B C26B 119.7(5) C20A C19A H19A 119.4 C8B C7B H7B 119.4 C23B C28B H28B 119.7 C18A C19A H19A 119.4 C6B C7B H7B 119.4 C29B#2 C29B P2 107.8(2) C19A C20A C21A 119.5(5) C7B C8B C3B 121.3(4) C29B#2 C29B H29A 110.1 C19A C20A H20A 120.3 C7B C8B H8B 119.4 P2 C29B H29A 110.1 C21A C20A H20A 120.3 C3B C8B H8B 119.4 C29B#2 C29B H29D 110.1 C20A C21A C22A 120.0(5) C10B C9B C6B 177.2(6) P2 C29B H29D 110.1 C20A C21A H21A 120.0 C9B C10B C11B 175.8(8) H29A C29B H29D 108.5 C22A C21A H21A 120.0 C12B C11B C16B 120.1(6)
166 cis BTF Crystal Data and Structure Refinement for cis BTF Identification code abby3 Empirical formula C80 H68 Cl4 N2 P2 Pt S2 Formula weight 1520.31 Temperature 100(2) K Wavelength 0.71073 Crystal system Monoclinic Space group P2(1)/n Unit cell dimensions a = 12.8880(12) = 90. b = 17.4517(14) = 97.971(2). c = 30.725(2) = 90. Volume 6843.9(10) 3 Z 4 Density (calculated) 1.476 Mg/m 3 Absorption coefficient 2.361 mm 1 F(000) 3080 Crystal size 0.27 x 0.05 x 0.05 mm 3 Theta range for data collection 1.34 to 27.50. Index ranges Reflections collected 96259 Independent reflections 15721 [R(int) = 0 .0515] Completeness to theta = 27.50 100.0 %
167 Absorption correction Numerical Max. and min. transmission 0.8891 and 0.5681 Refinement method Full matrix least squares on F 2 Data / restraints / parameters 15721 / 16 / 811 Goodness of fit on F 2 0.968 Final R indices [I>2sigma(I)] R1 = 0.0243, wR2 = 0.0498  R indices (all data) R1 = 0.0385, wR2 = 0.0584 Largest diff. peak and hole 0.905 and 0.580 e. 3 R1 = (||F o | |F c ||) / |F o | wR2 = [ [ w(F o 2 F c 2 ) 2 ] / [w( o 2 ) 2 ]] 1/2 S = [ w(F o 2 F c 2 ) 2 ] / (n p)] 1/2 w= 1/[ 2 (F o 2 )+(m*p) 2 +n*p], p = [max(F o 2 ,0)+ 2* F c 2 ]/3, m & n are constants. Crystal Structure Bond Lengths a nd Angles cis BTF Table B 3 Bond lengths () for cis BTF Bond Length ( ) Bond Length ( ) Bond Length ( ) Pt1 C27 2.010(3) C18' H18B 0.9500 C49 H49A 0.9900 Pt1 C1 2.013(3) C19' C20' 1.392(15) C49 H49B 0.9900 Pt1 P1 2.2649(7) C19' H19B 0.9500 C50 H50A 0.9800 Pt1 P2 2.2709(7) C20' C21' 1.360(15) C50 H50B 0.9800 S2 C43 1.727(3) C20' H20B 0.9500 C50 H50C 0.9800 S2 C42 1.761(3) C21' C22' 1.400(16) C51 C52 1.529(4) P1 C73 1.814(3) C21' H21B 0.9500 C51 H51A 0.9900 P1 C67 1.818(3) C22' N1' 1.382(6) C51 H51B 0.9900 P1 C53 1.849(3) C27 C28 1.201(4) C52 H52A 0.9800 P2 C55 1.809(3) C28 C29 1.438(4) C52 H52B 0.9800 P2 C61 1.814(3) C29 C34 1.408(4) C52 H52C 0.9800 P2 C54 1.845(3) C29 C30 1.413(4) C55 C56 1.394(4) Cl1 C79 1.769(3) C34 C33 1.381(4) C55 C60 1.395(4) Cl2 C79 1.762(3) C34 H34A 0.9500 C56 C57 1.388(4) Cl3 C80 1.764(4) C33 C32 1.405(4) C56 H56A 0.9500 Cl4 C80 1.757(4) C33 C35 1.530(3) C57 C58 1.383(4) N2 C42 1.303(3) C32 C31 1.392(3) C57 H57A 0.9500
168 Table B 3. Bond lengths () for cis BTF, c ontinued Bond Length ( ) Bond Length ( ) Bond Length ( ) N2 C48 1.393(3) C32 C41 1.461(3) C58 C59 1.384(4) C1 C2 1.203(3) C31 C30 1.379(4) C58 H58A 0.9500 C2 C3 1.439(4) C31 H31A 0.9500 C59 C60 1.378(4) C3 C8 1.407(4) C30 H30A 0.9500 C59 H59A 0.9500 C3 C4 1.409(4) C35 C36 1.527(3) C60 H60A 0.9500 C4 C5 1.391(4) C35 C49 1.538(4) C61 C66 1.385(4) C4 H4A 0.9500 C35 C51 1.550(4) C61 C62 1.400(4) C5 C6 1.393(4) C36 C37 1.385(3) C62 C63 1.390(4) C5 H5A 0.9500 C36 C41 1.408(3) C62 H62A 0.9500 C6 C7 1.407(4) C41 C40 1.387(3) C63 C64 1.373(5) C6 C15 1.471(4) C37 C38 1.402(4) C63 H63A 0.9500 C7 C8 1.377(4) C37 H37A 0.9500 C64 C65 1.372(5) C7 C9 1.529(4) C38 C39 1.403(4) C64 H64A 0.9500 C8 H8A 0.9500 C38 C42 1.468(4) C65 C66 1.410(4) C9 C10 1.527(4) C39 C40 1.384(4) C65 H65A 0.9500 C9 C23 1.536(4) C39 H39A 0.9500 C66 H66A 0.9500 C9 C25 1.541(4) C40 H40A 0.9500 C67 C72 1.394(3) C10 C11 1.381(4) C48 C47 1.397(4) C67 C68 1.396(4) C10 C15 1.411(4) C48 C43 1.402(4) C68 C69 1.386(4) C15 C14 1.383(4) C43 C44 1.404(4) C68 H68A 0.9500 C14 C13 1.387(4) C44 C45 1.385(4) C69 C70 1.385(4) C14 H14A 0.9500 C44 H44A 0.9500 C69 H69A 0.9500 C13 C12 1.403(4) C45 C46 1.388(5) C70 C71 1.382(4) C13 H13A 0.9500 C45 H45A 0.9500 C70 H70A 0.9500 C12 C11 1.403(4) C46 C47 1.383(4) C71 C72 1.388(4) C12 C16 1.471(4) C46 H46A 0.9500 C71 H71A 0.9500 C11 H11A 0.9500 C47 H47A 0.9500 C72 H72A 0.9500 C16 N1 1.270(4) C23 C24 1.516(4) C73 C78 1.386(4) C16 N1' 1.306(6) C23 H23A 0.9900 C73 C74 1.393(4) C16 S1' 1.753(5) C23 H23B 0.9900 C78 C77 1.391(4) C16 S1 1.761(3) C24 H24A 0.9800 C78 H78A 0.9500 S1 C17 1.755(4) C24 H24B 0.9800 C77 C76 1.380(4) C17 C22 1.409(5) C24 H24C 0.9800 C77 H77A 0.9500 C17 C18 1.409(5) C25 C26 1.383(5) C76 C75 1.382(4) C18 C19 1.387(5) C25 C26' 1.398(10) C76 H76A 0.9500 C18 H18A 0.9500 C25 H25A 0.9900 C75 C74 1.393(4) C19 C20 1.396(5) C25 H25B 0.9900 C75 H75A 0.9500 C19 H19A 0.9500 C25 H25C 0.9900 C74 H74A 0.9500 C20 C21 1.381(4) C25 H25D 0.9900 C53 C54 1.535(4) C20 H20A 0.9500 C26 H25C 0.8406 C53 H53A 0.9900 C21 C22 1.398(5) C26 H26A 0.9800 C53 H53B 0.9900 C21 H21A 0.9500 C26 H26B 0.9800 C54 H54A 0.9900 C22 N1 1.372(4) C26 H26C 0.9800 C54 H54B 0.9900
169 Table B 3. Bond lengths () for cis BTF, c ontinued Bond Length ( ) Bond Length ( ) Bond Length ( ) S1' C17' 1.742(6) C26' H26D 0.9800 C79 H79A 0.9900 C17' C22' 1.399(15) C26' H26E 0.9800 C79 H79B 0.9900 C17' C18' 1.399(16) C26' H26F 0.9800 C80 H80A 0.9900 C18' C19' 1.361(15) C49 C50 1.526(4) C80 H80B 0.9900 Table B 4. Bond angles (degrees) for cis BTF Bond Angle () Bond Angle () Bond Angle () C27 Pt1 C1 91.38(10) C34 C29 C30 119.4(2) C35 C49 H49B 108.4 C27 Pt1 P1 177.53(7) C34 C29 C28 119.4(2) H49A C49 H49B 107.5 C1 Pt1 P1 90.82(7) C30 C29 C28 121.2(2) C49 C50 H50A 109.5 C27 Pt1 P2 91.42(7) C33 C34 C29 119.9(2) C49 C50 H50B 109.5 C1 Pt1 P2 176.18(7) C33 C34 H34A 120.1 H50A C50 H50B 109.5 P1 Pt1 P2 86.33(2) C29 C34 H34A 120.1 C49 C50 H50C 109.5 C43 S2 C42 89.01(14) C34 C33 C32 119.8(2) H50A C50 H50C 109.5 C73 P1 C67 105.23(12) C34 C33 C35 129.0(2) H50B C50 H50C 109.5 C73 P1 C53 104.99(12) C32 C33 C35 111.2(2) C52 C51 C35 116.1(2) C67 P1 C53 106.64(12) C31 C32 C33 120.8(2) C52 C51 H51A 108.3 C73 P1 Pt1 119.57(9) C31 C32 C41 130.8(2) C35 C51 H51A 108.3 C67 P1 Pt1 112.31(9) C33 C32 C41 108.3(2) C52 C51 H51B 108.3 C53 P1 Pt1 107.23(9) C30 C31 C32 119.4(2) C35 C51 H51B 108.3 C55 P2 C61 104.46(13) C30 C31 H31A 120.3 H51A C51 H51B 107.4 C55 P2 C54 104.15(12) C32 C31 H31A 120.3 C51 C52 H52A 109.5 C61 P2 C54 108.25(13) C31 C30 C29 120.6(2) C51 C52 H52B 109.5 C55 P2 Pt1 116.63(9) C31 C30 H30A 119.7 H52A C52 H52B 109.5 C61 P2 Pt1 113.76(8) C29 C30 H30A 119.7 C51 C52 H52C 109.5 C54 P2 Pt1 108.91(9) C36 C35 C33 100.8(2) H52A C52 H52C 109.5 C42 N2 C48 110.2(2) C36 C35 C49 112.3(2) H52B C52 H52C 109.5 C2 C1 Pt1 170.8(2) C33 C35 C49 112.6(2) C56 C55 C60 119.7(2) C1 C2 C3 170.0(3) C36 C35 C51 108.2(2) C56 C55 P2 119.4(2) C8 C3 C4 119.0(2) C33 C35 C51 112.4(2) C60 C55 P2 120.8(2) C8 C3 C2 117.8(2) C49 C35 C51 110.1(2) C57 C56 C55 119.5(3) C4 C3 C2 123.2(2) C37 C36 C41 120.2(2) C57 C56 H56A 120.3 C5 C4 C3 121.1(3) C37 C36 C35 128.9(2) C55 C56 H56A 120.3 C5 C4 H4A 119.5 C41 C36 C35 110.9(2) C58 C57 C56 120.4(3) C3 C4 H4A 119.5 C40 C41 C36 120.8(2) C58 C57 H57A 119.8 C4 C5 C6 119.0(2) C40 C41 C32 130.5(2) C56 C57 H57A 119.8 C4 C5 H5A 120.5 C36 C41 C32 108.7(2) C57 C58 C59 120.2(3) C6 C5 H5A 120.5 C36 C37 C38 119.4(2) C57 C58 H58A 119.9 C5 C6 C7 120.4(2) C36 C37 H37A 120.3 C59 C58 H58A 119.9 C5 C6 C15 131.6(2) C38 C37 H37A 120.3 C60 C59 C58 120.0(3) C7 C6 C15 107.9(2) C37 C38 C39 119.5(2) C60 C59 H59A 120.0 C8 C7 C6 120.4(3) C37 C38 C42 120.4(2) C58 C59 H59A 120.0 C8 C7 C9 128.5(2) C39 C38 C42 120.0(2) C59 C60 C55 120.3(3) C6 C7 C9 111.1(2) C40 C39 C38 121.4(3) C59 C60 H60A 119.9 C7 C8 C3 120.0(2) C40 C39 H39A 119.3 C55 C60 H60A 119.9 C7 C8 H8A 120.0 C38 C39 H39A 119.3 C66 C61 C62 119.2(3) C3 C8 H8A 120.0 C39 C40 C41 118.8(2) C66 C61 P2 122.4(2) C10 C9 C7 100.7(2) C39 C40 H40A 120.6 C62 C61 P2 118.1(2) C10 C9 C23 114.1(2) C41 C40 H40A 120.6 C63 C62 C61 120.5(3) C7 C9 C23 113.4(2) N2 C42 C38 124.5(2) C63 C62 H62A 119.8 C10 C9 C25 110.5(2) N2 C42 S2 115.8(2) C61 C62 H62A 119.8
170 Table B 4. Bond angles (degrees) for cis BTF, c ontinued Bond Angle () Bond Angle () Bond Angle () C7 C9 C25 110.4(2) C38 C42 S2 119.8(2) C64 C63 C62 119.9(4) C23 C9 C25 107.6(3) N2 C48 C47 125.0(3) C64 C63 H63A 120.1 C11 C10 C15 120.2(2) N2 C48 C43 115.4(3) C62 C63 H63A 120.1 C11 C10 C9 129.2(2) C47 C48 C43 119.5(3) C65 C64 C63 120.7(3) C15 C10 C9 110.6(2) C48 C43 C44 121.7(3) C65 C64 H64A 119.6 C14 C15 C10 120.6(2) C48 C43 S2 109.6(2) C63 C64 H64A 119.6 C14 C15 C6 130.6(3) C44 C43 S2 128.7(2) C64 C65 C66 120.0(3) C10 C15 C6 108.6(2) C45 C44 C43 117.3(3) C64 C65 H65A 120.0 C15 C14 C13 119.1(3) C45 C44 H44A 121.4 C66 C65 H65A 120.0 C15 C14 H14A 120.4 C43 C44 H44A 121.4 C61 C66 C65 119.7(3) C13 C14 H14A 120.4 C44 C45 C46 121.4(3) C61 C66 H66A 120.1 C14 C13 C12 120.9(2) C44 C45 H45A 119.3 C65 C66 H66A 120.1 C14 C13 H13A 119.5 C46 C45 H45A 119.3 C72 C67 C68 119.4(3) C12 C13 H13A 119.5 C47 C46 C45 121.3(3) C72 C67 P1 122.3(2) C13 C12 C11 119.6(2) C47 C46 H46A 119.4 C68 C67 P1 118.3(2) C13 C12 C16 119.9(2) C45 C46 H46A 119.4 C69 C68 C67 120.1(3) C11 C12 C16 120.4(2) C46 C47 C48 118.8(3) C69 C68 H68A 119.9 C10 C11 C12 119.4(3) C46 C47 H47A 120.6 C67 C68 H68A 119.9 C10 C11 H11A 120.3 C48 C47 H47A 120.6 C70 C69 C68 120.2(3) C12 C11 H11A 120.3 C24 C23 C9 115.3(2) C70 C69 H69A 119.9 N1 C16 N1' 110.7(6) C24 C23 H23A 108.5 C68 C69 H69A 119.9 N1 C16 C12 123.6(2) C9 C23 H23A 108.5 C71 C70 C69 119.9(3) N1' C16 C12 125.7(6) C24 C23 H23B 108.5 C71 C70 H70A 120.0 N1 C16 S1' 7.1(3) C9 C23 H23B 108.5 C69 C70 H70A 120.0 N1' C16 S1' 117.2(6) H23A C23 H23B 107.5 C70 C71 C72 120.5(3) C12 C16 S1' 117.1(3) C23 C24 H24A 109.5 C70 C71 H71A 119.8 N1 C16 S1 115.2(2) C23 C24 H24B 109.5 C72 C71 H71A 119.8 N1' C16 S1 4.7(6) H24A C24 H24B 109.5 C71 C72 C67 119.9(3) C12 C16 S1 121.24(19) C23 C24 H24C 109.5 C71 C72 H72A 120.0 S1' C16 S1 121.7(3) H24A C24 H24C 109.5 C67 C72 H72A 120.0 C17 S1 C16 88.63(16) H24B C24 H24C 109.5 C78 C73 C74 119.2(2) C22 C17 C18 122.5(3) C26 C25 C26' 70.0(5) C78 C73 P1 118.9(2) C22 C17 S1 108.6(3) C26 C25 C9 118.7(3) C74 C73 P1 121.9(2) C18 C17 S1 128.9(3) C26' C25 C9 130.4(5) C73 C78 C77 120.4(3) C19 C18 C17 116.8(3) C26 C25 H25A 107.7 C73 C78 H78A 119.8 C19 C18 H18A 121.6 C26' C25 H25A 115.7 C77 C78 H78A 119.8 C17 C18 H18A 121.6 C9 C25 H25A 107.7 C76 C77 C78 120.3(3) C18 C19 C20 121.2(3) C26 C25 H25B 107.7 C76 C77 H77A 119.9 C18 C19 H19A 119.4 C26' C25 H25B 37.8 C78 C77 H77A 119.9 C20 C19 H19A 119.4 C9 C25 H25B 107.7 C77 C76 C75 119.8(3) C21 C20 C19 121.7(3) H25A C25 H25B 107.1 C77 C76 H76A 120.1 C21 C20 H20A 119.2 C26 C25 H25C 37.0 C75 C76 H76A 120.1 C19 C20 H20A 119.2 C26' C25 H25C 104.7 C76 C75 C74 120.1(3) C20 C21 C22 118.9(3) C9 C25 H25C 104.6 C76 C75 H75A 119.9 C20 C21 H21A 120.6 H25A C25 H25C 81.3 C74 C75 H75A 119.9 C22 C21 H21A 120.6 H25B C25 H25C 142 C73 C74 C75 120.2(3) N1 C22 C21 126.5(4) C26 C25 H25D 126.7 C73 C74 H74A 119.9 N1 C22 C17 114.6(4) C26' C25 H25D 104.7 C75 C74 H74A 119.9 C21 C22 C17 118.9(3) C9 C25 H25D 104.7 C54 C53 P1 109.70(18) C16 N1 C22 112.9(3) H25A C25 H25D 24.8 C54 C53 H53A 109.7 C17' S1' C16 88.5(7) H25B C25 H25D 85.1 P1 C53 H53A 109.7 C22' C17' C18' 135.9(11) H25C C25 H25D 105.7 C54 C53 H53B 109.7 C22' C17' S1' 108.3(12) C25 C26 H25C 45.2 P1 C53 H53B 109.7
171 Table B 4. Bond angles (degrees) for cis BTF, c ontinued Bond Angle () Bond Angle () Bond Angle () C18' C17' S1' 115.0(12) C25 C26 H26A 109.5 H53A C53 H53B 108.2 C19' C18' C17' 111.7(13) H25C C26 H26A 113.9 C53 C54 P2 111.94(18) C19' C18' H18B 124.2 C25 C26 H26B 109.5 C53 C54 H54A 109.2 C17' C18' H18B 124.2 H25C C26 H26B 65.8 P2 C54 H54A 109.2 C18' C19' C20' 117.8(14) H26A C26 H26B 109.5 C53 C54 H54B 109.2 C18' C19' H19B 121.1 C25 C26 H26C 109.5 P2 C54 H54B 109.2 C20' C19' H19B 121.1 H25C C26 H26C 135.3 H54A C54 H54B 107.9 C21' C20' C19' 125.7(15) H26A C26 H26C 109.5 Cl2 C79 Cl1 111.11(16) C21' C20' H20B 117.2 H26B C26 H26C 109.5 Cl2 C79 H79A 109.4 C19' C20' H20B 117.2 C25 C26' H26D 109.5 Cl1 C79 H79A 109.4 C20' C21' C22' 122.5(14) C25 C26' H26E 109.5 Cl2 C79 H79B 109.4 C20' C21' H21B 118.8 H26D C26' H26E 109.5 Cl1 C79 H79B 109.4 C22' C21' H21B 118.8 C25 C26' H26F 109.5 H79A C79 H79B 108 N1' C22' C17' 117.5(15) H26D C26' H26F 109.5 Cl4 C80 Cl3 112.7(2) N1' C22' C21' 136.2(15) H26E C26' H26F 109.5 Cl4 C80 H80A 109.1 C17' C22' C21' 106.2(11) C50 C49 C35 115.4(2) Cl3 C80 H80A 109.1 C16 N1' C22' 108.3(11) C50 C49 H49A 108.4 Cl4 C80 H80B 109.1 C28 C27 Pt1 178.1(2) C35 C49 H49A 108.4 Cl3 C80 H80B 109.1 C27 C28 C29 176.9(3) C50 C49 H49B 108.4 H80A C80 H80B 107.8
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182 BIOGRAPHICAL SKETCH Abigail Shelton was born in Flaherty, Kentucky to Jennifer and Bernard Hobbs. Abigail graduated summa cum laude in August 2006 from Western Kentucky University in Bowling Green, Kentucky, where she earned her B achelor of S cienc e in chemistry. Her undergraduate research, under the direction of Dr. Les Pesterfield, examined the synthesis, linkage isomerizations, and spectroscopic characterization of cobalt(III ) nitrito complexes. During her time at Western Kentucky University, Abigail also complete d two Research Experiences for Undergraduate (REU ) programs. The first, completed during the summer of 2005, took her to the NASA Glenn Research Center in Cleveland, Ohio, where she conducted research on aerogels and vanadium complexe s under the direction of Drs. Nicholas Leventis and Lynn Capadona. The second REU program was performed in Paris, France at Pierre and Marie Currie University during the 2006 summer where Abigail synthesized iron porphyrins complexes under the direction o f Dr. Eric Rose. Abigail then attended the University of Florida for graduate school in the area of physical inorganic chemistry under the direction of Dr. Kirk Schanze. Her research predominately focused on the synthesis and photophysical characterizatio n of platinum acetylides, but also involved the generation of new nanosecond instrumentation. During her time at the University of Florida, Abigail was awarded the Harry S. Sisler award, a Linton E. Grinte r fellowship, a Proctor and Gamble f ellowship a C ollege of Liberal Arts and Sciences dissertation fellowship, and a departmental Teaching Award.