Organic/inorganic Langmuir-Blodgett films based on metal phosphonates

MISSING IMAGE

Material Information

Title:
Organic/inorganic Langmuir-Blodgett films based on metal phosphonates
Physical Description:
xviii, 258 leaves : ill. ; 29 cm.
Language:
English
Creator:
Petruska, Melissa Ann, 1973-
Publication Date:

Subjects

Subjects / Keywords:
Thin films, Multilayered   ( lcsh )
Phosphonates   ( lcsh )
Organophosphorus compounds   ( lcsh )
Chemistry thesis, Ph.D   ( lcsh )
Dissertations, Academic -- Chemistry -- UF   ( lcsh )
Genre:
bibliography   ( marcgt )
theses   ( marcgt )
non-fiction   ( marcgt )

Notes

Thesis:
Thesis (Ph.D.)--University of Florida, 2000.
Bibliography:
Includes bibliographical references (leaves 244-256).
General Note:
Printout.
General Note:
Vita.
Statement of Responsibility:
by Melissa Ann Petruska.

Record Information

Source Institution:
University of Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
aleph - 024900823
oclc - 45638265
System ID:
AA00020433:00001

Full Text









ORGANIC/INORGANIC LANGMUIR-BLODGETT FILMS
BASED ON METAL PHOSPHONATES

















By

MELISSA ANN PETRUSKA


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


2000
































For all those who have gone before me,
making this journey possible...















ACKNOWLEDGMENTS


I was fortunate to have had an extremely wonderful undergraduate research experience,

and the years I worked at Mellon Institute were truly special. I am forever indebted to my

undergraduate research advisor Professor Richard D. McCullough for inspiring in me a passion

for research chemistry that I shall continue to embrace wherever life may take me. I have fond

memories of the years I spent working in his lab, as his enthusiasm and zeal for research and all

of its challenges were simply contagious. During my stint at Carnegie Mellon University, I had

the pleasure of working with John Belot, who took the time to teach an undergraduate who knew

nothing of bench chemistry everything she knows about organic synthesis and research. I could

not have asked for a better or more animated instructor and friend. Paul Ewbank has been a truly

wonderful friend and conversationalist throughout the years, and if he was not supplying me with

candy and chocolate, he was editing my graduate school essays and instructing me on the finer

points of lab safety. I certainly do miss those Ice Cubes.

While Professor McCullough was instrumental in kindling my fervor for research, my

graduate school advisor, Professor Daniel R. Talham, was responsible for honing my research

skills. I am grateful to him for all of the emphasis placed upon improving my written and spoken

communication skills. Because of his tremendous efforts, I am certain I have become a much

better chemist over the last five years. I wish to thank everyone in the Talham research group for

all of their help and support over the course of my stay. Special thanks go to Scott for making my

transition to graduate school much smoother and for being a great friend to me over the years and

to Jeff for our wonderful conversations and for our countless soul-searching trips to the Salty

Dog.









I thank Professor Mark Meisel and Brian Watson for obtaining all of the SQUID

measurements presented in this dissertation. I certainly have enjoyed our collaboration over the

years, as I feel I have gained a greater understanding of the physics behind some of the problems

we tackle in our chemistry world and the benefits of multidisciplinary efforts. Praise to Brian,

who spent countless hours trying to obtain transport measurements on some of the oxidized TMT

films discussed in Chapter 6 prior to our discovery that such measurements on these materials

might not necessarily be possible. I am sincerely grateful for his pains. I appreciate Dr. Hitoshi

Ohnuki's efforts on obtaining transport measurements on compressed powder samples and

SQUID measurements on magnetic materials during his stay here as a visiting scientist. Hitoshi's

Ph.D. dissertation focused on conducting TTF LB films, and I have benefited greatly from our

many conversations.

I gratefully acknowledge those professors and research groups whose equipment I have

"borrowed" at odd times throughout my stay. I thank Professor Kirk Schanze for use of both his

Hewlett Packard diode array spectrophotometer and his Hanovia lamp, as well as the entire

Schanze research group for enduring the countless hours of noise as a result of this lamp. Lidia

Matveeva and the students in the mass spec lab deserve recognition for their tireless efforts in

obtaining mass spec analyses on my hideously insoluble phosphonic acids. Thanks are also

extended to the Major Analytical Instrumentation Center for X-ray measurements and to Eric

Lambers for XPS training. Special thanks to everyone in the machine, electronic, and glass shops

for all of their help and efforts in quickly fixing the many problems I have encountered. I also

gratefully acknowledge the entire chemistry department staff, including Donna and Lori. Their

help, which has made my life easier, has not gone unappreciated. I thank the NSF for funding,

particularly through the fellowship I received my first three years here.

The people I have met throughout my time here and at Carnegie Mellon have certainly

made this experience more bearable and entertaining. My friends and our exploits have kept

things lively and interesting, and I must especially thank Craig, Debby, Eve, and Jennifer for their









support and friendship, especially through all of the rough patches. And of course I thank Tim

for his version of comic relief.

All of what I have accomplished in the last 27 years would not have been possible

without the love and support of my mother, Maria. Her generosity and selflessness is unrivaled

anywhere, and I am amazed at the good fortune I have had in being blessed with her in my life. I

thank John for all of his unfailing love and support and for becoming part of our family. I have

enjoyed getting to know him and his family, including his parents, Jim and Marian. I am grateful

to my grandmother, Margaret, for her prayers and phone calls, and to my Oma, Elisabetha, for her

subliminal messages from above. Thanks also to Aunt Aggie and Uncle Dave for their constant

support over the years.

I thank my brother, Bobby, for providing sanctuary for me in south Florida, for all of the

meals and entertainment, for our traditional Thanksgiving dinners, and for all of his love, support,

and "good-natured" harassment. I am also pleased to acknowledge the newest members of the

family, my sister-in-law Sandy and my niece (and goddaughter) Emily. I thank Mike for his

wonderful friendship and staunch support over the years, even after he realized that I am much

more the historical scholar than he. I am eternally grateful to Tom, whose love is a constant

source of strength for me. I am amazed by his patience and pleased that he asks of me nothing

more than I am. I hope some day to return the favor.



















v
















TABLE OF CONTENTS

Page

ACKNOWLEDGMENTS.................................................................................... iii

LIST OF TABLES............................................................................................. ix

LIST OF FIGURES............................................................................................ x

ABSTRACT ................................................................................................ xvii

CHAPTERS

1 MIXED ORGANIC/INORGANIC MATERIALS............................................... I

Mesoporous Materials................................................................................ 1
Intercalation Compounds............................................................................. 3
Self-Assembled Films................................................................................ 5
Layered Materials..................................................................................... 9
Layered Perovskites............................................................................ 10
Metal Phosphonates............................................................................ 11
Scope of the Dissertation........................................................................... 28


2 ZIRCONIUM PHOSPHONATE LANGMUIR-BLODGETT FILMS
CONTAINING FUNCTIONAL ORGANIC GROUPS....................................... 30

Results and Discussion............................................................................. 36
Synthesis and Characterization of Phosphonic Acid Amphiphiles...................... 36
Langmuir Monolayers......................................................................... 40
Deposition Procedure.......................................................................... 42
X-ray Photoelectron Spectroscopy.......................................................... 44
X-ray Diffraction............................................................................... 47
Attenuated Total Reflectance Infrared Spectroscopy...................................... 48
Optical Spectroscopy........................................................................... 63
Structural Analysis............................................................................. 66
Summary ............................................................................................. 69
Experimental Section............................................................................... 70
Synthesis......................................................................................... 70
Film s ............................................................................................. 87






vi









3 AN AZOBENZENE-DERIVATIZED PHOSPHONIC ACID FORMS CONTINUOUS
LATTICE LAYERS WITH DIVALENT AND TRIVALENT METAL IONS............89

Results and Discussion............................................................................. 94
Deposition Procedure.......................................................................... 94
Characterization of Metal Phosphonate LB Films......................................... 96
Structural Analysis........................................................................... 106
Magnetic Properties........................................................................... 112
Summary ........................................................................................... 118
Experimental Section.............................................................................. 119
M materials ....................................................................................... 119
Substrate Preparation ......................................................................... 120
Instrumentation ............................................................................... 120


4 THERMAL AND CHEMICAL STABILITY STUDIES
OF METAL PHOSPHONATE LANGMUIR-BLODGETT FILMS....................... 122

R results .............................................................................................. 125
Thermal Stability.............................................................................. 125
Chemical Stability............................................................................ 132
Discussion .......................................................................................... 133
Summary ........................................................................................... 138
Experimental Section.............................................................................. 139
Materials ....................................................................................... 139
Substrate Preparation......................................................................... 139
Instrumentation ............................................................................... 140


5 TETRATHIAFULVALENE-FUNCTIONALIZED METAL PHOSPHONATE
SOLIDS AND LANGMUIR-BLODGETT FILMS: STRUCTURE AND
MAGNETISM .................................................................................... 141

Results and Discussion........................................................................... 145
Synthesis and Characterization............................................................. 145
Langmuir Monolayers........................................................................ 150
Deposition Procedure........................................................................ 154
Structural Characterization.................................................................. 154
Magnetic Properties........................................................................... 175
Summary............................................................................................ 189
Experimental Section.............................................................................. 191
Synthesis....................................................................................... 191
F ilm s ........................................................................................... 201


6 TETRATfIAFULVALENE-FUNCTIONALIZED METAL PHOSPHONATE
LANGMUIR-BLODGETT FILMS: CONDUCTIVITY.................................... 204

Results and Discussion........................................................................... 207
Iodine as an Oxidant.......................................................................... 207
Carbon Tetrachloride as an Oxidant........................................................ 214









Other Oxidants................................................................................ 232
Sum m ary ........................................................................................... 235
Experimental Section.............................................................................. 235
M materials ....................................................................................... 235
Substrate Preparation......................................................................... 236
Instrumentation ............................................................................... 237
Transport Measurements..................................................................... 239


7 EPILOGUE ....................................................................................... 241


REFERENCES ............................................................................................. 244

BIOGRAPHICAL SKETCH.............................................................................. 257















LIST OF TABLES


Table Page

2-1. Interlayer Spacings and Relative Intensities of the Zirconium and Phosphorus
XPS Signals of the Zirconated Template LB Monolayers and LB Bilayer Films..........46

2-2. Dichroic Ratios, D, of IR Modes and the Corresponding Molecular Axis Tilt
Angles for Zirconated Template Layers......................................................... 53

2-3. Dichroic Ratios, D, of IR Modes and the Corresponding Molecular Axis Tilt
Angles for Capping Layers Deposited onto Zirconated OPA Templates.................... 56

2-4. Dichroic Ratios, D, of IR Modes and the Corresponding Molecular Axis Tilt
Angles for Capping Layers in the B4 and A4 Bilayer Samples.............................. 60

2-5. Twist Angles for the Aryl Moieties within the Films............................................. 68

3-1. Deposition Conditions for the A4 LB Bilayers................................................... 97

3-2. Interlayer Spacings Measured from X-ray Diffraction and Relative Intensities of the
Metal and Phosphorus XPS Signals for the A4 LB Bilayer Films........................ 100

4-1. Film Loss in Single Bilayer Samples of Octadecylphosphonic Acid and A4 with
V various M etals..................................................................................... 133

5-1. Deposition Conditions for the TTF LB Bilayers................................................. 155

5-2. Exchange Constants, Weiss Constants, and Ordering Temperatures for TTF-
Based Metal Phosphonate LB Films and Solid-State Materials............................. 179















LIST OF FIGURES


Figure Page

1-1. Two proposed pathways for the synthesis of mesoporous materials............................. 2

1-2. The layered structure of FeOCI ........................................................................ 4

1-3. Construction of multilayers of alkylsilane derivatives by self-assembly........................ 7

1-4. Self-assembly approach for the fabrication of noncentrosymmetric thin films of a
stillbazolium derivative for NLO.................................................................. 8

1-5. Proposed model for the organization of azobenzene-terminated alkylthiols on gold...........9

1-6. Crystal structure of (C1OH21NH3)2CdCI4........................................................ 10

1-7. (A) Cross-sectional view of two layers of a-Zr(HPO4)2-H20 and
(B) cross-sectional view of two layers of y-Zr(PO4)(H2PO4)'H20 ........................ 12

1-8. Crystal structure of zirconium phenylphosphonate................................................ 13

1-9. Schematic representation of a zirconium phosphonate material containing
m acrocyclic ligands................................................................................. 15

1-10. Schematic illustrating the porous nature of [(ZrF)2(P04)
(03PCH2CH2-bipyridinium-CH2CH2PO3)]+X-3H2O ..................................... 16

1-11. Crystal structure of manganese phenylphosphonate.............................................. 16

1-12. Crystal structure of barium phenylphosphonate................................................ 17

1-13. Crystal structure of lanthanum phenylphosphonate............................................... 18

1-14. Schematic illustrating the topochemical polymerization of diacetylenes within the
metal phosphonate network........................................................................ 20

1-15. Procedure for the self-assembly of zirconium phosphonate films.............................. 23

1-16. Schematic illustrating the three-step procedure for the self-assembly of zirconium
phosphonate films of an oriented azobenzene derivative for SHG........................... 24




x








1-17. Formation of a Langmuir monolayer............................................................... 25

1-18. Deposition of an LB film........................................................................... 26

2-1. Introduction of a kink in the cylindrical symmetry of the alkyi chains as a result
of the incorporated aryl moiety.................................................................... 31

2-2. Organophosphonic acids synthesized for this study.............................................. 33

2-3. Zirconium organophosphonate LB films prepared for this study............................... 34

2-4. Three-step deposition scheme for the preparation of zirconium organophosphonate
LB film s.............................................................................................. 35

2-5. Synthetic scheme for the preparation of P0, BO, P4, B4, dP4, and dB4..................... 37

2-6. Synthetic scheme for the preparation of AO and A4.............................................. 38

2-7. Optical absorbance spectra of A4 and AO in chloroform/ethanol solution before and
after irradiation at 365 rnm.......................................................................... 39

2-8. Pressure vs. area isotherms for BO, AO, B4, and A4 on a pure water subphase
at pH 5.5.............................................................................................. 41

2-9. ATR-FTIR spectra of zirconated monolayer templates of OPA, B4, and A4................. 50

2-10. FTIR spectra of(a) a chloroform solution of dB4 and (b) a KBr pellet of dB4
and an ATR-FTIR spectrum of (c) dB4 as a template layer................................... 51

2-11. ATR-FTIR spectra of capping monolayers of BO, AO, B4, and A4 on OPA.................. 54

2-12. ATR-FTIR spectra often bilayers of(a) BO on OPA and (b) AO on OPA.................... 57

2-13. Polarized ATR-FTIR spectra of fifteen bilayers of BO on an OPA template............... 57

2-14. ATR-FTIR spectra often bilayers of(a) dB4 on OPA and (b) A4 on OPA................... 59

2-15. ATR-FTIR spectra of capping monolayers of dB4 on a dB4 template and
an OPA tem plate.................................................................................... 61

2-16. ATR-FTIR spectra of four bilayers of an A4 capping layer on an OPA template (a)
before irradiation at 365 nm, (b) after irradiation at 365 rnm, and (c) after the film
in (b) has been irradiated........................................................................ 63

2-17. Optical absorbance spectra often bilayers of A4 and AO as capping layers on
zirconated OPA templates before and after irradiation at 365 nm............................ 64

2-18. Vectorial representation of the molecular axes of the aryl and alkyl groups.................. 67









3-1. Crystal structure of manganese phenylphosphonate.............................................. 91

3-2. Interaction of magnetic moments in materials which order as ferromagnets,
antiferromagnets, and canted antiferromagnets................................................. 92

3-3. Schematic illustrating the concept of a mixed organic/inorganic LB film.................. 93

3-4. Azobenzene-derivatized phosphonic acid amphiphile, A4, used in these studies............ 93

3-5. Deposition of divalent and trivalent metal organophosphonate LB films..................... 95

3-6. Room-temperature optical spectra of five-bilayer metal phosphonate films of A4
with lanthanum, barium, and manganese......................................................... 98

3-7. Optical spectra before and after irradiation at 365 nm of (a) A4 in a chloroform/
ethanol solution and (b) five bilayers of a lanthanum A4 LB film........................... 99

3-8. X-ray diffraction pattern from ten bilayers of a lanthanum A4 LB film..................... 100

3-9. ATR-FTIR spectrum showing the carbon-hydrogen stretching modes of four bilayers
of a lanthanum A4 film ........................................................................... 102

3-10. Comparison of the ATR-FTIR spectrum of a lanthanum A4 LB film
to IR spectra of KBr pellets of pure A4 and lanthanum butylphosphonate................ 103

3-11. Comparison of the IR spectra of LB films and solid-state powders........................ 105

3-12. Comparison of the IR spectra of LB films and solid-state powders........................ 106

3-13. Pressure vs. mean molecular area isotherms of OPA and A4 as a function
of tem perature...................................................................................... 109

3-14. Pressure vs. mean molecular area isotherms of A4 as a function of temperature............ 110

3-15. Schematic illustrating a mixed organic/inorganic LB film where the organic and
inorganic networks have different preferred spacings........................................ 111

3-16. Room temperature ESR linewidth as a function of sample orientation....................... 113

3-17. ESR linewidth as a function of temperature for the manganese A4 LB film................ 114

3-18. Temperature dependence of the inverse integrated area of the ESR signal for the
m anganese A4 LB film ........................................................................... 115

3-19. Temperature dependence of the integrated area of the ESR signal for the manganese
A 4 LB film .......................................................................................... 115

3-20. Magnetization vs. temperature for a 100-bilayer sample of manganese A4 with the
measuring filed applied parallel to the film plane.......................................... 117








4-1. Azobenzene-derivatized phosphonic acid, A4, used in these studies......................... 124

4-2. ATR-FTIR spectra of five-bilayers of lanthanum octadecylphosphonate at
24 "C, 50 "C, 100 "C, 150 *C, and 200 "C...................................................... 126

4-3. A plot of the full width at half maximum (fwhm) of the asymmetric methylene
stretch vs. temperature for five- and ten-bilayer samples
of lanthanum octadecyiphosphonate............................................................ 126

4-4. A plot of the full width at half maximum (fwhm) of the asymmetric methylene
stretch vs. temperature for five-bilayer samples of lanthanum A4,
manganese octadecylphosphonate, and lanthanum octadecylphosphonate................ 127

4-5. Room temperature optical spectra of a five-bilayer sample of gadolinium A4
recorded after cycling to the indicated temperatures.......................................... 129

4-6. A plot of the full width at half maximum (fwhm) of the asymmetric methylene
stretch in a five-bilayer sample of lanthanum A4 vs. temperature.......................... 130

4-7. Transmission FTIR spectra of a ten-bilayer sample of lanthanum octadecylphosphonate
on OTS-coated silicon recorded at room temperature after cycling to 24 "C,
100 "C, 180 "C, 200 -C, and 260 C ............................................................. 131

4-8. X-ray diffraction data for a ten-bilayer gadolinum A4 LB film............................... 132

5-1. Crystal structure of TTF-TCNQ.................................................................... 143

5-2. TTF-substituted phosphonic acids used in the preparation of the LB films and solid-
state compounds discussed in this Chapter................................................... 144

5-3. Traditional synthetic procedures for the preparation of substituted TTF derivatives....... 146

5-4. Synthetic scheme for the preparation of TTF-derivatized phosphonic acids 2T2,
m 2T2, and 1EDT2................................................................................. 148

5-5. Synthetic scheme for the preparation of TTF-derivatized phosphonic acids 2T1,
EDTI, and EDT12.............................................................................. 149

5-6. Synthetic scheme for the preparation of mBS2 and mB2.................................... 150

5-7. Pressure vs. mean molecular area isotherms of 2T2, 2T1, and 1EDT2....................... 152

5-8. Pressure vs. mean molecular area isotherms as a function of temperature................... 152

5-9. Pressure vs. mean molecular area isotherm of amphiphile EDT12........................... 153

5-10. Comparison of the IR spectra of(a) Mn(03PC4H9)H20, (b) Mn2(mBS2)2H20,
and (c) a manganese mB2 powder .............................................................. 157








5-11. IR spectrum of Mn2(m2T2)2H20 ............................................................... 159

5-12. IR spectra of (A) Mn(03PC2H5)H20 and (B) Mn2(m2T2)2H20
(a) as-formed, (b) after dehydration, and (c) after rehydration.............................. 160

5-13. IR spectra of (a) LaH(03PC4H9)2 and (b) La(m2T2)............................................ 161

5-14. (a) ATR-FTIR spectrum ofathree-bilayer LB film sample of manganese 2T2 and
(b) IR spectrum of Mn2(m2T2)2H20........................................................... 163

5-15. Optical absorbance spectrum of a five-bilayer LB film sample of manganese 2T2.........163

5-16. (a) ATR-FTIR spectrum of a three-bilayer LB film sample of lanthanum 2T2 and
(b) IR spectrum of La(m2T2).................................................................... 164

5-17. Optical absorbance spectrum of a five-bilayer LB film sample of lanthanum 1EDT2.....165

5-18. IR spectrum of Mn(EDT1).......................................................................... 167

5-19. IR spectra of (a) MnH3(EDT1XPO4), (b) Mn(O3PC4Hg)H20, and (c) KMn(P04)H20...169

5-20. IR spectra of (a) MnH3(EDTI )(PO4), (b) Mn(EDT1), and (c) hureaulite..................... 170

5-21. (a) ATR-FTIR spectrum of a five-bilayer LB film sample of manganese 2T1(P04) and
(b) IR spectrum of MnH3(EDT1XPO4)......................................................... 172

5-22. (a) IR spectrum ofMn(EDT12)H20 powder and (b) ATR-FTIR spectrum of a two-
bilayer LB film sample of manganese EDT12................................................ 173

5-23. Pressure vs. mean molecular area isotherms of the amphiphile EDT12 on a water
subphase containing either a 0.5 mM concentration of La(IIH) or Mn(II).................. 174

5-24. (a) ATR-FTIR spectrum of a five-bilayer LB film sample of lanthanum EDT12 and
(b) IR spectrum of La(m2T2).................................................................... 175

5-25. ESR signals of Mn2(mBS2)2H20 collected at 21 K, 55 K, and 295 K...................... 176

5-26. Temperature dependence of the ESR linewidth for Mn2(mBS2)2H20........................ 177

5-27. Temperature dependence of the integrated area of the ESR signal for the
Mn2(m2T2)2H20 solid-state powder........................................................... 178

5-28. Temperature dependence of the inverse integrated area of the ESR signal for the
Mn2(m2T2)2H20 solid-state powder........................................................... 179

5-29. Room temperature ESR linewidth as a function of sample orientation for the LB film
m anganese 2T2.................................................................................... 180








5-30. Magnetization vs. temperature for (a) a Mn2(mBS2)2H20 powder,
(b) a Mn2(m2T2)2H20 powder, and (c) a 100-bilayer film sample of
manganese 2T2 with the measuring field applied parallel to the film plane............... 181

5-31. Magnetization vs. temperature for MnH3(EDT1XPO4)....................................... 184

5-32. Magnetization vs. temperature for a 100-bilayer LB film sample of manganese
2T1(P04) with the measuring field applied parallel to the film plane...................... 185

5-33. Temperature dependence of the integrated area of the ESR signal for a 100-bilayer
LB film sample of manganese 2T1(P04)....................................................... 186

5-34. Room temperature ESR linewidth as a function of sample orientation for the
LB film manganese EDT12...................................................................... 188

5-35. Magnetization vs. temperature for a 100-bilayer LB film sample of manganese EDT12
with the measuring field applied parallel to the film plane.................................. 189

6-1. Molecules EDT-TTF(SC18)2, BEDO, and EOET used in the preparation of conducting
LB films reported in the literature............................................................... 206

6-2. Amphiphiles 2T2, 2T1, 1EDT2, and EDT12 used in the preparation of conducting
metal phosphonate LB films discussed in this Chapter....................................... 207

6-3. ATR-FTIR spectra of five bilayers of an EDT-TTF(SCsg)2/behenic acid (1:1) LB
film (a) before exposure to iodine, (b) immediately following iodine exposure, and
(c) after annealing at 40 "C for two days....................................................... 209

6-4. Optical spectra of five bilayers of an an EDT-TTF(SC1g)2/behenic acid (1:1) LB
film as prepared, immediately following iodine exposure, and after annealing at
40 C for 6 hours................................................................................... 210

6-5. Transmission IR spectra of an eight-bilayer LB film sample of manganese EDT12
(a) as-prepared and (b) immediately following iodine exposure............................ 211

6-6. Optical spectra of(a) a five-bilayer LB film sample of manganese 2T1(P04) and
(b) a five-bilayer LB film sample of lanthanum IEDT2 as-prepared, immediately
following iodine exposure, and and after annealing at 40 "C ............................... 212

6-7. Optical spectra of a solution of 2T1 in ethanol/chloroform and in
ethanol/chloroform/carbon tetrachloride....................................................... 216

6-8. Optical absorbance spectra of a 20-bilayer LB film sample of lanthanum EDT12
and a 35-bilayer LB film sample of manganese EDT12 before irradiation and
following irradiation of the film in carbon tetrachloride..................................... 217

6-9. Transmission IR spectra of a 10-bilayer LB film sample of lanthanum EDT12 and a
10-bilayer LB film sample of manganese EDT 12 following irradiation in
carbon tetrachloride...............................................................................219








6-10. XPS multiplex scans over the Clzp region in (a) a five-bilayer LB film sample of
manganese EDT12 and (b) a three-bilayer LB film sample of lanthanum EDT12.......221

6-11. Temperature dependence of the integrated ESR radical signal for a 40-bilayer
LB film sample of lanthanum EDT12 as-prepared............................................ 223

6-12. Angular dependence of the radical signal in a 70-bilayer LB film sample of manganese
EDT12 at 100 K, illustrating the g-value anisotropy....................................... 223

6-13. ESR signals for a 70-bilayer LB film sample of manganese EDT12 as-prepared
and following irradiation at 365 nm in carbon tetrachloride................................. 224

6-14. Temperature dependence of the integrated area of the radical signal for a 70-bilayer
LB film sample of manganese EDT12 following photooxidation in
carbon tetrachloride............................................................................... 225

6-15. Temperature dependence of the inverse of the integrated area of the radical signal
for a 70-bilayer LB film sample of manganese EDT12 following photooxidation
in carbon tetrachloride............................................................................ 226

6-16. The difference in the FC and ZFC magnetization as a function of temperature
for the manganese EDT12 LB film before and after photooxidation....................... 227

6-17. AFM image of a one-bilayer LB film sample of lanthanum EDT12.......................... 230

6-18. AFM image of a three-bilayer LB film sample of 1:1 EDT-TTF(SCis)2/behenic acid .... 230

6-19. Transmission IR spectrum of a ten-bilayer LB film sample of lanthanum EDT12
following oxidation with bromine............................................................... 233

6-20. Optical spectra of a 30-bilayer LB film sample of lanthanum EDT12 as-prepared,
immediately following bromine exposure, and after annealing at 40 "C for five days...233

6-21. Mask designs for transport measurements........................................................ 239

6-22. Circuit diagram for four-probe AC measurements on LB film samples...................... 240














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

ORGANIC/INORGANIC LANGMUIR-BLODGETT FILMS
BASED ON METAL PHOSPHONATES

By

Melissa Ann Petruska

August 2000

Chairperson: Daniel R. Talham
Major Department: Chemistry

Metal phosphonate Langmuir-Blodgett (LB) films have been prepared in which

biphenoxy, azobenzyloxy, and tetrathiafulvalene (TTF) functional groups are found in the organic

region of the LB bilayers. As demonstrated with previous work where octadecylphosphonic acid

was employed as the amphiphile, the metal phosphonate lattice is found in between the polar

headgroups in the LB bilayers of these functionalized organic amphiphiles. Including this metal

phosphonate lattice in the LB films is shown to enhance the thermal and chemical stabilities of

the resulting materials compared with the traditional metal carboxylate LB films.

Zirconium phosphonate LB films incorporating biphenyl and azobenzene moieties are

investigated as model systems, in which constraints regarding the size and substitution pattern of

the organic moiety are determined. Based on these results, it is evident that larger functional

groups can be incorporated into the metal phosphonate LB films while retaining the organization

and close-packed nature of the amphiphiles within the LB bilayers. From studies of an

azobenzene-functionalized phosphonic acid, which has been shown to aggregate on a water

surface, with divalent and trivalent metal ions, the effect of organic interactions on the formation

of the metal phosphonate lattice is determined. For these films it is found that film transfer is


xvii









facile when the spacing of the inorganic network and the packing of the chromophores is

commensurate, while a mismatch in these preferred spacings affects the deposition process.

TTF-based manganese phosphonate LB films were designed and prepared as a means of

generating mixed organic/inorganic LB films in which both the organic and the inorganic

networks are responsible for the physical properties of interest. The magnetic ordering

temperatures in the manganese phosphonate LB films can be tuned by simply exploiting the

geometry of the TTF molecule, where different phosphonic acid derivatives of TTF give rise to

varying metal phosphonate lattices with different magnetic properties. A new strategy for

oxidizing the TTF-based metal phosphonate LB films has been developed. Photooxidation of the

TTF films in solutions of carbon tetrachloride generates mixed-valence TTF molecules with

semiconducting properties.


xviii














CHAPTER 1
MIXED ORGANIC/INORGANIC MATERIALS



The impetus for studying mixed organic/inorganic materials stems from the drive of the

researcher to construct unique structures with interesting properties. By engineering into a

framework components featuring both organic-organic and inorganic-inorganic interactions, the

possibility of achieving a vast array of properties in one hybrid structure can be realized by

careful selection of the individual building blocks. The resulting heterostructures can exhibit

properties tunable to meet the requirements of a variety of applications including catalysis,

sensing, information storage and processing, and electronics. These types of hybrid architectures

are found throughout the literature,1'2 and recent research interest has focused on examples such

as supramolecular-templated mesoporous materials,3-12 host-guest intercalation compounds, 12-
20 self-assembled thin films, 21-31 and layered structures,32-36 just to name a few.



Mesoporous Materials



With the synthesis of the MCM-41 and the M41S family of molecular sieves in 19923

came the advent of research initiatives emphasizing focus on these mesoporous solids.4-12 The

discovery of this class of compounds led to the realization of assemblies comprised of well-

ordered arrays of uniform pores in the 15-100 A range.4 These sizes expand upon the prior pore

restrictions of <15 A for zeolites and related molecular sieve-type structures.4'12 While zeolites

have been, on occasion, constructed from single alkylammonium ion templates, which dictated

their smaller pore size, the vacancies in the mesoporous materials are a direct result of the

templating effect of organic assemblies of surfactant molecules.4'5'9 The pore sizes in these









"ultra large pore" structures are therefore tuned by the rational selection of the amphiphile,

solvent, and reaction conditions.

Although various models have been proposed to define the mechanism for mesostructure

formation, researchers agree with the basic premise that the organic component and the inorganic

network act synergistically. In their 1992 letter detailing the synthesis of MCM-41, researchers

at Mobil suggested two mechanisms for its formation, both based on this "liquid-crystalline

templating effect".3 As is shown in Figure 1-1,5 the spontaneous formation of micelles in water

occurs for surfactant molecules, such as hexadecyltrimethylammonium ions, to maximize their

favorable interactions and to minimize their undesirable interactions with the solvent. At

increasing concentration of the amphiphiles in water, the micelles can organize into mesophases

such as the hexagonal array shown here. According to Mobil researchers, the inorganic

precursor may create walls between the micellar cylinders, perhaps to balance the cationic

surface of the micelles.3 In contrast, the aluminosilicate may mediate the ordering of the organic

amphiphiles.3 While the former theory has since been disproved,4'8,10 new ideas have surfaced

since 1992 regarding the mechanistic model.4 Still, it is the cooperation between the organic and

inorganic networks which results, when the surfactants are removed through calcination, in a

uniformly porous material.



Rod-shaped Micelle Hexagonal Liquid Hexagonal Array MCM-41 with
Crystal with Silicate Layer Cylindrical Pore


Pathway 1


Preorganization
-Silicate Calcination


Pathway 2 Packing


Figure 1-1. Two proposed pathways for the synthesis of mesoporous materials. Adapted from
reference 5.








Since the original achievement in 1992, researchers have explored a myriad of structures

based on the initial MCM-41 parent compound. Derivative synthesis has involved the use of

anionic amphiphiles as well as the cationic surfactants initially employed, and the types of

inorganic precursors utilized have been expanded to include transition metal oxides.4,6,7

Resulting materials have exploited the synergy of these organic and inorganic components, and

the solids fabricated have been highly coveted as catalysts and sorbents.4'5'12 Other researchers

have focused on the deposition of the solids as films where the application of these porous

mesophases can be extended to membranes, low dielectric constant interlayers, and optical

sensors.11



Intercalation Compounds



A variation on this hybrid organic/inorganic theme is the intercalation compound, where

guest molecules occupy vacant sites within a host lattice without major rearrangement in its

structure. A beautiful illustration of this type of behavior is found in the class of compounds

referred to as transition metal oxyhalides, which includes the well-studied example FeOCI shown

in Figure 1-2.12-20 FeOCI is a layered material consisting of two-dimensional polymeric sheets

of iron and oxygen where the chlorine atoms extend into the interlamellar spacing.13,14,18'20

Guest molecules can occupy vacancies between the two-dimensional sheets of the FeOCI host

through redox chemistry, which normally proceeds with electron transfer from the guests to the

host.14-16

One such guest exploited for its reducing potential is tetrathiafulvalene (TTF, 1). TTF

and its derivatives are known for their ready ability to undergo electron oxidation and to form

radical cation/anion charge-transfer salts with acceptors like tetracyanoquinodimethane

(TCNQ)37 or with molecular anions, such as PF6,38 and these salts have been found to be

conducting or superconducting.37-43 When TTF is introduced to FeOCI, an electron is
























000
Cl 0 Fe

Figure 1-2. The layered structure of FeOCl. Adapted from reference 15.



transferred to the host yielding a 4% Fe(II)/Fe(III) mixed valent lattice, as determined by Fe

Mossbauer spectroscopy.20 The resulting semiconducting behavior is 103-105 times that of the

starting material, but intercalation of the guest species destroys the long-range magnetic

interactions between the Fe(III) cores coupled along the interlayer axis in the pristine host

lattice.20 In a similar analysis, the hydrocarbon compounds perylene (2) and tetracene (3) served

as guest molecules in FeOCI, and the resulting semiconducting material, whose behavior

originates from electron hopping throughout the mixed Fe(II)/Fe(III) lattice, displayed

conductivity values 105 times greater than those values determined for the pure FeOCI

structure.15








1 2 3








FeOCI has also served as a host lattice for conducting polymer guests.12'14'16'17 In
general, monomer units are exposed to FeOCI and undergo in situ polymerization during

intercalation, with the host acting as the oxidant. When pyrrole (4) or 2,2'-bithiophene (5) were

employed as the monomers, metallic behavior was observed in the resulting material, which was

comprised of organic polymeric chains occupying the vacancies between the layered inorganic
extended structure.16'17 Applications for macromolecules in layered inorganic hosts include use

in battery electrodes, electrochromic displays, and molecular electronic components.12

0

N S
H s^^
4 5



Self-Assembled Films


While a number of these hybrid organic/inorganic architectures are probed as bulk
powders, the manipulation of these structures as thin films offers attractive advantages from an

applications standpoint. The processibility of such two-dimensional geometries, including the

precise control over the components on a molecular level and the assembly of these components

into highly ordered materials, suggests unique possibilities for these structures in the engineering

of materials. The self-assembly of films of organic molecules at an inorganic surface is a

creative alternative to the preparation of hybrid organic/inorganic materials as bulk solids. The

pioneering work of researchers such as Allara,22-25 Nuzzo,22-26 Whitesides,25-28 and Sagiv29-31

explored the formation of layers of surfactant molecules with different polar components on
diverse substrates. The formation of such assemblies is defined by the spontaneous adsorption of

molecules onto a surface when a substrate is immersed into a solution of the surfactant
molecules.21 This procedure relies on the affinity of the amphiphiles for the substrate as well as

for each other. In terms of the energetic of the deposition, the chemisorption of the headgroup








at the surface is the strongest interaction, and this is followed by the interlayer interactions

between the surfactant molecules.21

Preliminary thin film research focused on monolayers and multilayers exploiting the
reaction of alkylsilane derivatives with hydroxylated surfaces such as Si02.21'29 By utilizing a

chlorinated silane precursor, reaction between the Si-Cl functionality and the OH groups from

the hydroxylated surface results in adsorption of the surfactants through a network of formed Si-

0-Si bonds, as shown in Figure 1-3.21 Van der Waals interactions between the hydrocarbon

chains of the amphiphiles serve to increase the order in the resulting monolayer. Multilayer

materials are fabricated through functionalization of the monolayer surface to create terminal

hydroxyl groups onto which another self-assembled monolayer can be adsorbed (Figure 1-
3).21,30 The stability of the monolayers is a result of the polysiloxane inorganic backbone

created during the self-assembly process.21 Various organic groups have been incorporated into

the amphiphilic chain, including aromatics.44-49 As an example, this process can be applied to

deposit noncentrosymmetric films of chromophores for nonlinear optical (NLO) applications.

One study has shown second harmonic generation (SHG) in a self-assembled multilayer film of

chromophoric silanes demonstrating a high degree of order and stability (Figure 1-4).46-49

In the deposition of alkanethiols or dialkyldisulfides on gold, a gold(I) thiolate (RS-)

species is formed from the chemisorption of the surfactant onto the surface.21 The resulting

symmetry of the assembly is a direct result of the face of the substrate onto which the surfactants

are adsorbed. While deposition of docosanethiol onto the Au( 11) surface results in hexagonal

symmetry, it has been shown that the Au(100) surface directs formation of a base-centered

square.21 Organic groups occupying the termini of the chains could dominate the structures of

the resulting self-assembled monolayers (SAMs) of thiols on gold, causing the surface of the

film to have a morphology independent from the organization of the thiols on gold.50 If organic

groups such as azobenzenes, which are know to aggregate in films, are included in the

amphiphilic component of thiols, the SAMs on a Au( 111) surface have an organic component














CO2Me



solution


0-

CI3Si E
1


LiAIH4


1


Multilayers -


Figure 1-3. Construction of multilayers of alkylsilane derivatives by self-assembly. The inset
shows an example of the proposed structure of the polysiloxane linkages formed during the
assembly process, where the alkyl chains are in axial positions. Adapted from reference 21.








incommensurate with the underlying inorganic network.50'51 This type of organization is

illustrated in Figure 1-5.51 SAMs can also be deposited onto silver, copper, or platinum

surfaces through thiols as well as via other functionalities, such as isocyanides.21,25,27,52 The

chemistry of the SAM can be exploited in the formation of complex one-, two-, and three-

dimensional architectures where the building blocks can be organized into the superstructures via

the linkages provided through SAMs.53 An example of this is seen in the tethering of gold

colloids to gold wires through 1, 9-nonanedithiol.54


HO OH HO ( OH
N N
HO OH


N+
Br Br Br Br- $ Br-

SiC13 )' ) N (F i f-
OH OH OH NSi 0 0 %Si o Si-



OH OH
0. 1 0-" 10^.1^0"/'
Si Si" Si
O 0 0
o\ 5o \o;0

N N




I I
)Br- Br-

repeat -7Si Sj- S
S^0^ 0


Figure 1-4. Self-assembly approach for the fabrication of noncentrosymmetric thin films of a
stillbazolium derivative for NLO. Adapted from reference 49.























= azobenzenes I = alkane tethers


Figure 1-5. Proposed model for the organization of azobenzene-tennrminated alkylthiols
assembled on a Au(1II) surface. The azobenzene groups are spaced 4.5 A apart while the S
atoms from the thiol groups are spaced at a distance of 5.0 A. The alkyl chains tilt inward so that
the azobenzene groups may adopt their preferred packing arrangement. The domains are
indicated by large circles. Adapted from reference 51.


Layered Materials


Layered structures present an excellent medium for assembling into one material
contributions from both an inorganic and an organic network. As demonstrated with the FeOCI
intercalation material discussed above, from alternating layers of organic and inorganic materials
the interlayer interactions giving rise to organic and inorganic properties can easily be detected.
Layered materials also provide the opportunity for studying these types of organic-organic and
inorganic-inorganic interactions in the confines of two-dimensions, an attractive feature when
the desire is to study the behavior of materials outside a three-dimensional framework.








Layered Perovskites


In the layered perovskite structures, represented chemically as (RNH3)2MX4 where R is

a hydrogen or an organic substituent, M is a divalent metal ion, and X is a halide, metal halide

octahedra are linked in a square array, and ammonium ions separate the sheets of two-

dimensional metal-halide planes.32 R substituents can be grafted onto the ammonium ions,

resulting in an alternating organic/inorganic layered structure, an example of which is shown in
Figure 1-6 with (CiOH2lNH3)2CdCI4.32 These hydrocarbon chains have been functionalized

with organic moieties such as diacetylene groups or other units of unsaturation, which give rise

to polymerization within the two-dimensional organic network.33 Paramagnetic metal ions such

as copper (II), chromium (II), and manganese (II) have been the focus of two-dimensional

magnetic investigations in the perovskite materials.55'56


Figure 1-6. Crystal structure of (ClOH2lNH3)2CdCI4. This perovskite material is clearly
comprised of alternating layers of organic and inorganic networks. Adapted from reference 32.








Metal Phosphonates



Zirconium phosphates. Although layered metal phosphonate salts have been known for

quite some time, it is only rather recently, with the synthesis and characterization of the

prototype a-zirconium phosphate (a-Zr(HPO4)2-H20),57 that researchers have begun to explore

their potential in supramolecular architectures.34'58'59 The crystal structure of a-

Zr(HPO4)2-H20 is shown in Figure 1-7 A.57'59 The material is clearly layered, and each

zirconium ion is six-coordinate. Three of the four oxygen atoms participate in metal binding,

and the fourth oxygen extends as an OH group into the interlamellar space. The water

molecules, although not depicted, can be found near the OH groups between the zirconium ion

planes, and consecutive layers are held together through van der Waals interactions.34'57 A

second zirconium phosphate phase, y-Zr(P04)(H2P04)-H20, has also been synthesized and

characterized.60 In this phase, two planes of zirconium ions are formed through coordination

with each of the four oxygens from the orthophosphate groups. Two of the oxygens from two

different H2P04 groups complete the octahedral coordination environment, leaving the two

hydroxyl groups directed toward the interlayer region, as can be seen in Figure 1-7 B.59 Once

again the water molecules can be found near the OH groups, and adjacent layers are linked

through a series of interlayer hydrogen bonding interactions between the hydroxyl groups and

waters.59'60

In both the a- and y-zirconium phosphate phases, the hydrogens from the hydroxyl

groups are free to participate in ion exchange reactions. Monovalent cations such as Li+, Na+,

and K+ can replace the exchangeable hydrogens under neutral conditions in the a-zirconium

phosphate solids, while basic conditions cause swelling of the interlayer spacing, thereby

allowing the larger Rb+ and Cs+ cations to be accommodated.58'61 Intercalation of amines into

a-zirconium phosphate also occurs as a result of the highly acidic nature of the protonated

structure, and these intercalation compounds can serve as starting materials for the ion exchange









A B












*=Zr O=P 0=0 *=OH *=Zr O=P 0=0 *=OH
Figure 1-7. (A) Cross-sectional view of two layers of a-Zr(HPO4)2-H20 and (B) cross-sectional
view of two layers of y-Zr(P04)(H2P04)-H20. In each case the layered nature of the material is
apparent. Adapted from reference 59.



of larger cations.58'61'62 The y-zirconium phosphate phase undergoes exchange with larger

cations more readily.58 Both phases have been shown to accommodate molecules such as TTF

(1) in its oxidized form, the a-phase after the layers of the host had been preexpanded with

ammonium surfactants.63 Results of this study show metal-like conductivities greater than

values observed for the individual precursors.

Zirconium phosphonates. The hydroxyl groups of the a-zirconium phosphate phase

can be replaced with organic substituents, resulting in the zirconium organophosphonate

materials. Lamellar phosphonate salts of zirconium are prepared by combining aqueous

solutions of the zirconium ion and the phosphonic acid precursor. The structure of zirconium

phenylphosphonate is shown in Figure 1-8.64 The inorganic lattice is similar to that of the a-

zirconium phosphate phase with the zirconium ions octahedrally coordinated by oxygens from

six different phosphonate groups. In the phenylphosphonate structure, the phenyl groups extend

into the interlayer region and separate the zirconium ion planes, creating a structure clearly

comprised of alternating organic and inorganic layers.









A B














Figure 1-8. (A) Cross-sectional view of two layers of zirconium phenylphosphonate, showing
the layered nature of the material and (B) in-plane structure of zirconium phenyiphosphonate
with crystallographic data taken from reference 64. Key: oxygen, small, open circles;
phosphorus, large, dotted circles; zirconium, thatched circles.



The size constraints imposed by the inorganic network restrict the area limitations to

24 A2 per organic molecule to allow for the pendant groups to occupy adjacent positions in the

zirconium phosphonate lattice.34,59'65 Alkyl chains and phenyl groups can easily be

incorporated into the zirconium phosphonate structure given these constraints. For larger groups

to be accommodated, filler ions such as phosphate groups can be added to complete the lattice,

resulting in mixed phosphonate/phosphate phases.34 In addition, the inorganic lattice may adopt

a different structure in order to contain the larger organic groups.34

Crown ether derivatives of phosphonic acids have recently been prepared and reacted to

form layered zirconium phosphonate salts as a means of achieving metal ion separation for

various applications.66,'67 The zirconium phosphonate linkage tethers the crown ether to a solid

support to prevent loss of the macrocyclic ligand during the separation process. In this case the

metal phosphonate materials are exploited for their highly insoluble nature. The bulkiness of the

crown ether moiety precludes formation of the aC-zirconium phosphate-type inorganic lattice

because the organic group exceeds the 24 A2 area restriction. However, with the addition of

phosphoric acid to the reaction mixture, new phases, depending on the relative concentrations of

the precursors, are obtained. In one case, the phosphate groups occupy vacancies left by the








larger phosphonate moieties in the same layer to produce an a-zirconium phosphate-type phase,

as seen in Figure 1-9 A.66 A different structure is the result when phosphate groups bind the

zirconium ions in the inorganic plane while the organic layer contains phosphate groups

interspersed with macrocyclic phosphonate ligands (Figure 1-9 B).66

Porous pillared zirconium phosphonate solids are formed from bis(phosphonic acids)

and have applications in catalysis and sorption.34'58'59'68-70 The pore size can be controlled by

the selection of the organic groups and filler ions. The porous compound

[(ZrF)2(PO4)(O3PCH2CH2-bipyridinium-CH2CH2PO3)]+X-"3H2O (X is a halide), shown in

Figure 1-10, can be prepared where the bis(phosphonic acid)-substituted viologens act as pillars

for the inorganic lattice, and the phosphate groups coordinate the zirconium ions in the inorganic

plane.68'70 Three oxygens from the organophosphonate participate in metal binding, and the

viologen groups bridge adjacent inorganic layers, leaving vacancies in the organic region of the

structure. Metal halide complexes (M = Pt or Pd) can ion exchange with the halide ions found in

the cavities, and following hydrogen reduction of the metal complexes, platinum or palladium

colloids are formed.69 These inorganic particles catalyze the reduction of viologen, which then

serves as a reducing agent for the direct production of hydrogen peroxide.69 The catalytic

applications can therefore be tuned by judicious choice of the organic groups.

Divalent and trivalent metal phosphonates. While the organophosphonic acids can

dictate the metal binding in the inorganic network, so too can the selection of the metal ion direct

the resulting structure in the inorganic plane. By simply replacing the tetravalent metal ion in

zirconium phenylphosphonate with a divalent metal ion from the series Mg(II), Mn(II), Zn(II),
Co(II), and Cd(II), a new structure represented by the formula M(O3PC6H5)-H20 is formed.71-

73 These compounds are synthesized from the reaction of the appropriate metal salts with

phenylphosphonic acid in aqueous media. As seen in Figure 1-11, the metal ions are coordinated

with six oxygen atoms in a distorted octahedral environment.72 Five of the coordination sites are

occupied by phosphonate oxygens while the sixth coordination spot is held by a molecule of








IIIIIII II
Zr Zr Zr Zr Zr Zr Zr Zr
OH OH OH OH OH OH


r 1 r r 1 r- r i
O0 0 C
0 0 0 0 0
CJ

Zr Zr Zr Zr Zr Zr Zr Zr




1Zr ^L Zr. ^Zr_^l l Z
Pro ^ ^ E Pr I
/ O .. rP04, Zr-PO4-;:...Zr _i- P Oo.. Zr... PO+- 0- ZrL P04-,


0 0
CrO


r0
Q\^


000

v-I


0 0 0 0



?OH1 OH OH
4-- ^ Sr Zr -- Zr -
::P4 r_ P04- 7---- r, r r-- P04 Zf PO ,


Figure 1-9. Schematic representation of a zirconium phosphonate material containing
macrocyclic ligands. The large area of the macrocyclic ligand precludes formation of the a-
zirconium phosphate-type phase, which is seen in the zirconium phenylphosphonate material.
Addition of phosphoric acid to form a layered structure can give rise to two phases. (A) The
additional phosphate groups take up void spaces to complete the zirconium phosphonate lattice,
and (B) the phosphate groups complex the zirconium ions within the inorganic layers as well as
participate in bonding within the organic layer. The phase formed depends on the amount of
phosphoric acid added to the reaction mixture. Adapted from reference 66.

















n H20


Figure 1-10. Schematic illustrating the porous nature of [(ZrF)2(P04)(O3PCH2CH2-
bipyridinium-CH2CH2PO3)]+X'-3H20 (X is a halide). The void spaces accommodate Pt or Pd
complexes, and this zirconium phosphonate material serves as an efficient catalyst for the
production of hydrogen peroxide. Adapted from reference 69.


Figure 1-11. (A) Cross-sectional view of two layers of manganese phenylphosphonate, showing
the layered nature of the material and (B) in-plane structure of manganese phenylphosphonate
with crystallographic data taken from reference 72. Key: oxygen, small, dotted circles;
phosphorus, thatched circles; manganese, cross-hatched circles.








water. Two of the oxygen atoms from the phosphonate groups bridge more than one metal

center, resulting in a series of M-O-M linkages. (This is different from the zirconium

phosphonate case where each metal center is connected to the next through M-O-P-O-M bonds.)
A series of metal alkylphosphonates with composition M(O3PCnH2n+l)'H20 were also

prepared, and similar structures were found for Mg(II), Mn(II), Cd(II), Zn(II), Co(II), Ca(II),

Fe(II), Cr(II), and Cu(II), although in some cases the metal salts crystallize in different space

groups.72-77 However, when the length of the alkyl chain is five carbons or longer, the calcium
metal ion forms the new six-coordinate structure shown by the formula Ca(HO3CnH2n+l)2.72-

74 The larger Ba(II) and Pb(II) divalent metal ions also crystallize in a layered motif with

phenylphosphonic acid but adopt an eight-coordinate geometry and form with stoichiometry

M(HO3PR)2 (Figure 1-12).78


A B














Figure 1-12. (A) Cross-sectional view of two layers of barium phenylphosphonate, showing the
layered nature of the material and (B) in-plane structure of barium phenylphosphonate with
crystallographic data taken from reference 78. Key: oxygen, small, dotted circles; phosphorus,
thatched circles; barium, cross-hatched circles.


Reaction of phosphonic acids with trivalent metal ions in water yields layered materials

with yet another structural motif. The lanthanide metals La(III), Ce(III), and Sm(III) react with
phenyl- or alkylphosphonic acids to yield salts of composition MH(O3PR)2 (Figure 1-13).74,79

In these materials the metal ions are dodecahedrally coordinated to eight phosphonate oxygens.








Depending on the synthetic conditions, different phases of Fe(III) organophosphonates can be

isolated as well.80


A B













Figure 1-13. (A) Cross-sectional view of two layers of lanthanum phenylphosphonate, showing
the layered nature of the material and (B) in-plane structure of lanthanum phenylphosphonate
with crystallographic data taken from reference 79. Key: oxygen, small, open circles;
phosphorus, large, dotted circles; lanthanum, thatched circles.



The properties of the inorganic lattice can be tuned by careful selection of the metal ion.

The magnetic behavior is often studied in these systems, and the results are affected by the metal

ion, the organic substituents, and the metal phosphonate structure. Recently Peter Day and co-

workers investigated the magnetic behavior of a series of manganese alkylphosphonate solid-

state materials along with the potassium or ammonium salts of the purely inorganic manganese

(II) phosphate and iron (II) phosphate structures.81-84 Static susceptibility measurements

revealed a transition to a canted antiferromagnetic state in the range of 14.8-15.1 K for the

manganese organophosphonate solids82'83 and near 18 K and 24 K for the manganese and iron

inorganic phosphates, respectively.81,84 The observation of spontaneous magnetization in these

materials is due to incomplete spin cancellation as a result of the canting of the moments on

neighboring metal ions.

An interesting feature of the homologous series of divalent metal phosphonates that form
with stoichiometry M(O3PR)-H20 relates to the liability of the water molecule coordinated to the








metal ion. In some cases the water can be removed thermally leaving an open coordination site

on the metal, oftentimes replaceable with ammonia or small chain alkylamines. Dehydration of

zinc or cobalt methyl phosphonates, followed by exposure to ammonia or alkylamine vapors,

yields a product of composition M(O3PR)-NH2R (R=H, CnH2n+l, n=l-8) with coordination of

the amine derivative to the metal ion through the nitrogen atom.85'86 These reactions have been

shown to be shape selective. The dehydrated zinc or cobalt methylphosphonate will intercalate

n- and isobutylamines, but the environment prohibits uptake of the sec- or tert-butylamines.85 In

a similar experiment, phenylphosphonate salts of cobalt and zinc have been shown to coordinate

ammonia molecules in the vacant site, but uptake of long chain amines or carbon dioxide did not

occur under analogous reaction conditions as a result of the steric restrictions imposed by the

bulky phenyl group.86 In contrast, thermal treatment of nickel methylphosphonate causes a

change in the environment around the metal ion such that octahedral coordination is

maintained.85

The organic component of the metal phosphonate system can be varied to complement

the corresponding inorganic network in size and properties. The investigator can exploit the

inorganic lattice structure in order to direct the packing of the organic groups in a predictable

manner. As an example, the solid-state polymerization of diacetylene monomers requires

precise positioning of the precursors in order to achieve high molecular weight polymers.

Phosphate derivatives of these diacetylene units have been incorporated into the metal lattice of

various divalent and trivalent metal ions.35'87 When the diacetylene monomers are contained

within the M(O3PR)-H20 lattice type, the organic groups align in a coplanar fashion and the

headgroup spacing of 4.8 A (dictated by the inorganic lattice) is a sufficient distance to allow for

a high degree of polymerization (Figure 1-14). However, for the lanthanide phosphonate or

phosphate structures, the headgroups are separated by 5.3-5.6 A due to the inorganic lattice

spacing, and the organic groups are forced to tilt in a noncoplanar arrangement. Here the

diacetylenes are not oriented for optimum polymerization, and the result is short oligomeric







chains. In this case the propensity of the inorganic layer to direct the organic packing is utilized
to achieve a predictable geometry for specific applications.


P P
/I y, ,i,/Y /
0 0 0 0 /0
-?C - hv t% .c" J\cc\ c:
o/ f / / r o
1 0' 0'_ 1' \\, & C
C- C P.C,:,


/Al A\ /P,\-_ ,, 1 \ /P\
Figure 1-14. Schematic illustrating the topochemical polymerization of diacetylenes within the
metal phosphonate network. Adapted from reference 87.


In some cases, the inorganic network will adopt a different structure to contain bulky
organic moieties. The M-O network in the M(O3PR)-H20 series of salts only permits an area of
28 A2 per phosphonate group, and larger groups cannot be accommodated with this lattice.73
Reaction of benzhydrylphosphonic acid with magnesium sulfate generates the product
Mg(HO3PCH(C6H5)2)2-8H20.73 The bulkiness of this organic moiety precludes formation of
the structural motif seen for magnesium phenylphosphonate (M(O3PR)-H20) since the area of
the functionality exceeds the limitations imposed by the inorganic network.
Derivatization of the organic region has led to the study of porphyrin groups
immobilized in the metal phosphonate network. Interest in porphyrins stems from their catalytic
behavior, and anchoring these chromophores to an insoluble network allows for their easy
recovery once the catalytic cycle is complete. Manganese porphyrins tetrasubstituted with
phosphonic acids (6) form a zinc phosphonate salt whose catalytic behavior in the epoxidation of
cyclooctene is deemed similar to the porphyrin phosphonic acid precursor.88 In this case,
however, the zinc inorganic lattice that is obtained is restructured to accommodate the larger
porphyrin moieties.


















HO3PCH \|
SCH3H2 / H20 P0311H2
6 7 8


The zinc phosphonate lattice easily forms new phases to contain the desired organic

units. The flexibility of the zinc ion may stem from the stable four, five, and six coordinate

structures it can adopt. In the case of the zinc materials, the organic phosphonic acid precursor

can exert tremendous control over the resulting inorganic lattice. Reaction of zinc nitrate with

(R)-H203PCH2P(OXCH3)(C6H5) (7) yields the enantiomerically pure zinc phosphonate (R)-

Zn[O3PCH2P(O)(CH3)(C6H5)]-H20 in which the zinc atom is tetrahedrally coordinated by

three phosphonate oxygens and the oxygen from the phosphane oxide moiety.89 In this lattice,

the water molecule does not coordinate the metal ion.

While a, oo-alkylene bis(phosphonic acids) and 1,4-arylene bis(phosphonic acids) are

normally employed for forming pillared, mesoporous metal phosphonate materials, a new

approach to synthesizing metal organophosphonate salts relies on bis(phosphonic acid)

precursors where the phosphonic acids neighbor each other in fixed positions. In one example, a

phenyl ring containing meta methylphosphonic acid substituents was prepared (8).90 A

bis(phosphonate) analogue of the cadmium monophosphonate salts previously described was

prepared, suggesting that the spacing between the neighboring phosphonic acids was sufficient to
achieve the M-O network in the Cd(O3PR)-H20 lattice. However, the coordination environment

in a zinc salt of the bis(phosphonic acid) was slightly different. One zinc ion coordinated a water
molecule in a six-coordinate environment reminiscent of the M(O3PR)-H20 lattice while the








other metal ion did not pick up a water molecule and remained five-coordinate. Once again such

behavior for the zinc phosphonate salts arises from the flexibility in its coordination chemistry.

Metal phosphonate self-assembled films. For little more than a decade, researchers

have been investigating the deposition of single layer analogues of the metal phosphonate solid-

state materials.35'36'91-101 By simply exploiting the inherent properties of the metal phosphonate

system, a strategy for the layer-by-layer assembly of the solid-state metal phosphonates as thin

films was defined by Mallouk and co-workers.91'92 In this procedure, which was initially

applied to preparing zirconium phosphonate films, a substrate is first derivatized with terminal

phosphonic acids, and this is followed by the alternate adsorption of zirconium ions and a,

o)-bis(phosphonic acids). Sequential repetition of these steps builds up multilayer materials, as

shown in Figure 1-15.91,92 This process relies on the strong affinity of the metal ion for the

phosphonic acids and takes advantage of the highly insoluble character of the zirconium

phosphonate inorganic network and the highly soluble nature of the phosphonic acid and

zirconyl chloride precursors. With this method, robust, well-ordered films can be deposited.

The application of this method has been extended to the growth of thin films of divalent metal

(zinc and copper) alkane bis(phosphonates) on gold, and these films have also been shown to be

well-ordered.102

The processibility of thin films and the molecular-level control over the individual

components makes these materials excellent candidates for use in optical and electronic devices.

Katz and co-workers developed a three-step deposition process to orient dye molecules in a polar

manner in zirconium phosphonate/phosphate multilayers for SHG (Figure 1-16).96 Initially,

zirconium ions are allowed to bind to a phosphonic acid-terminated substrate in much the same

way as shown in Mallouk's scheme. In the next step, this zirconated template is immersed in a

solution containing the phosphonic acid chromophore, and the phosphonic acid groups bind the

zirconium ions. The result is oriented, asymmetrically-substituted azobenzene derivatives
capped with hydroxyl groups. These hydroxyl groups are derivatized with POCI3 to form










H203P- -P03H2 zr031P- --3,
H203P- P03H2 ZIOC2 'Zr 0- I p03 Zr
H203P- -P03H2 (a) 0 N P- -P0-3' r
H203P -P03H2 0P-_oP0 3 '""


H203P----P03H2
(b)


H203P-- PO3N Zr-03P P03 -103P -- P03H2
multilayers formed _____S H23P ----PO 0,O3P-- Zr-O P _POH
by repeating Steps - "Zr ,- ----- 3& 3P-P03H2
(a) and (b) H203P----P _P- --P03< ,P---P03H2
H203P-K---- 1.13 03P-3P 03P-P03H2

Figure 1-15. Procedure for the self-assembly of zirconium phosphonate films. Adapted from
reference 91.



phosphate functionalities which are free to bind zirconium ions when the substrate is again

immersed in the metal solution. By avoiding a bis(phosphonic acid) precursor in this deposition,

the asymmetric nature of the chromophoric precursors can be preserved, thereby generating a

multilayer film with an NLO response on the same order of magnitude as in LiNbO3, a widely-

used, inorganic NLO material. Other dye-type compounds have been subjected to the same

deposition scheme, generalizing the method to a wide range of precursors.93'98,99'

The nature of the layer-by-layer deposition procedure also provides a medium for

fabricating alternating layers of organic materials. In a study by Katz and co-workers,

alternating layers of a porphyrin and a viologen zirconium phosphonate film assembly showed a

diminished fluorescence intensity from that observed in a pure multilayer film of porphyrins.95

The quenching observed in the viologen/porphyrin system was attributed to the interlayer

electron transfer from the porphyrin donor to the viologen acceptor. When an aliphatic

zirconium phosphonate layer was introduced between the porphyrin and viologen layers,

quenching of the porphyrin fluorescence was not observed because of the insulating character of

the alkyl segment.










ZrOCI2 -P%zK




0 3-,O Z r. O 3P I _.OPO 3 H 2
-P0- P 31
2.0 3 I--OH
[-- -- 3Zr3 OR }OP03H2
.-"- 3_ P,03P-- tOP03H2


\ -03 -03P IOH
'PO-- 103P -- No }OH
I-.POC13 f'''^-^- m^ oV- O
2.H20 L_-PO3" 0O3P- W ~fOH



H203P- --OH= H203P =-N j, --


OH
Figure 1-16. Schematic illustrating the three-step procedure for the self-assembly of zirconium
phosphonate films of an oriented azobenzene derivative for SHG. Adapted from references 36
and 96.



Metal phosphonate Langmuir-Blodgett films. Originally the self-assembly procedure

for depositing monolayers was developed as an alternative to the previously-conceived

Langmuir-Blodgett (LB) methodology of film deposition.21,103-106 In the LB method, organized

monolayers of amphiphilic organic molecules are first prepared at a water surface and then

transferred onto a solid support. Because film formation relies on weak hydrophobic and

hydrophilic interactions, the resulting films are often metastable and are criticized for their lack

of long term stability.21,103,'105,'106 Figure 1-17 depicts the formation of a Langmuir monolayer,

developed by Irving Langmuir in the early part of the twentieth century.107 Initially amphiphilic

molecules, or molecules with a polar component and a nonpolar component, are dissolved in a

volatile spreading solvent, such as chloroform. Drops of this solution are carefully placed on a

water surface, which is housed within the constraints of a "trough". These LB troughs are








normally constructed of an inert material, such as Teflon. After the solvent evaporates the

amphiphiles orient themselves so that their polar heads are immersed in the aqueous subphase

while their hydrophobic tails are directed away from the water. At this stage the interactions

between the molecules are minimal. This state is often labeled as a two-dimensional gas

analogous phase. 108


/


Gas Analogous


H (mN/m)


Liquid-Expanded


I I In I I


Liquid-Condensed


ill I Iii II


Mean Molecular Area (A/molecule)

Figure 1-17. Formation of a Langmuir monolayer. Initially the molecules interact very weakly.
As the barriers are compressed, an increase in surface pressure is measured, signifying the onset
of interactions between amphiphiles. In the liquid-condensed state, the molecules exist in a
close-packed state.


Once mechanical compression of the amphiphiles with moveable barriers commences,

the interactions between the amphiphiles begin to grow appreciable. These interactions change

the surface tension of the water, and this surface tension can be related to the surface pressure

(II) with equation 1-1:

S= Yo-Y, (1-1)


I A


4. 4' -"-


\^^_^4








where Yo is the surface tension of the pure water and y is the surface tension of the film-covered

subphase. The surface pressure is measured with a Wilhelmy plate (a piece of platinum or filter

paper) suspended from a microbalance. The surface pressure and how it relates to the

amphiphiles lends insight into the organization of the monolayer on the water surface. The

phase transition denoted by the initial interactions of the amphiphiles on the water surface,

measured as an increase in surface pressure, is assigned as the liquid-expanded state.109 At this

stage the surfactant molecules are near each other but are not closely packed. Further

compression leads to a transition to a liquid-condensed state where the closely packed, uniformly

oriented hydrophobic tails and polar headgroups result in a well-ordered monolayer.109

Transfer of a Langmuir monolayer onto a solid support was first investigated by

Katherine Blodgett and Irving Langmuir in 1935.104 Their procedure involved moving a

substrate vertically through a monolayer of amphiphiles held at a constant surface pressure on an

aqueous subphase. The pressure at which transfer occurs normally corresponds to the

arrangement of the molecules in a close-packed state. When a substrate that has been modified

to be hydrophobic is used, transfer on the downstroke relies on hydrophobic interactions between

the substrate and the hydrophobic alkyl tails of the amphiphiles, as seen in Figure 1-18. As the

substrate is withdrawn, the hydrophilic interactions between the polar headgroups cause a second

monolayer to be deposited. These two monolayers, one transferred on the downstroke and the

second transferred on the upstroke, are referred to as a bilayer.




I|_-_ ________








Figure 1-18. Deposition of an LB film. The schematic illustrates transfer of an LB film using
the conventional vertical dipping technique. The film depicted on the substrate is an LB bilayer.








The LB deposition technique has historically been a method of organizing and

transferring organic molecules. Long-chain fatty acid amphiphiles (or surfactants where the

polar head group is a carboxylic acid and the hydrophobic component is a hydrocarbon chain)

were some of the first surfactants studied, and now LB films incorporating such functionalities as

steroids, porphyrins, phospholipids, chromophores, monomers, or polymers are routinely

prepared.21'103,105 In the past, the use of inorganic ions was predominantly limited to the

tethering of the organic components. When metal ions were dissolved in the subphase, they

were incorporated into LB monolayers and bilayers during deposition, in some cases enhancing

the stability of the films. In fact, LB films of cadmium arachidate represent some of the most

studied LB materials to date.21',103,110 However, the absence of a continuous lattice inorganic

network in these types of organic/inorganic assemblies restricts the types of physical properties

available. It is only more recently that inorganic networks and the phenomena associated with

them have been examined in LB films. For example, LB films incorporating polyoxometalate

clusters in films with ammonium surfactants have been studied, but cooperative magnetism has

not been observed down to 2K despite their high-spin ground state.111 LB films of single-

molecule nanomagnets have received considerable attention with the recent discovery that

individual metal clusters can act as magnets and exhibit magnetic hysteresis. 112

Talham and co-workers have modeled LB films after the layered metal phosphonates in

an effort to enhance the stability of the resulting architectures as well as to achieve properties

from the LB assembly associated with the continuous solid lattice of the metal phosphonate

materials.113-127 Early work with the tetravalent zirconium ion demonstrated that the

organization and order in the organic region is greatly enhanced when monolayers are deposited

via the LB technique rather than by a self-assembly procedure.113-116 A three-step deposition

process was developed to prepare these films,'113,114 and incorporation of the zirconium

phosphonate lattice into the LB films has been shown to improve the chemical stability of these

LB materials.113








Octadecylphosphonic acid (OPA) films with divalent and trivalent metal ions form

bilayer structures where the metal phosphonate in-plane binding is analogous to that observed in

the solid-state materials.117-122 This inorganic network differs from the amorphous inorganic

lattice found in the self-assembled films, which results from the deposition process. In these LB

films, the organic OPA was chosen for no other purpose than to separate the inorganic planes. A

magnetic LB film was prepared when OPA was deposited with Mn(II), and the static

susceptibility measurements showed a transition to a canted antiferromagnetic state at 13.5 K in

these films.118,119 These magnetic properties are analogous to what Peter Day and co-workers

observed in the solid-state manganese alkylphosphonate materials.82'83 LB films of OPA with

Co(II) lose water when treated with heat, and these dehydrated films have been shown to

coordinate ammonia when exposed to the vapors.120



Scope of the Dissertation



The work embodied in this dissertation investigates the mixed organic/inorganic concept

as it relates to metal phosphonate LB films. Research exploring the functionalization of the

organic layer in metal phosphonate LB films begins in Chapter 2. At this point, the initial efforts

were focused strictly on the organic region, and the motivation was to learn how larger organic

groups contained within the alkyi chains would pack given the constraints of the metal

phosphonate lattice. These initial experiments were performed on zirconium phosphonate films

to exploit the large lattice energy of this network. The challenge of Chapter 3 was to learn how

organic groups that have their own preferred packing arrangements would fair given the

restrictions placed on them by the metal phosphonate lattice. Several different divalent and

trivalent metal ions were deposited with an azobenzene-functionalized phosphonic acid.

Azobenzenes have been widely studied in LB films, and the results from other investigators have

been used to better understand our metal phosphonate systems. It is also shown that LB films of








azobenzenes deposited with Mn(II) exhibit a transition to a canted antiferromagnetic state,

similar to what is observed in the solid-state manganese materials.

One motivation for including the continuous solid metal phosphonate inorganic lattice in

the LB films was to enhance the thermal and chemical stability of the resulting LB assemblies.

Chapter 4 summarizes chemical and thermal stability studies on OPA and an azobenzene-

derivatized phosphonic acid with divalent, trivalent, and tetravalent metal ions. Comparisons to

previously-studied LB films, including the well-researched cadmium arachidate mono- and

multilayers, demonstrate an improved stability to both chemical and thermal treatments in the

metal phosphonate LB materials.

The research presented in Chapters 5 and 6 explores the final steps taken toward

achieving mixed organic/inorganic LB films based on the metal phosphonates. In order to obtain

a metallic, magnetic, hybrid composite, TTF molecules were included in the organic region of

the manganese phosphonate LB films. Chapter 5 discusses the structural and magnetic

properties in films of various ITTF-based phosphonic acid derivatives with manganese. In

addition, the electronic properties of oxidized TTF derivatives in metal phosphonate films are

examined in Chapter 6.














CHAPTER 2
ZIRCONIUM PHOSPHONATE LANGMUIR-BLODGETT FILMS
CONTAINING FUNCTIONAL ORGANIC GROUPS



The Langmuir-Blodgett (LB) technique provides an elegant method for the layer-by-

layer deposition of organic films.21,103,104 In the LB method, organized monolayers of

amphiphilic organic molecules are first prepared at a water surface and then transferred onto a

solid support. Multilayer films are fabricated through the successive repetition of this procedure,

and organized assemblies of functionalized organic molecules have been prepared in this way for

applications that include studies of membrane dynamics,103 investigations of energy transfer in

controlled geometries,128 and molecular electronics,129 just to name a few.

Previous work1 13-119 has shown that it is possible to incorporate known solid-state

inorganic layered structures into LB films and to use the inorganic lattice to organize the organic

component of the films. LB films of octadecylphosphonic acid (OPA) with the tetravalent

Zr(IV) ion have been described.113-116 Analysis has shown the resulting bilayer and multilayer

film samples adopt structures similar to the solid-state zirconium organophosphonate

(Zr(O3PR)2) materials. In contrast to the self-assembled zirconium phosphonate films studied

previously, the LB technique deposits a well-defined "template" layer that can then serve as the

organized surface for additional LB layers or for layers of molecules assembled from

solution.114,115 In this way, the order of the initial LB layer can be transferred to the subsequent

layers, and the template can therefore exert tremendous control on the organization and

architecture of the resulting materials.

The metal phosphonate network provides an opportunity to form mixed

organic/inorganic LB films where both components add function to the LB assembly. Previous

metal phosphonate LB films have been deposited with OPA, and studies have focused on the








formed inorganic lattice within these assemblies. 113-119 For the organic component to contribute

properties, organic moieties demonstrating function must be built into the hydrocarbon chain of

the amphiphilic molecules. Many of these functional organic systems are based on aromatic

structures, and by including such larger groups within the alkyl segment, the symmetry of the

once cylindrical hydrocarbon tail will be altered, as shown in Figure 2-1.21,130 The kink due to

the units of unsaturation may introduce disorder into the organic component of the monolayer

and bilayer films. By exploring a variety of bulky moieties within the organized hydrocarbon

segments, the conditions for forming well-organized monolayer and bilayer films with these

organic amphiphiles can be determined. These details would then allow for precise control over

the molecular orientation and packing of the molecules, ultimately leading to the desired

properties. Ulman and co-workers have performed similar investigations on self-assembled

films of silanes and thiols, where the previously-studied alkyltrichlorosilanes and alkylthiols

were modified to include aromatic groups, such as phenyl rings.44,'130 These model studies

defined the constraints for achieving well-organized self-assembled films. Similarly, the range

of organic functional groups that can be assembled into metal phosphonate LB films is explored

to determine the effect the larger moieties can have on the packing and organization within these

materials.



Alkyl chain




f Rigid it-system


Alkyl chain


Head group

Figure 2-1. Introduction of a kink in the cylindrical symmetry of the alkyl chains as a result of
the incorporated aryl moiety. Adapted from reference 130.








In addition to investigating the impact aryl moieties such as phenyl and biphenyl systems

have on the organization of zirconium phosphonate films, groups exhibiting function are also

explored. Azobenzenes have been widely studied in LB and self-assembled films with interests

related to their optical properties,131'132 nonlinear optical phenomena,48'96'133 and the

photochemically induced trans-cis isomerization reaction.134-137 As a result, much is known

about how azobenzene amphiphiles organize in LB films and how this organization can be

probed with optical spectroscopy. This information can be used to understand the packing

arrangement of the organic chromophores within the metal phosphonate films.

In this Chapter, zirconium phosphonate LB films where the organophosphonate

component contains phenoxy, biphenoxy, and azobenzyloxy groups at different positions along

the eighteen-carbon organic tail are investigated. The organophosphonic acids (1-8) used for this

study are shown in Figure 2-2, and the films prepared are illustrated in Figure 2-3. When

discussing the LB films, the molecules will be referred to using the abbreviations P0, BO, P4, B4,

dP4, dB4, AO, and A4 where P, B, and A indicate a phenoxy, a biphenoxy, or an azobenzyloxy

functional group, respectively, "0" and "4" refer to the number of carbon atoms separating the

aryl group from the phosphonic acid group, and the prefix "d" indicates that the alkyl tail is

perdeuterated. These functionalized phosphonic acids serve as models for determining whether

larger organic groups can be organized within the metal phosphonate LB framework. By varying

the organic group as well as its position in the alkyl segment, questions regarding the optimal

position of the bulky aromatic group within the chain and the effect of size and aggregation on

the packing of the molecules within the films can be answered.

While the zirconium phosphonate lattice does not add any potentially interesting optical,

electronic, or magnetic properties to the organic/inorganic assemblies, the strong oxophilicity of

the Zr(IV) ion brings high inorganic lattice energy to the layered films, making the LB films

extremely stable. In fact, since the zirconium/phosphonate interaction is so strong, the usual LB

deposition procedure where metal ions are present in the subphase is not possible because the











OCXn+X 1 Y
N N\\
OCAn+l N



CmH2mP(OXOH)2 CmH2mP(O)(OH)2 CmH2mP(OXOH)2

1 X=H, n=18, m--=0 2 X=H, n=18, m=0 7 X=H, n=18, m=0
3 X=H, n=14, m=4 4 X=H, n--14, m=4 8 X=H, n=14, m=4
5 X=D, n=14, m=4 6 X=D, n=14, m=4

Figure 2-2. Organophosphonic acids synthesized for this study.



zirconium ions crosslink the organophosphonate Langmuir monolayers, making the films too

rigid to transfer.113 An alternative stepwise deposition procedure that takes advantage of the

strong zirconium phosphonate binding was previously developed for preparing zirconium

octadecylphosphonate LB films (Figure 2-4).113,114 This deposition procedure allows for the

convenient fabrication of symmetric as well as alternating-layer Y-type LB films, and the strong

oxophilicity of the zirconium ion guarantees the deposition of the films, even in the presence of

the bulky chromophores. Because of the nature of metal binding in zirconium phosphonate

films, strict attention can be focused on the organic component of the films, and the effect of the

organic network on the inorganic lattice can be neglected. In addition, the stepwise deposition

procedure permits complete structural characterization of the individual layers deposited on

either the downstroke or the upstroke of the deposition cycle, generating a picture detailing the

arrangement of the amphiphiles within each layer of the film.

Each of the alternating layer and symmetric bilayer zirconium phosphonate films that

have been prepared and characterized are shown in Figure 2-3. Structural characterization of the

deposited films includes attenuated total reflectance (ATR)-FTIR, absorbance spectroscopy, X-

ray photoelectron spectroscopy (XPS), and X-ray diffraction studies. The results show that





















































Figure 2-3. Zirconium organophosphonate LB films prepared for this study.










Step 1


Phosphonic Acid
Langmuir Monolayer


Sample Vial with Phosphonic Acid
Template


Step 2


/Zr4I


1. 20 minutes
ZrOCI2 solution
2. Rinse sample
with pure water


Step 3


t Deposition


P03H P03o, PO3H2
> ZrOP -
> ZrO3P -
> ZrO3P -
> ZrO-3P -


P03I2
PO3Zr<
PO3Zr<
PO3Zr<
P03Zr<


I Phosphonic Acid
Langmuir Monolayer


P03H2 POH2


Figure 2-4. Three-step deposition scheme for the preparation of zirconium organophosphonate
LB films.








phenoxy, biphenoxy, and azobenzyloxy groups can be incorporated into zirconium phosphonate

LB films. In general, the functionalized molecules behave rather similarly with the exception of

BO and AO, which strongly aggregate, even at the water surface. Because of the nature of the

stepwise deposition procedure and the strong zirconium phosphonate bonding, subtle differences

in the organization of molecules within a layer can be observed that depend on whether the layer

is deposited on the downstroke or on the upstroke.



Results and Discussion



Synthesis and Characterization of Phosphonic Acid Amphiphiles



Compounds 1 8 (P0, BO, P4, B4, dP4, dB4, AO, A4) were synthesized as outlined in

Figures 2-5 and 2-6. The methods employed to form P-C bonds are well established.98'99'138-141

In the case of P0, metal-halogen exchange was followed by reaction with the appropriate

phosphorous electrophile, a procedure outlined by Katz and co-workers for the synthesis of

aromatic phosphonate compounds.98'99 The reaction proceeded in only modest yield, as it

appears that the long alkyl chains necessary for forming stable Langmuir monolayers hinder the

normally high yields of this method. For BO, better yields were realized using the palladium-

catalyzed phosphorylation reaction developed by Hirao and co-workers.140'141 The synthesis of

AO initially required the preparation of p-nitrophenylphosphonic acid.142 Following

esterification of this phosphonic acid,143 the azobenzene unit was synthesized. The Arbuzov

reaction139 furnished the aliphatic phosphonate esters in a straightforward manner. Dealkylation

with (CH3)3SiBr proved a facile method for the convenient hydrolysis of all phosphonate esters,

yielding the final, analytically pure product in each case.98'99,144 For the azobenzene derivative

A4, triethylamine was added during the hydrolysis step to react with any formed HBr,145 thereby

preventing reduction of the azo functionality.









S= -0- or ---

OH OCjgH37 OC18H37

Br Br P(O)(OEt)2
9 10
11 12


OC18H37

P(OXOH)2
10= phenyl, P0
20= biphenyl, BO


OC14H29
6 -


OC14H29 OC14H29


C(OXCH2)3Br C4H8Br
14 15
18 19


OCH3 OCH3 OCH3
6 V Vi VW
6 -~ y^-^ -^
C(OXCH2)3Br C4HgBr
21 22
26 27

OC 14D29

C4H8P03H2
5 0= phenyl, dP4
60= biphenyl, dB4


OH
S Vii

C4H8Br
23
28


OC1i4H29

C4H8P(OXOEt)2
16
20

OH


C4HsP(OXOEt)2
24
29


OC14H29

C4H8PO3H2
30= phenyl, P4
40 = biphenyl, B4

OC14D29


C4HsP(OXOEt)2
25
30


(i) ClH37BrK2CO3 (ii) 0 = phenyl: BuLi, CIP(O)(OCH2CH3)2; 0 = biphenyl: Pd[P(C6H5)3]4,

(C2H5)3N, HP(OXOCH2CH3)2 (iii) BrSi(CH)3, H20 (iv) C4H29Br, K2CO3 (v) ClC(OXCH2)3Br,
AIC13 (vi)Zn(Hg),HCI (vii) P(OCH2CH3)3 (vii) BBr3, H20 (ix)Cl4D29BrK2C03

Figure 2-5. Synthetic scheme for the preparation of P0, BO, P4, B4, dP4, and dB4.


The photochemistry of azobenzene and its derivatives is well-established.146-149 The

trans form of azobenzene, the more stable of the two isomers, is characterized by a r-x*

transition in the UV region and a weak, symmetry-forbidden n-n* transition near 450 nm that

accounts for the yellow color of the azobenzene solid. Irradiation of trans azobenzene with 365


OH
6b










jI
N N%.
I N



N02 N02 NO2 N2 NH2 OH








W V I
NH2 N2BF4 P(O)(OH)2 P(0)(OEt)2 P(OXOEt)2 P(O)(OEt)2
33 34 35 36 37

OC18H37 OC18H37
I VI I
N N
I I
P(O)(OEt)2 P(OXOH)2
38 7, AO

N02 NH2 OH OC 14H29 OC 14H29 OC1i4H29
iT l v V. IT I I .. v I IW ix I. x I
-- I N -- N N -N-NN
I I I I
C4H8OH C4H8OH C4H8OH yC4HlOH C4HgBr C4HgP(OC X)OEt)2
39 40 41 42 43

OC14H29
VII
-N

C4HgP(OXOH)2
8,A4

(i) NaN02, NH4BF4 (0i) PCI3, CuBr, HC1 (W7i) PCI5, CH3CH20H, Na (Qv) Sn/HCI
(v ) NaN02/HCI, phenollNaOH (vi) Cl8H37Br, K2C03 (vii) N(CH2CH3)3, BrSi(CH3)3, CH30H
(viii ) C14H29Br, K2C03 (ix) p-toluenesulphonyl chloride, LiBr (x ) P(OCH2CH3)3

Figure 2-6. Synthetic scheme for the preparation of AO and A4.


nm light produces rotation about the N=N double bond to form the cis isomer. On conversion to

the cis form, the r-x* transition shifts to shorter wavelengths, and the band corresponding to the

n-i* transition, which is symmetry allowed in the cis isomer, becomes more intense. The cis








isomer is normally short-lived, and conversion back to trans azobenzene can be effected

thermally or photochemically (with light of wavelength greater than 440 nm).

The behavior of A4 is typical of many azobenzene derivatives. In a chloroform/ethanol

solution, its it-n* transition is found at 354 nm (e = 18,000 M-1 cm-1), as seen in Figure 2-7, a

value expected for a nonaggregated, azobenzene chromophore substituted in a similar

manner.146'150 Upon irradiation, as A4 is converted to its cis isomer, the n-x* transition shifts to

310 nm (c = 7500 M-1 cm"1) and the n-7t* transition at 442 nm increases in intensity (E = 2700

M'1 cm-1) (Figure 2-7). The isomerization is nearly quantitative for A4 in solution. This

process is completely reversible, and after three hours the short-lived cis isomer has almost

completely reverted back to the trans form.

Tt-n* A4 trans
l\ t-7I*
A4 trans
S-A4 cis


A4ci
S"f n-n*
o
n-71
< --AO trans
SJ\ - AO cis


n-lt*


300 400 500 600
Wavelength (nm)

Figure 2-7. Optical absorbance spectra of A4 and AO in chloroform/ethanol solution before and
after irradiation at 365 nm. Band assignments are discussed in the text.



In contrast, the x-rC* transition for AO in a chloroform/ethanol solution has its maximum

at a higher energy than what is observed in the A4 solution spectrum. For AO, the Xmax of 304

nm (e = 11,800 M-1 cm-1) is blue-shifted from the 354 nm value, which is a typical maximum








for isolated azobenzene units.146'150 According to the molecular exciton model,151 this shift to

higher energy indicates that the azobenzene units pack as H-aggregates in solution, with a

parallel alignment of the chromophores. For H-aggregates, the transition allowed exciton state

of the aggregate is at a higher energy than the allowed excited state of the monomer, thereby

accounting for the observed hypsochromic shift. The shoulder present on the low energy side of

the transition has its maximum near 350 nm, indicating there are areas in solution where the

azobenzene chromophores are not aggregated but rather exist as monomers or dimer units, which

do not exhibit a blue shift in the n-n* transition.132 Upon irradiation with 365 nm light, the

shoulder on the low energy side of the main band disappears, and a weak n-x* (e = 900 M"-1

cm"1) transition appears near 440 nm. Based upon this evidence, it appears as though

isomerization occurs for the nonaggregated chromophores while the aggregated species do not

readily undergo rotation about the N=N double bond.



Langmuir Monolayers



Compounds BO, B4, AO, and A4 were characterized at the air/water interface. Figure 2-8

shows pressure vs. area isotherms of each compound during compression on a pure water

subphase at pH 5.5. While Langmuir monolayers of B4 and A4 give reasonable pressure vs. area

isotherms, BO and AO behave very differently.

Isotherms of B4 and A4 are similar with nearly parallel slopes in well-defined liquid-

condensed (LC) regions and with mean molecular areas (MMA) at collapse of 24.2 and 24.0 +

0.3 A2, respectively. Film collapse is defined as the point on the compression curve where

deviations from the linear region of the LC region are first observed. Areas at collapse for B4

and A4 are greater than the 20 A2 MMA at collapse reported for OPA on a water subphase.152

A MMA between 24 and 25 A2 corresponds nicely to the cross-sectional areas of biphenoxy or

azobenzyloxy units oriented with their long axes tilted slightly from the normal to the











80-

70- B4 ............ Transfer
A4.. Collapse
c'60-
AO._
S50- B0 .

40'

S30-
S20 '

10

0-
'5 2' --
10 15 20 25 30 35 40
Mean Molecular Area (A2)

Figure 2-8. Pressure vs. area isotherms for BO, AO, B4, and A4 on a pure water subphase at pH
5.5. Pressures and areas at which the films are transferred to substrates and at which the films
collapse are highlighted with circles and squares, respectively. Compounds B4 and A4 behave
reasonably at the air/water interface while monolayers of BO and AO are rigid.



surface44,'153 and indicates that interactions between the aromatic groups are responsible for

determining the areas per molecule within the Langmuir monolayers. Similar results were

observed for isotherms of P4 and P0, although the flatter slope, unreasonable area/molecule, and

lack of a well-defined LC phase in the P0 isotherm are attributed to the increased rigidity of this

film.124

The observation of film rigidity is far more pronounced for BO and AO monolayers. For

both BO and AO, the isotherms suggest unreasonably low MMAs of 19 and 20 + 0.5 A2,

respectively, at collapse. Unlike in B4 and A4, where the four-carbon tether between the

aromatic and phosphonate groups provides flexibility, the biphenyl group in BO and the

azobenzene group in AO are incorporated into positions adjacent to the phosphonate head groups.

The biphenyl- and azobenzylphosphonate groups aggregate at the water surface, resulting in

more rigid films, and optical spectra indicate that H-aggregates of AO are already present in the

chloroform spreading solutions, confirming this aggregation. The rigidity of the film is also








apparent during film deposition, as discussed below. In the case of the Langmuir monolayers,

the rigidity of the film, resulting from aggregation of the molecules, precludes accurate

measurement of the surface pressure using the Wilhelmy plate method. In some cases, the

Wilhelmy plate can be observed to drift. Based on the pressure vs. area isotherm alone, the exact

state of the BO and AO monolayers at the air/water interface cannot be determined. However,

from studies of transferred films, which are described below, close-packed Langmuir monolayers

are present at a reasonable MMA, similar to those observed for B4 and A4.

Studies of the pressure vs. area isotherms for the biphenyl phosphonic acids as a function

of subphase pH show that at higher pH, typically greater than 7, the slopes of the solid

compression region become flatter. Deuteration of the fourteen-carbon segments in B4 does not

affect the behavior of monolayer isotherms, and this is similar to the behavior identified for

dP4.124



Deposition Procedure



A three-step deposition procedure was utilized for preparing the zirconium

organophosphonate films described in this Chapter. This stepwise deposition method was

developed previously for preparing LB bilayers of zirconium octadecylphosphonate.113,114 As

illustrated in Figure 2-4, the first step involves creation of an LB monolayer by dipping an

octadecyltrichlorosilane (OTS)-coated substrate down through a compressed monolayer on a

pure water subphase into a vial sitting in the dipping well of the trough. We refer to this layer

deposited on the downstroke as the "template" layer. The Langmuir monolayer is then

decompressed, and the vial containing the template-coated substrate is removed from the trough.

In the second step ZrOCI2 is added to the vial containing the substrate to bring the Zr ion

concentration in the vial to 5 mM. These conditions permit zirconium binding to the phosphonic

acid, and after 20 minutes the substrate containing the zirconated template layer is removed from

the solution and rinsed with pure water. The zirconated template is a stable film, and








information regarding its organization and structure can be obtained. Without zirconation,

however, the template monolayer is metastable, and characterization cannot be performed. This

substrate is next returned to the trough, which is filled with a fresh subphase of pure water. For

the final step, a new Langmuir monolayer is compressed at the air-water interface, and a new LB

monolayer is deposited as the substrate is drawn upward through the film. The layer deposited

onto the zirconated template is referred to as the "capping" layer. This capping layer can also be

individually characterized. Multilayer assemblies can be prepared by repeating this three-step

procedure.

By exploiting the versatility of this deposition procedure, particularly the ability to

prepare bilayers where the template layer is different from the capping layer, a variety of Y-type

zirconium organophosphonate LB films were generated. Transfer ratios, calculated from

comparing the area of the monolayer removed from the water surface to the area of the substrate

covered by the monolayer film, were 1.1 + 0.15 in each case, indicating that one monolayer was

deposited in each of the steps 1 and 3. For depositions, all LB films were compressed with a

linear compression rate of 8 mN/m/min and with maximum barrier speeds of 20 mm/min.

Typically 100-350 .L of a 0.3 mg/mL solution was spread on the water surface for each

experiment.

In addition to using OPA as a template layer,1 13,'114 template layers can be formed with

B4 and A4. However, despite several attempts under various conditions, quality template layers

of BO and AO monolayers could not be deposited. This difference in behavior indicates that the

position of the aryl group along the aliphatic chain plays a significant role in the processibility of

these Langmuir monolayers. Differences between the molecules with the four-carbon alkyl

tether (B4, A4) and the arylphosphonates (BO, AO) were also seen in the pressure vs. area

isotherms, where it was observed that the BO and AO molecules tended to aggregate on the water

surface. Aggregation of the organic functionalities when they are adjacent to the phosphonate

head groups not only affects the behavior of the film on the water surface, but also appears to

cause difficulties in the transfer of these films. In contrast, the four-carbon tethers in B4 and in








A4 separate the aryl groups from the phosphonate head groups, leading to a less rigid, more

processible film. The four-carbon tethers allow the two sections of the molecules to organize

relatively independently of one another, separating the polar headgroups from the constraints of

the aromatic groups' preferred packing scheme. This flexibility of the headgroup appears to lead

to well-behaved isotherms and to successful downstroke depositions of B4 and A4 monolayers.

Similar results were observed for the deposition of the phenyl films described previously, where

P4 was successfully transferred as a template layer while the phenylphosphonate P0 could not be

deposited on the downstroke of the deposition. 124

Although quality template layers of BO and AO could not be formed, these films, along

with B4 and A4, were successfully deposited as capping layers. Here, the position of the organic

moiety along the alkyl chain has less influence on the film processibility. Transfer of the

capping layers is aided by the affinity of the phosphonate groups for the zirconium ions on the

substrate. The strength of this interaction is the driving force for the deposition of the capping

monolayers, and it overcomes any rigidity or disorganization of the monolayer on the water

surface. Alternating-layer films were formed by transferring BO, B4, AO, and A4 onto OPA

template layers. In addition, symmetric bilayer films of B4 and A4 were prepared by

transferring B4 and A4 capping layers onto the appropriate template layers.



X-ray Photoelectron Spectroscopy



From XPS analyses, the elements present in the films, along with their relative ratios,

can be determined. In this experiment, monochromatic X-rays bombard the film sample, causing

electrons to be ejected from core orbitals.154 A detector measures the kinetic energy with which

these electrons escape from the film, and the binding energy of the electrons can be calculated

from the relation KE = hv BE e, where e is the charge of the electron, + is the work function,

and eo is defined as the minimum energy required to eject an electron from the solid into a

vacuum. These binding energies are then correlated to orbital energies according to Koopman's








theory. Based on the characteristic binding energies for each element, a plot of binding energy

vs. counts of electrons can be used to determine the elemental composition of each film. For

these zirconium organophosphonate films, XPS analyses show that C, 0, P, and Zr are the

elements present in each of the bilayer samples, and N signals are observed in the azobenzene

materials. Signals due to Si also appear and can be attributed to the silicon wafer substrates onto

which the films are deposited.

Quantitative analysis of XPS results is more involved. The experimentally-determined

relative intensities are found from the integrated areas of the peaks corresponding to the

particular elements of interest. These values are normally corrected internally with atomic

sensitivity factors.155 To obtain calculated relative intensities, the kinetic energies and the mean

free paths of the escaping photoelectrons through the organic film must be considered.156 The

intensity of the XPS signal for an element A is given by

I = (f)exp(-dm/(X.msinO)) (2-1)

where FI is the atomic sensitivity factor, dm is the overlayer thickness of the material through

which the electron is travelling, Xm is the inelastic mean free path of the electron through

material m, and 0 is the take-off angle with respect to the surface parallel.157'158 The equation

for determining the intensity describes the attenuation of the photoelectron by the organic film.

The overlayer thickness corresponds to the distance of the element in the sample and can be

estimated from known molecular coordinates. The relative concentration of element A is

calculated by ratioing the intensity signal for element A to the sum over all of the intensities for

all of the elements of interest.

The relative percentages of Zr and P observed for each sample are listed in Table 2-1.

The percentages listed in Table 2-1 have not been corrected for differences in photoelectron

escape depths.156'158 Because the photoelectron energies of the Zr3d (185.9 eV, 183.6 eV) and

P2p (134.3 eV) are similar and the Zr and P atoms are at nearly the same depth in the films,
corrections for photoelectron escape depths are less than 1% of the observed intensities. Within

the uncertainties of the XPS method (3%), the observed Zr:P ratio in the zirconated templates








of OPA, B4, and A4 is 1:1, indicating that after zirconation, one zirconium ion is bound for each

phosphonate group in the template layer. For the bilayer samples, Zr:P ratios are all near 1:2,

indicating complete transfer of the capping layer. The 1:2 ratio is consistent with the Zr:P ratios

and the ionic charges present in solid-state zirconium organophosphonates.


Table 2-1. Interlayer Spacingsa and Relative Intensitiesb of the Zirconium and Phosphorus XPS
Signals of the Zirconated Template LB Monolayer and LB Bilayer Films.

Zr ( 3%) P ( 3%) Interlayer Interlayer
Zr3d P2p spacing, spacing,
experimental calculated
(2A) (2A)

Zirconated Templates:
OPA Zr 48 52
B4 Zr 46 54
A4 Zr 53 47

Bilayer Samples:
OPA Zr BO 34 66 57 58
OPA Zr B4 32 68 54 54-56
B4 Zr-B4 32 68 62 61-63
OPA Zr AO 31 69 58 58
OPA Zr A4 33 67 54 NA
A4 Zr A4 32 68 63 NA

a X-ray samples consisted of ten bilayers of deposited films. b Relative intensity percentages for
zirconium and phosphorus were calculated by integrating areas of the corresponding peaks after
correcting for the instrument and atomic sensitivity factors. c The Zr3d and P2p peaks were used
for this calculation. d Calculated d-spacings were determined as described in the text. For those
films having a four-carbon tether, a range is reported since the orientation of this four-carbon
chain is not known. The smaller value is obtained when the four-carbon chain is allowed to tilt
at the same angle as the fourteen-carbon chain, while the larger value results if the four-carbon
chain is oriented perpendicular to the surface. A van der Waals distance of 5 A was used for all
calculations.



In bilayer samples where OPA is the template layer, there is a mismatch between the

MMA of the molecules in the template and capping layers because of the larger aryl group in the

organic tails of the capping layer. The MMA of OPA in a monolayer film is 24 A2, while the

MMA in transferred monolayers of BO, AO, B4, and A4 is 27 + 2 A2 (note that the MMA during








transfer of Langmuir monolayers is greater than the MMA at the collapse point, which was

referred to earlier during the discussion of the pressure vs. MMA isotherms). The incommensurate

spacing between the capping layer and the zirconated template, resulting from the different sizes of

the molecules, leads to expected values of 34.6% Zr and 65.4% P, or a Zr:P ratio of 1:1.9 for the

alternating-layer films. The observed XPS ratios are consistent with the expected percentages,

although we cannot actually observe that the phosphonate coverages are incommensurate because

of the magnitude of the uncertainty in elemental composition when determined by XPS.



X-ray Diffraction



The layered nature of the films was established by X-ray diffraction. Interlayer spacings

were determined from samples containing ten bilayers of deposited materials. On average three

or four orders of 001 reflections were observed for each sample, and the interlayer spacings for

each film, determined from the 001 peaks, are reported in Table 2-1. In general, the layers

containing the larger organic groups are of comparable thicknesses, which suggest that the

organization between the biphenyl and the azobenzene films differs since larger thicknesses

would be expected for the azobenzene films given the increased length of the chromophore.

Interestingly, even though the BO, B4 and AO, A4 pairs have the same size (i.e., BO contains the

same number of methylene groups as B4 and should be the same size), the OPA-Zr-BO and

OPA-Zr-AO layers are slightly thicker than the corresponding OPA-Zr-B4 and OPA-Zr-A4 films.

The different layer thicknesses reflect different modes of molecular packing. The arrangement

of molecules within the transferred layers is discussed below after considering the results of the

FTIR analyses.








Attenuated Total Reflectance Infrared Spectroscopy



Total internal reflection occurs within a material when the angle of incidence exceeds a

critical value, which is the angle for which the refracted ray emerges tangent to the surface.159

For total internal reflection to be observed, Snell's law states that the index of refraction of the

second medium must be less than that of the first medium.160 This principle was applied to

infrared spectroscopy independently by Harrick and Fahrenfort in the 1960s, leading to ATR

spectroscopy (or internal reflection spectroscopy (IRS)).161'162 This characterization method

determines molecular absorption on a surface and relies on the total internal reflection of the

radiation throughout an internal reflection element (IRE). In a typical experiment for studying

these zirconium phosphonate LB films, LB monolayers or bilayers are deposited onto a

parallelogram-shaped IRE (10 mm x 3 mm x 50 mm), normally of germanium or silicon. The

IRE is placed in the sample compartment of the infrared instrument, and the infrared beam enters

the IRE at a 45* angle. Entrance of the crystal face from this angle causes the beam to be totally

internally reflected within the crystal, resulting in the formation of an evanescent wave that

decays exponentially into the sample.159 Spectroscopic sampling of the surface occurs through

this evanescent wave via its three electric field vectors that interact with the sample. Because

several parts of the film are sampled during the reflection, the signal-to-noise ratio in the

resulting spectrum is enhanced. This technique allows for the convenient analysis of a small

amount of material, even a monolayer of molecules.

To investigate the organization of the organophosphonate groups in samples shown in

Figure 2-3, ATR-FTIR31,163,164 spectra of the zirconated template monolayers and of the

subsequent capping monolayers were obtained. For these studies, ATR-FTIR scans were

acquired after the second and final steps of the deposition procedure. Ratioing to the appropriate

background produced spectra of the individual template monolayers and capping monolayers.

Information regarding the arrangement of the aryl moieties was obtained through analysis of

spectra of multilayer samples.








Template layers. The template layers of OPA display the organized structure necessary

for constructing stable, well-ordered multilayer films. 13-115 Successful transfers of B4 and A4

on the deposition downstroke result in new template layers that may be compared with the

template layer of OPA. Figure 2-9 compares ATR-FTIR spectra from 2700 to 3100 cm-1 of

zirconated template monolayers of OPA, B4, and A4. In all spectra, three C-H stretching bands

are resolved corresponding to the asymmetric methyl stretch (va(CH3)) at 2953 cm'1, the

asymmetric methylene stretch (va(CH2)) at 2918 cm'1, and the symmetric methylene stretch

(vs(CH2)) at 2850 cm-1. These modes are commonly used to assess the conformational order

and the extent of organization of the aliphatic chains. In particular, the frequency of the

asymmetric methylene stretch reflects the conformational order of the alkyl chains,31,164',165 and

its fwhm is a measure of the degree to which the alkyl chains are close-packed.31,163 For an all-

trans conformation of the alkyl chains in a crystalline solid of OPA, Va(CH2) occurs near 2918

cm-1, and this value increases in energy to 2928 cm"1 in a liquid-like assembly where the alkyl

chains possess a large number of gauche bonds.44 The fwhm is a measure of the orientational

order in the film, and typical values of 16 cm"1 have been observed for a close-packed

monolayer of OTS, whereas a randomly oriented film can result in a fwhm for va(CH2) of

greater than 26 cm' 1.44 In the spectra shown in Figure 2-9, a peak position of 2918 cm'1 for the

asymmetric methylene vibration indicates that all three template layers possess alkyl chains

arranged in an all-trans conformation. For the OPA template, where the alkyl chains have

previously been shown to be close-packed, the fwhm of va(CH2) is 20 cm'-1.113 In contrast, the

fwhm values for B4 and A4 are 29 cm"1. The bands are broadened in the B4 and A4 monolayer

spectra because they contain contributions from both the fourteen-carbon and four-carbon

segments. A similar analysis yielded a fwhm value for the P4 template of 27 cm-1.124

To differentiate the signals originating from the fourteen-carbon and four-carbon

segments in B4, ATR-FTIR studies of dB4, where the fourteen-carbon chain was perdeuterated,

were performed. To determine how the C-D stretching modes shift as a function of the state of




























Wavenumbers (cm')

Figure 2-9. ATR-FTIR spectra of zirconated monolayer templates of OPA, B4, and A4. Band
assignments are discussed in the text.


the molecule, spectra were first taken of the deuterated sample in a CHCI3 solution and as a solid

(KBr pellet). Spectra showing the C-D stretches of dB4 are compared in Figure 2-10. The

solution sample of dB4 has the asymmetric methylene stretch (va(CD2)) at 2198 cm"1 and the

symmetric methylene stretch (vs(CD2)) at 2096 cm" 1. This is in contrast to the va(CD2) and

vs(CD2) positions in the spectra of the solids at 2193 cm"1 and 2089 cm"1, respectively. The

asymmetric CD2 stretch also has a large fwhm of 35 cm"1 in the solution spectra as opposed to

the 20 cm"1 value for that of the solid. Figure 2-10 also shows the C-D stretch region of a

template monolayer of dB4 where the va(CD2) and vs(CD2) bands appear at 2195 cm"1 and

2090 cm 1, respectively. The bands are narrow, with a fwhm of 20 cm" 1, and appear essentially

identical to the solid-state KBr spectrum of dB4 shown in Figure 2-10. This result indicates that

the fourteen-carbon alkyl chains in the template of dB4 are well-organized and are arranged in an

all-trans conformation. Organized hydrocarbon tails are also observed for the template layer of

dP4,124 suggesting that the broadened va(CH2) stretch observed in the spectrum of the non-







deuterated B4 template layer (Figure 2-9) does not result from any disorder in the fourteen-
carbon segment. Although a perdeuterated sample of A4 was not prepared, it is likely that the
fourteen-carbon segment in this molecule is also well-ordered based on its analogous behavior to
B4 on the water surface and during transfer.


v.(CD2)
v.(CD2)

-^"^ ~-^ \^ Liquid
J(a)
U._ Solid





(c) dB4 Fillm

2300 2200 2100 2000 1900
Wavenumbers ( cm-')
Figure 2-10. FTIR spectra of(a) a chloroform solution of dB4 and (b) a KBr pellet of dB4 and an
ATR-FTIR spectrum of (c) dB4 as a template layer. Band assignments are discussed in the text.
The spectra are scaled in intensity for comparison of band shapes and frequencies.


Inspection of the C-H modes resulting from the four-carbon segment in monolayer
spectra of the dB4 template reveals that these modes closely resembles those C-H stretching
modes observed in a solid-state spectrum of butylphosphonic acid, where individual CH2 units
can be distinguished. The four-carbon segment, therefore, is responsible for the broad C-H
stretching modes seen in undeuterated templates of B4 and A4. However, because of their
disordered state, the organization of the four-carbon chains in templates of B4 and A4 cannot be
determined.








The tilt angles of the alkyl chains with respect to the surface normal in the template layer

of dB4, as well as in OPA, were determined from linear dichroism spectroscopy.44'159,166'167

From ratios of the absorbance intensity of a given IR mode with light polarized parallel and

perpendicular to the film surface, a dichroic ratio, defined as

D = (Ax + Az)/ Ay, (2-2)

where (Ax + Az) is the absorbance with p-polarized light (light polarized parallel to the plane of

incidence) and Ay is the absorbance with s-polarized light (light polarized perpendicular to the

plane of incidence), can be calculated. This ratio is used in the analysis of molecular orientation.

The model used for determining the tilt angles of the various transition dipole moments within

the films is based on the assumption that the transition dipole moments have uniaxial symmetry

with respect to the surface normal.44'159 From the electric field vectors of the evanescent wave
(Ex, Ey, and Ez) and the absorption coefficients, a relationship between the dichroic ratio and the

angle the transition dipole moment makes with the surface normal can be found. For the

methylene vibrations, the CH2 dipole moment is oriented 90' with respect to the alkyl chain

axis.44 By taking the ratio of the absorbance intensities of Va(CH2) and vs(CH2) with p-

polarized light to the intensities with s-polarized light and by noting the relationship between the

CH2 dipole moment and the molecular axis, the angle that the alkyl chains make with respect to

the surface normal was determined. Measured dichroic ratios and calculated tilt angles for the

eighteen-carbon chain in OPA and for the fourteen-carbon chain in the dB4 template are given in

Table 2-2. On average, the tilt angle for the eighteen-carbon segment in the zirconated OPA

template is 30", which correlates well with the tilt required to achieve close-packing of the alkyl

chains given the constraints of the P032- headgroup (24 A2 MMA at deposition as opposed to

20 A2 for the cross-sectional area of the all-trans alkyl chain). For the templates of dB4, the tilt

angle of the fourteen-carbon segments is 44'. The larger alkyl chain tilt angle in dB4 relative to

the OPA template arises from a greater spacing between molecules because of the larger MMA

(27 A2 at transfer) imposed by the aryl group. This result is similar to the previously determined









Table 2-2. Dichroic Ratiosa, D, of IR Modes and the Corresponding Molecular Axisb Tilt
Angles for Zirconated Template Layers.


Template Mode Frequency (cm-1) Dichroic Ratio (D) Tilt Angle (')b
Monolayer

OPA Va(CH2) 2918 1.04+0.02 30+2
vs(CH2) 2850 1.04 + 0.01 30 + 1
dB4 Va(CD2) 2195 NAc NAc
vs(CD2) 2090 1.25 + 0.02 44 + 1
C=C(8a) 1608 3.4+0.2 20 + Id
C C (19a) 1502 3.8+0.2 19 + ld
A4e C=C(8a) 1602 NAf NAf
C C (19a) 1500 2.5 24d4g
a Dichroic ratio, D, is defined as (Ax + Az)/(Ay). b Molecular axes are defined along the C1 -C4
axis for the biphenyl and azobenzene moieties and at 90 to the methylene C-H bonds for the
alkyl chains. c Tilt angles for the perdeuterated fourteen-carbon chains were calculated from the
symmetric methylene stretch only. d Tilt angles for the aryl groups are averaged over the
template and capping layers for the symmetric bilayer films. e Tilt angles for the fourteen-
carbon chains were not determined. f Only mode 19a was used to determine the tilt of the
azobenzene ring. g Tilt angle data obtained from one set of measurements.



tilt angle of 46" for the fourteen-carbon chain in dP4.124 The larger distance between molecules

requires the chains to tilt more to maximize van der Waals interactions. Because of the nature of

the IR signals for the four-carbon segments in the dB4 template, an analysis of their molecular

axis tilt angle is not meaningful.

Capping layers on an OPA template. Although quality template monolayers of BO and

AO could not be transferred, monolayer films of these materials were successfully transferred as

capping layers onto zirconated OPA templates. This behavior has also been demonstrated for

monolayers of P0.124 The organization of the alkyl chains and aryl groups in these capping

monolayers was determined from non-polarized and polarized IR data. Figure 2-11 shows non-

polarized ATR-FTIR spectra of capping monolayers of BO and AO as deposited onto zirconated
OPA templates. In these spectra the asymmetric methylene vibration, va(CH2), occurs at 2918

cm-1, indicating that the eighteen-carbon alkyi chains in both arylphosphonates are arranged in








an all-trans conformation. The fwhm values of the asymmetric methylene vibrations in the

spectra of BO and AO are 16 cm-1, demonstrating that the alkyl chains are close-packed.

Based on the pressure vs. area isotherms shown in Figure 2-8, it was not clear if BO and

AO formed stable Langmuir monolayers. Analysis of the transferred films, however, indicates

that they do. From Figure 2-11 it can be seen that the intensities of the IR bands for the capping

layers of BO and AO are similar to those of the other capping layers. Coupled with the XPS

results that show that a single layer of the phosphonate group is deposited and the X-ray

diffraction that illustrates the layered structure of the alternating-layer films, it is clear that BO

and AO transfer as organized LB monolayers. The Langmuir monolayers of BO and AO at the

air/water interface are too rigid to behave ideally, but they can be transferred onto the zirconated

OPA template layers.


v (CH)


v.(CHI) v,(CH2)
BO


A~ =l 0.005
AO _____ > -\ _____






A4 A_

3100 3000 2900 2800 2700
Wavenumbers (cm"')

Figure 2-11. ATR-FTIR spectra of capping monolayers of BO, AO, B4, and A4 on OPA. Band
assignments are discussed in the text.



The tilt angles of the alkyl chain axis in capping monolayers of BO and AO were
determined from polarized ATR-FTIR experiments. Dichroic ratios for the va(CH2) and








vs(CH2) bands in each film and calculated tilt angles for the alkyl chain molecular axes are

reported in Table 2-3. The measured dichroic ratios, determined from both the asymmetric and

symmetric methylene vibrations, indicate that in BO the alkyl chains tilt an average of 20.5' with

respect to the surface normal, and in AO this value is 30'. These tilt angle values are smaller than

the large tilt angles seen for the alkyl chains in template layers of P4 and B4 (46"124 and 44',

respectively), where the MMA is determined by the size of the aryl groups and where the alkyl

chains must tilt to maximize van der Waals interactions. The smaller tilt angle averages

observed for the BO and A0 layers appear anomalous and suggest that the mode of

intermolecular interaction is different in these films than in the other monolayer template and

capping layers. The relationship between the tilt angles of the alkyl chain axis and the aryl

moiety will be discussed further below after all of the IR data have been presented.

Tilt angles of the biphenoxy and azobenzyloxy groups in capping monolayers of B0 and

AO on OPA were determined from IR modes corresponding to the C-C skeletal deformations of

the aryl groups.44'168-172 The C-C skeletal deformation modes 8a and 19a for para-substituted

benzene rings are typically found in the regions of 1570-1628 cm-1 and 1460-1530 cm-1,

respectively.168 Assuming C2v symmetry for the phenyl moieties in the biphenyl and

azobenzene groups, modes 8a and 19a have their net transition dipole moments located along the

C1 -C4 axis of the aryl group.168 The intensities of these modes in monolayer spectra of BO and

AO are weak, making quantitative analysis of these bands difficult. To enhance the intensity of

these modes, multilayer samples (5-20 bilayers) were used for polarized IR experiments. No

structural differences in the early layers as compared to the top layers were observed. Figure 2-

12 shows non-polarized ATR-FTIR spectra of a ten-bilayer sample of B0 on OPA and of a ten-

bilayer sample of AO on OPA. The insets in the figure show the C-C skeletal deformation modes

of 8a and 19a occurring at 1608 cm-1 and 1495 cm"1, respectively, for the BO multilayer sample

and occurring at 1604 cm"1 and 1502 cm-1, respectively, for the corresponding A0 film. Since

no bands originating from the zirconated OPA template overlapped with modes 8a or 19a,

multilayer samples were used for the measurement of the dichroic ratios for these IR modes.








The peak at 1467 cm-1 is the alkyl C-H bend mode that contains contributions from both the

template and capping monolayers, but it does not distort the aryl modes.


Table 2.3. Dichroic Ratiosa, D, of IR Modes and the Corresponding Molecular Axisb Tilt
Angles for Capping Layers Deposited onto Zirconated OPA Templates.


Capping Mode Frequency (cm-1) Dichroic Ratio (D) Tilt Angle (*)b
Monolayer

BO Va(CH2) 2918 0.97+0.01 18+2
vs (CH2) 2850 0.99+ 0.02 23 +2
C = C (8a) 1608 4.0+0.1 18+1
C = C (19a) 1495 NAc NAc
AO Va(CH2) 2918 1.05+0.01 32 +2
Vs (CH2) 2850 1.03+ 0.03 28+ 3
C = C (8a) 1604 NAd NAd
C = C (19a) 1502 2.4+0.2 26 +1
dB4 Va (CD2) 2195 NAe NAe
vs (CD2) 2090 1.18+0.04 40+3
C =C (8a) 1608 4.1+0.4 18+1
C C (19a) 1501 3.9+0.3 19+1
A4f C = C (8a) 1602 NAd NAd
C C (19a) 1500 2.4+0.1 26+1
a Dichroic ratio, D, is defined as (Ax + Az)/(Ay). b Molecular axes are defined along the C 1-C4
axis for the biphenyl and azobenzene moieties and at 90 to the methylene C-H bonds for the
alkyl chains, c Only mode 8a was used to determine the tilt of the biphenyl moiety, d Only
mode 19a was used to determine the tilt of the azobenzene moiety, e Tilt angles for the
perdeuterated fourteen-carbon chains were calculated from the symmetric methylene vibration
only. f Tilt angles for the fourteen-carbon chains were not determined.



Figure 2-13 shows the ATR-FTIR spectra taken in two polarizations of a fifteen-bilayer

sample of BO on OPA demonstrating how the intensities of modes 8a and 19a change as a

function of polarization. The measured dichroic ratios and calculated tilt moieties are

summarized in Table 2-3 and were determined from samples consisting of five, ten, and fifteen

bilayers of BO on OPA and of AO on OPA. The measured values did not change as the number




























3200 2800 2400 2000 1600 1200 800
Wavenumbers (cm')
Figure 2-12. ATR-FTIR often bilayers of (a) BO on OPA and (b) AO on OPA. Insets show an
enlarged view of the region containing aryl C-C skeletal deformation modes. Band assignments
are discussed in the text.




90 polarized C-H Bend
--- 00 polarized

9 A =0.005

8aa
8a A





1650 16 00 1550 1500 1450 1400 1350
Wavenumbers (cm')

Figure 2-13. Polarized ATR-FTIR spectra of fifteen bilayers of BO on an OPA template, taken at
90" and 0" polarization showing the aryl C-C skeletal deformation modes. Superposition of the
spectra shows differences in absorbance intensities for the two polarizations.








of bilayers was increased, and the numbers reported in Table 2-3 are an average of the samples

with different numbers of bilayers. Since the transition dipole moment of both skeletal modes is

oriented along the same direction, either or both of these modes can be used to calculate the tilt

angles of the aryl moieties. For BO on OPA, mode 8a was used to determine the tilt angle of 180

for the biphenyl group. The long axis of the azobenzene moiety was found to be tilted 26" from

the surface normal in films of AO on OPA. This value was an average over mode 19a alone.

For capping layers of B4 and A4 on OPA, IR spectra revealing the C-H stretches are

shown in Figure 2-11. The asymmetric methylene stretch is broadened in each spectrum due to

overlapping contributions from both the four-carbon and fourteen-carbon chains. The peak

position of the va(CH2) at 2918 cm-1 in both cases indicates that there are alkyl chain segments

in the B4 and A4 capping monolayers that possess an all-trans conformation. More information

can be extracted from these films by looking at the capping monolayer of dB4, where the

fourteen-carbon and four-carbon segments are separated in the IR spectra. The C-D stretch

region of a dB4 capping monolayer on an OPA template is identical to the C-D stretch regions of

the dB4 template, shown in Figure 2-10. In this IR spectrum, the C-D peak positions are nearly

identical to those of its solid KBr spectrum, with va(CD2) and vs(CD2) appearing at 2195 cm-1

and 2090 cm-1, respectively. These positions indicate that the fourteen-carbon alkyl chains are

in an all-trans conformation. The narrow fwhm value for the asymmetric methylene vibration of

20 cm- 1 suggests that the long alkyl chains are close-packed in the films. Table 2-3 reports the

measured dichroic ratios and calculated tilt angles for the fourteen-carbon alkyl chains in dB4.

From tilt angle analysis of the symmetric methylene vibration, the fourteen-carbon segments tilt

an average of 40' for dB4. This is similar to the tilt angle determined for the dP4 monolayer on

OPA of 37.124

The tilts of the biphenyl and azobenzyl moieties were determined from five, ten, and

fifteen bilayers of dB4 on OPA and A4 on OPA. Figure 2-14 shows non-polarized ATR-FTIR

spectra of a ten-bilayer sample of dB4 on OPA and of a ten-bilayer sample of A4 on OPA. The

insets in Figure 2-14 show the C-C skeletal deformations with modes 8a and 19a labeled for dB4








at 1608 cm"1 and 1501 cm-1, respectively, and labeled for A4 at 1602 cm'1 and 1500 cm-1,

respectively. For dB4 on OPA, both modes were used to determine the tilt from the surface

normal of 18.5* for the biphenyl group, while mode 19a was used for finding the 26" tilt average

of the azobenzene moiety in the capping layer of A4 on OPA. The reported tilt angles (Table 2-

3) are an average of all the samples studied and were found not to change as the number of

bilayers changed.


Wavenumbers (cm"')


Figure 2-14. ATR-FTIR spectra of ten bilayers of (a) dB4 on OPA and (b) A4 on OPA. Insets
show an enlarged view of the region containing the aryl C-C skeletal deformation modes. Band
assignments are discussed in the text.



Capping layers in symmetric films. Symmetric bilayers of B4 on a B4 template and of

A4 on an A4 template were also prepared. Again the organization of the different alkyl chain

segments was analyzed by studying the partially deuterated biphenyl molecule. Tilt angles of the

fourteen-carbon segments in capping layers of dB4 in the symmetric bilayers are reported in

Table 2-4, along with the tilt angles of the aryl groups in the symmetric bilayers of dB4 and A4.

However, for the symmetric films it was not possible to distinguish the aryl moieties in the








templates from those in the capping layers, and the aryl tilt angles listed in Tables 2-2 and 2-4

for these bilayers are an average over both the template and capping layers. Polarized IR

analysis of both the 8a and 19a modes for the dB4 symmetric films yielded a tilt for the biphenyl

group of 19.5". The tilt for the azobenzene ring in the symmetric A4 film is 24', averaged from

mode 19a.


Table 2-4. Dichroic Ratiosa, D, of IR Modes and the Corresponding Molecular Axisb Tilt
Angles for Capping Layers of the B4 and A4 Bilayer Samples.


Capping Monolayer Mode Frequency (cm-1) Dichroic Ratio (D) Tilt Angle (')b
(Symmetric)

dB4 on B4 Va(CH2) 2195 NAc NAc
vs(CH2) 2090 1.17 + 0.01 40 + 1
C C (8a) 1608 3.4+0.2 20+ ld
C C (19a) 1502 3.8+0.2 19+ ld
A4onA4e C=C(8a) 1602 NAf NAf
C = C (19a) 1500 2.5 24dg
a Dichroic Ratio, D, is defined as (Ax + Az)/(Ay). b Molecular axes are defined along the C 1-C4
axis for the biphenyl and azobenzene moieties and at 90' to the methylene C-H bonds for the
alkyl chains, c Tilt angles for the perdeuterated fourteen-carbon chains were calculated from the
symmetric methylene vibration only. d Tilt angles for the aryl groups are averaged over the
template and capping layers for the symmetric bilayer films, e Tilt angles for the fourteen-carbon
chains were not determined. f Only mode 19a was used to determine the tilt of the azobenzene
group, g Tilt angle data obtained from one set of measurements.



There are slight differences between the organization of the dB4 capping layer in the

symmetric bilayers relative to its organization when deposited onto an OPA template. Since the

deposition conditions for the capping layer are identical on both templates, the organization of

the template must influence the subsequent organization of the capping layer. The largest effect

is seen in the four-carbon segment. Figure 2-15 shows the difference in the C-H stretch modes

between capping layers of dB4 on an OPA template and a dB4 template. Because the material is

deuterated, the C-H signals in the spectra are originating from only the four-carbon segments.























3050 3000 2950 2900 2850 2800 2750
Wavenumbers ( cm" ')

Figure 2-15. ATR-FTIR spectrum of a capping monolayer of dB4 on a dB4 template
superimposed over an ATR-FTIR spectrum of a capping monolayer of dB4 on an OPA template.
The peak at 2953 cm-1 in the film of dB4 on OPA originates from the methylene unit adjacent to
the phosphonate group.


The va(CH2) band is much narrower for the capping layer on the OPA template than on a dB4

template suggesting a more uniform arrangement in the four-carbon segment in the alternating

layer film. As discussed above, the four-carbon chains in the templates of dB4, B4, and A4 are

randomly ordered. Disorder among the phosphonate head groups in the template directly affects

the order in the zirconium layer. When the capping layer is deposited onto an organized

zirconium phosphonate surface, as in the zirconated OPA template, the arrangement of the four-

carbon segment is more uniform than when the same capping layer is deposited onto the less-

organized zirconium phosphonate surface provided by the B4 and A4 templates. The more

uniform zirconium phosphonate surface of the zirconated OPA template leads to a better-

organized capping layer even though the B4 and A4 capping layers are incommensurate with the

OPA template layers.

Because the zirconium/phosphonate binding interaction is so strong, the inorganic layer

is not expected to be highly crystalline (the crystallinity of solid-state zirconium phosphonates

and phosphates is generally quite poor)58'59,64 so epitaxy between the capping and template








layers is not necessary for good film transfer. The orientation and intermolecular packing of the

aryl and fourteen-carbon segments in dB4 show only slight differences when transferred onto

both templates, indicating that these segments are less influenced by the organization of the

zirconated surface. The four-carbon segment buffers the rest of the molecule from the surface,

and the packing of the aryl and fourteen-carbon chain groups is determined by intermolecular

forces and not by interactions with the surface. Similar behavior has been seen for the dP4

molecule,124 and it is expected that analogous observations would result for the packing and

ordering of the separate alkyl segments in films with the A4 amphiphile, although deuterated

studies were not undertaken.

Isomerization in A4 and AO films. Irradiation of a four-bilayer sample of A4 as a

capping layer on OPA with 365 nm light produces observable changes in the ATR-FTIR

spectrum. The post-irradiation spectrum (Figure 2-16) of A4 on an OPA template shows a

marked decrease in the relative intensities of modes 8a and 8b upon conversion to the cis isomer.

The band at 1500 cm-1, which corresponds to the 19a mode, broadens and shifts to higher energy

during this transformation as well. This result is similar to literature studies where Raman

spectroscopy has assigned a new band near 1500 cm-1 corresponding to the -N=N- stretching

mode of the cis isomer.135,172 It is likely that the emergence of a new peak near 1500 cm-1 is

responsible for the observable changes in the spectrum near the 19a mode. The isomerization is

reversible, and following irradiation of the infrared sample with visible light of wavelengths

greater than 440 nm, the fwhm of the 19a mode decreases, and the relative intensities of the 8a

and 8b modes return to their state in the original, as-formed film spectrum. The symmetric

bilayer films of A4 with zirconium show behavior analogous to that for the alternating A4 film.

A similar analysis was performed on three bilayers of an AO capping layer on an OPA template.

The broadening of the 19a mode is again observed, but the intensities of the 8a and 8b modes do

not change, indicating very little, if any, shift in the orientation of the phenyl rings during the

photoirradiation. The changes observed in the infrared are weaker than changes seen in the








optical spectra, and after considering the optical data, an analysis of the infrared results will be

presented.










I A = 0.01









1700 1600 1500 1400 1300
Wavenumbers (cm"')

Figure 2-16. ATR-FTIR spectra of four bilayers of an A4 capping layer on an OPA template (a)
before irradiation at 365 nm, (b) after irradiation at 365 nm, and (c) after the film in (b) has been
irradiated. Mode 19a is observed to broaden after irradiation at 365 nm, and the relative
intensities of modes 8a and 8b change. After irradiation at 440 nm, the observed spectrum in (c)
appears much the same as the initial spectrum in (a). Cis trans isomerization can also be
observed under thermal conditions.



Optical Spectroscopy



In the optical spectrum of ten bilayers of an A4 capping layer on a zirconated OPA

template, Figure 2-17, the it-n* transition of the azobenzene chromophore observed in a

chloroform/ethanol solution of the amphiphile is blue-shifted. This shift to higher energy

indicates that the azobenzene groups are packing as H-aggregates in the films, an arrangement

typical for azobenzenes in LB films.131'135'150 From the magnitude of this shift (50 nm) it is

likely that there is long-range organization in the azobenzene packing.132 The azobenzene units

have also been observed to pack as H-aggregates in five bilayers of the totally symmetric A4








zirconium films, as determined by the similar hypsochromic shift in the x-i* transition (%max =

304 nm). The magnitude of the shift observed upon incorporating the AO amphiphiles into the

zirconium phosphonate films is smaller than what is seen for the A4 films since aggregation is

already present in solution (Figure 2-7). The position of the x-x* transition in the ten bilayer

sample of AO on a zirconated OPA template (294 nm) suggests there is long-range organization

in the azobenzene packing in this film as well.



OPA-Zr-A4, before irradiation
- OPA-Zr-A4, after irradiation


4 c^. n-ir*I
u I^ ii / I .. "- '


R -- OPA-Zr-AO, before irradiation
--- OPA-Zr-AO, after irradiation
7 t-7t*


n-*



300 400 500 600
Wavelength (nm)
Figure 2-17. Optical absorbance spectra of ten bilayers of A4 and AO as capping layers on
zirconated OPA templates before and after irradiation at 365 n. The blue shift of the n-n* band
to near 300 nm indicates H-aggregation of the azobenzene chromophores in the as-formed films.
Band assignments are discussed in the text.



A second x-x* band is observed at 250 nm in the absorbance spectra of each of the

azobenzene films studied. The relative intensities of the two x-x* bands change from the
solution spectra to the LB film spectra. This 250 nm band has its transition moment

perpendicular to the long axis of the chromophore while the transition moment of the lower
energy band is parallel to the azobenzene long axis. The stronger intensity of the 250 nm band,

relative to the 304 nm peak (294 nm in the AO films) in the transferred films, indicates that the

long axes of the chromophores are oriented nearly perpendicular to the substrate.135 This has

been confirmed with the infrared tilt angle analyses discussed above. Shoulders present on the








low-energy side of the 304 nm band (294 nm in AO films) are at the same energy as the 7-n**

transition in the nonaggregated A4 solution spectrum. It is likely that there are areas in the films

in which the azobenzene units are present as isolated monomers or dimers.

Irradiation of the n-n* transition with UV light to effect a trans-cis isomerization

produces an observable change in the optical spectra of both the symmetric and alternating-layer

zirconated A4 films. As can be seen in Figure 2-17, the primary changes occurring after

isomerization are a decrease in the intensity of the shoulder (near 365 nm) and an increase in the

n-n* transition near 450 nm. Unlike in the solution spectrum, the variations in the film spectra

with photoirradiation are weak. It is likely that the photochemical isomerization occurs at the

defect areas and domain boundaries in the films.136 The isomerization in each film is reversible,

and conversion to the trans form occurs with visible light as well as with temperature.

A similar analysis of the AO films as capping layers on zirconated OPA templates

indicates that isomerization occurs to a lesser degree in the AO films. A very weak n-it*

transition appears following irradiation with UV light, as seen in Figure 2-17, suggesting that the

trans-cis isomerization in this film is inefficient. It is expected that the amount of defect areas in

this film are similar to the amount found in the A4 films since the defects are typically a result of

the deposition process. However, because the azobenzene moiety neighbors the phosphonate

head group in AO, it is harder for the rotation to occur given the constraints of the zirconium

phosphonate lattice. In this case, the inherent geometry restrictions account for the inefficient

isomerization in the A0 film. In the A4 materials, trans-cis isomerization occurs to a larger

extent since the four-carbon chains can twist to accommodate the disruption imparted by the

rotation process, thereby allowing it to occur more readily. The optical data is in agreement with

the infrared spectra, where the changes observed in the AO spectrum were much weaker than

those seen in the A4 film spectra.








Structural Analysis



Accumulated data from IR experiments lead to models for the orientations of the aryl

phosphonate molecules within the zirconium phosphonate films. One possible solution that

coordinates the observed tilt angle values with the inherent geometry constraints within the

molecules is to allow the aryl group to twist about its C1-C4 axis. The angles determined from

polarized IR experiments are with respect to the surface normal. The structure shown in Figure

2-18 was generated graphically from a z-matrix representation of BO based on the experimentally

determined tilt angles for the different segments of the molecule.124 Also shown in Figure 2-18

is a representation of the aryl and alkyl group axes as vectors on a coordinate axis. In both cases,
0 is the experimentally determined angle that the C2v axis of the aryl moiety makes with respect

to the z-axis, P3 is the experimentally determined tilt angle of the alkyl chain, y is the angle that

the alkyl chain makes with respect to the aryl C2v axis (determined from the internal structure of

the molecule and 31" is used here), and 4 is the angle of rotation about the C2v axis. The

relationship between these angles is given by the equation124

cos P = cosOcosy sinOsinycos>. (2-3)

As the aryl group is rotated through 0 from 0 to 180, the vector representing the alkyl chain

will sweep out a cone in which the various positions create different angles with respect to the z-

axis. For 0 20 and y 31", a value of0 = 0 gives P3 = 50, while 0 = 180" gives 3 = 10. The

observed P3 fall in between these two extremes, as can be seen in Table 2-5. It should be pointed

out that this description provides only one possible model for the structure. This equation is

based on the assumption that the bond angle of the ether in the films does not differ from that of

an isolated molecule whose ether bond angle was determined from molecular mechanics in

HyperChem. Also, the planes defined by the phenyl ring and the C-O-C bond angle are normal

to one another, thus allowing for no rotation of the aryl C-O bond. Any orientational constraints

imposed by the four-carbon chains were ignored since they appear to be disordered in each case.

Differences in the twist angle of the aryl groups should be tied to different orientations of the






four-carbon segments, or in the cases of BO and AO, different modes of interaction between the
phosphonate headgroup and the zirconium ions. With the present data, details of these
interactions cannot be discerned.






z z 1
;/




Figure 2-18. Vectorial representation of the molecular axes of the aryl and alkyl groups. The
graphical representation of the organization of the aryl group and alkyl chain in BO molecules on
an OPA template was generated from a z-matrix written in HyperChem, where it was
subsequently converted into a Brookhaven Protein Data Bank (PDB) format. A graphical
display of the molecule was achieved using RasMol (references 124 and 173). The projection
was chosen to show the twist of the biphenyl group required to view the measured alkyl chain tilt
angle in the plane of the figure. The dihedral angle between phenyl rings is not represented in
this interpretation.

Based on the analysis described above, the orientation of the arylphosphonates is different
from those members of the "4" series. Unlike in dP4 and dB4, where the long alkyl chain tilts with
respect to the normal in the same direction as the aryl group, in the BO and AO capping layers, the
alkyl chain tilts back toward the normal so that the overall tilt of the alkyi chains is much smaller
(20.5" in BO and 30" in AO vs 36" to 46" in the other films). Since the alkyl chains will tilt to
maximize van der Waals overlap, and the IR analysis indicates that the alkyl chains are indeed
close-packed, these results suggest that the aryl groups are packed more tightly in the BO and AO
films than in any of the other films. The difference in organization of BO and AO in the transferred
films is consistent with the different behavior shown by BO and AO in the pressure vs. area
isotherms at the air/water interface. It appears that aggregates of BO and AO formed at the








air/water interface are preserved upon transfer to the zirconated OPA template. As seen in other

films, the strong zirconium phosphonate bonding gives the capping layer little opportunity to relax

upon transfer under pressure, and the molecular arrangements within the transferred film strongly

resemble the structure of the Langmuir monolayer.

Table 2-5. Twist Angles (() for the Aryl Moieties within the Films


Monolayer p3a Q) b () V (+ 2*)

Template:
OPA 30 NAd NAd
dB4 44 19.5 +59
Capping:
BO 20.5 18 +140
AO 30 26 +115
dB4 (OPA) 40 18.5 +73
dB4 (dB4) 40 19.5 + 76
a P3 is the tilt of the alkyl chain from the surface normal, as determined from polarized IR
experiments. The values reported in this table are the averages from Tables 2-2, 2-3, and 2-4. b 0 is
the tilt of the aryl moiety from the surface normal, as determined from polarized IR experiments.
The values reported in this table are the averages from Tables 2-2, 2-3, and 2-4. c 0 is obtained
from the equation cos3 = cosOcosy sin0cososiny, where y is 31" in all cases, d Values of 0 and 0j
for OPA are not applicable.


The molecular orientations can be correlated with the layer thicknesses determined by X-

ray diffraction. To calculate the length of each molecule, distances of 1.2 A44 were used for the
length of each CH2-CH2 unit on the all-trans alkyl chains, 1.2 A44 for the C(alkyl)-O bond length,

2.8 A44 for the length of the phenyl rings, 1.8 A124 for the C-P bond length, 1.4 A44 for the

C(aryl)-O bond length, 1.2 A153 for the N=N distance, and 1.4 A'53 for the C-N bond length. The

P-Zr-P distance is assumed to be 4.4 A,64 which is the distance observed in crystalline samples of

zirconium phenylphosphonates. A distance of 4-5 A was added to molecule lengths to account for

the average van der Waals gap between adjacent layers.86 The P-Zr-P distance and the van der

Waals interlamellar spacing are the values with the largest uncertainties, since these are distances

determined for the bulk metal phosphonate solids. Calculated thicknesses of 58 + 2 A for BO on








OPA and 58 + 2 A for AO on OPA are in excellent agreement with the measured interlayer

distances (Table 2-1). However, it becomes difficult to extend this approach to films containing

B4 and A4 layers because of the disorder in the four-carbon chains. Since the exact orientation of

the four-carbon segment in any of the films is not known, a maximum (with a tilt of 0 of the four-

carbon segment) and a minimum (with a tilt equal to that of the fourteen-carbon segment)

interlayer spacing in the dB4 films can be calculated. The observed thickness is in agreement with

the calculated value in the B4 case (Table 2-1).



Summary


Alternating-layer zirconium phosphonate LB films have been prepared from the

biphenoxy- and azobenzyloxy-containing organophosphonates BO, AO, B4, and A4, using a

previously developed three-step deposition procedure. In each case, OPA is the template layer.

Using the same procedure, symmetric bilayer films of B4 and A4 were also constructed. In

general, Langmuir monolayers of B4 and A4, where a four-carbon tether separates the aryl group

from the phosphonate head group, were found to be more processible than the BO and AO

analogues, where the aryl groups are adjacent to the head groups. In transferred films, the

organization of the BO and AO molecules is significantly different from the organization of the

molecules in the "4" series, which exhibit similar modes of packing. The different orientation of

the BO and AO molecules is attributed to a high degree of aggregation at the air/water interface,

which is preserved when the film is transferred to a zirconated template layer. A result of the

stepwise deposition method is that the organization of the template layer influences the

organization of the capping layer. Capping layers of B4 and A4 are better organized when

deposited onto OPA templates than when they are part of the symmetric bilayers B4-Zr-B4 and

A4-Zr-A4, respectively. This difference is attributed to a relaxation of the four-carbon segment of

the B4 and A4 template layers, which is maintained after zirconation, providing a less-organized

zirconium phosphonate surface for depositing the capping layer.








Because of the strength of the metal-head group interactions, zirconium phosphonate films

provide a viable approach to the formation of extremely stable LB assemblies. This study

demonstrates that zirconium phosphonate-based LB films can be prepared from groups different

than simple alkylphosphonates. Increasingly sophisticated organophosphonates should lead to

functionalized organic/inorganic metal phosphonate LB films.



Experimental Section


Synthesis



Materials. Unless otherwise indicated, all reagents were purchased from either Aldrich

(Milwaukee, WI) or Fisher Scientific (Pittsburgh, PA) and used as received. All synthetic

reactions were performed under Ar or N2 using glassware dried in an oven at 140"C overnight

unless otherwise specified. Tetrahydrofuran was dried over Na benzophenone ketyl radical and
freshly distilled prior to use. Dichloromethane was dried over P205 and freshly distilled prior to

use. Toluene, triethyl phosphite, and diethyl phosphite were dried and distilled over Na.

Triethylamine and pyridine were dried and distilled over CaH2. The molecules 4-nitrophenyl-

diazotetrafluoroborate (33),174 4-nitrophenylphosphonic acid (34),142 diethyl (4-nitrophenyl)-

phosphonate (35),143 4-(4'-hydroxybutyl)aniline (39),175 and 4-hydroxy-4'-(4"hydroxybutyl)-

azobenzene (40)175 were prepared as previously described.

Instrumentation. All NMR spectra were obtained on a Varian VXR-300 spectrometer
and are referenced to the chemical shifts of the residual solvent resonances (1H: CHC13-

7.26ppm; 13C: CDCI3-77.0ppm). Elemental analyses and mass spectrometry analyses were

performed by the University of Florida Spectroscopic Services laboratory, where high-

resolution mass spectral data were collected on a MAT 95Q, Finnigan MAT (San Jose, CA).

Melting points were obtained on a Thomas Hoover Capillary melting point apparatus and are

uncorrected. UV-vis spectra were obtained on a Hewlett-Packard 8452A diode array








spectrophotometer. IR spectra as KBr pellets were recorded on a Mattson Instruments

(Madison, WI) Research Series-I FTIR spectrometer with a deuterated triglycine sulfate

(DTGS) or a mercury-cadmium-telluride (MCT) detector.

1-Bromo-4-octadecyloxybenzene (9). A mixture of 4-bromophenol (3 g, 0.017 mol),

bromooctadecane (5.7 g, 0.017 mol), and potassium carbonate (7.21 g, 3 eq) in 30 mL acetone

was allowed to reflux overnight. At this time, 75 mL water and 50 mL diethyl ether were added,

forming two layers. The organic layer was collected and washed twice with 50 mL of a 2M
NaOH solution, once with 50 mL water, and dried over Na2S04. The solution was concentrated

in vacuo, and recrystallization from diethyl ether gave the product as a white, waxy solid in 64%
yield, mp 53-54 C; 1H NMR (CDC13) 8 7.35(d, 2H), 6.75(d, 2H), 3.85(t, 2H), 1.78(m, 2H),

1.42(m, 2H) 1.38-1.21(s, 28H), 0.88(t, 3H); 13C NMR (CDCI3) 8 158.2, 132.1, 116.2, 112.5,

68.2, 31.9, 29.7, 29.6, 29.4, 29.2, 22.7, 14.1; HRMS (FAB) found, m/z 426.2355; calcd for

C241H4 IBrO, m/z 426.2321 (M).

Diethyl 4-octadecyloxyphenylphosphonate (10). To a solution of 9 (2.125 g, 5 mmol)

in 70 mL THF at -78 'C was added n-BuLi in hexanes (3.75 mL, 1.5 eq). The mixture was

allowed to stir for 3 h, at which time diethylchlorophosphate (1.45 mL, 2 eq) was added. After 1

h at -78 "C, the mixture was allowed to warm to room temperature, and 50 mL diethyl ether and
50 mL of a saturated NaHC03 solution were added. The organic layer was washed once with 50

mL water, dried over Na2SO4, and concentrated in vacuo. Recrystallization from diethyl ether

afforded the product as a yellowish solid in 35% yield, mp 43-44 "C; 1H NMR (CDCI3) 5 7.72

(dd, 2H), 6.94(dd, 2H), 4.07(m, 4H), 3.86(t, 2H), 1.78(m, 2H), 1.42(m, 2H), 1.30(t, 6H), 1.32-
1.18(s, 28H), 0.86(t, 3H); 13C NMR (CDCI3) 8 162.4, 133.8, 133.6, 120.4, 114.5, 114.3, 68.1,

61.9, 31.9, 29.7, 29.6, 29.3, 29.1, 26.0, 22.7, 16.3, 14.1; HRMS (FAB) found, nm/z 483.3603;
calcd for C28H5204P, m/z 483.3603 (M+).

4-Octadecyloxyphenylphosphonic acid (1). To a solution of 10 (0.266 g, 0.55 mmol)

in 50 mL dichloromethane was added bromotrimethylsilane (1.76 mL, 24 eq). The solution was

allowed to stir for 18 h, at which time 20 mL water was added. After 15 min of stirring, the








product was collected and washed with water, ethanol, and dichloromethane. Recrystallization

from chloroform yielded the white solid in 34%. mp 131-133 "C; 1H NMR
(CDC13/CD3CD2OD) 8 7.58(dd, 2H), 6.77(dd, 2H), 3.84(t, 2H), 1.64(m, 2H), 1.30(m, 2H), 1.24-

1.06(s, 28H), 0.72(t, 3H); IR (KBr, cm-1) 2955, 2935(sh), 2917, 2873, 2850, 2287 (br), 1602,

1572, 1506, 1474, 1463, 1293, 1255, 1181, 1147, 1022, 1010, 949; HRMS (FAB) found, m/z
427.2979; calcd for C24H4404P, m/z 427.2977 (M+); Anal. Calcd for C24H4304P: C, 67.61;

H, 10.09. Found: C, 67.26; H, 10.45.

4-Bromo-4'-octadecyloxybiphenyl (11). A mixture of 4-(4'-bromophenyl)phenol (3.74 g,

0.015 mol), bromooctadecane (3.34 g, 0.01 mol), and potassium carbonate (4.1 g, 3 eq) in 60 mL

acetone was refluxed for 48 h. At this time 40 mL diethyl ether was added, and the organic layer

was washed once with 20 mL water, twice with 50 mL of a 2 M NaOH solution, once with 30 mL
water, dried over Na2SO4, and concentrated in vacuo. The white residue was recrystallized from a

diethyl ether/chloroform mixture to yield the white, waxy solid in 74%. mp 94-95 "C; IH NMR
(CDC13) 5 7.53(d, 2H), 7.48(d, 2H), 7.41(d, 2H), 6.96(d, 2H), 3.98(t, 2H), 1.80(m, 2H), 1.46(m,

2H), 1.40-1.18(s, 28H), 0.88(t, 3H); 13C NMR (CDC13) 8 159.0, 139.8, 132.2, 131.7, 128.2, 127.9,

120.7, 114.9, 68.1, 31.9, 29.7, 29.6, 29.4, 29.3, 26.7, 22.7, 14.1.

Diethyl 4'-octadecyloxybiphenylphosphonate (12). To a mixture of Pd(II) acetate

(0.01 g, 0.05 mmol), triphenylphosphine (0.05 g, 4 eq), diethyl phosphite (0.14 mL, 1.1 mmol),

and triethylamine (0.153 mL, 1.1 mmol) was added 11 (0.5 g, 1 mmol). Toluene (1 mL) was

added as a solvent, and the mixture was allowed to stir at 90 "C for 48 h, at which time 50 mL
diethyl ether was added. The white Et3N-HBr salt was removed by filtration, and the filtrate was

concentrated in vacuo. The residue was subjected to column chromatography on silica, and
elution with diethyl ether gave a white solid in 58% yield (Rf(100% diethyl ether) = 0.29). mp

57-58 "C; 1H NMR (CDC13) 8 7.84(dd, 2H), 7.64(dd, 2H), 7.54(d, 2H), 6.98(d, 2H), 4.13(m,

4H), 3.99(t, 2H), 1.80(m, 2H), 1.46(m, 2H), 1.33(t, 6H), 1.32-1.22(s, 28H), 0.88(t, 3H); 13C
NMR (CDCI3) 8 159.4, 144.8, 144.7, 132.3, 132.1, 132.0, 128.2, 127.2, 126.6, 126.4, 124.7,

114.8, 68.0, 62.0, 61.9, 31.9, 29.6, 29.5, 29.3, 29.2, 26.0, 22.6, 16.4, 16.3, 16.2, 14.0; HRMS








(FAB) found, m/z 559.3916; calcd for C34H5604P, m/z 559.3916 (M+); Anal. Calcd for

C34H5504P: C, 73.12; H, 9.86. Found: C, 73.05; H, 10.16.

4'-Octadecyloxybiphenylphosphonic acid (2). To a solution of 12 (0.25 g, 0.45 mmol)

in 30 mL dichloromethane was added bromotrimethylsilane (1.6 mL, 24 eq), and the solution

was allowed to stir for at least 18 h. At this time, 20 mL water was added, and after stirring for

10 min, the precipitate was collected by filtration and washed with water, ethanol, and

dichloromethane. Recrystallization from a chloroform/ethanol mixture afforded a white solid in

65% yield, mp 209-211 "C; IR (KBr, cm-1) 2955, 2918, 2874, 2851, 2299 (br), 1602, 1528,

1495, 1474, 1395, 1291, 1256, 1209, 1150, 1115, 1028, 949, 814, 652, 575, 525; HRMS (FAB)
found, m/z 503.3267; calcd for C30H4804P, m/z 503.3290 (M+); Anal. Calcd for C30H4804P:

C, 71.71; H, 9.36. Found: C, 71.92; H, 9.71.

Tetradecyloxybenzene (13). A mixture of phenol (2.8 g, 0.03 mol), bromotetradecane

(5.9 mL, 0.02 mol), and potassium carbonate (8.2g, 3 eq) in 60 mL acetone was refluxed

overnight. At this time, 50 mL diethyl ether and 50 mL water were added, forming two layers.

The organic layer was washed twice with 50 mL of a 2M NaOH solution, once with 50 mL
water, dried over Na2SO4, and concentrated in vacuo. Recrystallization of the residue from

diethyl ether yielded the white, waxy solid in 83%. mp 34-35 "C; 1I NMR (CDC13) 8 7.29(m,

2H), 6.26(m, 3H), 3.95(t, 2H), 1.78(m, 2H), 1.45(m, 2H), 1.40-1.18(s, 20H), 0.88(t, 3H); 13C
NMR (CDCI3) 8 159.1, 129.4, 120.4, 114.5, 67.8, 31.9, 29.7, 29.6, 29.4, 29.4, 29.3, 26.1, 22.7,

14.1.

4'-Tetradecyloxy-4-bromobutyrophenone (14). To a solution of 13 (1.5 g, 5 mmol) in

30 mL nitrobenzene was added 4-bromobutyryl chloride (0.90 mL, 1.5 eq). The mixture was
cooled in an ice bath and AIC13 (1.5 g, 2.25 eq) was added in small amounts. The orange

solution was allowed to warm to room temperature and was stirred for 45 min. Ice was added,

and the organic layer was extracted, washed twice with 50 mL of a dilute HC! solution, twice
with 50 mL of a saturated Na2CO3 solution, and dried over MgSO4. The nitrobenzene was

removed via vacuum distillation, and the residue in the distillation flask was recrystallized from








diethyl ether, yielding a pale tan solid in 60%. mp 57-59 "C; 1H NMR (CDCi3) 8 7.95(d, 2H),

6.92(d, 2H), 4.18(t, 2H), 3.54(t, 2H), 3.12(t, 2H), 2.28(m, 2H), 1.80(m, 2H), 1.45(m, 2H), 1.38-
1.18(s, 20), 0.87(t, 3H); 13C NMR (CDCI3) 8 197.2, 163.2, 130.2, 129.5, 114.1, 68.2, 36.1, 33.7,

31.9, 29.6,29.5,29.3, 29.0, 27.1, 25.9, 22.6, 14.1.
4'-Tetradecyloxy-4-bromobutylbenzene (15). To a solution of AICI3 (0.609 g) and

LiAIH4 (0.0879 g) in 10 mL THF at 0 *C was added 14 (0.5 g, 1.14 mmol) dissolved in 10 mL

THF. After warming for 4 h the solution was cooled, and 30 mL of a 2 M HCI solution was
slowly added. The mixture was extracted twice with 50 mL diethyl ether, dried over MgSO4,

and concentrated in vacuo. Recrystallization from methanol afforded the product as white
needles in 56% yield. The product was not further purified. 1H NMR (CDCI3) 8 7.08(d, 2H),

6.80(d, 2H), 3.92(t, 2H), 3.40(t, 2H), 2.57(t, 2H), 1.86(m, 2H), 1.76(m, 4H), 1.45(m, 2H), 1.38-
1.18(s, 20H), 0.87(t, 3H); 13C NMR (CDCI3) 8 157.4, 133.6, 129.2, 127.3, 114.4, 68.0, 34.0,

33.7, 32.2, 31.9, 30.1, 29.7,29.6,29.4,26.1, 22.7, 14.1.

Diethyl 4-(4'-tetradecyloxyphenyl)butylphosphonate (16). Compound 15 (0.5 g, 1.18

mmol) was warmed to 140C in a round-bottomed flask equipped with a distillation head and

receiving flask. At this temperature excess triethyl phosphite (0.67 mL, 3.4 eq) was added, and the

formed EtBr was allowed to distill from solution. The mixture was stirred at this temperature for 3

h, and the triethyl phosphite was then removed in vacuo. Column chromatography of the residue

on silica in 100% diethyl ether removed the starting material. Ethyl acetate was added to elute the
product (Rf(100% diethyl ether) = 0.25) as a yellowish oil in 88% yield. The oil was not further

purified. 1H NMR (CDC13) 8 7.06(d, 2H), 6.80(d, 2H), 4.08(m, 4H), 3.91(t, 2H), 2.57(t, 2H),

1.75(m, 4H), 1.64(m, 4H), 1.43(m, 2H), 1.29(t, 6H), 1.32-1.20(s, 20H), 0.87(t, 3H).
4-(4'-Tetradecyloxyphenyl)butylphosphonic acid (3). To a solution of 16 (0.140 g,

0.29 mmol) in 10 mL dichloromethane was added bromotrimethylsilane (0.9 ml, 24 eq). After

stirring for at least 18 h, 8 mL water was added, and the solution was stirred for an additional 90

min. The solvent was removed in vacuo, and recrystallization of the yellow residue twice from
chloroform yielded a white solid in 27%. mp 103-104 "C; 1H NMR (CDCI3) 8 7.05(d, 2H),








6.80(d, 2H), 3.89(t, 2H), 2.54(t, 2H), 1.74(m, 4H), 1.66(m, 4H), 1.42(m, 2H), 1.32-1.16(s, 20H),

0.87(t, 3H); IR (KBr, cm-1) 3455(br), 2954, 2835(sh), 2918, 2868(sh), 2851, 2293 (br), 1613,

1516, 1397, 1249, 1225, 1177, 1041, 985, 946, 761, 717; HRMS (FAB) found, m/z 427.2988;
calcd for C24H4404P, m/z 427.2977 (M+); Anal. Calcd for C24H4304P: C, 67.61; H, 10.09.

Found: C, 67.50; H, 10.39.

Tetradecoxybiphenyl (17). A solution of 4-phenylphenol (5 g, 0.029 mol),

bromotetradecane (5.75 mL, 0.019 mol), and potassium carbonate (7.87 g, 3 eq) in 100 mL acetone

was refluxed for 48 h. At this time, 70 mL diethyl ether was added, and the organic layer was

washed once with 50 mL water, twice with 50 mL of a 2 M NaOH solution, once with 50 mL
water, dried over Na2SO4, and concentrated in vacuo. Recrystallization from a diethyl

ether/chloroform mixture gave the white, waxy solid in 89% yield, mp 84-85 "C; 1H NMR
(CDCI3) 5 7.57(m, 2H), 7.53(d, 2H), 7.43(t, 2H), 7.31(m, 1H), 6.98(d, 2H), 4.08(t, 2H1), 1.82(m,

2H), 1.49(m, 2H), 1.42-1.24(s, 20H), 0.89(t, 3H); 13C NMR (CDCI3)S 158.7, 140.9, 133.5, 128.6,

128.0, 126.6, 126.5, 114.7, 68.0, 31.9, 29.7, 29.6,29.4,29.4, 29.3, 26.1, 22.7, 14.1.

4'-(4-Tetradecyloxyphenyl)-4-bromobutyrophenone (18). To a solution of 17 (2.2 g, 6

mmol) in 75 mL nitrobenzene was added 4-bromobutyryl chloride (1.0 mL, 1.5 eq). The mixture
was cooled in an ice bath and AICI3 (1.6 g, 2 eq) was added in small amounts. The orange

solution was allowed to warm to room temperature and was stirred for 45 min. At this time ice

was added, and the organic layer was extracted, washed twice with 50 mL of a dilute HCI solution,
twice with 50 mL of a saturated Na2CO3 solution, and dried over MgSO4. The nitrobenzene was

removed via vacuum distillation, and the residue was washed with methanol and then

recrystallized from a chloroform/ether mixture. The product was isolated as a white solid in 18%
yield, mp 114-116 "C; 1H NMR (CDCI3) 8 8.02(d, 2H), 7.65(d, 2H), 7.56(d, 2H), 6.98(d, 2H),

4.00(t, 2H), 3.56(t, 2H), 3.20(t, 2H), 2.32(m, 2H), 1.80(m, 2H), 1.46(m, 2H1), 1.40-1.18(s, 20H),
0.87(t, 3H); 13C NMR (CDCI3) 8 198.3, 159.5, 145.5, 134.7, 131.9, 128.6, 128.3, 126.6, 114.9,

681, 36.5, 33.6, 31.9, 29.6, 29.6,29.4,29.2, 26.9, 26.0, 22.7, 14.1.








4'-(4-Tetradecyloxyphenyl)-4-bromobutylbenzene (19). To a round-bottomed flask

containing zinc (0.42 g, 6.4 mmol) was added mercury(II) chloride (0.043 g, 0.16 mmol), 0.2 mL

HCI, and 5 mL water, and the resulting mixture was allowed to stir for 5 min. After decanting

the aqueous solution from the amalgamated zinc, 2 mL water, 5 mL HCI, 3.5 mL toluene, and 18

(0.515 g, 1 mmol) were added to the zinc, and the mixture was refluxed for at least 24 h. At this

time water was added and the solution was extracted twice with 50 mL diethyl ether. The
organic layer was washed with water and dried over Na2SO4. After removal of the solvent in

vacuo, the resulting solid was recrystallized from a methanol/diethyl ether mixture to yield the
product as a white solid in 68%. mp 68-70 "C; 1H NMR (CDC13) 8 7.49(d, 2H), 7.47(d, 2H),

7.24(d, 2H), 6.95(d, 2H), 3.98(t, 2H), 3.43(t, 2H), 2.66(t, 2H), 1.91(m, 2H), 1.79(m, 4H), 1.46(m,
2H), 1.40-1.18(s, 20H), 0.87(t, 3H); 13C NMR (CDC13) 8 158.5, 140.1, 138.5, 133.3, 128.7,

128.0, 127.9, 126.6, 114.7, 68.0, 34.5, 33.6, 32.2, 31.9, 29.8, 29.7, 29.6, 29.4, 29.3, 26.1, 22.7,

14.1.

Diethyl 4-(4'-tetradecyloxybiphenyl)butylphosphonate (20). Compound 19 (0.64 g,

1.3 mmol) was heated to 140 "C in a round-bottomed flask equipped with a distillation head and

receiving flask. When the temperature stabilized excess triethyl phosphite (0.8 mL, 3.6 eq) was

added, and the formed EtBr was allowed to distill from solution. After stirring for 5 h the excess

triethyl phosphite was removed. Column chromatography of the residue on silica in 100%
diethyl ether yielded the product as a white solid in 82% (Rf (100% diethyl ether) = 0.26). mp

55-57 C; 1H NMR (CDCI3) 8 7.48(d, 2H), 7.45(d, 2H1), 7.20(d, 2H11), 6.94(d, 2H1), 4.08(m, 4H),

3.98(t, 2H), 2.65(t, 2H), 1.78(m, 4H), 1.71(m, 4H), 1.46(m, 2H), 1.30(t, 6H), 1.32-1.20(s, 20H),
0.87(t, 3H); 13C NMR (CDCI3) 8 158.5, 140.3, 138.5, 133.4, 128.7, 127.9, 126.6, 114.7, 68.0,

61.4, 61.4, 35.0, 31.9, 29.6, 29.3, 26.0, 24.6, 22.7, 22.0, 16.4, 14.1.

4-(4'-Tetradecyloxybiphenyl)butylphosphonic acid (4). To a solution of 20 (0.25 g,

0.45 mmol) in 25 mL dichloromethane was added bromotrimethylsilane (1.4 mL, 24 eq). After

stirring for 18 h, 10 mL water was added to the solution, and it was allowed to stir for an

additional 45 min. At this time the solvent was removed in vacua, and recrystallization of the








residue twice from chloroform afforded the product as a white solid in 53% yield, mp 245 "C(d);
1H NMR (CDC13/CD3CD20D) 8 7.41(m, 4H), 7.19(d, 2H), 6.93(d, 2H), 3.98(t, 2H), 2.63(t,

2H), 1.74(m, 8H), 1.46(m, 2H), 1.12-1.05(s, 20H), 0.86(t, 3H); IR (KBr, cm-1) 3427 (br), 2955,

2918, 2872(sh), 2851, 2314 (br), 1609, 1503, 1474, 1396, 1277, 1254, 1213, 1180, 1140, 1038,
1001, 943, 808, 721, 536; HRMS (FAB) found, m/z 503.3297; calcd for C30H4804P, m/z

503.3290 (M+); Anal. Calcd for C30H4704P: C, 71.71; H, 9.36. Found: C, 71.33; H, 9.67.

4'-Methoxy-4-bromobutyrophenone (21). A 3-neck round-bottomed flask equipped
with an addition funnel, a condenser, and a stopper was charged with AICI3 (1.87 g, 1.4 eq). To

this was added 6 mL dichloromethane, and the flask was placed in an ice bath. From the

addition funnel was added a solution of 4-bromobutyryl chloride (2.52 g, 1.4 eq) in 5 mL

dichloromethane over a period of 15 min. A solution of anisole (1.08 g, 0.01 mol) in 3 mL

dichloromethane was then placed in the addition funnel and was added to the cooled acylation

mixture over a period of 30 min. After the addition was complete, the ice bath was removed, and

the mixture continued stirring for an additional 30 min. At this time the mixture was poured into

a beaker containing 25 mL ice and 12 mL HCI and was allowed to stir for 10 min. The organic

layer was collected and the aqueous layer was washed with 30 mL dichloromethane. The
combined organic fractions were washed with 30 mL of a saturated NaHCO3 solution and dried

over MgSO4, and the solvent was removed in vacuo. Column chromatography of the residue on

silica in a 1:1 diethyl ether/pentane mobile phase (Rf(100% diethyl ether) = 0.75) yielded the

product as a liquid in 95%. This liquid was not further purified. 1H NMR (CDCI3) 8 7.97(d,

2H), 6.95(d, 2H), 3.85(s, 3H), 3.53(t, 2H), 3.15(t, 2H), 2.24(m, 2H); 13C NMR (CDCI3) 8 197.4,

163.6,130.3, 129.8,113.7,55.5,36.15,33.7,27.1.

4'-Methoxy-4-bromobutylbenzene (22). To a round-bottomed flask containing zinc (4

g, 0.06 mol) was added mercury(II) chloride (0.4 g, 1.5 mmol), 1.9 mL HCI, and 47.5 mL water,

and the resulting solution was allowed to stir for 5 min. The aqueous solution was then decanted

from the amalgamated zinc, and 19 mL water, 48 mL HCI, 33 mL toluene, and 21 (2.44 g, 9.5

mmol) were added to the zinc. After refluxing for 24 h, water was added, and the resulting








solution was extracted twice with 50 mL diethyl ether. The organic layer was collected, washed
with water, and dried over Na2SO4. Removal of the solvent in vacuo gave 20 as a light yellow

liquid in 76% yield. The oil was not further purified. 1H NMR (CDCI3) 8 7.09(d, 2H), 6.83(d,

2H), 3.79(s, 3H), 3.41(t, 2H), 2.58(t, 2H), 1.88(m, 2H), 1.75(m, 2H); 13C NMR (CDCI3) 8

157.8,133.8,129.2,113.8, 55.2, 34.0, 33.7, 32.2, 30.0.

4'-Hydroxy-4-bromobutylbenzene (23). To a round-bottomed flask charged with 22

(1.77 g, 7.3 mmol) and immersed in an ice bath was added a 1M boron tribromide solution in

dichloromethane (8 mL, 1.1 eq) dropwise from an addition funnel. The resulting solution was

red-brown in color. After stirring overnight, the mixture was added to 100 mL ice at 0OC and

was stirred for an additional 30 min. The solution was extracted twice with 100 mL
dichloromethane, and the combined organic layers were dried over Na2SO4. Evaporation of the

solvent in vacuo gave the crude product, which was purified via column chromatography on
silica. Elution with 100% dichloromethane (Rf(100% dichloromethane) = 0.36) gave the

product as a oil in 81% yield. 1H NMR (CDCI3) 8 7.04(d, 2H11), 6.76(d, 2H), 4.80(s, broad, 1H),

3.42(t, 2H), 2.57(t, 2H), 1.88(m, 2H), 1.75(m, 2H); 13C NMR (CDCI3) 8 153.6, 134.0, 129.4,

115.2, 34.0, 33.7, 32.2, 30.0.

Diethyl 4-(4'-hydroxyphenyl)butylphosphonate (24). Compound 23 (1.35 g, 5.9

mmol) was heated to 140 "C in a 3-neck round-bottomed flask equipped with an addition funnel,

a stopper, and a distillation head and receiving flask. Once the temperature stabilized, triethyl

phosphite (2 mL, 2 eq) was added dropwise from the addition funnel, and the formed EtBr was

allowed to distill from the reaction. The mixture was allowed to stir at 140 "C overnight, at

which time the triethyl phosphite was removed. Column chromatography on silica in 1:1 diethyl
ether/acetone eluted the product (Rf(100% diethyl ether) = 0.14) as a yellowish oil in 94% yield.

This oil was not further purified. IH NMR (CDCI3) 8 8.03(s, IH), 6.96(d, 2H), 6.78(d, 2H),

4.07(m, 4H), 2.51(t, 2H), 1.76(m, 2H), 1.64(m, 4H), 1.28(t, 6H); 13C NMR (CDC13) 8 155.1,

132.6, 129.1, 115.2,61.3,61.5, 34.4, 32.6, 32.3, 26.3, 24.4, 21.9, 21.8, 16.4.








Diethyl 4-(4'-d29-tetradecyloxyphenyl)butylphosphonate (25). A mixture of 24 (0.7

g, 2.4 mmol), 32 (0.5 g, 1.6 mmol), and potassium carbonate (2 g, 7 eq) in 50 mL acetone was

refluxed overnight. At this time 75 mL water and 50 mL diethyl ether were added, forming two

layers. The organic layer was washed twice with 50 mL of a 2 M NaOH solution, once with 50
mL water, and dried over Na2SO4. The solution was concentrated in vacuo, and the crude

product was subjected to column chromatography on silica. Elution of the product with 100%
diethyl ether gave a light yellow oil (Rf (100% diethyl ether) = 0.29) in 59% yield. The oil

solidified in the freezer. 1H NMR (CDCI3) 8 7.05(d, 2H), 6.79(d, 2H), 4.07(m, 4H), 2.55(t, 2H),

1.77(t, 2H), 1.66(m, 4H), 1.30(t, 6H); 13C NMR (CDCI3) 8 157.3, 133.76, 129.2, 114.3, 61.4,

61.3, 34.5, 32.6,32.4, 28.3, 26.5, 24.6, 22.0,22.0, 16.5.
4-(4'-d29-Tetradecyloxyphenyl)butylphosphonic acid (5). To a solution of 25 (0.45 g,

0.88 mmol) in 30 mL dichloromethane was added bromotrimethylsilane (2.8 mL, 24 eq), and the

resulting solution was allowed to stir for 18 h. At this time, 25 mL water was added, and the

mixture was stirred for an additional hour. The mixture was concentrated in vacuo, and

recrystallization of the residue from chloroform afforded the product as a white solid in 50%

yield, mp 105-106 "C; IR (KBr, cm-1) 3097, 3041, 2995 (br), 2969, 2934, 2924, 2909, 2888,

2857,2613 (br), 2193,2158,2089, 1612, 1580, 1514, 1462, 1402,1298,1248,1225,1178,1123,

1090, 1040, 984, 945, 808, 755, 579, 525; HRMS (FAB) found, m/z 455.4718; calcd for

C24H14D2904P, m/z 455.4719 (M); Anal. Calcd for C24H14D2904P: C, 63.30; H, 9.45.

Found: C, 62.92; H, 9.70.

4'-(4-Methoxyphenyl)-4-bromobutyrophenone (26). A 3-neck round-bottomed flask
equipped with an addition funnel, a condenser, and a stopper was charged with AIC13 (1.5 g, 1.1

eq). To this was added 6 mL dichloromethane cautiously, and the flask was placed in an

ice/water bath. From the addition funnel was added a solution of 4-bromobutyryl chloride (2 g,

1.1 eq) in 5 mL dichloromethane over a period of 15 min. A solution of 4-methoxybiphenyl

(1.84 g, 0.01 mol) in 3 mL dichloromethane was placed in the addition funnel and was added to

the cooled acylation mixture over a period of 30 min. After the addition was complete, the ice








bath was removed and the mixture continued stirring for an additional 30 min. At this time the

mixture was poured into a beaker containing 25 mL ice and 12 mL HCI and was allowed to stir

for 10 min. The organic layer was then collected, and the aqueous layer was washed with 30 mL

dichloromethane. The combined organic fractions were washed with 30 mL of a saturated
NaHCO3 solution, dried over MgSO4, and concentrated in vacuo. Recrystallization of the

residue from an ethanol/chloroformn mixture gave the product as a white solid in 64% yield, mp
116-118 C; 1H NMR (CDCI3) 8 8.02(d, 2H), 7.65(d, 2H), 7.58(d, 2H), 7.00(d, 2H), 3.86(s, 3H),

3.57(t, 2H), 3.20(t, 2H), 2.32(m, 2H); 13C NMR (CDCI3) 8 198.1, 159.7, 145.3, 134.6, 131.9,

128.4, 128.1,126.4, 114.2, 55.2, 36.3, 33.5, 26.7.

4'-(4-Methoxyphenyl)-4-bromobutylbenzene (27). To a round-bottomed flask

containing zinc (2.5 g, 0.038 mol) was added mercury(II) chloride (0.25 g, 0.9 mmol), 1.2 mL

HC1I, and 30 mL water, and the resulting solution was allowed to stir for 5 min. The aqueous

solution was then decanted from the amalgamated zinc, and 12 mL water, 30 mL HCI, 21 mL

toluene, and 26 (2.1 g, 6 mmol) were added to the zinc. After refluxing for 24 h, water was

added and the resulting solution was extracted twice with 50 mL diethyl ether. The organic layer
was collected, washed with water, and dried over Na2SO4. The solvent was concentrated in

vacuo, and column chromatography of the residue on silica in 15:1 pentane/diethyl ether gave
the product (Rf(15:l pentane/diethyl ether) = 0.42) as a white solid in 63% yield. This solid was

not further purified. 1H NMR (CDCI3) 8 7.52(d, 2H), 7.48(d, 2H), 7.23(d, 2H), 6.96(d, 2H),

3.85(s, 3H), 3.44(t, 2H), 2.67(t, 2H), 1.92(m, 2H), 1.82(m, 2H); 13C NMR (CDCI3) 8 159.0,

140.2,138.5, 133.6, 128.7, 128.0, 126.7,114.1, 55.3, 34.5, 33.6,32.2,29.8.

4'-(4-Hydroxyphenyl)-4-bromobutylbenzene (28). To a round-bottomed flask charged

with 27 (0.4 g, 1.25 mmol) and immersed in an ice bath was added a 1 M boron tribromide

solution in dichloromethane (1.4 mL, 1.1 eq) dropwise from an addition funnel. The resulting

solution turned red-brown in color. After stirring overnight, the mixture was added to 100 mL

ice at 0 C and was stirred for an additional 30 min. The solution was extracted twice with 100
mL dichloromethane, and the organic layer was collected and dried over Na2SO4. Evaporation








of the solvent in vacuo gave the crude product, which was subjected to column chromatography
on silica. Elution with 100% dichloromethane gave the product (Rf (100% dichloromethane) =

0.29) as a white powder in 73% yield, mp 107-109 "C; 1H NMR (CDCI3) 8 7.46(d, 4H), 7.22(d,

2H), 6.89(d, 2H), 4.80(s, 1H), 3.44(t, 2H), 2.67(t, 2H), 1.92(m, 2H), 1.82(m, 2H); 13C NMR
(CDCI3) 8 154.9,140.3, 138.4, 133.9, 128.8, 128.2,126.7, 115.6,34.5,33.6,32.2,29.8.

Diethyl 4-(4'-hydroxybiphenyl)butylphosphonate (29). Compound 27 (1.2 g, 3.9

mmol) was heated to 140"C in a 3-neck round-bottomed flask equipped with an addition funnel,

a stopper, and a distillation head and receiving flask. Once the temperature stabilized, triethyl

phosphite (2.1 mL, 3 eq) was added dropwise from the addition funnel, and the formed EtBr was

allowed to distill from the reaction. The mixture was allowed to stir at 140 C overnight, at

which time the triethyl phosphite was removed. Column chromatography of the residue on silica
in a 1:1 diethyl ether/acetone mobile phase eluted the product (Rf(100% diethyl ether) = 0.14) as

a yellowish oil in 86% yield. This oil was not further purified. 1H NMR (CDCI3) 8 8.4(s, 1H),

7.43(d, 2H), 7.39(d, 2H), 7.16(d, 2H), 6.93(d, 2H1), 4.09(m, 4H1), 2.62(t, 2H), 1.76(m, 2H),
1.73(m, 4H), 1.29(t, 6H); 13C NMR (CDCI3) 6 156.6, 139.9, 138.7, 132.3, 128.6, 127.9, 127.8,

126.5, 115.7,61.6, 34.9, 32.2, 32.0, 26.3, 24.5, 22.0, 19.7, 17.8, 16.4.
Diethyl 4-(4'-d29-tetradecyloxybiphenyl)butylphosphonate (30). A mixture of 29

(1.0 g, 2.76 mmol), 32 (0.5 g, 1.6 mmol), and potassium carbonate (2 g, 7 eq) in 50 mL acetone

was refluxed overnight. At this time 75 mL water and 50 mL diethyl ether were added, forming

two layers. The organic layer was washed twice with 50 mL ofa 2 M NaOH solution, once with
50 mL water, and dried over Na2SO4. Evaporation of the solvent in vacuo gave the product as a

white solid in 43% yield. This solid was not further purified. 1H NMR (CDCI3) 8 7.48(d, 2H),

7.45(d, 2H), 7.20(d, 2H), 6.94(d, 2H), 4.05(m, 4H1), 2.62(t, 2H), 1.75(m, 2H1), 1.65(m, 4H),
1.26(t, 6H); 13C NMR (CDCI3) 8 158.3, 140.1, 138.3, 133.1, 128.5, 127.7, 126.4, 114.5, 61.2,

61.2, 34.8, 32.2, 31.9, 28.1, 26.3, 24.4, 21.9, 21.8, 16.3.
4-(4'-d29-Tetradecyloxybiphenyl)butylphosphonic acid (6). To a solution of 30 (0.6

g, 1 mmol) in 30 mL dichloromethane was added bromotrimethylsilane (3.2 mL, 24 eq), and the








resulting solution was allowed to stir for 18 h. At this time 25 mL water was added, and the

mixture was stirred for an additional hour. The mixture was concentrated in vacuo, and

recrystallization of the residue three times from chloroform afforded the product as a white solid

in 17% yield, mp 247 "C(d); IR (KBr, cm-1) 3043 (sh), 3030, 2955 (br), 2932, 2915, 2887,

2862, 2853, 2193, 2158, 2089, 1609, 1582, 1530, 1501, 1462, 1404, 1279, 1244, 1215, 1182,

1138, 1107, 1088, 1038, 995, 941, 812, 756, 721, 532; HRMS (FAB) found, m/z 531.5; calcd for

C30H18D2904P, m/z 531.5032 (M); Anal. Calcd for C30HIsD2904P: C, 67.80; H, 8.85.

Found: C, 67.26; H, 9.28.
d29-Tetradecanol (31). To a 3-neck round-bottomed flask containing LiAID4 (0.205 g,

4.9 mmol) and immersed in an ice/water bath was added 60 mL THF cautiously. The ice bath
was removed and a solution of CI3D27COOH (1 g, 3.9 mmol) in 80 mL THF was added quickly

enough to the LiAID4 solution to maintain a gentle reflux. After addition of the acid, a white

solid precipitated from solution. The mixture was stirred at room temperature for 15 min and

then heated for 45 min. At the end of the heating period the solid had disappeared and the

resulting solution was clear and grayish. The solution was cooled, and water was added

cautiously to quench any remaining LiAID4. Diethyl ether and 60 mL of a 10% H2S04 solution

were added. The organic layer was collected, washed twice with a 50 mL saturated NaHCO3

solution, once with 50 mL water, and dried over Na2SO4. Concentration of the solution in

vacuo afforded the product as a white solid in 91% yield, mp 34-35 "C (lit (C14H290H) 38-

40-C).
d29-Bromotetradecane (32). To p-toluenesulphonyl chloride (0.78 g, 1.3 eq) in 7 mL

pyridine was added 29 (0.77 g, 3.2 mmol) in 21 mL pyridine dropwise from an addition funnel

over 30 min. After the addition was complete, the mixture was placed in a refrigerator at 5"C

overnight. At this time the solution was added to a 50 mL ice/50 mL HC1 solution, and

chloroform was used to extract the product. The organic layer was washed once with a 50 mL
ice/HCI mixture, twice with a saturated NaHCO3 solution, and dried over MgSO4. Evaporation

of the solvent yielded the tosylated product, which was then refluxed with 4 g LiBr in 70 mL