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Application of Conjugated Polymers to Multi-Electrode Electrochromic Devices

Permanent Link: http://ufdc.ufl.edu/UFE0022848/00001

Material Information

Title: Application of Conjugated Polymers to Multi-Electrode Electrochromic Devices
Physical Description: 1 online resource (134 p.)
Language: english
Creator: Unur, Ece
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2008

Subjects

Subjects / Keywords: colorimetry, conjugated, devices, electrochromism, polymers
Chemistry -- Dissertations, Academic -- UF
Genre: Chemistry thesis, Ph.D.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: Electrochromism, change or bleaching of color with applied potential, is one of the most eminent properties of conjugated polymers and it originates from electronic structure changes induced upon redox doping/dedoping. Color tuning in conjugated polymers is possible by synthetic and physical means. New colors can be accessed either by structural modifications that allow the alteration of electronic properties (e.g., bandgap) or by newly developed analytical methods/devices that utilize the optical properties of existing polymers. The absorption spectra of the donor-acceptor based poly(3,4-alkylenedioxythiophene) (PXDOT) derivatives used in this work spans the full visible spectrum in their neutral state, and bleach upon oxidation due to the formation of lower energy states that are created at the expense of the HOMO-LUMO electronic transitions. The dual polymer film technique, which is an analytical method derived from color mixing theory, generates new colors by transmitting light through two films stacked together in an electrolyte solution and under separate potentiostatic control. Here, we report on three new multi-electrode electrochromic window devices, pseudo 3- electrode device (P3-ECD), 3-electrode device (3-ECD) and RGB 5-electrode device (RGB 5-ECD), made possible by the dual polymer film technique, comprising multiple active electrodes and non-color changing counter electrodes. Having spray-processable RGB to transparent switching polymers available along with non color changing, yet electroactive, counter electrode polymers for the first time, multi-electrode electrochromic devices under separate potentiostatic control promise a myriad of colors by combining optical properties of two or more films.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by Ece Unur.
Thesis: Thesis (Ph.D.)--University of Florida, 2008.
Local: Adviser: Reynolds, John R.
Electronic Access: RESTRICTED TO UF STUDENTS, STAFF, FACULTY, AND ON-CAMPUS USE UNTIL 2009-06-30

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2008
System ID: UFE0022848:00001

Permanent Link: http://ufdc.ufl.edu/UFE0022848/00001

Material Information

Title: Application of Conjugated Polymers to Multi-Electrode Electrochromic Devices
Physical Description: 1 online resource (134 p.)
Language: english
Creator: Unur, Ece
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2008

Subjects

Subjects / Keywords: colorimetry, conjugated, devices, electrochromism, polymers
Chemistry -- Dissertations, Academic -- UF
Genre: Chemistry thesis, Ph.D.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: Electrochromism, change or bleaching of color with applied potential, is one of the most eminent properties of conjugated polymers and it originates from electronic structure changes induced upon redox doping/dedoping. Color tuning in conjugated polymers is possible by synthetic and physical means. New colors can be accessed either by structural modifications that allow the alteration of electronic properties (e.g., bandgap) or by newly developed analytical methods/devices that utilize the optical properties of existing polymers. The absorption spectra of the donor-acceptor based poly(3,4-alkylenedioxythiophene) (PXDOT) derivatives used in this work spans the full visible spectrum in their neutral state, and bleach upon oxidation due to the formation of lower energy states that are created at the expense of the HOMO-LUMO electronic transitions. The dual polymer film technique, which is an analytical method derived from color mixing theory, generates new colors by transmitting light through two films stacked together in an electrolyte solution and under separate potentiostatic control. Here, we report on three new multi-electrode electrochromic window devices, pseudo 3- electrode device (P3-ECD), 3-electrode device (3-ECD) and RGB 5-electrode device (RGB 5-ECD), made possible by the dual polymer film technique, comprising multiple active electrodes and non-color changing counter electrodes. Having spray-processable RGB to transparent switching polymers available along with non color changing, yet electroactive, counter electrode polymers for the first time, multi-electrode electrochromic devices under separate potentiostatic control promise a myriad of colors by combining optical properties of two or more films.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by Ece Unur.
Thesis: Thesis (Ph.D.)--University of Florida, 2008.
Local: Adviser: Reynolds, John R.
Electronic Access: RESTRICTED TO UF STUDENTS, STAFF, FACULTY, AND ON-CAMPUS USE UNTIL 2009-06-30

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2008
System ID: UFE0022848:00001


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1 APPLICATION OF CONJUGATED POLYMERS TO MULTI ELECTRODE ELECTROCHROMIC DEVICES By ECE UNUR 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 2008

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2 2008 Ece Unur

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3 To my father, Irfan; my mother, Havva; my sister, Necibe; and my brother, Lutfu

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4 ACKNOWLEDGEMENTS Graduate school has been one of the most difficult times in my life. In addition to leaving home thousands miles away, I had to survive all the obstacles that come in to my way. I could have never achieved this without my family and friends support. Thus, I would like take a moment to acknowledge all those who have touched my life along these five years. First and foremost, I would like to thank my mother; Havva Unur and my father; Irfan Unur for dedicating themselves to raise three good kids. I respect them in working very hard, instead of enjoying their youth, just to offer us a better education, better life and better future. I sincerely thank them for being caring, loving, and supportive to all around them and standing the best sample of what should an honorable person be. I would like to extend those thanks to my brother; Lutfu Unur (Minik Gus) and my sister; Necibe Unur (Neco Can) for their support and encouragement over the years. They were always just a call away. Even at those times, I was ready to cry, hearing their cheerful voices took me back to those peaceful breezy endless summer nights in Mudanya. I always wished, I were there with them, enjoying Minik Guss jokes. Neco Can, thanks for teaching me that sometimes what may seem like an obstacle might be a plus for your life if you are wise enough to look at the issue from a different point of view. Believe me it helped a lot. Again, thanks to you all for caring for me more than anyone else could in this world. It might be a difficult sentence to repeat at all times, but I would like to take this chance to say it out loud, Sizleri canimdan cok seviyorum. Without you, I would never have made it here today. I would like to truly thank my advisor, Dr. John R Reynolds for his patience, u nderstanding and utmost respect for my work. I also thank him for all the opportunities he provided, such as attending conferences all over the USA and making me part of CIBA project, which helped me find my niche in science. I will always remember the g reat trip to his land

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5 California where Stefan, Aubrey and I had the chance to see the real end of the tunnel. I would like to thank Dianne Reynolds for being such an understanding wife, thus Dr.Reynolds could pay attention to all our academic and person al needs. I also want to thank her for being so friendly and caring since the day I started in this group. Sometimes a little is bigger. All her kind words during the first lonely years made me feel welcomed. I would like to thank my supervisory committ ee members Dr. Kenneth B. Wagener, Dr. Paul H. Holloway, Dr. Randy Duran and Dr. Valeria Kleiman for their interests in serving on my committee. I would like to thank Valeria for her guidance and valuable discussions. I would like to thank Dr. Wagener for trying to call my family when I burst into tears at my first year in his office. Such kindness could never be forgotten. I would like to thank Roger J. Mortimer for his collaboration, giving me feedbacks through the establishment of high quality work and taking his time to proofread my work. I thank him for his encouragement and trust. Friends like him make life easier, fun and they make the lab a bearable place. I want to thank my colleagues at Ciba Specialty Chemicals, Joe Babiarz, Mike Craig, Jennifer Jankauskas, Nancy Cliff, Shujun Wang, I -Chyang Lin, and David Yale for not only the incredible work we accomplished, funds and supplies, but also for their support and for welcoming me at all my visits. They have given me the opportunity a graduate stude nt could rarely have; they gave me the chance to take part in the real professional life. I would also like to thank Dr. Ryan M. Walczak and Dr. June Ho Jung for taking their precious times to have coffee breaks with me. They made me believe in myself aga in and have me started in the CIBA project with a great enthusiasm.

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6 I would like also to acknowledge all the people I worked with, and who helped enrich the work presented in this dissertation: Dr. Ben Reeves, Dr. June Ho Jung, Ciba Specialty Chemicals, D r. Stefan Ellinger and Pierre M. Beaujuge for sharing their precious babies (polymers and monomers) with me, Dr. Jeremiah Mawaura, Dr. Nisha Ananthakrishnan, Dr. Christophe Grenier and Dr. Avni A. Argun for training me, Dr. Evrim Atas, for being a great su pport through all my studies and giving me insight, Dr. Amelia Dempere, for sharing her experience and wisdom and caring enough to recognize your pain among all the others. I would like to thank all the members of Reynolds Group. You have all made it a great experience. I also would like thank the members of George and Josephine Butler Polymer Labs, for the help and making sure everything runs properly. I also would like to thank to the administrative staff, Cheryl Googins; for showing me the warmth that I could see from my family, Sara Klossner; for helping me at all the last moment runs with a patience that could only be seen in a prophet, Gena Borrer o,for dealing with all the weirdoes to get our orders in, Tasha Simmons and Lorraine Williams, who had been there with me at some parts of the journey. A special thank you goes to my labmates for their help and support, and my coffee break companions, Mar ia, Svetlana and Nate. I also would like to thank Dr. Svetlana Vasilyeva for the valuable discussions, collaboration, for sharing her wisdom, and for being such a dependable and honest friend at the most difficult times. I wish to thank Laura Moody for a lways cheering me up. I would like to thank Ken Graham for his collaboration and always smiling face. I cannot omit my MS. advisor and mentor, Dr. Levent K. Toppare. Without his trust and guidance, I would have not been here, doing PhD today. He turned m y life into an outstanding experience. I would like to thank him for helping me to learn who I really am.

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7 I would like to give my special thanks to the TURKISH MAFIA. Without the members of GOBEKVILLE (Nihan, Mete, Memet, Akin, Eray, Gogce, Sibel, Arpat, Stefan, Meryem, Huseyin, Emel), I couldnt have enjoyed but endured this journey. Gogce and Stefan, you have been my warmest place to run in this lonely town, you are my family. You all made me feel close to home. Nihan, you are a very special friend. W ords are not enough to tell how lucky I feel to be your friend/sister. I also would like to thank my dear Anaklara for being a great friend, neighbor, support and teaching us everything necessary to survive in USA, from partying to car shopping. I would like to thank you for giving me a basket before the sunrise and sending me to collect candies to experience an American tradition, red carpet nights and so many others. Last, I would like to thank Perihan Balikci Brown, for listening to me patiently, being there for me at all the good and bad times, and for sharing her life with me. I would like to thank my dear Georgios Pyrgiotakis (Chef) for all the great shopping and cooking experience, for showing me all the good parts of this town and for all the movi e nights. I also would like to thank DJ Webby for the great music he shared with me. I want to thank my dear girl friends Debra Anderson and Rania Habib, you were the ones who held my hand first, pulled me out of the darkness and started my beautiful lif e in Gainesville. I will remember you; Debra, Rania and Chef for this all through my life. I also want to thank the greatest dude ever, Dr. Jorge Chaves Benavides and his perfect wife Dr. Sara Lane and their little princess Victoria for bringing a joy in to our lives and their friendship. I also would like thanks all the girls, Laurel, Sara, Delmy, Fedra, Ozge, Marie and Gokce for our special event Girls Nights. It was always fun to be with you and know that there was someone to depend on. I also would like to thank the Fashion Police Daniel Kuroda. Thanks to him, I have a pair of red shoes and a red purse, now. Delmy, you and your daughters, your sweetness and friendship have influenced in so many ways. I will never forget the chats at

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8 the Reitz U nion. We know that a cup of coffee and a piece of cookie can build great bounds. I would like to thank all the Pacozs, Atay and Ceylan, for their endless support and cheering me up even if I am not an outstanding person. I also would like to thank to the ones who kept in touch and provided their support from thousands of miles away, Serdar T. Demir (I havent exchanged that many emails with anyone else in my life), Ipek Kerman, Pelin Edinc, Pinar Yilmaz. I would like extend my thanks to the members o f yawshax, Basak, Serra, Yeliz, Neco, Elif and Hande. Even looking at our pictures and reading emails made me laugh my head off, you have the power to turn the most stressful times into the most fun ones. Hande, you have never let me feel alone, you ca lled even at your most hectic times to make sure that I was OK, I really appreciate everything and all the trips you have done to meet me. Last, but not the least, I would like to thank Dr. Mete Yilmaz for everything he has done for me without expecting any rewards. He has been my best friend, greatest companion and support. He showed me, together, you can survive anything and most importantly helped me find the true friendship. I am proud and honored to be part of his life. He made me believe that, for the first in my life, someone other than your family could love you unconditionally, just for whom you really are. In the end, our close friends get us through the difficult times. They all have been my best friends for the last five years and they ma de me feel closer to home. I feel so lucky to meet them and I love them so profoundly.

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9 TABLE OF CONTENTS page ACKNOWLEDGEMENTS ................................................................................................................. 4 LIST OF TABLES .............................................................................................................................. 12 LIST OF FIGURES ............................................................................................................................ 13 LIST OF ABBREVIATIONS ............................................................................................................ 17 ABSTRACT ........................................................................................................................................ 18 CHAPTER 1 ELECTROCHROMISM AND COLOR IN CONJUGATED POLYMERS .......................... 20 1.1 Introduction ........................................................................................................................... 20 1.2 Electrochromism ................................................................................................................... 21 1.3 Color Control in Conjugated Polymers ............................................................................... 23 1.4 Electrochromic Devices ........................................................................................................ 27 1.5 Color and Colorimetry .......................................................................................................... 30 1.6 Color Mixing Theory ............................................................................................................ 38 1.7 Structure of Dissertation ....................................................................................................... 40 2 EXPERIMENTAL TECHNIQUES ........................................................................................... 41 2.1 Chemicals, Materials and Instrumentation .......................................................................... 41 2.2 Electrochemistry ................................................................................................................... 43 2.2.1 Electrochemical Setup ................................................................................................ 43 2.2.2 Electrochromic Polymer Film Formation ................................................................. 45 2.2.2.1 Electrochemical deposition ............................................................................. 45 2.2.2.2 Spray or drop casting ....................................................................................... 4 5 2.3 Electrochromic Film Characterizations ............................................................................... 46 2.3.1 Spectroelectrochemistry ............................................................................................. 46 2. 3.1.1 Dual method ..................................................................................................... 47 2.3.1.2 Electrochromic Devices .................................................................................. 47 2.3.2 Colorimetry ................................................................................................................. 47 2.3.3 Composite Coloration Efficiency (Tandem Chronocoulometry /Chronoabsorptometry) and Switching Times ........................................................... 48 2.3.4 Optical Stability of Polymer Films and Devices ...................................................... 49 2.4 Standard Two -Probe Surface Resistivity Measurement ..................................................... 49 2.5 Dual Film Technique ............................................................................................................ 50 2.6 Electrochromic ECD Construction ...................................................................................... 51 2.6.1 Window Type Absorption/Transmission Electrochromic Devices (ECDs) ........... 51 2.6.2 PseudoThree -Electrode ECDs .................................................................................. 52 2.6.3 Three Electrode ECDs ............................................................................................... 52

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10 2.6.4 RGB Color Space Five -Electrode ECDs .................................................................. 53 3 DUAL POLYMER ELECTROCHROMIC FILM CHARACTERIZATION USING BIPOTENTIOSTATIC CONTROL .......................................................................................... 55 3.1 Color Mixing ......................................................................................................................... 56 3.2 Choosing A System for Dual -Polymer Technique by Fundamenta l Properties (EDOT, ProDOP and ProDOT Hx2) ................................................................................... 57 3.2.1 Film Deposition .......................................................................................................... 58 3.2.2 Polymer CV and Scan Rate Dependence .................................................................. 60 3.2.3 Spectroelectrochemistry ............................................................................................. 61 3.2.4 Tandem Chronocoulometry and Chronoabsorptometry .......................................... 64 3.2.5 Colorimetry ................................................................................................................. 66 3.3 PProDOP/PEDOT and PProDOP/PProDOT Hx2 Dual Systems ...................................... 69 3.4 Conclusions ........................................................................................................................... 73 4 APPLICATION OF BIPOTENTIOSTATIC CONTROL IN A 3 -ELECTRODE ELECTROCHROMIC DEVICE: TOWARDS BLACK TO TRANSMISSIVE AND MULTI COLORED SWITCHING ........................................................................................... 75 4.1 Towards Black to Clear Switching ECDs -Fundamental Properties (SprayDOTTMPurple 101, SprayDOTTM-Green 145, PProDOP -N EtCN) ..................... 76 4.1.1 Film Deposition .......................................................................................................... 77 4.1.2 Polymer CV and Scan Rate Dependence .................................................................. 79 4.1.3 Spectroelectrochemistry ............................................................................................. 80 4.1.4 Setting Thicknesses .................................................................................................... 81 4.1.5 Tandem Chronocoulometry and Chronoabsorptometry .......................................... 84 4.1.6 Colorimetry ................................................................................................................. 86 4.1.7 Optical Stability .......................................................................................................... 88 4.2 SprayDOT -Purple 101/SprayDOT Green 145 Dual -Film Electrochromic System ......... 89 4.3 PseudoThree -Electrode ECD (SprayDOTTMPurple 101/SprayDOTTM-Green 145/PProDOP N EtCN) ......................................................................................................... 92 4.4 Three Electrode ECD ( SprayDOT -Purple 101/SprayDOT Green 145/PTMA) ............... 97 4.5 Conclusions ......................................................................................................................... 107 5 RGB COLOR SPACE 5 ELECTRODE ELECTROCHROMIC DISPLAY DEVICE ....... 109 5.1 RGB Color Space 5 Electrode ECD -Fundamental Properties (SprayDOTTMRed 252, SprayDOTTMGreen 179, SprayDOTTM-Blue 153, PTMA) ..................................... 110 5.1.1 Film Deposition ........................................................................................................ 111 5.1.2 Polymer CV, Scan Rate Dependence ...................................................................... 112 5.1.3 Spectroelectrochemistry ........................................................................................... 114 5.1.4 Tandem Chronocoulometry and Chronoabsorptometry ........................................ 116 5.1.5 Colorimetry ............................................................................................................... 119 5.2 Dual Absorptive/Transmissive Window ECDs ................................................................ 122 5.3 RGB Color Space 5 Electrode ECD .................................................................................. 124 5.4 Conclusions and Future Perspectives ................................................................................ 127

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11 LIST OF REFERENC ES ................................................................................................................. 129 BIOGRAPHICAL SKETCH ........................................................................................................... 134

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12 LIST OF TABLES Table page 4 1 Coloration efficiencies and switch times of SprayDOTTMPurple 101 and SprayDOTTMGreen 145 at various film thicknesses in 0.1 M TBAP/PC. ........................ 86 5 1 Change in a*/b* values from a single EC film to multi -electrode devices. ..................... 127

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13 LIST OF FIGURES Figure page 1 1 Doping mechanism of PEDOT .............................................................................................. 23 1 2 Spectroelectrochemical series of electrochemically deposited PEDOT film at applied potentials ................................................................................................................................. 25 1 3 Schematics of WO3 EC displays. ......................................................................................... 29 1 4 Schematic of a typical polymer dual type absorptive/transmissive window type ECD. ... 30 1 5 The luminosity of the human eye. ......................................................................................... 32 1 6 Calculation of CIE 1931 tristimulus values .......................................................................... 34 1 7 (a) CIE 1931 xy -chromaticity diagram, (b) 1976 CIE L*a*b* color space. .................... 36 1 8 Schematics of additive and subtractive color mixing system ............................................. 39 2 1 Setup for a standard two -probe surface resistivity measurement. ....................................... 50 3 1 Chemical structures of the polymers that are used in dual -polymer electrochromic method ..................................................................................................................................... 58 3 2 The repeated potential scanning electropolymerization of EDOT ..................................... 59 3 3 The repeated potential scanning electropolymerization of ProDOP ................................... 59 3 4 Cyclic voltammograms of PEDOT in 0.1 M LiClO4/PC at different scan rates. ............... 60 3 5 Cyclic voltammograms of PProDOP in 0.1 M LiClO4/PC at different scan rates. ............ 61 3 6 Cyclic voltammograms of PProDOT Hx2 in 0.1 M LiClO4/PC at different scan rates. .... 61 3 7 Spectroelectrochemistry of PEDOT film in 0.1 M LiCLO4/PC solution. .......................... 63 3 8 Spectroelectrochemistry of PProDOP film in 0.1 M LiCLO4/PC solution. ....................... 63 3 9 Spectroel ectrochemistry of PProDOT Hx2 film in 0.1 M LiCLO4/PC solution. ............... 64 3 10 Tandem chronoabsorptometry and chronocoulometry experiments for PEDOT .............. 65 3 11 Tandem chronoabsorptometry and chronocoulometry e xperiments for PProDOP ........... 65 3 12 Tandem chronoabsorptometry and chronocoulometry experiments for PProDOT Hx2........................................................................................................................................... 66

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14 3 13 Relative luminance as a function of applied potential of PEDOT ...................................... 68 3 14 Relative luminance as a function of applied potential of PProDOP .................................. 68 3 15 Relative luminance as a function of applied potential of PProDOT Hx2 ........................... 69 3 16 UV vis NIR spectra of PProDOP/PEDOT from dual -polymer electrochromic setup. ..... 71 3 17 L*a*b* color coordinates and photography for PProDOP/PEDOT ................................... 72 3 18 L*a*b color coordinates and photography for PProDOP/PProDOT Hx2 .......................... 73 4 1 Chemical structures of the polymers that are used in dual -polymer electrochromic method and in ECDs. ............................................................................................................. 77 4 2 Repeated potential scanning electropolymerization of ProDOP N -EtCN .......................... 78 4 3 Cyclic voltammograms of PProDOP N EtCN in 0.1 M TBAP/PC at different scan rates ......................................................................................................................................... 79 4 4 Cyclic voltammograms of the SprayDOTTM-Purple 101 in 0.1 M TBAP/PC at different scan rates. ................................................................................................................ 79 4 5 Cyclic voltammograms of the SprayDOTTMGreen 145 in 0.1 M TBAP/PC at different scan rates ................................................................................................................. 80 4 6 Spectroelectrochemistry of SprayDOTTM-Purple 101 film. ............................................... 82 4 7 Spectroelectrochemistry of SprayDOTTMGreen 145 film. ................................................ 82 4 8 Spectroelectrochemistry of PProDOP N -EtCN film. ......................................................... 83 4 9 Absorbance (a.u.) vs. thickness (Ao) linear fit plots for SprayDOTTMPurple 101 and SprayDOTTMGreen. .............................................................................................................. 83 4 10 Tandem chronoabsorptometry and c hronocoulometry experiment for SprayDOTTMPurple 101(at 574 nm) ........................................................................................................... 85 4 11 Tandem chronoabsorptometry and chronocoulometry experiments for SprayDOTTMGreen 145 (at 465 nm) ........................................................................................................... 85 4 12 Tandem chronoabsorptometry and chronocoulometry experiments SprayDOTTMGreen 145 (at 707 nm) ........................................................................................................... 86 4 13 % Relative Luminance as a function of applied potential of SprayDOTTMPurple 101 film at different thicknesses ........................................................................................... 87 4 14 % Relative Luminance as a function of applied potential of SprayDOTTMGreen 145 film at different thicknesses ................................................................................................... 88

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15 4 15 Electrochemic al and optical stability of SprayDOTTMPurple 101 and SprayDOTTMGreen 145................................................................................................................................ 89 4 16 UV vis NIR spectra of SprayDOTTM-Purple 101/SprayDOTTMGreen 145 from dual -polymer electrochromic setup ....................................................................................... 91 4 17 L*a*b* color coordinates and photography for SprayDOTTM-Purple 101/SprayDOTTMGreen 145. ............................................................................................... 92 4 18 Schematic of the P3 EC D under bipotentiostatic control .................................................... 94 4 19 UV vis NIR spectra of the P3 ECD. .................................................................................... 95 4 20 L*a*b* color coordinates and photography from the Spra yDOTTM-Purple 101/SprayDOTTMGreen 145 P3-ECD. ................................................................................ 95 4 21 P3 -ECD stability studies ........................................................................................................ 96 4 22 Schematic of the 3 ECD under bipotentiostatic control. ..................................................... 97 4 23 Schematic of the highly transmissive porous electrode (PETE/Au/PEDOT:PSS). ........... 99 4 24 Systematic % T ransmittance study of counter electrodes/counter electrode components ........................................................................................................................... 100 4 25 Cyclic voltammograms of PTMA in 0.1 M TBAP/PC at different scan rates ................. 101 4 26 Redox couples of PTMA. .................................................................................................... 101 4 27 PTMA formulation studies in 0.1 M LiClO4/PC ................................................................ 103 4 28 Spectroelectrochemistry of PTMA/PMMA.film ................................................................ 104 4 29 UV vis NIR spectra of the 3 -ECD. ................................................................................... 106 4 30 L*a*b* color coordinates and photography from the SprayDOT Purple 101/SprayDOT Green 145 3-ECD. ..................................................................................... 107 5 1 The schematic of the working principles of the 5 Electrode ECD. .................................. 111 5 2 Chemical structures of the polymers and the photographs of their neutral (N) and doped (D) states. ................................................................................................................... 111 5 3 Cyclic voltammogram s of SprayDOTTMRed 252 in 0.1 M TBAP/PC at different scan rates ............................................................................................................................... 112 5 4 Cyclic voltammograms of SprayDOTTMGreen 179 in 0.1 M TBA P/PC at different scan rates ............................................................................................................................... 113

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16 5 5 Cyclic voltammograms of SprayDOTTMBlue 153 in 0.1 M TBAP/PC at different scan rates ............................................................................................................................... 113 5 6 Spectroelectrochemistry of SprayDOTTMRed 252 film ................................................... 114 5 7 Spectroelectrochemistry of SprayDOTTMGreen 179 film ................................................ 115 5 8 S pectroelectrochemistry of SprayDOTTMBlue 153 film. ................................................. 115 5 9 Tandem chronoabsorptometry and chronocoulometry experiment for SprayDOTTMRed 252 ................................................................................................................................. 117 5 10 Tandem chronoabsorptometry and chronocoulometry experiment for SprayDOTTMGreen 179 (at 443 nm). ........................................................................................................ 117 5 11 Tandem chronoabsorptometry and chronocoulometry experiment for SprayDOTTMGreen 179 ( at 634 nm) ......................................................................................................... 118 5 12 Tandem chronoabsorptometry and chronocoulometry experiment for SprayDOTTMBlue 153 ................................................................................................................................ 118 5 13 Relative luminance as a function of applied potential and L*a*b* color coordinates and photography at redox extremes of SprayDOTTMRed 252 in 0.1 M TBAP/PC. ....... 120 5 14 Relative luminance as a function of applied potential and L*a*b* color coordinates and photography at redox extremes of SprayDOTTMGreen 179 in 0.1 M TBAP/PC. ... 121 5 15 Relative luminance as a function of applied potential and L*a*b* color coordinates and photography at redox extr emes of SprayDOTTMBlue 153 in 0.1 M TBAP/PC. ..... 121 5 16 SprayDOTTMRed 252/PTMA Window ECD. UV -vis NIR spectra and the L*a*b* color coordinates with the associated photographs at the redox extremes. ...................... 123 5 17 SprayDOTTMGreen 179 /PTMA Window ECD. UV -vis NIR spectra and the L*a*b* color coordinates with the associated photographs at the redox extremes. ........ 123 5 18 SprayDOTTMBlue 153 /PTMA Window ECD. UV-vis -NIR spectra and the L*a*b* color coordinates with the associated photographs at the redox extremes. ...................... 124 5 19 Sc hematic of the RGB 5 ECD. ........................................................................................... 126 5 20 UV vis NIR spectra of the individual colors obtained from the RGB 5 ECD, (a) red, (b) green and (c) blue. .......................................................................................................... 126 5 21 L*a*b* color coordinates and photography of the RGB 5 ECD. ..................................... 127

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17 LIST OF ABBREVIATION S PAc polyacetylene PANI polyaniline VB Valence band Eg bandgap energy CB conduction band CE coloration efficiency PC Propylene carbonate LiClO4 Lithium perchlorate TBAP tetrabutylam monium perchlorate CV Cyclic voltammetry PMMA pol(methyl methacrylate) PXDOT poly(3,4 alkylenedioxythiophene) PXDOP poly(3,4 alkylenedioxypyrrole) PTMA poly(2,2,6,6 tetramethylpiperidinyloxy4yl methacrylate) BTD 2,1,3 benzothiadiazole PEDOT:PSS poly(3,4 -e thylenedioxythiophene):poly(styrene sulfonate) PETE polyester membrane ECD electrochromic device P3 -ECD pseudo three electrode electrochromic device 3 ECD three electrode electrochromic device RGB 5 ECD RGB Color Space five -electrode electrochromic device C luminance contrast color contrast

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18 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 APPLICATION OF CONJUGATED POLYMERS TO MULTI ELECTRODE ELECTROCHROMIC DEVICES By Ece Unur December 2008 Chair: John R. Reynolds Major: Chemistry Electrochromism, change or bleaching of color with applied potential, is one of the most eminent properties of conjugated polymers and it originates from electronic structure changes induced upon redox doping/dedoping. Color tuning in conjugated polymers is possible by synthetic and physical means. New colors can be accessed either by structural modifications that allow the alteration o f electronic properties (e.g. bandgap) or by newly developed analytical methods/devices that utilize the optical properties of existing polymers. The absorption spectra of the donor acceptor based poly(3,4 alkylenedioxythiophene) (PXDOT) derivatives used in this work spans the full visible spectrum in their neutral state, and bleach upon oxidation due to the formation of lower energy states that are created at the expense of the HOMO -LUMO electronic transitions. The dual polymer film technique, which is a n analytical method derived from color mixing theory, generates new colors by transmitting light through two films stacked together in an electrolyte solution and under separate potentiostatic control. Here, we report on three new multi -electrode electroc hromic window devices, pseudo 3 electrode device (P3 -ECD), 3 electrode device (3 ECD) and RGB 5 -electrode device (RGB 5 -ECD), made possible by the dual polymer film technique, comprising multiple active electrodes and non-color changing counter electrodes Having spray processable RGB to transparent switching polymers available along

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19 with non color changing, yet electroactive, counter electrode polymers for the first time, multi electrode electrochromic devices under separate potentiostatic control promis e a myriad of colors by combining optical properties of two or more films.

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20 CHAPTER 1 ELECTROCHROMISM AND COLOR IN CONJUGATED POLYMERS 1.1 Introduction The interest in conjugated conducting polymers as a new class of electronic materials started with the Nobel Prize (Chemistry 2000) winning discovery. Researchers showed that the chemical doping of polacetylene (PAc) films with electron accep ting iodine vapor results in seven orders of magnitude increase in conductivity.1 Chemical doping is a charge transfer redox reaction, which can be conducted by exposing the material to a vapor or a solution of dopant. The doping levels can be controlled by varying the exposure times and dopant concentration, but still this method lacks the precise control and homogeneous distribution of dopants.2 Therefore, electrochemical doping in which the doping levels can be controlled by controlling the potential applied between counter and working electrodes, was invented.3 In electrochemical doping, redox charge is supplied to the conjugated polymer and ions diffuse into the polymer from the electrolyte in order to maintain charge neutrality.2 Similar studies were applied to conjugated polymers with more complex structures, suc h as polyaniline (PANI) which, by being stable in its conductive form, became an important polymer for industrial applications.4 Another polymer with a complex structure, the conjugated polyheterocyle polypyrrole (PPy), has found many applications. DallOlio et al. prepared the first polypyrrrole by oxidative polymerization and it ha d a conductivity of 8 S/cm at room temperature.5 Following that, Diaz et al. electropolymerized pyrrole to air stable freestanding films.6 Polythiophene subsequently found more interest due to its higher stability in both doped and neutral states and ease of 3 substitution which induces solubility.7 8 Conjugated polymers became popular in electronic applications not because of their better performance over inorganic semiconductors, but because of their unique combined properties.

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21 These neutral materials are charge transporting as semiconductors and have the physical and mechanical properties of typical plastics. Electrochemical doping of conjugated polymers has opened a new field with applications ranging from polymer batteries and supercapacitors, electrochromic displays to redox sensors.7, 9 This introduction will cover evolution of color in conjugated polymers and their electrochromic applications. 1.2 Electrochromism The term electrochromism was first introduced by Platt, and demonstrated by F ranz and Keldysh.10 Electrochromism is the evol ution of new optical absorption bands in an electroactive species upon reversible electrochemical oxidation/reduction reaction.1113 Due to the needs of modern technology the definiti on of electrochromism is not limited to the visible region, but extended to the ultraviolet (UV) and infrared (IR) regions of the electromagnetic spectrum. Electrochromism in the visible region is useful for display purposes. There are three classes of e lectrochromic materials; inorganic materials such as, transition metal oxides (e.g. tungsten trioxide, WO3) and Prussian Blue, molecular electrochromes such as, viologens (4,4 bipyridylium salts) and conjugated polymers.9, 1317 The mechanism of electrochromism, in other words electrochemical doping, in conjugated polymers is different from the earliest electrochromes, alkali halides. There are two main features to electrochromism in these crystals, first they must have F centers, and second they must constitute both ionic and electronic conductivity. F -centers, color centers, are crystallographic defects arising from anion vacancy. Upon application of potential, these vacancies fill with electrons and render a color to the material. The electrons migrating in to the film from a near source can maintain the charge neutrality.10 Conjugated polymer electrochromism evolves from the emergence of lower energy transitions between the valence ( -electron) and the conduction (lowest

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22 unoccupied) bands upon electrochemical doping. The energy difference between the conduction and valence bands, termed t he electronic bandgap (Eg), defines the intrins ic optical properties of z orbitals along the conjugated polymer backbone allows the free movement of charge carriers. When an electron is withdrawn from the valence band, a radical cation (known as a polaron), form s. The polymer chain partly gains a quinoid like geometry and thus new energy states. These half -filled new polaronic energy states are distributed symmetrically in the electronic bandgap. Further oxidation of the polymer results either in formation of new polarons upon withdrawal of electrons from different chains or withdrawal of electrons from an existing polaron, which results in a dication called a bipolaron and new energy states. (Figure 1 1) These charged defects along the polymer chain are neutr alized by the migration of counter anions into the polymer matrix, and this overall process is called p -doping. The exit of concurrent anions results in reduction of p-doped conjugated conducting polymer to its neutral insulating form. The color change or contrast between the doped and undoped forms of the polymer depends on the magnitude of the bandgap of the undoped polymer. Thin films of conjugated conducting polymers with Eg greater than 3 eV (~400 nm) are colorless and transparent in the undoped f orm, while in the doped form they generally absorb in the visible region. Those with Eg equal to or less than 1.8 1.9 eV (~650700 nm) tend to be highly absorbing in the undoped form but, after doping, the free carrier absorption is relatively weak in the visible region as it is transferred to the near infrared (NIR). Polymers with intermediate gaps have distinct optical changes throughout the visible region and can exhibit several colors. A spectroelectrochemical series obtained from a thin film of a con jugated polymer distinctly elucidates the doping induced optical changes. As shown in Figure 1 2 cathodically-

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23 coloring poly(3,4 ethylenedioxythiophene) (PEDOT), with a low bandgap of 1.6 eV shows an absorption in the visible region with a maximum at 632 nm (2 eV) and appears blue. Upon doping, a new absorption band emerges in the NIR region (~950 nm or 1.3 eV) due to the transition in the visible region diminishes. Upon further doping, new polarons and bipola rons form and the optical intensity increases in the NIR region. The tailing of the NIR absorption into the visible region gives the doped polymer a transmissive sky blue appearance in the doped state. Figure 1 1 Doping mechanism of PEDOT; neutral form, slightly doped radical cation (polaron) form and fully doped dication (bipolaron) form 1.3 Color Control in Conjugated Polymers Conjugated polymers provide the ability to access various electrochromic states in both the doped and neutral forms by controll ing the band gap through structural modification of the pendant groups or the conjugated backbone.18, 19 The range of colors obtained from conjugated polymers based on thiophene and pyrrole moieties such as poly(3,4 alkylenedioxythiophene) (PXDOT) and poly(3,4 alkylenedioxypyrrole) (PXDOP) together with their derivat ives spans the entire visible spectrum and extends into the UV and NIR regions.20 It has been shown that the electrochromic contrast of these two polymer families can be enhanced by increasing t he size of VB / CB / Eg VB / CB / VB / CB / neutral polaron bipolaron 1 -e-eA-A-A-

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24 the alkylenedioxy ring, or the bulkiness of the substituent attached to the ring.21, 22 Dietrich et al. first studied the electrochemical and optical properties of PEDOT and poly(3,4 propylenedioxythiophene) (PProDOT).23. In the first systematic study of the PXDOTs, our group reported on high optical contrasts and fast swi tching times for the di alkyl substituted (along the alkylene bridge) PProDOTs compared to the parent PProDOT.24 Di -substitution results in a more open polymer morphology that enhances charge -compensating dopant ion movement in and out of the matrix. Typically, a strong NIR absorption tailing into the visible region evolves as the polymer becomes conductive. It is the attenuated tailing of this NIR absorption as it crosses through the visible region that causes the higher transmissivity for the PProDOT derivatives. ProD OT Me2, substituted by dimethyl on the central carbon of the 22 More highly substituted PXDOT derivatives, prepared by both e lectrochemical and solution polymerization methods, exhibit high optical contrast, switching from deep red-purple to highly transmissive sky blue where the human eye is highly sensitive, and fast switching times because of the more open morphology. 2529 Of these polymers, SprayDOTTMClassic (PProDOT (CH2OEtHx)226 30 SprayDOTs have the advantage of being soluble in their reduced form in several organic solvents, allowing the deposition of high quality films by spraying or spin-coating.19, 26, 31 On the other hand, with their blue shifted absorption, the PXDOPs exhibit larger bandgaps compared to the PXDOTs. Poly(3,4 -ethylenedioxypyrrole) (PEDOP) exhibits a bright red color in its neutral state (bandgap 2.05 eV) and a light blue transmissive state upon oxidation while its

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25 Figure 1 2 Spectroelectrochemical series of electrochemically deposited PEDOT film at applied potentials between 1.45 V and +0.35 V vs. Fc/Fc+ in 0.1 V increments. The photographs of the neutral and the doped films are shown in the inset. thiophene counterpart PEDOT exhibits a blue color in its neutral state with a lower bandgap (1.6 eV). This difference is attributed to the higher LUMO of pyrroles relative to thiophe nes. Upon increasing the ring size of the alkylene bridge, even higher bandgaps are obtained (PProDOP, 2.2 eV vs. PProDOT, 1.7 eV).32 The neutral form of PProDOP has an orange color which bleaches upon doping after passing through a brown color state arising from intermediate doping. Our group has further increased the band gaps for PXDOP s by N -substitution. While inducing torsion along the heterocyclic backbone, N -substitution decreases the -conjugation and therefore increases the band gap while maintaining the low oxidation potentials. Due to higher t ransitions of the N -substituted PProDOPs blue shift into the ultraviolet region and the intragap polaron and bipolaron transitions occur in the visible region. 1.0 1.5 2.0 2.5 3.0 3.5 0.0 0.5 1.0 1.5 2.0 1.6 eV doped Absorbance (a.u.)Energy (eV) N eutral Ox Red D oped *polaron Bipolaron /polaron

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26 As such, these materials are anodically coloring. 33 The nature of the substituent has an effect on the extent to which the transition is shifted. For N -methyl PProDOP the bandgap occurs at 3.0 e V, compared to 2.2 eV for PProDOP. Both N [2 (2 Ethoxy-ethoxy) -ethyl] PProDOP ( N Gly PProDOP) and N -propanesulfonate PProDOP ( N -PrS PProDOP) are colorless when fully reduced and colored upon full oxidation. Walczak et al. invented a new synthetic route w hich eases the laborious N substituted 3,4 alkylenedioxypyrrole monomer synthesis by utilizing a synthetic intermediate, an ester substituted dihydroxypyrrole.34, 35 Some of the highly transmissive N -substituted PProDOPs, such as poly(3,4 propylenedioxythiophene N propionitrile) (PProDOP N EtCN), have been shown to exhibit electroactivity without a change of color. One major focus in developing processable, high contrast EC polymers has been to establish a full color palette for use in displays and printing. Red and blue polymers becoming highly transmissive upon oxidation have been reported.13 But synthesis of green polyme rs which absorb in the red and blue regions of the electromagnetic spectrum had been a challenge for scientists until the first electrochemically stable donor acceptor based green polymer was reported by Sonmez et al.36 The green poly(2,3 di(thien 3 -yl) 5,7 -di(thien 2 -yl)thieno[3,4 b ]pyrazine) PDDTP polymer obtained by oxida tive electro -deposition was shown to switch to a transmisive brown hue upon doping.37, 38 Toppare et al. reported on the first solution processable green polymer, poly(2,3 -bis(3,4 -bis(decyloxy)phenyl) 5,8 -bis(2,3 dihydrothieno[3,4 b][1,4]dioxin5 yl)quinoxaline) PDOPEQ, with a highly transmissive oxidized state.39 In parallel our group reported on a set of green polymers with all intended properties and one of them, poly(EDOT2(ProDOT (CH2O(2 EtHx))2BTD) SprayDOTTM-Green 145, was used for the electrochromic applications in this manuscript.40 The polymer was synthesized by alte rnative

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27 addition of electron rich EDOT and 2 -ethylhexyloxy-substituted 3,4 -propylenedioxythiophene ProDOT (CH2O(2 -EtHx))2 onto the strong acceptor 2,1,3 benzothiadiazole (BTD). The fabrication of full -color electrochromic display devices ECDs is possible by the achievement of materials that are processable and have the three primary colors, red, green and blue in their neutral states and all can be convert to transmissive forms.37, 38, 41 1.4 Electrochromic Devices The most widespread applications of electrochromic materials include rearview mirrors9, protective eyewear9, displays20, smart windows11, optical shutters16, optical data storage11 and electronic paper42. Conjugated polymers are finding growing utilization in electrochromic appl ications due to their extensive cathodic, anodic and multi -color control, ease of processability, flexibility, rapid redox switching, high optical contrast and long -term stability. It has been shown that if a device under applied electric field exhibits c hanges in optical properties (e.g. absorbance) in a reversible and controlled manner it could be utilized in displays and information storage mediums. There has been a tremendous growth in display technologies in the last decade; such as cathode ray tubes (CRT), liquid crystals (LCD), light emitting diodes (LED), electrophoretic displays and interferometric modular displays (IMOD). Electrochromic displays have been exploited by many researcher since they provide comparable characteristics and unique featu res. Electrochromic displays consume little power, images persist for some time due to the memory effect, a broad range in pixel size is possible, they provide long storage times, wide viewing angles and ease of processing. Electrochromic devices are ele ctrochemical cells that modulate absorbed, transmitted, or reflected incident electromagnetic radiation upon application of an electric field across the electrochromic materials within the device. It is also convenient to think of the color and bleach pro cess as the charging and discharging of a battery.

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28 Deb introduced the first electrochromic display in 1969 and the schematic of two ECDs proposed are illustrated in Figure 1 3.43, 44 In the first device a thin layer of inorganic electrochrome, tungsten oxide (WO3), was evaporated on a transparent conductive substrate (NESA glass ) and this was assigned as the working electrode (cathode). An insulating layer was deposited on tungsten oxide film. The transparent counter electrode (glass substrate with a thin layer of gold) was closed on top of the insulating layer to complete a solid state capacitor structure. When the NESA and gold electrodes are biased, electrons are injected through the cathode into the transparent tungsten oxide film and the film becomes deep blue. When a reverse bias is applied, Au becomes the new cathode an d the NESA glass becomes the new anode. The insulating layer prevents the electron injection from the Au cathode in to the WO3 film. The new anode pulls the previously injected electrons in the film back and the film returns to its original transmissive state. In the second type of device, the insulating layer was replaced with an acidic electrolyte, which conducts protons but electrons. The device was based on the double injection of electrons and protons in to the material. In this device the charges of electrons that were injected into the WO3 layer by the cathode (indium tin oxide) are counterbalanced by the protons that were supplied from the electrolyte and tungsten bronze (HxWO3, x~0.5) forms at the cathode. When the bias between ITO and carbon is reversed electrons leave at the anode, protons leave at the cathode, and the film is bleached. In this type of device, a high ion mobility is required since the coloration entails injection of positive ions and bleaching entails extraction of positive ions. Organic ECDs were first presented by Schoot et al.45 In that device an aqueous solution of heptyl viologen bromide was used as an active layer in between two transparent electrodes and aqueous potassium bromide (KBr) was used as an electrolyte. Upon the application of potential

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29 3 ( ) + + + 3 ( ) Figure 1 3 Schematics of WO3 EC displays heptyl viologens dication reduces to purple colored radical cation at the cathode. This reduction is followed by a reaction between radical cation and bromide ions to form an insoluble purple max=545 nm) at the cathode which bleaches when the bias is reversed. This highly stable device (105 redox cycles) exhibits 20% reflectance contrast. 44, 45 ECDs have found utilization in conjugated conducting polymer applications. Other than the absorptive/transmissive type ECD in which both working and counter electrodes are transparent so that light can pass through, reflec tive ECDs have also been developed. In reflective ECDs the active electrochromic polymer is deposited onto an outward-facing reflective electrode, such as gold deposited onto a flexible, ion permeable substrate.46 In this work, we have constructed new types of absorptive/transmissive window type ECDs The schematic of an absorption/transmission window type ECD which is used in polymeric applications is given in Figure 1 4. The device switches from a colored to transmissive state and is composed of a working electrode with an active layer and a counter electrode separated by a gel electrolyte. The dual polymer electrochromic device design constitutes the use of a second electrochromic material on the counter electrode to bal ance the reaction in the working electrode and prevent CE WE glass substrate Transparent/conductive Layer (NESA) WO3Insulating layer Thin layer of Au CE Liquid electrolyte WE glass substrate Transparent/conductive Layer (ITO) WO3carbon layer stainless steel

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30 early degradation of the functional material. Unfortunately, the use of these devices is limited to electrochromic materials with complementary optical properties, one anodically coloring and the other cathodically coloring.30, 47 Rece ntly Otero and Padilla have reported that the contrast achieved in dual electrochromic systems could not exceed the contrast obtained from a single system. Higher contrast of dual electrochromic windows is possible only through the careful design and use of an electroactive yet non -electrochromic highly transmissive polymers as a counter electrode material.48 Anodically coloring ProDOP derivatives are strong candidates for use as counter electrode materials due to their poorly saturated colors. Figure 1 4 Schematic of a typical polymer dual type absorptive/transmissive wi ndow type ECD 1.5 Color and Colorimetry The perceived color of an object depends on the wavelengths of the electromagnetic spectrum it reflects (transmits)/absorbs, under which light source it is being observed and the response of the observer. Since colo r is a perceptual property, it needs a quantitative definition. Colorimetry is a term used for the quantitative description of colors as they appear to the human eye.49 By the twentieth century, it was accepted that there are two fundamental ways to describe colors quantitatively. The first system is spectra, which doesnt take into account any vision CE WE glass substrate ITO Anodically coloring EC polymer Gel electrolyte Cathodically coloring EC polymer CE WE glass substrate ITO Anodically coloring EC polymer Gel electrolyte Cathodically coloring EC polymer

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31 factors. The second system is based on the physiological properties (the human eye response to visible light of various wavelengths and inten sities). The CIE Commission Internationale de lEclairage system that will be detailed later in this section is the most widely used system. In order to quantify color, every component responsible for the perception, light source, reflectance from the obj ect and human eye response, must be quantified first. The sensitivity of human eye over the visible range under illumination is called photopic luminosity while it is called scotopic luminosity in the dark. There are two types of photoreceptors in the hu man eye, cone shaped and rod shaped receptors. Three different types of cone shaped receptors function under illuminated conditions and they are responsible for red, green, and blue trichromatic (more accurately long -, medium and short -wavelength) sensat ion, separately. The rod shaped receptors function in the dark and they are responsible for the night vision (monochromatic vision). The photopic luminosity reaches a maximum at 555 nm while the scotopic luminosity reaches a maximum at 500 nm and they bo th decrease down to zero at 400 and 700 nm. As shown by Figure 1 5 the human eye is most sensitive to wavelengths around 555 nm during the day and 500 nm at night. In addition to human eye sensitivity, the color of an object also depends on the light sou rce. Objects with different reflectance spectra may appear to have the same color under one light source, and appear different under another one. The dependence of color on the light source is called metamerism If the color appears the same under a wide range of light sources it is, then, called color constancy .5054 The first mathematically standardized color space, CIE 1931 XYZ, was introduced by the International Commission on Illumination (CIE) The system is based on quantifying the visual stimulant and the trichromatic response of the human eye to this stimulant. The visual

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32 Figure 1 5 The luminosity of the human eye. (Plots are derived from spectral data distributed by CIE Technical report. 55) stimulant is the combined effect of a light source and the object being observed under that light source. A light from a physical source appears white and can be dispersed in to wavelengths by a prism as shown by Newton. An illuminant is a plot of relative energy distribution of a light source over the entire vi sible spectrum. In other words, illuminants are used to quantify physical Figure 1 6 (a ). Illuminant A simulates incandescent light, illuminant C simulates aver age daylight, illuminants D 65 and D 50 simulate natural daylight at different temperatures. In our labs, to date we have used illuminant D50 for Colorimetry experiments. The colorants in objects modify light by absorption, transmission or reflection. T he amount of reflected or transmitted light from an object can be can be quantified by a spectrophotometer. A transmittance spectrum 1 6 (b ). The last step in qu antification of color, the quantification of human eye perception of light, was accomplished after series of experiments. Observers were sat in front of a screen with a 2 400 450 500 550 600 650 700 750 0.0 0.2 0.4 0.6 0.8 1.0 555 nm Relative Responsewavelength (nm) scotopic photopic500 nm

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33 degree viewing aperture. Half of the screen was illuminated. Subjects were asked t o match that light by adjusting red green and blue lights This procedure was repeated for all the colors in the visible spectrum The functions that quantify the red ( x () green ( y ( ) ) and blue ( sensitivity of human eye were derived an d they were called CIE 1931 20 standard observer (Figure 1 6 ( c) ) In 1964, 10-degree viewing standard observer was defined due to the findings that cones are more spread at the back of the eye meaning that human eye has a wider vision. The quantified da ta for the source, transmitted/reflected light from the object and observer perception (standard observer) can be multiplied at every wavelength over the entire visible spectrum and then summed to obtain CIE X Y Z tristimulus values of the color. The proc ess can also be summarized by the following equations.49, 54, 56 =100 ( ) ( ) 2 1 ( ) ( ) ( ) 21 =100 ( ) ( ) 2 1 ( ) ( ) ( ) 21 =100 ( ) ( ) 2 1 ( ) ( ) ( ) 21 The factor 100 ( ) ( ) 2 1 was used to assign the value Y= 100 to a perfect reflecting diffuser or to a perfect transmitter. 49 We have obtained the CIE 1931 tristimulus values for neutral PEDOT film as X= 10, Y= 9.8 and Z= 33.6 f rom integration of curves in Figure 1 6. The tristimulus values (the amount of red, green and blue primaries perceived) are used to map the color on 3D vector space. In addition, Y is arranged to correspond exactly to the average luminous curve for an ave rage eye, thus, it is a direct measure of luminosity.

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34 Figure 1 6 Calculation of CIE 1931 tristimulus values, (a) Relative power distributions of CIE illuminants A, C, D65 and D50,( b) Transmittance of PEDOT film on ITO/glass electrode at 1.35 V vs. Fc/Fc in 0.1 M LiClO4/PC, (c) CIE 1931 2degree observer (color matching functions), (d) CIE 1931 XYZ tristimulus values for PEDOT film, (e) Tristimulus values, chromaticity coordinates and a photograph of PEDOT film. (Results are derived from spectra l data distributed by CIE Technical report. 55 ) 400 450 500 550 600 650 700 750 0.0 0.5 1.0 1.5 2.0 z ySensitivitywavelength (nm) xc 400 450 500 550 600 650 700 750 0 10 20 30 40 50 60 70 Intensitywavelength (nm) X Y Zd Tristimulus X = 10 Y = 9.8 Z = 33.6 Chromaticity x = 0.187 y = 0.183 e 400 450 500 550 600 650 700 750 0 50 100 150 200 250 Relative Power ( S ( ) )wavelenght (nm) A -incandescent D65 -daylight at 6500 K C -average daylight D50 -daylight at 5000 Ka 400 450 500 550 600 650 700 750 0.0 0.2 0.4 0.6 0.8 1.0 Transmittancewavelength (nm)b

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35 In order to be able to represent color on 2D space, new quantities called the chromaticity coordinates x, y, z were derived. G iven that, + + = 1 = + + = + + = + + If luminosity is disregarded, x and y alone are sufficient to describe a color. In the CIE chromaticity diagram, x is the abscissa and y is the ordinate as shown in Figure 1 7 (a ). The colors of the spectrum (monochromatic) lie on the parabolic curve. A chromatic colors lie on a line perpendicular to that color plane. The dominant wavelength is given by the point at which a straight line drawn from the white point (W) through color point (P) intersects the spectral curve. The xy -chromaticity coordinates of the PEDOT film were calculates from its tristimulus values as x= 0.183 and y= 0.187 which corresponds to the point P in the blue region of the chromaticity diagram (Figure 1 7 (a) ). Purity, p, is the ratio of distance between W and P to distance betwe en W and dominant wavelength. The purity of the PEDOT film is 64%. The nearer the is color to the spectral curve the purer it is. Extrapolation of the straight line to the opposite end gives the dominant wavelength of the complementary color. Complemen tary colored lights add up to white light. The dominant wavelength for PEDOT is 480 while the dominant wavelength of its complementary color is 575 nm. Luminosity, dominant wavelength and purity constitute three main characteristics of color, brightness, hue and saturation.17, 54

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36 Figure 1 7 (a) CIE 1931 xy-chromaticity diagram, (b) 1976 CIE L*a*b* color space Colorimetry has been utilized to precisely map the colors associated with samples. Color imetry experiments can be done with a portable colorimeter under a specified light source or by a colorimetric spectrophotometer. Colorimeters have red, green and blue filters. Light transmitted from the object passes through each filter, is detected sep arately, and the CIE XYZ values are determined. Variations in color measurements are due primarily to differences between the photodetector -filter spectral response and that of the1931 CIE standard observer. Another source of error is variation in the int ensity of the illumination source. 57 As an example of that the D50 illuminant we utilize in our labs introduces an error of 5% in x -chromaticity coordinate and 7% in y -chromaticity coordinate. (for CIE 1931 2degree observer, CIE D50 Illuminant (x= 0.346, y= 0.358), D50 illuminant in our l abs (x= 0.363, y= 0.386)) Colorimetric spectrophotometers break the light that is reflected from the object into wavelengths and the intensity at each wavelength is recorded. The spectral data then is multiplied by selected illuminant and standard observe r data. Spectrophotometers are typically used in high-precision color measurement applications and provide the greatest accuracy of the different types of color measurement systems.57 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 R (575 nm)Q.y x .W700 nm 400 nm.P D a L*=100 L*= 0 b

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37 In 1976, CIE recommended the LAB system as standard (CIELAB or CIE L*a*b*), in order to provide standard and uniform color space that allows comparison of color values. In this system L* represents lightness, a* and b* represents hue and chroma. The minimu m L* is zero representing black and maximum L* is 100 representing a perfect reflecting diffuser. Positive a* represents red and negative a* is green, while positive b* is yellow and negative b* is blue. These values have no numerical limits. (Figure 1 7 ( b) ). This system has the advantage that colors are equally spaced and the differences between the points plotted on that color space correspond to visual differences between the colors. 53 Color coordinates can be recorded as Y (Lv) (photometric luminance with units of cd/m2) and xy (the chromaticity coordinates), then, these values are converted tristimulus values. X, Y, Z tristimulus values can be converted to L*, a* and b* coordinates of CIE 1976 ( L* a*, b*) color space (CIELAB) by the following equations where Xn, Yn and Zn are the tristimulus values for the standard il luminant.49, 55, 56 = 116 1 3 16 = 500 1 3 1 3 = 200 1 / 3 1 / 3 Where X/Xn, Y/Yn and Z/Zn are all greater than 0.008856. The total color, Q, which is a magnitude of 3D vector in a color space or the distance from the origin, can be represented as follows; = ( 2+ 2+ 2) The color difference, which is the magnitude of a vector between two specified points in color spac e can be calculated as follows.

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38 = ( 2) + ( 2) + ( 2) difference between the colored and the bleached state of the film). 55 Color difference is used in industry for matching c olors of the products to the standards set. 1.6 Color Mixing Theory There are two color systems that match a humans trichromatic vision; the additive color system and subtractive color system. The primaries for the additive color system are red, green, b lue (RGB) while the primaries for the subtractive color system are cyan, magenta, and yellow (CMY). In the additive color system, different colored light at different intensities add to make a new color and this system is utilized in TV screens and monito rs. In the subtractive color system, an object subtracts certain wavelengths from white light by absorption and transmits or reflects the rest. Subtractive color mixing system is utilized in dyes, pigments and in printing. In Figure 1 8, the large circl es on the corners of the large triangles represent primary colors, colors that cannot be obtained by mixing other colors in their system. Small circles on the dashed triangles represent secondary colors; colors obtained from mixtures the of primary colors Equal intensities of the three primary colors (red, green and blue) add to white light in the additive system. Equal intensities of pigments of three primary colors (cyan, magenta a nd yellow) block all the wavelengths and the object appears black in the subtractive system. As shown in Figure 1 8, when white light strikes the magenta cube, first the subtractive principle causes the dye subtract/absorb green and reflect red and blue. Then the reflected red and blue light combine to produce magenta with respect to additive principles.55, 56

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39 Figure 1 8 Schematics of (a) additive color mixing system, (b) subtractive color mixing systems, (c) additive color mixing, (d) color generation from a reflective object a nd (e) color generation from a transmissive object. In this dissertation, the combined effect of subtractive and additive color mixing was utilized in the development of multicolor electrochromic displays. Electrochromic films that are deposited on transp arent electrodes were used as color filters. Films were illuminated by D50 white light at the back and observed from the front. As in Figure 1 8, when the light is transmitted through the magenta film, the green portion is absorbed and the red and blue portions are transmitted. Then the blue and red wavelengths (lights) add to magenta. M Y C G R BCMYK R G B C Y MRGB Additive Additive Subtractive white light a b d c e

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40 1.7 Structure of Dissertation The focus of this work is the electrochemical and optical characterization of conjugated polymers and their application to newly developed multi -electrode electrochromic devices. Chapter 2 briefly summarizes the optical and electrochemical characterization methods for electrochromic polymers. The details for the device constructions are given in the associated chapters. A new dual polymer electrochromic film characterization method using bipotentiostat control is introduced in Chapter 3. This method, which depends on the separate control of doping levels in multiple electrochromic films, allows color mixing by physical means. Chapter 4 uti lizes the dual -polymer electrochromic film characterization technique in the development of two new multi -electrode electrochromic devices; the Pseudo 3 Electrode Electrochromic Device (P3 ECD) and 3 -Electrode Electrochromic Device (3 ECD). The working pr inciples of the device is similiar to the dual -polymer electrochromic film characterization method in that the doping levels of the electrochromic components are independently controlled. These devices exhibit switches from black to transmissive upon colo r mixing of green and purple absorbing electrochromic components. A new highly transmissive, conductive and porous electrode material is introduced and used to serve as a counter electrode to the electrochromic components of the 3 ECD. In Chapter 5 a new RGB 5 Electrode electrochromic device (RGB 5 ECD) is elucidated. The device constitutes 3 electrochromic films with primary colors red, green and blue, that switch to transmissive upon doping. Independent control of doping levels, thus colors of electr ochromic films allows the establishment of an RGB color space electrochromic device.

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41 CHAPTER 2 EXPERIMENTAL TECHNIQ UES The intent of this chapter is to provide an overview of the materials, techniques, and instrumentation used during the course of this research. Complete characterization methods of conjugated electroactive polymers and their applications to various devices explained here will be detailed and frequently referred to in the subsequent chapters. 2.1 Chemicals, Materials and Instrumentation Propylene carbonate (PC) was obtained from Acros Organics, lithium perchlorate (LiClO4) and poly(methyl methacrylate) (PMMA, Mw 996,000 g/mol) were obtained from Aldrich and they were all used as received. Tetrabutylammonium perchlorate (TB AP) was prepared by mixing a 1:1 mole ratio of tetrabutylammonium bromide dissolved in water with perchloric acid. The precipitate was filtered, recrystallized from a 1:1 molar ratio ethanol and water and dried in the vacuum oven for 24 hours at 60C. Fer rocene (Fe(C5H5)2) was obtained from Fluka. The monomer, 3,4 -ethylenedioxythiophene (EDOT) (Baytron M V2) was provided by H.C. Starck and distilled under vacuum from CaH2. The monomer, 3,4 propylene dioxythiophene (ProDOP) and poly(2,2,6,6 tetramethylpip eridinyloxy4yl methacrylate) (PTMA) were provided by CIBA Specialty Chemicals. Poly(3,3 dihexyl 3,4 dihydro 2 H thieno[3,4 b ][1,4]dioxepine) (PProDOT Hx2) (Mw 66,000 g/mol, PDI 1.7) was synthesized as previously described.26 Poly(3,4 propylenedioxythiophene N -propionitrile) (PProDOP N EtCN) SprayDOT -Green 145 (Mw 12,600 g/mol, PDI 1.4), SprayDOT -Purple 101 (Mw 84,900 g/mol, PDI 2.1) SprayDOT Red 252 (Mw 17,900 g/mol, PDI 2.2), SprayDOT Green 179 (Mw 88,600 g/mol, PDI 2.1) and SprayDOT -Blue 153 (Mw 42,700 g/mol, PDI 2.6) were synthesized by Reynolds Group.40, 58, 59 All polymer solutions were filtered throu gh 0.45 m Whatman Teflon (PTFE) syringe filters prior to spraying. Formulated aqueous dispersion of poly(3,4 -

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42 ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), Clevios PH 500, was purchased from H.C.Starck. (resistivity = 0.1 ohm -cm, bulk conductivity = 500 S/cm, mean particle size = 30 nm, solids content = 1.2%). The formulation requires prior addition of 5 w % dipolar organic solvent such as DMSO in order to achieve high conductivity films. ITO coated polished float glass slides CG 51IN C UV (7 50 0.7 mm, Rs= 8 CG 51IN -S107 (25750.7 mm Rs = 8 coated glass slides were wiped off with acetone to remove the immediate residue and air dried prior to use. Contacts to the ITO s lides were made using conductive Cu tape (1131) purchased from 3M. Gass beads (100 micron) were obtained from BioSpec Products, Inc. and washed with acetone and air dried before use. Track etched polyester (PETE) membranes (PETI00SP, 20 25 cm sheets) w ere purchased from Sterlitech Corporation. Membranes were 9 m thick with 10 5 pores/cm2 and is resistant to organic solvents such as acetonitrile (ACN), propylene carbonate (PC) and dim ethyl sulfoxide (DMSO). Pure gold coins (99.99%) were purchased from National Coin Investors, Inc. (Gainesville, FL) and cut into pieces for metal deposition. Platinum wire and sheets and silver wire were purchased from Alfa Aesar. Platinum button electr odes and electrode polishing kit were purchased from BASi (www.bioanalytical.com). Spectrosil Quartz cuvettes (1/Q/1) with a useable range of 170 to 2700 nm and with a 10 mm path length were obtained from Starna Cells. The potentials for fundamental ele ctrochemical studies, spectroelectrochemistry, tandem chronoabsorptometry/chronocoulometry and devices were controlled by EG&G PAR model 273A potentiostat/galvanostats (controlled using CorrWare software (Scribner Associates)) in a three-electrode cell con figuration. The potential in multi -electrode systems was controlled by Pine Bipotentiostat model AFCBP1. When performing two electrode studies with

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43 the standard potentisostats the reference and the counter electrodes were shorted together as a single cou nter electrode. All absorption/transmission, spectroelectrochemistry, and chronoabsorptometry experiments were carried out on a Varian Cary 500 Scan UV vis -NIR max in order to control the thickness of films while spraying were done by Genesys 20 Spectrophotometer (Thermo Electron Corporation). Colorimetry was carried out using a Minolta CS 100 Chroma Meter. Digital photographs were taken with a Fujifilm FinePix S7000 digital camera by back illumination with a D50 (5000K) light source. Veeco Dektak 150 Profilometer was used for thickness measurements (UF Nanofabrication Facility). Airbrush, iwata -eclipse HP BS (purchased from www.iwata -medea.com ), was used for spraying films. Keithley 2400 source meter was used for two -probe surface resistivity measurements. 2.2 Electrochemistry 2.2.1 Electrochemical Setup Electrochemical measurements were performed in a three-electrode c ell configuration via potentiostatic or potentiodynamic methods. In this set up the potential is applied to the system through working and reference electrode. The three -electrode cell configuration eliminates the potential drop error that arises because of the resistance of solution and contacts. The current response is recorded through working and counter electrodes. The glass cylindrical cell was filled with 0.1 M electrolyte/solvent couple and the working, counter and reference electrodes were immers ed in the solution. Components of the electrolyte solution (salt and solvent) and electrode materials must be chosen to ensure wide electrochemical window. Electrode materials must be highly conductive. The Pt button working electrode with a surface area of 0.02 cm2 was polished prior to use, as detailed below, in order to remove the immediate adsorbed material. The platinum flag or Pt wire counter electrode with a surface area greater than or equal to the

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44 surface area of the working electrode was flamed before use to remove any residue. A pseudo reference Ag wire electrode was used in this work and was calibrated vs Fc/Fc+ by using 5 mM ferrocene/0.1 M electrolyte solution. Before and after each experiment, the cell was filled with the ferrocene soluti on and the potential range was scanned two times. Anodic and cathodic peak potentials (Epa and Epc) for Fe+2/Fe+3 redox reaction (also denoted as Fc/Fc+) were determined from these CV scans. The average of these peak potentials gives the half -wave potent ial (1 / 2=+ 2 ) of the Fc/Fc+ against the silver wire. The E1/2 value was subtracted from the experimental potentials in order to convert them from vs. Ag wire to vs. Fc/Fc+. Since the Ag wire has a high impedance the current passing through t ends to shift the potential noticeably during the experiment. Therefore, calibrations must be done constantly. The solution was bubbled with and inert gas (Ar) for 10 minutes before starting the experiment to remove oxygen which can react (reduce). As it has been extensively reviewed by a previous researcher in the Reynolds Group and Pavlishchuk et al., the Fc/Fc+ redox couple will be considered 5.1 eV below the vacuum in this work.60, 61 2.2.1.1 Pt -button electrode preparation The polishing kit, obtained from BASi, consist of two disk pads, a brown velvety Texmet pad an d a white nylon pad. After dampening the disk pads with distilled water, a few drops of the 1 Texmet pads, respectively. The electrode surface was placed on the nylon pad and polished using circular motions. The same procedure was followed on the Texmet pad. Then the electrode was rinsed with methanol or acetone.62

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45 2.2.2 Electrochromic Polymer Film Formation Polymer films can be electrochemically deposited from their monomers. If we have soluble EC polymers they can be drop cast on small surfaces such as Pt button electrodes and spray cast on large surfaces such as ITO/glass electrodes. 2.2.2.1 Electrochemical deposition Electrochemical polymerization to form an electroactive and electorchromic polymer films was carried out in a 0.1 M electrolyte, 10 mM monomer, sol ution potentostatically, galvanostatically or potentiodynamically. For electro -deposition of a polymer film on a Pt button (0.02 cm2) electrode, the three -electrode cell with a platinum flag counter electrode, and Ag/Ag+ reference electrode was used. For electro -deposition of a polymer film onto ITO/glass electrode (2.27 cm2 active film area) the three-electrode cell configuration in a quartz cell with a platinum wire counter electrode, and a Ag wire reference electrode was used. Higher surface resistivit ies and larger surface areas as compared to of button electrodes ITO/glass electrodes (8 4 ohms) results in high IR drops across the film and gives broader voltammetric peaks. 2.2.2.2 Spray or drop casting The soluble polymer films were drop cast from their neutral form on Pt button electrodes for fundamental electrochemical studies. For optical studies polymers were spray -coated onto ITO coated glass slides using an airbrush at 20 psi Argon pressure. Polymers were sprayed from a solution of polymer in an appropriate solvent such as toluene which has a low vapor pressure. The solution concentrations of 15 mg polymer/1 mL solvent were used. Polymer films were then air dried. (The detailed information about each polymer film is given in the associated chapter.) max of each polymer film while spraying. (In Chapter 4, for each polymer, a set of films with various

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46 ma x) was prepared and thicknesses were measured. The absorbance versus thickness plots provided the linear calibration equations.) 2.3 Electrochromic Film Characterizations 2.3.1 Spectroelectrochemistry Spectroelectrochemistry plays the main role in examini ng the optical changes that occur upon doping or dedoping of electrochromic films and devices. It provides information about the polymers band gap and intraband states created upon doping. For spectroelectrochemical analysis, a quartz cell which utilizes a Ag wire pseudo reference electrode, a Pt wire counter electrode and ITO/glass working electrode was used. In a typical experiment, 0.1 M electrolyte solution and a blank ITO slide were placed in both the sample and the blank cuvettes. Solutions in bo th cuvettes were degassed with argon for 10 minutes prior to background collection. The background was collected over the range of 1600 nm to 350 nm every 1 nm. Spectral data could be converted to eV by the equation given below. It must be kept in mind that eV plot will highly compress the data especially near IR region (many points in a very small range). ( ) = =6 626 10 34 2 99 108 1 ( ) 10 9 1 ( ) =1 98 10 16 ( ) 1 1 602 10 19 1 =1240 ( ) After background collection, the polymer coated ITO/glass was placed in the sample cuvette and leads were attached. The polymer film was conditioned by sweeping the potential between the oxidized and neutral potentials predetermined by CV studies on a Pt -b utton electrode and IT0/glass electrode for 20 cycles. Most of the polymers in this work were stable in their neutral state therefore the scan was started from the neutral potential. While the potential was held where the polymer is neutral the energy wa s scanned from 1600 nm (0.775 eV) near -IR

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47 to 350 nm (3.54 eV) uvregion. Then, the potential was stepped in 50 mV or 100 mV increments until the completely oxidized states were reached. 2.3.1.1 Dual method Two blank ITO/glass slides were stacked together back to back and inserted into an electrolyte solution in a quartz cell to be used as a blank. One blank was placed in the sample compartment while the other one was placed in the reference compartment. The background was collected. The electrochromic polymer was replaced with the blank in the sample compartment. The absorbance spectra were monitored at applied potentials. 2.3.1.2 Electrochromic Devices Blank devices, ITO -coated glass slides with a gel electrolyte sandwiched between them without the electroactive polymer layer, were used as references for the background collection. Then, the real devices were placed in the sample compartment and leads were attached (the counter and the reference leads are connected to one another) to control potential and the absorption (or %transmission) was monitored. 2.3.2 Colorimetry In situ Colorimetry has also been utilized to precisely map the colors associated with EC polymers. In situ Colorimetry experiments were done with a CIE recommended normal/normal (0/0 ) illuminating/viewing geometry in which the sample was illuminated from behind by a D50 (5000 K) light source in a light booth that eliminates the external light. The experimental setup used for colorimetric analysis of single polymer films and devices is similar to the one used for spectroelectrochemistry. Color coordinates were recorded in CIE 1931 Y xy format. Y (Lv) stands for photometric luminance with units of cd/m2 and xy are the chromaticity coordinates. Relative luminance, Y/Yn, is the normal ized luminance of the sample relative to the standard (reference white). The

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48 relative luminance could be multiplied by 100 to report % relative luminance, (Y/Yn100). Relative values are more practical since it is very difficult to reproduce absolute val ues. We report data in L*a*b* color coordinates since they are all relative to the standard illuminant and the reference and this eliminates the experimental errors that might arise from the viewing angle, aging of light source and etc. Note that L* in L *a*b* color space stands for lightness and it is a function of luminance (Y).55 The most essential feature of displays, the contrast, is the ratio of the darkest color to the brightest color. High contrast displays are desired since they are much better perceived by human eye. Contrast can arise either from luminance or color differences and it is dependent on the illuminant and the viewing angle. Luminance contrast (Michelson contrast) is calculated as follows, =( ) ( + ) where Ymax and Ymin are the maximum and minimum luminance of the brightest and the darkestpoints on the display. The contrast, C, ranges from O to 1. 63, 64 2.3.3 Composite Coloration Efficiency (Tandem Chronocoulometry /Chronoabsorptometry) and Switching Times Composit e coloration efficiency method introduced by our group allows the quantitative comparison of different systems.21 A tandem chronoabsorptometry/chronocoulometry experiment was used to calculate composite coloration efficiency and switch time at 95% of the total change in optical contr max. Coloration efficiencies were assessed by monitoring the %T at a constant wavelength as a function of inserted (injected/ejected) charge. max) between two extreme redox states was obtained from spectro electrochemistry experiments. To obtain polymer and device switching times and composite coloration efficiency, the Cary 500 spectrophotometer was switched to Kinetics -

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49 Transmission mode and average time was set to minimum (0.033 s.). The %T was recorded a t max by time (chronoabsorptometry) while the film was brought to two redox extremes by the applied square potential waveform at intervals of 10 s. The change in charge density versus time (30 data points/s.) was recorded for further calculations (chronocoulometry). The composite coloration efficiencies were calculated from the following equations.19, 21, 65 = = ( ) d is the injected/ejected charge per unit electrode area calculated using the following equations. The ideal material or device would exhibit a large transmittance change with a small amount of charge. = = | 0 95 | = log % 0 95% Injected ejected charge difference; = 0 95 Switching time; = 0 95 2.3.4 Optical Stability of Polymer Films and Devices The optical stability data of polymer films and ECDs were obtained by monitoring the lightness (L*) or % T (at the specified wavelength) as a function of time while a square potential waveform is applied at desired time intervals (5 10 seconds). 2.4 Standard Two-Probe Surface Resistivity Measurement A conventional two -probe conductivity measurement method, derived from Ohms Law, thin PEDOT:PSS film and a thin film of gold (Au) deposited on a non -conducting polyester membrane (P ETE) was measured. The surface resistance (Rs) is the ratio of DC voltage (V)

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50 applied to two parallel electrodes to the current flowing between the electrodes ( = ) The etween electrodes to the current per unit length of electrodes, as shown by the following equation.46, 66, 67 = Even though it is common to see the unit of ohms/square, the correct way to report surface resistivity is in ohms. The setup for the two probe surface resistivity measure ment is illustrated in Figure 2 1. Copper tape contacts were deposited on the films parallel to each other. The distance between the electrodes was maintained equal to their length, giving a square area. The sheet resistance between the parallel copper tape electrodes was measured with a multi -meter. The geometry (lengths) is not important since they cancel each other out in the equation. Figure 2 1 Setup for a standard two -probe surface resistivity measurement 2.5 Dual Film Technique Two electrochromic polymer films with different absorption ranges along the visible spectrum were either electro -deposited or sprayed onto cuvette size ITO coated glass slides. All polymer films were conditioned under repeated potential scanning before use Two ITO electrodes with polymer films on them were placed back -to -back in a 1 cm quartz cell filled with Rs a b t

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51 0.1 M electrolyte solution. The potentials on these two working electrodes (ITO electrodes) were controlled separately by a bipotentiostat and they were set as working electrodes 1 and 2. A Ag wire was used as a pseudo reference electrode and a Pt wire as a counter electrode. Counter and reference electrode wires were arranged so that they face both working electrodes. In situ color coordinates, re lative luminance values, and electromagnetic spectra in the visible region were recorded from the dual polymer system upon application of different potentials to different working electrodes. 2.6 Electrochromic ECD Construction General schemes and more d etailed explanations for the construction of ECDs will be given in the following chapters. Preparation of gel electrolyte: The transparent, highly conductive (2.5 mS/cm) gel electrolyte used in the devices discussed in this work was composed of a solution of 10 mL PC, 1.1 g PMMA, 0.5 M TBAP and 10 mg glass beads. The gel was stirred and heated on a hot plate (<60 C) for about four hours until it reached a honey-like consistency. 2.6.1 Window Type Absorption/Transmission Electrochromic Devices (ECDs) Wi ndow type absorption/transmission ECDs were constructed by pairing a cathodically coloring polymer to non -electrochromic but electroactive transparent polymer. Polymers were deposited on ITO/glass (1''1'') electrodes. Electrochromic polymer was oxidativel y doped while the other was neutral prior to device assembly in order to ensure charge balance. Then, these two films were sandwiched with a gel electrolyte between them. The device was encapsulated by a paraffin wax that is resistant to propylene carbonat e and stopped the immediate leakage of the gel electrolyte. The wax was melted and hardened immediately after application to the four sides of the device with cotton swabs. Since in its solid phase the wax is brittle, it was supported by a

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52 commercial epox y that cures in 60 seconds. The same encapsulation method was followed for all types of devices that will be introduced in this dissertation. 2.6.2 Pseudo-Three -Electrode ECDs Electrochromic polymer films SprayDOT Green 145 and SprayDOT -Purple 101 were sp rayed on ITO/glass electrodes (1''1''). PProDOP -N EtCN, the non -color changing but electroactive counter electrode polymer, was electropolymerized on ITO -coated glass slides by repeated potential scanning from a 0.1 M tetrabutylammonium perchlorate (TBAP) /propylene carbonate (PC) solution containing 10 mM monomer. All polymer films were electrochemically conditioned by sweeping the potential. Physically, the construction of the Pseudo 3 Electrode Device is similar to absorptive/transmissive windows in suc h that it consists of two absorptive/transmissive windows in series sharing a counter electrode. The thicknesses of the PProDOP N EtCN films on the counter electrodes were set to ensure charge balance with the polymer they were facing. Cathodically coloring polymer films were fully oxidized (brought to their transparent state) and non-color changing films of PProDOP N EtCN were fully neutralized to improve the charge balance prior to the assembly of the device. The SprayDOT Green 145 and SprayDOT Purple 101 films were then coated with gel electrolyte and then the PProDOP N EtCN films were closed on top of them. Two devices were connected in series so that the counter electrode of each device was back to back and connected with a copper tape to serve as a conjunct counter electrode to the whole device. The SprayDOT Green 145 serves as a working electrode 1 and the SprayDOT -Purple 101 serves as working electrode 2. The devices were encapsulated to allow long-term testing. 2.6.3 Three -Electrode ECDs Three El ectrode electrochromic display device consists of 2 working electrodes and a counter electrode whose potentials are controlled separately. Working electrodes were prepared

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53 as explained above for pseudo3 electrode ECDs. Counter electrode that is to be sand wiched between working electrodes 1 and 2 was made of a flexible, porous, transparent and conductive material. In order to establish this type of electrode (PETE/PEDOT:PSS), highly transmissive polyester membranes were soaked in PEDOT:PSS/DMSO formulation and they were cured for 2 hours in a vacuum oven at 120 oC to reach a highly conductive state. Highly soluble, non electrochromic, electroactive, transparent polymer, PTMA, was blended with PMMA in order to prevent its dissolution in to the gel electrolyt e. PTMA and PMMA were dissolved in toluene in a weight ratio of 1:4 (w/w) and the final concentration of solution was 1.25 mg polymer/mL of solvent. The solution was sprayed on to the new type of electrode PETE/PEDOT:PSS to be utilized as a counter electro de (PETE/PEDOT:PSS/PTMA). Electrode layers were separated by a gel electrolyte which utilizes the charge transport. The device was encapsulated. 2.6.4 RGB Color Space Five -Electrode ECDs RGB Color Space 5 -electrode electrochromic display device consists o f 3 working electrodes and two counter electrodes whose potentials are controlled separately. ITO/glass was chosen as an electrode material for the outermost electrodes, working electrode 1 and working electrode 3, in order to establish a strong foundation for the multi layered device. Inner electrodes were made of (PETE/PEDOT:PSS/PTMA) of whose preparation was described above for 3 -electrode ECDs. Electrochromic polymers which are red and green at their neutral states were sprayed on to ITO/glass electro des. Electrochromic polymer which is blue at its neutral state was sprayed on PETE/PEDOT:PSS and named working electrode 2. PTMA:PMMA, nonelectrochromic, electroactive, transparent polymer blend, was sprayed on PETE/PEDOT:PSS to be utilized as counter e lectrodes 1 and 2. Counter electrodes 1 and 2 were sandwiched in between the working electrodes 1, 2 and 3 and maintained the charge balance in the device.

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54 Electrode layers were separated by a gel electrolyte which utilizes the charge transport. The devi ce was encapsulated.

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55 CHAPTER 3 DUAL POLYMER ELECTROCHROM IC FILM CHARACTERIZA TION USING BIPOTENTIOSTATIC CON TROL Conjugated conducting polymers receive particular attention for their potential use in controllable light reflective or lighttransmis sive electrochromic displays for optical information and storage.13 They have fast switching speeds, high contrast ratios and high coloration efficiencies. Several are available as solution -processable materials, and their electrochromic properties and color states can be synthetically tuned.19 ECDs are designed to modulate absorbed, transmitte d, or reflected incident electromagnetic radiation, through the application of an electric field across the electrochromic materials within the device.13 Often, an ECD includes two electrochromic materials that have complementary optical (cathodic and anodic coloring) properties allowing both electrochromes to contribute to the optical response of the device. The absorptive/transmissive type ECD operates with a reversible switching of the electrochrome between a colored state and a bleached state. Both working and counter electrode are transparent so that light can pass through the device. Reflective ECDs have also been developed where the active electrochromic polymer is deposited onto an outward -facing reflective electrode, such as gold deposited onto a flexible, ion permeable substrate.29 Although choice of electrochromic conjugated conducting polymers can provide colors across the entire range of the visible spectrum, colors achieved through color addition, especially in intermediate oxidation sta tes is not always obvious in dual polymer additive devices. Here, we introduce a novel analytical method, which allows the systematic variation of color states of pairs of electrochromic conjugated conducting polymers with simultaneous spectroelectrochemi cal and colorimetric characterization of the resulting color summation. In this method, the polymers are prepared as films on ITO/glass substrates and mounted back to -

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56 back in transmission mode in a spectroelectrochemical cell. A bipotentiostat provides s eparate electrochemical control of individual polymer color states. By the dual polymer electrochromic technique through bipotentiostatic control, we demonstrate the generation of new color states by coupling existing polymers. Our choices of polymers fo r this study, with examples prepared both by monomer electropolymerization and the spray-coating of soluble polymers,26 have been from the available PXDOT and PXDOP families, although, in principle, this approach is applicable to numerous electrochromes. 3.1 Color Mixing In its simplest sense, color mixing allows the matching of complex colors through the combination or formulation of color components.49, 56 In the dual -polymer electrochromic film characterization technique reported here, the results can be used to design dual polymer ECDs where the color summation of the films in any of their color states c an be accessed as the films oxidation states are controlled independently. The key to this is understanding the coloration process during the doping /dedoping of the polymer films. These primary colors can be summed to more complex colors by passing white light simultaneously through two films and observing the transmitted light. Color engineering for ECDs will let us foresee colors that are accessible after the primary components are matched logically. Each dual system will have a palette of colors a vailable made possible by independently varying the oxidation state of the two films. According to color mixing theory, it is possible to obtain all colors required once additive or subtractive primary colors are available.38, 41 The theory also states that, when colors are mixed, the chromaticiy coordinates of the resulting color lies on the line joining the tw o original chromaticity coordinates. Thus, one can determine the approximate hue of the device that constitutes several layers of electrochromic polymers. Other than structural modifications, a fine

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57 tuning of color is also possible by adjusting doping le vels and the film thickness in electrochromic devices. The ideal electrochromic device should exhibit high coloration efficiency, meaning that very high optical contrast by introduction of least amount of charge, high stability and fast switch times.19 Until now, multicolor displays have been shown to be possible by combining two ECDs in series and controlling them independently or by patterning the electrode surfaces.19, 41, 68, 69 3.2 Choosing A System for Dual -Polymer Technique by Fundamental Properties (EDOT, ProDOP a nd ProDOT -Hx2) In this work we have used PEDOT, PProDOP and dihexyl substituted poly(3,4propylenedioxythiophene) (PProDOT Hx2) as exemplary EC polymers whose colors can be summed to provide new colors not possible with the single films alone.26 The repeat unit structures of the polymers, along with photographs of the polymer films in their oxidized and reduced states are shown in Figure 3 1. Each of these polymers is cathodically coloring with orange, blue, and purple/magenta colors in their fully neutral states. Also shown in Figure 3 1 is a schematic of the cell used for the dual -polymer EC characterization method. In this construction, EC polymer films are deposited onto separate ITO/glass slides and placed back to back in a cuvette in order to mimic the combined light absorption properties of a dual polymer ECD. The redox state of each film (WE 1 and WE 2) is the n controlled independently with a bipotentiostat. Understanding the coloration process during the oxidation and charge neutralization of the polymer films is of paramount importance in establishing the new color palettes. To understand this fully, it is necessary to obtain the electrochemical and optical properties of the separate polymer films. Electrochemical characterizations on Pt -button electrodes and

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58 spectroelectrochemical experiments on ITO -coated glass electrodes were used to establish baseline properties. Figure 3 1 Chemical structures of the polymers that are used in dual -polymer electrochromic method and the photographs of their neutral (N) and doped (D) states on ITO/glass electrode with the schematic of the dual -polymer electrochromic char acterization cell. 3.2.1 Film Deposition In order to obtain thin films of the EC polymers, both EDOT and ProDOP were electrochemically polymerized onto Pt -button electrodes from a 0.1 M LiClO4/PC solution containing 10 mM monomer by repeated scanning as shown in Figure 3 2 and Figure 3 3, respectively. During the first anodic scans, a single peak was observed corresponding to irreversible oxidation of the monomers indicating formati on of radical cations (Figure 3 2 inset). The peaks of monomer oxidation a re observed at +1.02 V for EDOT and +0.56 for ProDOP vs. Fc/Fc+. Subsequent scanning shows evolution of a redox response at lower potentials attributed the polymer oxidation and charge neutralization. PProDOT Hx2 was drop cast from a 5mg/mL polymer/tolue ne solution onto a Pt filter. CE RE WE 2 WE 1 CE RE WE 2 WE 1

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59 Figure 3 2 The repeated potential scanning electropolymerization of EDOT from 10 mM monomer in 0.1 M LiClO4/PC solution on a Pt -button electrode at a scan rate of 20 mV/s. Figure 3 3 The repeated potential scanning electropolymerization of ProDOP from 10 mM monomer in 0.1 M LiClO4/PC solution on a Pt -button electrode at a scan rate of 20 mV/s. -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 -6 -4 -2 0 2 4 6 8 10 12 Current Density ( mA/cm 2 )Potential (V) vs. Fc/Fc + -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 -1 0 1 2 3 4 5 Current Density ( mA/cm 2 )Potential (V) vs. Fc/Fc + -1.5 -1.0 -0.5 0.0 0.5 1.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 Current Density ( mA/cm 2 )Potential (V) vs Fc/Fc +

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60 3.2.2 Polymer CV and Scan Rate Dependence After deposition, all films we re rinsed with monomer -free electrolyte solutions and cyclic voltammograms (CVs) were recorded at scan rates ranging from 20 to 300 mV/s as shown in Figures 3 4 to 3 6. A linear increase of the current with scan rate is observed for each film, indicative of a surface adhered electroactive polymer film. An important aspect observed in these experiments is that the current passing through the PEDOT film is an order of magnitude greater than the current passing through the PProDOP (prepared with the same num ber of deposition scans) and PProDOT Hx2 films. This demonstrates the highly effective electropolymerization and switching characteristics of PEDOT. This shows that during the preparation of dual film devices, it is important to balance the overall amoun t of electroactive polymer on each electrode, usually using film thickness as the operational parameter, in order to obtain a balanced optical response. Figure 3 4 Cyclic voltammograms of PEDOT in 0.1 M LiClO4/PC at scan rates of (a) 20, (b) 50, (c) 100, (d) 150, (e) 200, and (f)300 mV/s. Film was electrochemically polymerized onto the Pt -button electrode from a 0.1 M LiClO4/PC solution containing 10 mM monomer by repeated scanning. -2.0 -1.5 -1.0 -0.5 0.0 0.5 -30 -20 -10 0 10 20 30 40 f a Current Density ( mA/cm 2 )Potential (V) vs Fc/Fc + a f

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61 Figure 3 5 Cyclic voltammograms of PProDOP in 0.1 M LiClO4/PC at scan rates of (a) 20, (b) 50, (c) 100, (d) 150, and (e) 200 mV/s. Film was electrochemically polymerized onto the Pt -button electrode from a 0.1 M LiClO4/PC solution containing 10 mM monomer by repeated scanning. Figure 3 6 Cyclic voltammograms of PProDOT Hx2 in 0.1 M LiClO4/PC at scan rates of (a) 20, (b) 50, (c) 100, (d) 150, (e) 200, and (f) 300 mV/s. Film was prepared by dropcasting onto a Pt -button electrode from 5 mg/mL polymer/toluene solution. 3.2.3 Spectroelectrochemistry Using the above CV experim ents as a means of determining the correct potential ranges for switching and evaluating the stability of the electroactivity of the polymer films, -1.2 -1.0 -0.8 -0.6 -0.4 -4 -3 -2 -1 0 1 2 3 4 5 6 e a Current Density ( mA/cm 2 )Potential (V) vs Fc/Fc + a e -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 f a Current Density ( mA/cm 2 )Potential (V) vs Fc/Fc + a f

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62 spectroelectrochemical and colorimetric experiments were conducted to elucidate the separate optical charact eristics of the polymer films alone. Films were deposited on ITO coated glass slides potentiostatically for PEDOT (1.6 V for 20 s), galvanostatically for PProDOP (0.11 mA for 1000 s) and by spray casting (5 mg/mL from toluene) for PProDOT Hx2. The film thicknesses were adjusted to between 100300 nm so that the absorbances of the polymer films at max in their neutral states were equal. The spectroelectrochemical series for each of the polymer films are shown in Figures 3 7 to 3 9. In their neutral states, PEDOT appears deep blue (absorbing between 1.6 and 2.75 eV), PProDOP appears orange (absorbing between 2.2 and 3.0 eV) and, PProDOT Hx2 appears purple (absorbing between 1.8 and 3.0 eV). As these polymer films are doped, charge carrier st ates emerge with the majority of the light absorption for each polymer being in the NIR which results in highly transmissive films. Note, in the spectroelectrochemical series for PProDOP, we step to +0.5 V which is substantially higher than the potential window used in the CV. This higher applied potential allowed us to fully oxidize the film and attain the most transmissive form. This ability to form a transmissive state for each of these cathodically coloring polymers is important when considering them for use in EC max (632 nm, 522 nm and 571 nm) are 55%, 73% and 65% for PEDOT, PProDOP and PProDOT Hx2, respectively.

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63 Figure 3 7 Spectroelectrochemistry of potentiostatically deposited, redox switched, PEDOT film at applied potentials of (a) 1.45 to (s) +0.35 V vs Fc/Fc+ in increments of 0.1 V in 0.1 M LiCLO4/PC solution. Figure 3 8 Spectroelectrochemistry of galvanostatically d eposited, redox switched, PProDOP film at applied potentials of (a) 1.7 to (s) +0.1 V vs Fc/Fc+ in increments of 0.1 V in 0.1 M LiCLO4/PC solution. 400 600 800 1000 1200 1400 1600 0.0 0.5 1.0 1.5 s a Absorbance (a.u.)wavelength (nm)a s 400 600 800 1000 1200 1400 1600 0.0 0.5 1.0 1.5 2.0 s a Absorbance (a.u.)wavelength (nm)a s

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64 Figure 3 9 Spectroelectrochemistry of spray-cast, redox -switched, PProDOT Hx2 film at applied potentials of (a) 0.67 to (m) +0.53 V vs Fc/Fc+ in increments of 0.1V, in 0.1 M LiCLO4/PC solution. 3.2.4 Tandem Chronocoulometry and Chronoabsorptometry Tandem chronoabsorptometry and chronocoulometry experiments allow calculation of composite coloration efficiency (CE). By choosing 95% of the optical density change the transmittance of the reduced films is compared to that the of oxidized films. The amount of time to reach 95% of the full optical density is chosen as nearly all of the optical change has occurred and a direct comparison of polymers that switch at different rates can be made.21 Polymer films with similiar switching times and contrast ratios were chosen for application to the dual -film technique. The coloration efficiency for PEDOT is 280 cm2/C and the 95% switch time is 1.7 s with a charge density of 3.4 mC/cm2, while for PProDOP the coloration efficiency is 224 cm2/C and the 95 % switch time is 0.9 s with a charge density of 1.6 mC/cm2, and for PProDOT Hx2 the coloration efficiency is 519 cm2/C and the 95% switch time is 0.6 s with a charge density of 1.4 mC/cm2 (Figures 3 10 to 312). All three polymer films have substantial EC switching occuring in the sub -second time frame and are fully switched within two seconds at most. 400 600 800 1000 1200 1400 1600 0.0 0.2 0.4 0.6 0.8 1.0 m m a Absorbance (a.u.)wavelength (nm)a

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65 Figure 3 10 Tandem chronoabsorptometry and c hronocoulometry experiments for PEDOT in 0.1 M LiClO4/PC solution. ( 1.45 to +0.55 V vs. Fc/Fc+, held for 10 s at each potential at 632 nm) Figure 3 11 Tandem chronoabsorptometry and chronocoulometry experiments for PProDOP (1.7 to +0.1 V vs Fc/Fc+, held for 10 s at each potential at 522 nm) in 0.1 M LiClO4/PC solution. 0 2 4 6 8 10 12 14 16 18 20 0 1 2 3 4 5 6 time (sec.)Charge Density ( mC/cm 2 ) 10 20 30 40 50 60 % Transmittance 0 2 4 6 8 10 12 14 16 18 20 0.0 0.5 1.0 1.5 2.0 2.5 3.0 time (sec.)Charge Density ( mC/cm 2 ) 25 30 35 40 45 50 55 60 65 % Transmittance

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66 Figure 3 12 Tandem chronoabsorptometry and chronocoulometry experiments for PProDOT Hx2 in 0.1 M LiClO4/PC solution. ( 0.67 to +0.53 V vs. Fc/Fc+, held for 10 s at each potential at 571 nm) 3.2.5 Colorimetry Since color is subject to the response, sensitivity, and perception of the human eye, elaboration on EC properties are best accomplished with an accurate quantitative measure of the color. In situ color coordinates (hue and s aturation) and relative luminance (the amount of light transmitted through the polymer film) values were recorded for each polymer film separately (Figures 3 13 to 3 15). Considering the three polymer films in their fully reduced forms, PEDOT has a and b values of 5 and 37, respectively, giving it a dark blue color with a relative luminance of 32%, PProDOP has a* and b* values of 31 and 75, respectively, giving it an orange color with a relative luminance of 50%, and PProDOT Hx2 has a* and b* values of 1 4 and 45 giving it a purple color with a relative luminance of 24%. Note, there is variability in the measured L*, a*, and b* values measured as a function of subtle changes in film thickness and applied potential. For example, in earlier work we measure d neutral PEDOT as L* = 20, a* = 15, and b* = 43.70 While in both instances the PEDOT films are obviously a deep blue, this 0 2 4 6 8 10 12 14 16 18 20 0.0 0.5 1.0 1.5 2.0 2.5 time (sec.)Charge Density ( mC/cm 2 )10 20 30 40 50 60 70 80 %Transmittance

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67 points out the sensitivity of the method. Also note that the a* and b* values reported for PEDOT in this earlier work are close to th e values reported here for PProDOT Hx2, even they have different colors. The color difference in this case arises from different L* values they have. When the films are completely oxidized they all are converted into highly transmissive and sky -blue col ored films. Now, PEDOT exhibits a* and b* values of 2 and -4, respectively, with a relative luminance of 82%, PProDOP exhibits a* and b* values of 3 and -6, respectively, with a relative luminance of 57%, and PProDOT Hx2 exhibits a* and b* values of 2 and 4, respectively, with a relative luminance of 86%, demonstrating the cathodic coloration properties of each of these polymers. As shown by t he luminance change in Figure 3 15, PProDOT Hx2 possesses the highest contrast ratio in the visible region o PEDOT and PProDOP have 50% and 10 20% (from fully neutral to the oxidized form), respectively. The reduced contrast of PEDOT relative to PProDOT Hx2 is due to the strong NIR absorption that is found in the oxidized form of PEDOT providing a visible light absorption tail in the red region of the spectrum, which is lower in intensity for the substituted PProDOTs. The simple loss of absorption in the visible region for the thiophene derivatives upon oxida tion is seen to be more complicated in PProDOP. As the polymer has a higher band gap, the neutral form is more transmissive to visible light than either of the thiophene derivatives. The initial formation of a polaron during oxidation gives an absorption in the visible region, which results in an init ial loss of luminance (Figure 3 14). This polaron absorption is subsequently bleached upon full oxidation and a highly transmissive (%Y ~ 60%), light gray state is ultimately reached. These luminance change s with applied potential will play a strong role in the EC response of the dual film systems to be described below.

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68 Figure 3 13 Relative luminance as a function of applied potential of PEDOT in 0.1 M LiClO4 solution Figure 3 14 Relative luminance as a function of applied potential of PProDOP in 0.1 M LiClO4 solution -1.6 -1.4 -1.2 -1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 30 40 50 60 70 80 90 Relative Luminance (%Y)Potential (V) vs. Fc/Fc + -1.4 -1.2 -1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 25 30 35 40 45 50 55 60 65 Relative Luminance (%Y)Potential (V) vs. Fc/Fc +

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69 Figure 3 15 Relative luminance as a function of applied potential of PProDOT Hx2 in 0.1 M LiClO4 solution 3.3 PProDOP/PEDOT and PProDOP/PProDOT -Hx2 Dual Systems Two ITO working electrodes with different EC polymer films on them were prepared in a similar manner to the films that were used for spectroceletrochemical and colorimetric characterizations. Both ITO electrodes with two different polymer films on them and under separate potentiost atic control were placed back to back in a 1cm quartz cell, with a Ag wire as a reference electrode and a Pt wire as a counter electrode. ITO -coated glass slides were used as the working electrodes (Figure 3 1). In situ color coordinates and electromagne tic spectra in the visible region were recorded from the dual -polymer system upon application of different potentials to different working electrodes in a 0.1 M LiClO4/PC solution. Absorbance spectra of PEDOT and PProDOP films, were taken separately at their reduced (both at 1.35 V vs. Fc/Fc+) and oxidized (PEDOT at +0.45 V and PProDOP at 0.05 V vs. Fc/Fc+) states and these spectra were summed theoretically in order to attain a perspective of the -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 20 30 40 50 60 70 80 90 Relative Luminance (%Y)Potential (V) vs. Fc/Fc +

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70 combination of the optical response expected from the dual -film EC method. This is demonstrated by the single film red and black curves in Figure 3 16, along with the theoretical summation represented by the green curve (Not e the green curve in Figure 3 16 ( b ) is difficult to see behind the blue curve). The blue curves in Figure 316 show the direct spectral response from the combined films. The theoretical and experimental spectra are shown to overlay one another completely for the oxidized films, and are quite similar for the reduced films. The color transmitted through the stacked films thus appears completely different from the component films and is difficult to foresee. The experimental summation spectrum proves that the dual system enables the physical addition of the optical properties of two different polymer systems thus motivating the perception of new colors which are the mixtures of each polymer. Two dual -film systems were studied colorimetrically from the three polymer films employed. The color palettes in Figures 3 17 and 3 18 show the photographs and the L*a*b* color coordinates as a function of the separate potential applied to each film. These color palettes can be used to tune in the accessible colors from a dual -film EC device. Fo r example, as shown in Figure 3 17 as PProDOP is reduced and held in its orange state while sequentially oxidizing PEDOT, the luminance of the dual -film system increases from 59 to 68 as PEDOT is converted from a dark blue to a transmissive film. Along this track, the orange color dominates as the film retains an o range/brown hue. Holding PEDOT in the deep blue neutral state while sequentially oxidizing the PProDOP yields a more distinct visual response with the brown/orange film changing to a green -tinted gray. Full oxidation of both films gives the lightest gray state.

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71 Figure 3 16 UV vis -NIR spectra of PProDOP/PEDOT from dual -polymer electrochromic setup at (a) reduced, and (b) oxidized states in 0.1 M LiClO4/PC solution 400 600 800 1000 1200 1400 1600 0.0 0.5 1.0 1.5 2.0 2.5 PProDOP PEDOT theoretical summation of PProDOP and PEDOT experimantal summation of PProDOP and PEDOT Absorbance (a.u.)wavelength (nm)a 400 600 800 1000 1200 1400 1600 0.0 0.5 1.0 1.5 2.0 2.5 PProDOP PEDOT theoretical summation of PProDOP and PEDOT experimantal summation of PProDOP and PEDOT Absorbance (a.u.)wavelength (nm)b

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72 Figure 3 17 L*a*b* color coordinates and photography for PProDOP/PEDOT in 0.1 M LiClO4/PC The color changes are even more distinct in the PProDOP/ PProDOT Hx2 couple seen in Fi gure 3 18. When the PProDOP film is held reduced while oxidizing the PProDOT Hx2 film the luminance value increases from 56 to 72 due to the PProDOT Hx2 converting from dark purple to transmissive blue and resulting in a distinct reddish/purple to orange color change in the dual -film system. As the PProDOP is oxidized and the PProDOT Hx2 held reduced, the conversion to the blue state is observed as the PProDOP becom es highly transmissive. Finally the highest luminance is observed as both films are oxidized. 1.35 Vvs. Fc / Fc+1.20 V 1.05 V 0. 90 V 0. 75 V 0. 60 V 0.45 V L*=64 a *= 5 b*= 37 L*=63 a *= 6 b*= 38 L*=64 a *= 6 b*= 37 L*=64 a *= 6 b*= 37 L*=65 a *= 6 b*= 36 L*=70 a *= 4 b*= 28 L*=79 a *= 2 b*= 17 1.35 V L*= 76 a*=3 1 b*=75 L*=59 a*=25 b*=50 L*=56 a*=25 b*=43 L*=58 a*=25 b*=48 L*=56 a*=26 b*=44 L*=59 a*=26 b*=50 L*=58 a*=28 b=*47 L*=68 a*=30 b*=64 1. 20 V L*= 76 a*=32 b*=74 L*=53 a*=25 b*=36 L*=51 a*=24 b*=27 L*=53 a*=25 b*=35 L*=51 a*=24 b*=27 L*=53 a*=26 b*=35 L*=52 a*=24 b*=27 L*=59 a*=29 b*=43 1.05 V L*= 75 a*=31 b*=72 L*=58 a*=24 b*=43 L*=55 a*=24 b*=39 L*=50 a*=18 b*=14 L*=55 a*=24 b*=39 L*=59 a*=25 b*=47 L*=57 a*=26 b*=43 L*=67 a*=28 b*=59 0. 90 V L*= 68 a*=25 b*=50 L*=51 a*=19 b*=18 L*=50 a*=18 b*=15 L*=50 a*=19 b*=18 L*=50 a*=19 b*=16 L*=51 a*=19 b*=18 L*=52 a*=18 b*=14 L*=57 a*=21 b*=26 0. 75 V L*= 67 a *= 11 b *= 8 L*=56 a *= 2 b*= 17 L*=53 a *= 6 b*= 11 L*=59 a *= 2 b*= 15 L*=52 a *= 8 b*= 8 L*= 56 a *= 6 b*= 11 L*= 55 a *= 10 b *= 2 L*=64 a *= 5 b *= 1 0. 60 V L*= 73 a *= 2 b *= 5 L*=57 a *= 2 b*= 17 L*=56 a *= 2 b*= 15 L*=57 a *= 1 b*= 17 L*=57 a *= 1 b*= 16 L*=58 a *= 1 b*= 16 L*=59 a *= 3 b*= 11 L*=64 a *= 2 b *= 8 0.45 V L*= 78 a *= 1 b *= 5 L*=60 a *= 0 b*= 18 L*=61 a *= 0 b*= 18 L*=61 a *= 0 b*= 18 L*=62 a *= 1 b*= 18 L*=62 a *= 0 b*= 17 L*=64 a *= 0 b*= 15 L*=67 a *= 1 b*= 11 PProDOP PEDOT

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73 Figure 3 18 L*a*b color coordinates and photography for PProDOP/PProDOT Hx2 in 0.1 M LiClO4/PC 3.4 Conclusions This work demonstrates a new dual -polymer elect rochromic film characterization technique allowing electrochromic polymer film couples to be studied and new colors generated. The color observed and thus the color coordinates read from the dual -polymer set up for the coupled polymer films were different than the data collected from these polymers when they were studied separately. For example; coupling PEDOT and PProDOP films in their neutral states resulted in a new color red/brown (L*=59 a*=25 b*=50) which is totally different than the original colors these polymers show at their neutral states, dark blue (L=64* a*= 5 b*= 38) and -0. 85 V -0. 65 V -0.45 V -0.25 V -0.05 V 0. 15 VL*= 56 a*= 14 b*= 45 L*= 5 6 a*= 14 b*= 45 L*= 56 a*= 14 b*= 4 5 L*= 59 a*= 1 2 b*= 40 L*= 81 a*= 8 b*= 11 L*= 9 2 a*= 1 b*= 3-1.35 VL*= 76 a *= 3 1 b *= 75 L*= 56 a *= 21 b *=1 6 L*= 54 a *= 23 b *= 16 L*= 5 4 a *= 23 b *= 15 L*= 5 5 a *= 2 2 b *= 14 L*= 6 6 a *= 2 7 b *= 33 L*= 72 a *= 2 4 b *= 39-1.20 VL*= 76 a *= 32 b *= 74 L*= 55 a *= 21 b*= 15 L*= 55 a *= 22 b *= 16 L*= 55 a *= 22 b*= 15 L*= 54 a *= 24 b*= 16 L*= 67 a *= 2 6 b *= 35 L*= 72 a *= 23 b *= 38-1.05 VL*= 75 a *= 31 b *= 72 L*= 55 a *= 20 b*=1 3 L*= 53 a *= 22 b *= 15 L*= 52 a *= 22 b *= 13 L*= 5 5 a *= 22 b = 14 L*= 6 8 a *= 25 b *= 32 L*= 7 2 a *= 22 b *= 37-0 .90 VL*= 68 a *= 25 b *= 50 L*= 5 2 a *= 16 b*= 2 L*= 52 a *= 18 b *= 1 L*= 5 2 a *= 17 b *= 1 L*= 53 a *= 18 b *= 3 L*= 65 a *= 20 b *= 21 L*= 7 0 a *= 17 b *= 26-0. 75 VL*= 67 a *= 11 b *= 8 L*= 5 4 a *= 9 b*= 21 L*= 5 3 a *= 11 b*= 18 L*= 5 4 a *= 10 b*= 17 L*= 55 a *= 11 b*= 14 L*= 68 a *= 9 b *= 2 L*= 7 3 a *= 4 b *= 2-0.60 VL*= 73 a *= 2 b *= 5 L*= 57 a *= 7 b*= 28 L*= 56 a *= 7 b*= 2 7 L*= 57 a *= 7 b*= 2 5 L*= 59 a *= 7 b*= 2 2 L*= 72 a *= 5 b *= 6 L*= 76 a *= 0 b *= 3-0.45 VL*= 78 a *= 1 b *= 5 L*= 60 a *= 7 b*= 28 L*= 5 8 a *= 8 b*= 28 L*= 5 9 a *= 7 b*= 27 L*= 6 0 a *= 8 b*= 2 4 L*= 7 4 a *= 4 b *= 7 L*= 7 9 a *= 1 b *= 4PProDOP PProDOT Hx2

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74 orange (L*=76 a*=31 b*=75), respectively. A full palette of colors is accessible by the logical coupling of electrochromic polymers in the dual -polymer electrochromic set up and this method eliminates the need to synthesize new families of polymers to generate different colors. With the correct choice of materials, the dual system promises many intermediate colors which will enable the formation of a wide color scale for ECDs

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75 CHAPTER 4 APPLICATION OF BIPOT ENTIOSTATIC CONTROL IN A 3 -ELECTRODE ELECTROCHROMIC DEVICE: TOWARDS BLACK TO TRANSMISSIVE AND MUL TI COLORED SWITCHING The focus of endeavoring synthesis of processable, high contrast EC polymers is to establish full color palettes for use in displays and printing. Printing technologies and electronic information transformation displays demand high contrast devices that could be perceived by a human eye with minimum blurring. This need brings out the requirement for a mate rial switching in between two extreme optical states, from opaque black to transmissive. There are inorganic displays switching from black to clear available, yet they are brittle.11 Synthesis of black to clear switching and processable conjugated polymers had been a challenge for synthetic chemists until, recently, the work reported and disclosed by Beaujuge et al.71 Other than synthetic means, new colors can be achieved by physical me thods. Researcher have utilized dual absorptive/ transmissive ECDs which are connected in series for color mixing.36 Since, these devices constitute many EC layers one can mix colors and determine the approximate hue of the device. Unfortunately, the use of these devices is limited to electrochromic materials with complem entary optical properties, one anodically coloring and the other cathodically coloring.30, 47 Other than that, as reported by Otero and Padilla, the contrast achieved in dual electrochromic systems are limited when compared to the contrast from single films. Higher contrast of dual electroc hromic windows is possible only through the careful design and use of an electroactive yet non -electrochromic highly transmissive polymers as a counter electrode materials.48 We utilized the dual -polymer electrochromic film characterization method in this chapter in establishing a new color profile including black to transmi ssive by mixing green and purple. Here, we introduced the first two black to transmissive switching conjugated polymer ECDs, the Pseudo 3 -Electrode Electrochromic Device (P3 -ECD) and 3 Electrode Electrochromic Device

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76 (3 ECD). These devices add colors by transmitting light through two working electrodes (coated with two different electrochromic polymer films) and counter electrodes (coated with non electrochromic yet electroactive polymer films) stacked together with a gel electrolyte between the layers. The electrodes are all under separate potentiostatic control, which enables the multi color switching. In this work, we utilized non-color changing, highly transmissive, electroactive polymers, PProDOP N -EtCN and PTMA, as counter electrode materials. The P3 ECD and 3 ECD stand out with their optical contrasts comparable to single films. By utilizing P3 ECD and 3 ECD, other than black and white scripts colored images can be displayed on information displays. P3 ECD and 3 ECD could also serve as reflectiv e type of devices (i.e. e-book) by use of a diffuse back -plane such as white paint or a cellulose based support. 4.1 Towards Black to Clear Switching ECDs -Fundamental Properties (SprayDOTTMPurple 101, SprayDOTTMGreen 145, PProDOP -N -EtCN) In this work di -ester substituted poly(3,4 propylenedioxythiophene) (PProDOT (CH2COOC12H25)2), SprayDOTTM-Purple 101 and SprayDOTTMGreen 145 were chosen as primary colors. The SprayDOTTMGreen 145, P(EDOT2(ProDOT (CH2O(2 EtHx))2)2BTD), was synthesized by alternative addition of electron rich EDOT and 2 -ethylhexyloxy -substituted 3,4 propylenedioxythiophene ProDOT (CH2O(2 -EtHx))2 onto the strong acceptor 2,1,3 benzothiadiazole (BTD). These primaries can be summed to provide new colors, especially black which has not be en available by synthetic means until the recent work that was published by Beaujuge et al.71 SprayDOTTM-Purple 101 and SprayDOTTMGreen 145 are cathodically coloring polymers, SprayDOTTMPurple 101 switching from a deep magenta (L*= 41 a*= 22 b*= 48) to a highly transmissive gray/blue (L*= 87 a *= 2 b*= 7) and SprayDOTTMGreen 145 switching from a deep green (L*= 60 a*= 23 b*= 12) to transmissive sky blue (L*= 84 a*= 4

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77 b*= 6). The repeat unit structures of the polymers, along with photographs of the polymer films in their oxidized and reduc ed states are shown in Figure 4 1. Figure 4 1 Chemical structures of the polymers that are used in dual -polymer electrochromic method and in ECDs, the photographs of their neutral (N) and doped (D) states on ITO/glass electrodes. Understanding the electrical response and coloration process of the polymer films is paramount in color and device engineering. Hence, it is essential to obtain the electrochemical and optical properties of the separate polymer films. Electrochemical characterizations on Pt button electrodes, spectroelectrochemical and colorometric experiments on ITO coated glass electrodes were used to set optimum conditions and foresee the outcome from the devices. 4.1.1 Film Deposition In order to obtain thin films of the EC polymers for electrochemical and optical studies, SprayDOTTMPurple 101 and SprayDOTTM-Green 145 were drop -cast (on Pt -button electrodes) or spray -cast (on ITO coated glass electrodes) from 2 mg/mL polymer/toluene solutions after filters. SprayDOTTM-Purple 101 and SprayDOTTMGreen 145 films sprayed on ITO/glass were dried under vacuum overnight. D N Ox Red N D Ox Red N N S S O O S O O O O R R S O O S O O O O R R n R = 2 E t h y l H e x y l S O O R R R = D o d e c y l O O O O SprayDOT Purple 101 SprayDOT Green 145 PProDOP-N -EtCNN D Ox RedPProDOT -(CH2COOC12H25)2P(EDOT2(ProDOT -(CH2O(2 -EtHx))2)2BTD)

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78 PProDOP N EtCN was electrodeposited on the same set of electrodes by potential scanning. Cyclic voltammograms for electrodeposition of PProDOP -N EtCN on a Pt -button electrode are shown in Figure 4 2 (20 cycles, 50 mV/s, 0.3 V to +0.6 V vs. Fc/Fc+). During the first anodic scan on Pt -button electrode, a single peak was observed corresponding to irreversible oxidation of the monomers ind icating formation of radical cations. The peak of monomer oxidation was observed at +0.4 V vs Fc/Fc+. Subsequent scanning shows evolution of a redox response at lower potentials attributed to the polymer oxidation and charge neutralization. PProDOP N Et CN films did not adhere strongly to ITO/glass, probably due to the N -substitution which enhances solubility. In order to stabilize the polymer on the transparent electrode, films were heated at 55 oC under vacuum for 30 minutes. This process might be ini tiating a cross linking between CN groups and decreasing the solubility of the polymer. Figure 4 2 Repeated potential scanning electropolymerization of ProDOP N EtCN from a 10 mM monomer in 0.1 M TBAP/PC solution on a Pt -button electrode (20 cycles, 50 mV/s, 0.3 V to +0.6 V vs. Fc/Fc+). -0.2 0.0 0.2 0.4 0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 Current Density ( mA/cm 2 )Potential ( V vs. Fc/Fc + ) -0.2 0.0 0.2 0.4 0.6 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 (mA/cm2 )V vs. Fc/Fc+

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79 4.1.2 Polymer CV and Scan Rate Dependence CVs were recorded at scan rates ranging from 25 to 300 mV/s as shown in Figures 4 3 to 4 5. A linear increase of the current with scan rate is observed for each film, indicat ive of a surface adhered electroactive polymer film. Figure 4 3 Cyclic voltammograms of PProDOP N -EtCN in 0.1 M TBAP/PC at scan rates of (a) 25, (b) 50, (c) 75, (d) 100, (e) 150, (f) 200 and (g) 300 mV/s, on a Pt button electrode. Film was prepared by potential scanning from a 10 mM monomer in 0.1 M TBAP/PC solution (20 cycles, 50 mV/s, 0.3 V to +0.6 V vs. Fc/Fc+). Figure 4 4 Cyclic voltammograms of the SprayDOTTM-Purple 101 in 0.1 M TBAP/PC at scan rates of (a) 25, (b) 50, (c) 75, (d) 100, (e) 150, (f) 200 and (g) 300 mV/s, on a Pt button electrode. Film was prepared by drop -casting onto a Pt -button electrode from a 2 mg/mL polymer/toluene solution. -0.3 -0.2 -0.1 0.0 0.1 0.2 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 g a g Current Density (mA/cm 2)Potential ( V vs. Fc/Fc + ) a -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 -1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 Current Density ( mA/cm 2 )Potential ( V vs. Fc/Fc + ) a g a g

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80 Figure 4 5 Cyclic voltammograms of the SprayDOTTMGreen 145 in 0.1 M TBAP/PC at scan rates of (a) 25, (b) 50, (c) 75, (d) 100, (e) 150, (f) 200 and (g) 300 mV/s, on a Pt button electrode. Film was prepared by drop -casting onto a Pt -button electrode from a 2 mg/mL polymer/toluene solution. 4.1.3 Spectroelectrochemistry Spectroelectrochemistry was used to assess the electronic structure and the nature of electrochromism in conducting polymers since -dimers all factor into the overall properties of organic EC polymers. Spectroelectrochemical and colorimetric studies were conduct ed to acquire the optical characteristics of the polymer films in the correct potential ranges determined by the CV experiments. The spectroelectrochemical series for polymer films are shown in Figures 4 6 to 4 8. In their neutral states, SprayDOTTM-Purp le 101 appears purple (absorbing mainly at 574 nm), SprayDOTTMGreen 145 appears green (absorbing at 465nm and 707 nm) and PProDOP N -EtCN appears very transmissive (transmitting along the full visible region). As these polymer films are doped, charge carr ier states emerge with the majority of the light absorption for each polymer being in the near infrared, which results in highly transmissive films. In case of SprayDOTTMGreen 145, going from 0.35 to +0.55 V (vs. Fc/Fc+), %T values for lower band (at 46 5 nm) increases from 12% to 64%, resulting in a 52% change in %T. But, -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0-8 -6 -4 -2 0 2 4 6 8 10 Current Density ( mA/cm 2 )Potential ( V vs. Fc/Fc + ) g a a g

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81 this change in %T is limited to 36% at higher band (at 707 nm), starting from 4% in the neutral state increasing to 40% as it is doped. This lower contrast at the higher band results in a light blue hue in the trasnmissive state ap pearance of the film.(Figure 4 7) With green polymers while the interband transition bleaches during oxidative doping there is a lower energy carrier band that tends to tail into the region of the initial ba nd, so the truly bleached state is never observed. On the other hand, PProDOP N EtCN appears transmissive in the entire visible region at every redox state, even though it is proved to be ele ctrochemicaly active (Figure 4 8). The interesting behavior of PProDOP N EtCN is attributed to the conformational changes that lead to changes in the conjugation length. While bulky substituents disrupt planarity, lower conjugation length and induce tailing into the visible region, small N -substituents allow for free rotation in the neutral state, thus the onset of the transition is located at the boundary of the visible and ultraviolet regions of the spectrum. As such, the polymer is colorless in the neutral state. Bipolaron undergoes like -charge repulsions an d because of small N -substitution the polymer is free to rotate into planarity as well. This red -shifts the bipolaron peak further into the NIR. Moreover, the substitution which allows rotation and positioning of alkyl groups above and below the plane of -stacking. More open and less dense polymer morphology will allow more dopant ion accommodation in the film resulting in higher transmittance due to higher doping. 4.1.4 Setting Thicknesse s The effect of thickness on color and optical contrast is inevitable. In order to study this effect and be able to pick the optimum thicknesses for the EC polymers that are to be utilized in devices, we have generated absorbance vs. thickness calibration plots. For this purpose, 8 films of both SprayDOTTM-Purple 101 and SprayDOTTMGreen 145 were sprayed on ITO/glass. Each max). The film thicknesses

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82 Figure 4 6 Spectroelectrochemis try of spray -cast, redox switched, SprayDOTTMPurple 101 film at applied potentials of (a) 0.35 (b) 0.30 (c) 0.25 (d) 0.20 (e) 0.15 (f) 0.10 (g) 0.05 (h) 0.00 (i) +0.05 (j) +0.10 (k) +0.15 (l) +0.25 (m) +0.30 and (n) +0.35 V vs. Fc/Fc+. Figure 4 7 Spectroelectrochemistry of spray -cast, redox switched, SprayDOTTMGreen 145 film at applied potentials of (a) 0.35 to (s) +0.55 V vs. Fc/Fc+ at intervals of 50 mV/s. Inset: Change in %T (absorbance) at two peak wavelengths, 465 nm and 707 nm, by applied potential. 400 600 800 1000 1200 1400 1600 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 na a Absorbance (a.u.)wavelength (nm)n a 400 600 800 1000 1200 1400 1600 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 s a s Absorbance (a.u.)wavelength (nm)a b -0.6 -0.3 0.0 0.3 0.6 0 15 30 45 60 75 40% 64% 12% 4% 465 nm % TransmittancePotential ( V vs. Fc/Fc+)707 nm

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83 Figure 4 8 Spectroelectrochemistry of potential -scan deposited (10 scans, at 50 mV/s, from 0.63 to +0.57 V vs. Fc/Fc+), redox switched, PProDOP -N EtCN film at applied potentials of (a) 0.08 to (h) +0.27 V vs. Fc/Fc+ at intervals of 50 mV/s. Inset: Scan rate dependence of the PProDOP N -EtCN on Pt button electrode in 0.1 M TBAP/PC. were measured by a profilometer after each film was conditioned by potential stepping between its reduced and oxidized states. Since spra y cast films are rough, 5 measurements were made on each film and the average of these data were used for Absorbance (a.u.) vs. thickness (A0) plots. In each case the thickness scaled linearly with Absorbance, allowing us to correlate film thickness to absorbance by linear fit equations as shown in Figure 4 9. Figure 4 9 Absorbance (a.u.) vs. thickness (Ao) linear fit plots. (a) SprayDOTTMPurple 101 max=574 nm) and (b) SprayDOTTMmax=707 nm) 400 600 800 1000 1200 1400 16000.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 h Absorbance (a.u.)wavelength (nm) a -0.3 -0.2 -0.1 0.0 0.1 0.2 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 g a g mA/cm2V vs. Fc/Fc+ a 0.00 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00 1500 3000 4500 6000 7500 9000 Film thickness ( A0)Absorbance (a.u.) y = 3715 x + 1219 R2 = 0.95a 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00 1000 2000 3000 4000 5000 6000 Film thickness ( Ao)Absorbance (a.u.) y = 2725 x + 606 R2 = 0.93b

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84 4.1.5 Tandem Chronocoulometry and Chronoabsorp tometry Polymer films with similiar switching times and giving the highset contrast ratios were chosen for application in to the dual -film technique, P3 ECD and 3 ECD. A tandem chronoabsorptometry/chronocoulometry experiment was used to calculate composit e coloration max.19, 21, 65 Coloration efficiencies of the films at specific thickne sses are plotted in Figures 4 10 to 4 12. The effect of film thickness on coloration efficiency and switch time is tabulated in Table 4 1. Since SprayDOTTMGreen 145s enhanced electrochromism is not limited to a single wavelength, the max. CE values of SprayDOTTMPurple 101 are higher than SprayDOTTMGreen 145s CE values. The bulkier structure of SprayDOTTMGreen 145 holds more charge than SprayDOTTM-Purple 101 and has a lower optical contrast due to the enhanced tailing of the NIR absorption in to the red absorbing region in the conductive state. The SprayDOTTMPurple 101 film with a thickness of 500 nm has a charge density of 1.1 mC/cm2 with a change in %T of 52% resulting in a CE of 707 cm2max of 574 nm (Figure 4 10), whereas, the thinner SprayDOTTMGreen 145 film (380 nm thick) has a charge density of 1.8 mC/cm2 with a change in %T of 48% resulting in a CE of 299 cm2max of 465 nm (Figure 4 11) and a change in %T of 39% resulting in a CE of 430 cm2max of 707 nm (Figure 4 12). Since PProDOP derivative s (PProDOP N -EtCN) and nitroxyl radical polymers (PTMA) have unsaturated pastel colors or no colors, the optical properties of the dual or multi EC systems are dominated by the saturated colors of cathodically coloring polymers such as PProDOT derivatives. Switch times are regulated by the diffusion of the counterions through the films during redox switching. Enhanced optical response times (in seconds) were observed in these systems since the open morphology of the polymer (bulky structures) promotes the mobility of charge

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85 compensating counterions. The switch times strongly depend on the thickness of the films, thus thinner films bleach in subseconds while the thicker ones bleach in longer times. (Table 4 1). In contrary to switch times, the coloratio n efficiency is shown to be independent of film thickness for these systems. This behavior is attributed to the compensation of the increase in change in Figure 4 10 Tandem chronoabsorptometry and chronocoulometry experiment for 500 nm thick SprayDOTTMPurple 101 (stepped from 0.2 V to +0.4 V vs. Fc/Fc+, held for 10 s at each potential at 574 nm) in 0.1 M TBAP/PC solution. Figure 4 11 Tandem chronoabsorptometry and chronocoulometry experiments for 380 nm thick SprayDOTTMGreen 145 stepped from 0.30 to +0.60 V vs. Fc/Fc+, held for 10 s at each potential at 465 nm in 0.1 M TBAP/PC solution. 0 2 4 6 8 10 12 14 16 18 20 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 time (sec.)Charge Density ( mC/cm 2 )at 574 nm10 20 30 40 50 60 70 % Transmittance 0 2 4 6 8 10 12 14 16 18 20 0.5 1.0 1.5 2.0 2.5 3.0 time (sec.)Charge Density ( mC/cm 2 )20 30 40 50 60 70 % Transmittanceat 465 nm

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86 Figure 4 12 Tandem chronoabsorptometry and chronocoulometry experiments for 380 nm thick SprayDOTTMGre en 145 stepped from 0.30 to +0.60 V vs. Fc/Fc+, held for 10 s at each potential at 707 nm in 0.1 M TBAP/PC solution. Table 4 1 Coloration efficiencies and switch times of SprayDOTTMPurple 101 and SprayDOTTMGreen 145 at various film thicknesses in 0.1 M TBAP/PC. Values are reported at 95% of full switch. Green 145 Purple 101 Absorbance (a.u.) Thickness (nm) CE at 465nm t0.95 a CE at 707 nm t0.95 a Absorbance (a.u.) Thickness (nm) CE at 574 nm t0.95 a 0.42 a.u. 180 nm 333 cm 2 /C 1.2 s 485 cm 2 /C 0.4 s 0.19 a.u. 190 nm 651 cm 2 /C 1.0 s 0.59 a.u. 220 nm 291 cm 2 /C 2.3 s 317 cm 2 /C 1.3 s 0.64 a.u. 360 nm 758 cm 2 /C 2.0 s 0.84 a.u. 290 nm 284 cm 2 /C 1.5 s 414 cm 2 /C 1.2 s 0.93 a.u. 470 nm 692 cm 2 /C 1.4 s 1.17 a.u. 380 nm 299 cm 2 /C 1.0 s 430 cm 2 /C 1.2 s 1.03 a.u. 500 nm 707 cm 2 /C 2.2 s 1.68 a.u. 520 nm 237 cm 2 /C 2.1 s 568 cm 2 /C 1.8 s 1.40 a.u. 640 nm 855 cm 2 /C 1.6 s 1.82 a.u. 560 nm 296 cm 2 /C 2.1 s 428 cm 2 /C 2.3 s 1.79 a.u. 790 nm 780 cm 2 /C 2.9 s a Switch times for 95% of full switch. 4.1.6 Colorimetry The effect of thickness on color and contrast was studied by recording % relative luminance values at applied potentials from films with various thicknesses. As shown in Figures 0 2 4 6 8 10 12 14 16 18 20 0.5 1.0 1.5 2.0 2.5 3.0 time (sec.)Cherge Density ( mC/cm 2 )10 20 30 40 50 % Transmittanceat 707 nm

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87 4 13 and 4 increases by increasing film thickness. For SprayDOTTM-Purple 101, as the thickness increases from 190 nm to 790 nm the luminance contrast increases from 0.2 to 0.8 and the color contrast increases from 17 to 78. For SprayDOTTMGreen 145, as the thickn ess increases from 150 nm to 520 nm the luminance contrast increases from 0.1 to 0.5 and the color contrast increases from 14 to 38. The contrast was observed to increase as the films thickness increases and level off. Upon doping, the bipolaron carrier bands shift into the NIR region by repressing the absorbance in the visible region, thus the optical contrast increases. Thicker films of sterically bulk structures can incorporate more counter ions to compensate for the oxidation, therefore, as the thick ness increases, polymers high luminance at the oxidized state maintains and the luminance in the reduced state decreases. Figure 4 13 % Relative Luminance as a function of applied potential of SprayDOTTMPurple 101 film at thicknesses of 190 nm (0.19 a.u.), 360 nm (0.64 a.u.), 500 nm (1.03 a.u.), 640 nm (1.40 a.u.), 790 nm (1.79 a.u.) in 0.1 M TBAP/PC. -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 0.4 0.5 0 10 20 30 40 50 60 70 80 90 100 790 nm 190 nm C=0.8 C=0.8 C=0.6 C=0.2 % Relative LuminancePotential ( V vs. Fc/Fc + )aC=0.5

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88 Figure 4 14 % Relative Luminance as a function of applied potential of SprayDOTTMGreen 145 film at thicknesses of 150 nm (0.34 a.u.), 220 nm (0.60 a.u.), 320 nm (0.97 a.u.), 450 nm (1.42 a.u.), 520 nm (1.70 a.u.) in 0.1 M TBAP. 4.1.7 Optical Stability One of the major aspects of ECDs is longterm optical stability in ambient conditions. Therefore, optical stabilities of the EC polymers were investigated prior to device constructions. The stability experiments were performed by stepping the potential between the extreme redox states of SprayDOTTM-Purple 101 and SprayDOTTMGreen 145 films (sprayed on ITO/glass) in 0.1 M TBAP/PC. In order to express the change in the color as well as the luminance, the lightness, L*, of the films at their neutral states were recorded over time. The charge densities, Qred, associated with the neutralization of the films were also re corded along the time. SprayDOTTMPurple 101 film on ITO/glass retained 50% of its optical response after 5000 double potential steps while SprayDOTTMGreen 145 retained 70% of its optical response after 15 000 double potential s teps.(Figure 4 15) The redox reaction of molecular oxygen in air is accepted as the threshold for air stability. (E (O2/H2O)= 0.5 V vs. SCE or 0.12 V vs Fc/Fc+) 60, 61, 72 Since the onset of oxidation for SprayDOTTM-Purple 101 and SprayDOTTMGreen 145 ( 0.2 and 0.3 V vs. Fc/Fc+, respectively -obtained from polymer CVs) are below the threshold for air -0.4 -0.2 0.0 0.2 0.4 0.6 0 10 20 30 40 50 60 70 80 90 100 150 nm 520 nm C=0.5 C=0.5 C=0.4 C=0.2 % Relative LuminancePotential ( V vs. Fc/Fc + )bC=0.1

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89 stability these films tend to maintain their color (neutral state) at amb ient conditions. Therefore, the minor fading of the colors of the films at longterm switching studies is ascribed mainly to the electrochemical dissolution of the films and partly to the accumulation of high levels of O2 in the medium at long switch time s. Over oxidation might also be responsible for the optical loss. Since both polymer films dont show any optical loss to a certain cycle (SprayDOTTM-Purple 101 is stable up to 2500 cycles and SprayDOTTMGreen 145 is stable up to 6000 cycles) we can spec ulate on formation of double bonds between S on thiophene units and O in air. This irreversible reaction results in a sudden optical loss. The degree of over oxidation affects the degree of optical and charge loss. Figure 4 15 Electrochemical and opti cal stability of (a) SprayDOTTMPurple 101(thickness 410 nm, 8 s delay time) and (b) SprayDOTTMGreen 145 (thickness 380 nm, 7 s delay time) films on ITO/glass in 0.1 M TBAP/PC solution. ( L*, Lightness at neutral state and Qred, charge density) 4 .2 SprayDOT -Purple 101/SprayDOT Green 145 Dual -Film Electrochromic System The dual EC -film film characterization method was utilized to predict the colors that could be generated by multi -electrode devices whose working principles are based on color mixing. Both, SprayDOTTMGreen 145 and SprayDOTTM-Purple 101 on ITO electrodes under separate potentiostatic control were placed back to back in a 1cm quartz cell as to serve as two working 0 1000 2000 3000 4000 5000 0 20 40 60 80 100 # of redox cyclesLightness (L*)0.5 1.0 1.5 2.0 2.5 3.0 Qred( mC/cm2)a 0 3000 6000 9000 12000 15000 0 20 40 60 80 100 # of redox cyclesLightness (L*) 0 1 2 3 4 5 6 Qred( mC/cm2)b

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90 electrodes, with a Ag wire as a reference electrode and a Pt wire as a counter electrode. In situ color coordinates and electromagnetic spectra in the visible region were recorded from the dual polymer system upon application of different potentials to different working electrodes in a 0.1 M TBAP/PC.73 In order to get an insight of the addition of optical properties by means of the dual -film EC, absorbance spectra of SprayDOTTMPurple 101 and SprayDOTTMGreen 145 films, were taken separately at reduced (both at 0.66 V vs. Fc/Fc+) and oxidized (both at +0.74 V vs. Fc/Fc+) states and these spectra were summed theoretically. This is demonstrated by the single film purple and green curves in Figure 4 16, along with the theoretical summation represented by the red curve. Black curve represents the spectral response of films combined in dual -EC method. The theoretical and experimental spectra are shown to overlay one another for the oxidized and reduced films. The dual -film system was studied colorimetrically. The photographs and the L*a*b color coordinates as a functi on of the separate potential applied to each film are shown in Figure 4 17. The film thicknesses were set by utilizing the contrast data and plots that were reported in earlier sections, thus the optimum contrast is obtained from the dual EC system in addition to full palette of colors As it was shown in Figures 4 13 and 4 14 the maximum contrast that could be obtained from SprayDOTTMPurple 101is 0.8 while this value is only 0.5 for SprayDOTTMGreen 145. Therefore, SprayDOTTMPurple 101 with a thicknes s of 605 nm (A=1.30 a.u.) switching from deep purple (L*= 41, a*= 22, b*= 48, Q= 67) to highly transmissive sky blue (L*= 87, a*= 2, b*= TMGreen 145 with a thickness of 360 nm (A=1.10 a.u.) swi tching from deep green (L*= 60, a*= 23, b*= 12, Q= 65)

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91 to highly transmissive sky blue (L*= 84, a*= 4, b*= 6, Q= 84) open doping with C= 0.40 and ti -electrode systems. (Figure 4 17) Figure 4 16 UV vis -NIR spectra of SprayDOTTMPurple 101/SprayDOTTM-Green 145 from dual -polymer electrochromic setup at (a) reduced and (b) oxidized states in 0.1 M TBAP/PC solution. The new color palette we established extends from deep blue -black (L*= 21, a*= 3, b*= 28, Q= 35) to clear (L* = 75, a*= 6, b*= 12, Q= 76) and embodies all tones of mixtures of green 400 600 800 1000 1200 1400 1600 0.0 0.5 1.0 1.5 2.0 SprayDOT-Purple 101 SprayDOT-Green 145 theoretical summation of SprayDOT-Purple 101 and SprayDOT-Green 145 experimantal summation of SprayDOT-Purple 101 and SprayDOT-Green 145Absorbance (a.u.)wavelength (nm)a 400 600 800 1000 1200 0.0 0.5 1.0 1.5 2.0 SprayDOT-Purple 101 SprayDOT-Green 145 theoretical summation of SprayDOT-Purple 101 and SprayDOT-Green 145 experimantal summation of SprayDOT-Purple 101 and SprayDOT-Green 145 Absorbance (a.u.)wavelength (nm)b

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92 and purple. The luminance contrast for this color gamut is 0.90 and the color contrast is 69. It is Furthermore, having two colors mixed and absorbance extended along the full visible range (formation of black) any hindrance to contrast due to the chroma is eliminated to noticeable extent. Figure 4 17 L*a*b* color coordinates and photography for SprayDOTTMPurple 101/SprayDOTTMGreen 145 in 0.1 M TBAP/PC (all potentials are reported vs. Fc/Fc+) 4.3 Pseudo -Three-Electrode ECD (SprayDOTTM-Purple 101/SprayDOTTMGreen 145/PProDOP -N -EtCN) We applied dual -EC method to electrochromic devices. P3 -ECD that we propose can be utilized either as a window type device or as a display by use of a reflective background such as 0.66 V 0.46 V 0.26 V 0.06 V 0.14 V 0.34 V 0.54 V 0.74 V L =60 a* = 23 b =12 L =60 a = 24 b =12 L =64 a = 15 b =3 L =68 a = 11 b = 4 L =76 a = 6 b = 8 L =78 a =11 b = 8 L =82 a =3 b = 6 L =84 a = 4 b = 6 0.66 L =41 a =22 b = 48 L =21 a =3 b = 28 L =22 a =0 b = 27 L =22 a =10 b = 33 L =27 a =8 b = 36 L =28 a =15 b = 44 L =30 a =18 b = 48 L =31 a =19 b = 49 L =31 a =22 b = 51 0.46 L =41 a =23 b = 49 L =22 a =5 b = 29 L =22 a =6 b = 30 L =23 a =8 b = 34 L =25 a =14 b = 40 L =27 a =16 b = 45 L =30 a =17 b = 48 L =31 a =18 b = 49 L =32 a =18 b = 50 0.26 L =45 a =21 b = 43 L =23 a =3 b = 27 L =24 a =3 b = 28 L =25 a =6 b = 32 L =26 a =6 b = 35 L =27 a =16 b = 44 L =30 a =19 b = 48 L =32 a =18 b = 48 L =32 a =21 b = 50 0.06 L =60 a =17 b = 23 L =28 a = 1 b = 20 L =29 a =0 b = 20 L =30 a =1 b = 24 L =33 a =8 b = 31 L =36 a =11 b = 36 L =38 a =14 b = 39 L =40 a =15 b = 39 L =41 a =13 b = 39 0.14 L =79 a =4 b = 4 L =42 a = 9 b = 3 L =42 a = 7 b = 4 L =43 a = 3 b = 8 L =45 a =0 b = 13 L =50 a =4 b = 18 L =54 a =5 b = 19 L =56 a =8 b = 19 L =58 a =8 b = 19 0.34 L =82 a =14 b = 3 L =51 a = 20 b =7 L =52 a = 18 b =5 L =54 a = 11 b = 1 L =58 a = 9 b = 6 L =63 a = 4 b = 11 L =67 a = 3 b = 12 L =70 a = 3 b = 11 L =71 a = 3 b = 11 0.54 L =86 a =0 b = 5 L =54 a = 21 b =5 L =54 a = 20 b =5 L =56 a = 16 b =0 L =59 a = 13 b = 6 L =65 a = 9 b = 12 L =70 a = 6 b = 13 L =73 a = 5 b = 12 L =74 a = 4 b = 12 0.74 L =87 a = 2 b = 7 L =55 a = 22 b =6 L =55 a = 21 b =4 L =57 a = 15 b = 1 L =61 a = 11 b = 7 L =66 a = 8 b = 12 L =71 a = 6 b = 13 L =74 a = 6 b = 12 L =75 a = 6 b = 12 Purple 101 Green 145 vs Fc/Fc+

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93 a cellulose paper or white paint. Physically the construction of the P3 E CD is very similar to dual absorptive/transmissive windows in such that it consists of two absorptive/transmissive windows in series whose counter electrodes are shorted. (Figure 4 18) SprayDOTTMGreen 145, SprayDOTTMPurple 101 and PProDOP N -EtCN films o n ITO electrodes were prepared as described before. PProDOP N EtCN, non -color changing counter electrode polymer, was electropolymerized on to ITO -coated glass slides and heated as detailed in the spectroelectrochemistry section. The thicknesses of the n on -color changing PProDOP N EtCN films on the counter electrodes were set to ensure the charge balance with the polymer it was facing and retain high transmissivity. After 10 potential scans, a highly transparent polymer film, which has the capability to balance charges, was obtained. Further scans result in thicker films with less transmissivity. PProDOP N -EtCN films were dried at 55 oC under vacuum for 30 minutes. All polymer films were electrochemically conditioned by sweeping the potential. Cathodi cally coloring SprayDOTTMGreen 145 and SprayDOTTMPurple 101 were fully oxidized (brought to their transparent state) and non -color changing films of PProDOP N EtCN were fully neutralized to improve the charge balance prior to assembling of the device. T he SprayDOTTMGreen 145 and SprayDOTTM-Purple 101 films were then coated with gel electrolyte and then the PProDOP N EtCN films were closed on top of them. Two devices were connected in series so that the counter electrode of each device is back -to -back a nd connected with a copper tape to serve as a conjunct counter electrode to the whole device. The SprayDOTTMPurple 101 serves as a working electrode1 and the SprayDOTTMGreen 145 serves as working electrode 2. The devices were encapsulated by paraffi n wax and epoxy to allow long -term testing. In situ color coordinates were recorded from the P3 -ECD upon application of different potentials to different working electrodes.

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94 Figure 4 18 Schematic of the P3-ECD under bipotentiostatic control and a side view of the device The absorbance spectra and the colorimetric data with photographs obtained from the first P3 -ECD device is shown in Figures 4 19 and 4 20. When a potential of +1.4 V is applied to both WE1 (SprayDOTTMPurple 101) and WE2 (SprayDOTTMGreen 145), the device becomes highly transmissive (L*= 75, a*= 7, b*= 7) and when a potential of 0.2 V is applied to both working electrodes, both films become absorptive and the device appears blue black absorbing along the full visible region (L*= 26, a*= 3, b*= max of 582 nm. When a potential of 0.2 V is applied to WE1 (SprayDOTTMPurple 101) and +1.4 V to WE2 (SprayDOTTMGreen 145), green film becomes transmissive and having purple in neutral state the device appears deep purpl e (L*= 56, a*= 7, b*= 15). When a potential of +1.4 V is applied to WE1 (SprayDOTTMPurple 101) and 0.2 V to WE2 (SprayDOTTMGreen 145), green film becomes absorptive and purple becomes transmissive leading the device to appear deep green (L*= 57, a*= 17, b*= 4). The P3-ECD device shows a luminance contrast of 0.82 and a color contrast of 50. WE 2 WE 1 CEo observer WE 1 WE 2 CE

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95 Figure 4 19 UV vis -NIR spectra of the P3 -ECD. Working electrode 1 (coated with SprayDOTTMPurple 101) reduced (purple line), working electrode 2 (coated with SprayDOTTMGreen 145) reduced (green line), both of the working electrodes reduced (black line) and both working electrodes oxidized (blue line). Figure 4 20 L*a*b* color coordinates and photography from the SprayDOTTM-Purple 101/SprayDOTTMGreen 145 P3-ECD P3 -ECD device having a reasonable contrast value between the darkest and the lightest states beats other devices utilized in information display technology by offering a full color 400 600 800 1000 1200 1400 1600 0.0 0.5 1.0 1.5 2.0 Absorbance (a.u.)wavelength (nm) 582 nm L = 6 0 a* = 23 b* = 12 L = 84 a* = 4 b* = 6 L = 41 a* = 22 b* = 48 L *= 26 a *= 3 b *= 17 L *= 56 a *= 7 b *= 15 L = 87 a* = 2 b* = 7 L *= 57 a *= 17 b *= 4 L*= 75 a*= 7 b*= 7 Purple 101 Green 145

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96 palette. Other than that, the device shows a reasonable optical stabi lity. In order to study that, the device was potential stepped between its darkest and brightest states. %T was recorded at 582 nm over time. While bipotentiostat was utilized to supply potential to the device in the earlier parts, two computer controll ed potentiostats were utilized for long term studies. The P3 ECD retained 50 % of its optical contrast after 1000 deep potential cycles. ( Figure 4 21) The counter electrode material PProDOP N EtCN with and oxidation onset of 0.15 V vs Fc/Fc+ is stable in air, but still more prone to oxidation when compared to the other components of the device. The oxidation of counter electrode material could render the charge compensation that is paramount for device function. If the O2 penetration to the device can be eliminated by a better insulation or if the device is constructed in an inert medium, longer switch times can be attained. Figure 4 21 P3 ECD stability studies. %Transmittance over time was recorded from the SprayDOTTMPurple 101/SprayDO TTMGreen 145 P3-ECD. 0 500 1000 1500 2000 2500 0 10 20 30 40 50 % Transmittance (at 582 nm)# of redox cycles 32% 16%

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97 4.4 Three -Electrode ECD ( SprayDOT -Purple 101/SprayDOT Green 145/PTMA) The P3 -ECD was a device composed of two dual EC window type devices connected in series and the outcome of the result was the summation of the optical properties of all components at a given state. Here, we propose a threeelectrode electrochromic display device, 3 ECD, which combines two cells in the P3 -ECD into one single cell. A schematic of the 3 EC D is given in Figure 4 22. The 3 ECD includes two transmissive working electrodes coated with EC polymers coupled to a counter electrode that has an electroactive material that exhibits little to no optical transition in the visible region, and a gel electrolyte to separate the layers to provide contact between them. Electrical potentials can be independently applied between the first working electrode and the counter electrode and second working electrode and the counter electrode. The device displays a color depending upon the combination of colors seen through th e two working electrodes, whose colors depend on the potentials that are independently applied. Figure 4 22 Schematic of the 3 ECD under bipotentiostatic control WE 2 WE 1 CE WE 1 WE 2 CE observer

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98 The unique aspect of this device is the counter electrode, sandwiched between the working electrodes, which is porous to allow electrolyte transfer, highly transparent as to not limit optical contrast, and conductive on both sides to supply sufficient charge to both working electrodes for complete redox reactions. The counter electrode we developed in this work, of which the s chematic is given in Figure 4 23, has three components, polyester membrane, PEDOT:PSS and gold. Track -etched polyester membrane (10 micron pore diameter), PETE, serves as the porous support. In order to provide conductivity in 3D, high conductivity PEDOT:PSS formulation, was spin coated on both sides of the membrane at 3000 rpm for 30 sec., and the films were dried under vacuum at 120 oC for 2 hours. As the thickness of the PEDOT:PSS increased on PETE, the conductivity i ncreased at the expense of transmittance in the visible range. One layer of film, resistance measurements were made with contacts on each film side. Due to the porosity of the film, these contacts could not be perfectly opposed, making exact conductivity measurements difficult. It was seen that the through film resistance decrea of PEDOT:PSS layers decreased the film quality since comet -like structures appeared due to the accumulation of particles. Uneven counter electrode films disrupted the final appearance of the devices. Therefore, a thin layer of Au was utilized. PETE coated with only 1.5 nm Au on each Incr easing the thickness of Au layer increased the conductivity but films became highly reflective. We have decided to utilize Au to form low resistance clusters on the surface of the film and made the contacts through these clusters by PEDOT:PSS. Evaporatio n of 1.5 nm of Au

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99 on PETE which was already coated with one layer of PEDOT:PSS on each side decreased the Figure 4 23 Schematic of the highly transmissive porous electrode (PETE/Au/PEDOT:PSS) In F igure 4 24, transmisivity of the counter electrode material components is studied systematically. All counter electrode components were sandwiched between glass slides with a gel electrolyte fo r %Transmittance measurements. ITO shows an average transmittance of ~87% along the visible region with a surface resistance of 8 10 shows an average transmittance of ~75%. When a layer of PEDOT:PSS is deposited on PETE, number of PEDOT:PSS increases the resistance decreases to 150decreases to ~60%. When 1.5 nm Au was evaporated to both sides of PETE it shows a 550 nm. When 1.5 nm Au is evaporated on PETE, coated with one layer of PEDOT:PSS on each side, the transmissivity goes down to 57% with a minimum at 55% while the resistance 1 layer PEDOT:PSS 500 /500 / Track etched PETE membrane 1.5 nm Au

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100 Figure 4 24 Systematic % Transmittance study of counter electrodes/counter electrode components, ITO, PETE, PETE/Au, PETE/PEDOT:PSS and PETE/Au/PEDOT:PSS. (All materials were covered with g el electrolyte and sandwiched between glass slides for measurements) The transmissive porous electrode, PETE/PEDOT:PSS/Au was coated with an electroactive polymer layer that does not change color yet undergoes an electrochemical redox reaction and acts to balance charge during switching in 3 ECD. In this work we employed a nitroxide radical polymer, PTMA. PTMA is a polymethacrylate derivative with a 2,2,6,6tetramethyl 1 piperidinyloxy, TEMPO, stable free radical in the repeat unit. TEMPO containing comp ounds are known to have redox behavior and they find application in batteries due to their high capacities of charge storage.74 77 We use PTMA as a charge storage material on our counter electrodes. The electrochemical properties of PTMA was investigated in order to set the baseline conditions prior to the device cons truction. PTMA solution (2mg polymer/1mL toluene) was drop cast on to the Pt -button electrode after being filtered. After the film was air -dried, it was immersed in to the 0.1 M TBAP/PC solution for scan rate studies. The potentials were swept at differ ent scan rates. As shown in Figure 4 25, the peak currents increases linearly with increasing scan rates indicating the existence of well adhered electroactive film. The redox 400 600 800 1000 1200 1400 1600 0 10 20 30 40 50 60 70 80 90 100 % Transmittancewavelength (nm) PETE PETE/Au PETE/PEDOT:PSS/Au 1 PEDOT:PSS 3 PEDOT:PSS 4 PEDOT:PSS ITO

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101 reaction of PTMA takes place in a 0.5 V potential window and the anodic oxidat ion of the stable nitroxide radical results in an oxoammonium cation. (Figure 4 26) The sharp increase in current (sharp and narrow peaks) is indicative of fast electron movements. Figure 4 25 Cyclic voltammograms of PTMA in 0.1 M TBAP/PC at scan rates of (a) 25, (b) 50, (c) 75, (d) 100, (e) 150, (f) 200 and (g) 300 mV/s, on a Pt button electrode. Film was prepared by drop casting from 2mg/mL polymer/toluene solution. Figure 4 26 Redox couples of PTMA. While the PTMA adhered to the Pt button and gave a sufficient redox behavior, it showed a weak adherence to ITO/glasss. The PTMA was sprayed onto ITO/glass from a 15 mg PTMA/60 mL toluene solution and air dried. Then the film was immersed in to the 0.1 M LiClO4/PC for cyclic voltammetry character izations. As the potential was swept between the extreme states the film dissolved into the solution which is seen by a decrease in the peak current -0.1 0.0 0.1 0.2 0.3 0.4 0.5 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 Current Density ( mA/cm 2 )Potential ( V vs. Fc/Fc + ) ag a g

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102 by increasing numbe r of scans. (Figure 4 27 (a)) In order to overcome this solubility, the PTMA was blend ed with a high molecular weight PMMA in 1:4 weight ratio (15 mg PTMA/60 mg PMMA/60 mL toluene) and sprayed onto ITO/glass and air dried. As seen in Figure 4 27 (b) PTMA/PMMA blend film was stable upon potential scanning and did not dissolve in to the electrolyte solution, but the electroactivity decreased by 50%, even there was the same amount of electroactive polymer on the electrode. The PTMA/PMMA blend film was annealed at 90 oC, under vacuum, for 1 hour, and cooled down slowly. The temperature 90 oC was chosen after series of electrochemical studies which proved it to be the optimum temperature and because it is lower than the decomposition temperatures of both PTMA and PMMA which are determined to be 240 oC and 165 oC, respectively, by TGA studies and it is higher or equal to the glass transition temperatures,Tg, of each polymer. (Tg (PTMA)= 76 oC and Tg(PMMA)= 105 oC )75 Complete melting of the polymer blend and reorganization upon cooling helped form more continuous matrix and enhanced the charge mobility, hence electroactivity. (Figure 4 27 (c)). These studies were repeated in different electrolyt es such as TBAP/PC and TBAP/ACN in our labs. Similar electrochemical behavior was observed. Studies in our labs also showed an electrochemical stability of thousands of potential cycles for annealed PTMA/PMMA blends. PTMAs optical properties also make it a good candidate in use for counter electrodes. PTMA films are transmissive over the entire visible range and show no change in absorbance upon redox reactions as sh own in Figure 4 28. When PTMAs are used on counter electrodes in ECDs they do not limi t the contrast, but supply charge and stability to devices.

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103 Figure 4 27 PTMA formulation studies in 0.1 M LiClO4/PC. Films were spray cast on ITO/glass from (a) 15 mg PTMA/60 mL toluene solution and used as it is, (b) 15mg PTMA/60 mg PMMA/60 mL tolue ne solution and used as it is and, (c) 15mg PTMA/60 mg PMMA/60 mLsoluion and annealed at 90 oC under vacuum for 1 hour before use. -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 -0.20 -0.15 -0.10 -0.05 0.00 0.05 0.10 0.15 0.20 Current Density ( mA/cm 2 )Potential ( V vs. Fc/Fc + ) 2 10 20 a -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 -0.08 -0.06 -0.04 -0.02 0.00 0.02 0.04 0.06 0.08 Current Density ( mA/cm 2 )Potential ( V vs. Fc/Fc + ) 2 10 20b -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 -0.16 -0.12 -0.08 -0.04 0.00 0.04 0.08 0.12 0.16 Current Density ( mA/cm 2 )Potential ( V vs. Fc/Fc + ) 2 10 20c

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104 Figure 4 28 Spectroelectrochemistry of spray cast, redox switched, PTMA/PMMA.film at applied potentials of 0.23 V to+0.37 V vs. Fc/Fc+ at intervals of 200 mV/s in 0.1 M TBAP/PC. Inset: Scan rate dependence of the PTMA on Pt button electrode in 0.1 M TBAP/PC. The 3 ECD was constructed after the optimization of porous, transmissive counter electrode, PETE/PEDOT:PSS/Au and the non-color changing, electroactive counter electrode polymer layer, PTMA/PMMA/Heat. First, SprayDOTTMGreen 145 and SprayDOTTM-Purple 101 were spray cast onto ITO electrodes and dried under vacuum. Then, to provide enough redox sites at the counter electr ode, first, a layer of (2mL) PTMA solution was sprayed on to the PETE/PEDOT:PSS/Au electrode, and then several layers of PTMA/PMMA blend solution was sprayed until the film takes a milky opaque color (This opaque color disappears when the film is inserted in a solution). Film was annealed in vacuum oven for an hour at 90 oC. Cathodically coloring SprayDOTTMGreen 145 and SprayDOTTM-Purple 101 were fully oxidized (brought to their transparent state) and non-color changing PTMA/PMMA blend films was fully ne utralized to improve the charge balance prior to assembling of the device. The SprayDOTTMGreen 145 400 600 800 1000 1200 1400 1600 0.0 0.2 0.4 0.6 0.8 1.0 Absorbance (a.u.)wavelength (nm) -0.1 0.0 0.1 0.2 0.3 0.4 0.5 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 Current Density ( mA/cm 2 )Potential ( V vs. Fc/Fc + ) ag a g

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105 and SprayDOTTM-Purple 101 films were then coated with gel electrolyte and then the counter electrode was sandwiched between them. The SprayDOTTMPurple 101serves as a working electrode 1 and the SprayDOTTMGreen 145 serves as working electrode 2 and the counter electrode is utilized by both working electrodes. The device was encapsulated by a paraffin wax. In situ color coordinates were recorded from th e 3 -ECD upon application of different potentials to different working electrodes. The absorbance spectra and the colorimetric data with photographs obtained from the first 3 ECD are shown in Figures 4 29 and 4 30. UV vis -NIR spectra from SprayDOTTMPurple 101/SprayDOTTMGreen 145 3max of 608 nm over the entire visible range upon reduction of both EC polymers. (Figure 4 29 (a)) The device becomes totally clear/transmissive upon doping of both EC layers. When a p otential of 1.5 V is applied to both WE1 (SprayDOTTM-Purple 101) and WE2 (SprayDOTTMGreen 145), films become highly transmissive (L*= 62, a*= 0, b*= 1) and when a potential of 0.5 V is applied to both working electrodes, both films become absorptive and the device appears blue black absorbing along the full visible region (L*= 25, a*= 7, b*= 1). When a potential of 0.5 V is applied to WE1 (SprayDOTTMPurple 101) and +1.5 V to WE2 (SprayDOTTMGreen 145), green film becomes transmissive and having pur ple in neutral state the device appears deep purple (L*= 35, a*= 21, b*= 38). When a potential of +1.5 V is applied to WE1 (SprayDOTTMPurple 101) and 0.5 V to WE2 (SprayDOTTMGreen 145), green film becomes absorptive and purple becomes transmissive l eading the device to appear deep green (L*= 61, a*= 22, b*= 16). The 3-ECD device shows a luminance contrast of 0.74 and a color contrast of 43.

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106 Figure 4 29 UV vis -NIR spectra of the 3 ECD. Working electrode 1 (coated with SprayDOT Purple 101) reduc ed (purple line), working electrode 2 (coated with SprayDOT Green 145) reduced (green line), both of the working electrodes reduced (black line) and both working electrodes oxidized (blue line). (a) Absorbance over the visible region, (b) absorbance over t he UV -vis NIR. 400 500 600 700 800 0.0 0.1 0.2 0.3 0.4 0.5 Absorbance (a.u.)wavelength (nm)a 400 600 800 1000 1200 1400 1600 0.0 0.2 0.4 0.6 0.8 Absorbance (a.u.)wavelength (nm)b

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107 Figure 4 30 L*a*b* color coordinates and photography from the SprayDOT -Purple 101/SprayDOT Green 145 3-ECD. 4.5 Conclusions In this work, we introduce the first two polymer black to transmissive and multi colored switching electrochromic d isplay devices, P3 ECD and 3 ECD. To accomplish this, we have developed a new transmissive, porous counter electrode which is composed of PETE, PEDOT:PSS and Au. We also introduced the first use of non-electrochromic yet electroactive polymers, PProDOP N -EtCN and PTMA, as counter electrode materials in ECDs. These highly transparent polymers help eliminate the contrast limitations in dual systems. P3 ECD and 3 ECD add colors by transmitting light through two working electrodes (coated with two different electrochromic polymer films) and a counter electrode/counter electrodes (coated with PProDOP N EtCN or PTMA) stacked together with a gel electrolyte between the layers. Further, the electrodes are all under separate potentiostatic control allowing the i ndependent control of color in each working electrode, thus wide range of color mixing. Utilizing SprayDOTTMPurple 101 and SprayDOTTM-Green 145 in the P 3 -ECD yield blue -black with L = 6 0 a*= -23 b* = 12 L = 84 a*= -4 b* = -6 L = 41 a*= 22 b* = -48 L = 87 a*= -2 b* = -7 L*= 25 a *= 7 b *= -21 L*= 35 a *= 21 b *= -38 L*= 62 a *= 0 b *= -1 L*= 61 a *= -22 b *= 16 Purple 101 Green 145

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108 color coordinates of L*= 26 a*= 3 b*= 17 switching to clear with color co ordinates of L*= 75 a*= 7 b*= 7. The device had a high luminance contrast of 0.82. Utilizing SprayDOTTMPurple 101 and SprayDOTTM-Green 145 in the 3 ECD yield blue -black with color coordinates of L*= 25 a*= 7 b*= 21 switching to clear with color coordinates of L*= 62 a*= 0 b*= 1. The device had a high luminance contrast of 0.74 that is lower than the contrast obtained from P3-ECD. The use of PEDOT:PSS and Au in the counter electrode adds a blue hue to the transmissive state of 3 ECD and limits the c ontrast of the device to a certain degree. Separate potential control over the electrodes utilized the color mixing in these devices showing that full palette of colors is accessible through smart choice of EC materials. Switches in between any colors are possible independent of the existing state. By utilizing P3-ECD and 3 ECD other than black and white scripts colored images can be displayed on information displays. P3 -ECD and 3 ECD stand out with their optical contrasts comparable to single films.

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109 CHAPTER 5 RGB COLOR SPACE 5 ELECTRODE ELECTROCHROMIC DISPLAY DEVICE In 1861 Maxwell demonstrated the first color photograph and initiated color display technology. His demonstration was based on the trichromatic vision of the human eye. This demonstration led to a great variety of color displays utilizing both additive and subtractive color mixing.78 Color display technologies benefit from a human vision mishap and use the halftoning principle. Halftoning is the conversion of continuous images into regular sequences of stripes, dots or rectangles on displays or prints. The color that a human sees at a pixel is dependent on the pixel and all the other pixels in the viewing angle. When humans view these patte rns from a distance the eye automatically adds the colors and the pattern appears as a continuous image.49, 78 As an example, the most widely used color display, cathode ray tube (CRTs), consists of a regular sequence of red, green and blue dot s, rectangles or stripes (pixels). These pixels are made of inorganic compounds doped with metal ions, and referred to as phosphors. Red contains yttrium oxysulfide (Y2O2S) doped with europium ions (Eu3+), while the green and blue contain zinc sulfide do ped with copper (Cu+) and silver (Ag+) ions, respectively. These pixels are hit by electron beams whose direction and intensity is controlled by shadow masks and they emit red, green and blue light which add up to new colors when viewed from a proper dist ance.53 The need for small volume and lower weight portable displays such as laptops, palm computers, and navigation devices lead to the invention of flat panel displays. In flat panel displays, liquid crystals sandwiched between transparent electrodes mimic a color filter. These displays switch between opaque and transparent states upon the application of a potential. The only drawback of these devices is their high costs and limited viewing angles.79 Electrochromic polymers that switch from a colored to transmissive state upon application of potential could be

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110 utilized as color filter s and imitate the behavior of liquid crystals in transmitting/reflecting or absorbing the light. Now having three primary color polymers, red, green and blue switching to transmissive upon doping available we can develop an electrochromic full color displ ay. It should be understood that the working and color mixing principles of the full color ECDs we propose are different from additive color mixing displays. The working principles of the RGB color space 5 -electrode ECD we propose are summarized in Figur e 5 1. In the RGB 5 -ECD, the red, green and, blue polymers are sprayed onto transparent electrodes as color filters. When all of the polymers are brought to their neutral -colored states the secondary subtractive colors red, green and blue will absorb ove r the entire visible range, block the light, and the device will appear black. The same effect in the same device could be obtained by mixing primary subtractive colors cyan, magenta and yellow. The intensity of the transmitted light can be controlled by precisely controlling the doping levels of the polymers. When all the films are fully doped the device appears clear and transmits all the light. In constructing devices certain details have to be taken into account. Since we will be controlling the c olor by the potential applied (doping level) and the thicknesses of the films (the intensity of transmitted light) we should set the conditions before the device is constructed. Therefore, full electrochemical and optical characterizations had to be carr ied out prior to device construction. 5.1 RGB Color Space 5-Electrode ECD Fundamental Properties (SprayDOTTM-Red 252, SprayDOTTMGreen 179, SprayDOTTMBlue 153, PTMA) Alkoxy substituted thiophene copolymers with desirable properties, such as low bandgap and low oxidation potentials were used in this work. Alternative additions of donor acceptor groups (alkoxy thiophenes and BTDs) in the repeat units resulted in polymers that absorb mainly at two (high and low energy) bands and transmit unique hues of gre en and blue. The structures of

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111 the polymers SprayDOTTMRed 252, SprayDOTTM-Green 179, SprayDOTTMBlue 153 and their ph otographs are shown in Figure 5 2. Figure 5 1 The schematic of the working principles of the 5 Electrode ECD Figure 5 2 Chemical stru ctures of the polymers and the photographs of their neutral (N) and doped (D) states 5.1.1 Film Deposition In order to obtain thin films of the EC polymers for electrochemical and optical studies, SprayDOTTMRed 252, SprayDOTTMGreen 179 and SprayDOTTMBlu e 153 were drop-cast (on All films neutral All films oxidized N O Ox Red N O Ox Red N O Ox Red SprayDOT -Red 252 SprayDOT -Green 179 SprayDOT -Blue 153

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112 a Pt -button electrode) or spray -cast (on ITO coated glass electrode) from a 2 mg/mL ITO/glass were dried under vacuum overnight. Non-color changing, electrochemically active PTMA/PMMA was sprayed and treated on ITO/glass for use in absorptive/transmissive window type ECDs, and on PETE/PEDOT:PSS/Au electrodes for use in RBG 5 ECDs as detailed in Chapter 4. 5.1.2 Polymer CV, Scan Rate Dep endence CVs were recorded at scan rates ranging from 25 to 300 mV/s as shown in Figures 5 3 to 5 5. A linear increase of the current with scan rate is observed for each film, indicative of a surface adhered electroactive polymer film. These polymers comp leted their redox cycles in narrow potential windows. SprayDOTTMBlue 153 was shown to switch between its extreme redox states with a potential difference of only 0.5V. This behavior is promising for low potential electronic device applications. Figu re 5 3 Cyclic voltammograms of SprayDOTTMRed 252 in 0.1 M TBAP/PC at scan rates of (a) 25, (b) 50, (c) 75, (d) 100, (e) 150, (f) 200, and (g) 300 mV/s, on a Pt -button electrode. Film was prepared by drop -casting onto a Pt button electrode from 2 mg/mL p olymer/toluene solution. -0.5 -0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 -0.12 -0.09 -0.06 -0.03 0.00 0.03 0.06 0.09 0.12 0.15 0.18 ga Current Density ( mA/cm 2 )Potential ( V vs. Fc/Fc + ) ag

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113 Figure 5 4 Cyclic voltammograms of SprayDOTTMGreen 179 in 0.1 M TBAP/PC at scan rates of (a) 25, (b) 50, (c) 75, (d) 100, (e) 150, (f) 200, and (g) 300 mV/s, on a Pt button electrode. Film was prepared by drop -casting onto a Pt button electrode from 2 mg/mL polymer/toluene solution. Figure 5 5 Cyclic voltammograms of SprayDOTTMBlue 153 in 0.1 M TBAP/PC at scan rates of (a) 25, (b) 50, (c) 75, (d) 100, (e) 150, (f) 200, and (g) 300 mV/s, on a Pt -button electrode. Film prepared by drop -casting onto a Pt -button electrode from 2 mg/mL polymer/toluene solution. -0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 0.4 -1.2 -0.9 -0.6 -0.3 0.0 0.3 0.6 0.9 1.2 Cu rrent Density ( mA/cm 2 )Potential ( V vs. Fc/Fc + ) a g a g -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 -3 -2 -1 0 1 2 3 Current Density ( mA/cm 2 )Potential ( V vs. Fc/Fc + ) ag a g

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114 5.1.3 Spectroelectrochemistry Spectroelectrochemical and colorimetric studies were conducted to acquire the optical characteristics of the polymer films in the corre ct potential ranges determined by the CV experiments. The spectroelectrochemical series for the polymer films are shown in Figures 5 6 to 5 8. In their neutral states, SprayDOTTM-max at 528 nm), SprayDOTTMmax at 443nm and 634 nm) and SprayDOTTMBlue 153 appears blue max at 398 nm and 652 nm). As these polymer films are doped, charge carrier states emerge with the majority of the light absorption for each polymer being in the NIR, which results in highly transmissive films. In case of SprayDOTTMGreen 179 and SprayDOT Blue 153 the addition of a strong acceptor, BTD in the strong donor alkoxy thiophene based structures, red shifts the main band while introducing a blue shifted secondary band. As seen in F igure 5 7 and 5 8 the higher energy absorption of SprayDOT Blue 153 is more blue shifted than the SprayDOT Green 179. The lower contrast at the lower energy due to the enhanced near IR tailing results in a light blue hue in the transmissive state appearances of both green and blue polymer films.(Figure s 5 7 and 5 8) Figure 5 6 Spectroelectrochemistry of spray-cast, redox switched, SprayDOTTMRed 252 film on ITO/glass at applied potentials of (a) 0.47 to (o) +0.23 V vs. Fc/Fc+ at intervals of 50 mV/s in 0.1 M TBAP/PC solution. 400 600 800 1000 1200 1400 1600 0.0 0.2 0.4 0.6 0.8 1.0 1.2 oa Absorbance (a.u.)wavelength (nm) 528 nm ao

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115 Figure 5 7 Spectroelectrochemistry of spray-cast, redox switched, SprayDOTTMGreen 179 film on ITO/glass at applied potentials of (a) 0.42 to (q) +0.38 V vs. Fc/Fc+ at intervals of 50 mV/s in 0.1 M TBAP/PC solution. Figure 5 8 Spectroelectrochemistry of spray -cast, redox switched, SprayDOTTMBlue 153 film on ITO/glass at applied potentials of (a) +0.11 to (l) +0.66 V vs. Fc/Fc+ at intervals of 50 mV/s in 0.1 M TBAP/PC solution. 400 600 800 1000 1200 1400 1600 0.0 0.2 0.4 0.6 0.8 1.0 1.2 a a q634 nm Absorbance (a.u.)wavelength (nm) 443 nm q 400 600 800 1000 1200 1400 1600 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 a652 nm Absorbance (a.u.)wavelength (nm) 398 nm al l

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116 5.1.4 Tandem Chronocoulometry and Chronoabsorptome try A tandem chronoabsorptometry/chronocoulometry experiment was used to calculate composite coloration efficiency (CE) and switch times (t0.95) at 95% of the total optical change max. The SprayDOTTMRed 252 film with an absorbance of 0.9 a.u. at max (528 nm) has a charge density of 1.3 mC/cm2 2/C. (Figure 5 9) SprayDOTTMGreen 179 film with an absorbance of 1 a.u. at 634 nm has a charge density of 2.1 mC/cm2 a CE of 287 cm2/C (Figure 5 10) and a 2/C (Figure 5 11). The SprayDOTTM-Blue 153 max (652 nm) has a charge density of 1.7 mC/cm2 with 2/C. (Figure 5 12) Switching times, which are dependent on the migration of the counterions through the films during redox switching, were also found to be twice as much for SprayDOTTMRed 252 when compared to Sp rayDOTTMGreen 179 and SprayDOT Blue 153. All three polymers utilized in this study have solubilizing alkoxy groups along the chains. These groups tend to interact/entangle and close the pathway of ions. The addition of BTD to the structure in the case of SprayDOT -Green 179 and SprayDOT -Blue 153 hinders the side chain interactions to a certain degree and opens the morphology to allow the migration of ions in and out of the polymer matrix resulting in faster switch times compared to SprayDOTTMRed 252. S prayDOTTMRed 252 has a long switch time of 4.8 s, while SprayDOTTMGreen 179 and SprayDOTTM-Blue 153 have switch times of 2 2.5 s and 2.2 s, respectively. SprayDOTTMGreen 179 and SprayDOT Blue 153 also have lower optical contrast due to the high degree tailing of the NIR absorption in to the red absorbing region in the oxidized state, thus they end up with lower CEs.

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117 Figure 5 9 Tandem chronoabsorptometry and chronocoulometry experiment for SprayDOTTMRed 252 (stepped from 0.43 V to +0.22 V vs. Fc/Fc+, held for 10 s at each potential at 528 nm) in 0.1 M TBAP/PC solution. Figure 5 10 Tandem chronoabsorptometry and chronocoulometry experiment for SprayDOTTMGreen 179 (stepped from 0.33 V to +0.37 V vs. Fc/Fc+, held for 10 s at each potential at 443 nm) in 0.1 M TBAP/PC solution. 0 2 4 6 8 10 12 14 16 18 20 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 time (sec.)Charge Density ( mC/cm 2 ) 10 20 30 40 50 60 70 % Transmittance 0 2 4 6 8 10 12 14 16 18 20 1.0 1.5 2.0 2.5 3.0 3.5 time (sec.)Charge Density ( mC/cm 2 ) 10 20 30 40 50 60 70 % Transmittance

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118 Figure 5 11 Tandem chronoabsorptometry and chronocoulometry experiment for SprayDOTTMGreen 179 (stepped from 0.33 V to +0.37 V vs. Fc/Fc+, held for 10 s at each potential at 634 nm) in 0.1 M TBAP/PC solution. Figure 5 12 T andem chronoabsorptometry and chronocoulometry experiment for SprayDOTTMBlue 153 (stepped from 0.13 V to +0.57 V vs. Fc/Fc+, held for 10 s at each potential at 652 nm) in 0.1 M TBAP/PC solution. 0 2 4 6 8 10 12 14 16 18 20 0.5 1.0 1.5 2.0 2.5 3.0 3.5 time (sec.)Charge Density ( mC/cm 2 ) 10 20 30 40 50 60 % Transmittance 0 2 4 6 8 10 12 14 16 18 20 1.5 2.0 2.5 3.0 3.5 4.0 time (sec.)Charge Density ( mC/cm 2 ) 10 20 30 40 50 60 % Transmittance

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119 5.1.5 Colorimetry In situ color coordinates and relative lu minance values were recorded for each of the three electrochromic polymer films with primary colors in their fully reduced states. (Figures 5 13 to 5 15) SprayDOTTMRed 252 has a* and b* values of 49 and 5, respectively, giving it a red color with a relative luminance of 28%, SprayDOTTMGreen 179 has a* and b* values of 15 and 5, respectively, giving it a green color with a relative luminance of 25%, and SprayDOTTMBlue 153 has a* and b* values of 21 and 36 giving it a blue color with a relative lumina nce of 25%. When the films are completely oxidized they all are converted into highly transmissive states. Now, SprayDOTTMRed 252 exhibits a* and b* values of 1 and 2, respectively, with a relative luminance of 69%, SprayDOTTMGreen 179 a* and b* values of 3 and 8, respectively, with a relative luminance of 64%, and SprayDOTTMBlue 153 exhibits a* and b* values of 4 and 2, respectively, with a relative luminance of 65%. All three cathodically coloring polymers possess a luminance contrast ratio of C ~0.4 of optical studies, films with absorbance values of 1 a.u. at th max were utilized in the device applications. Increasing the thickness of the films above that value results in a lower contrast ratio and decreasing it results in less saturated colors. The limited contrast of these films hindered the contrast of t he ECDs. As shown in Figures 5 13 to 5 15, the change of relative luminance as a function of applied potential show hysteresis. In other words, the optical responses of EC polymer films are path dependent, and the films behave differently upon oxidation a nd reduction. When the EC

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120 polymer film is first oxidized an electron is removed from the top of valence band and a radical cation with a partial quinoid structure forms and intermediate polaronic levels emerge. The reduction of the film in the reverse direction results in a diradical due to the addition of electron to the newly formed, half -filled intermediate energy levels (polaronic states). After that addition, the polymer chain spontaneously relaxes to its neutral state. The difference in the mec hanism and energy results in lower or higher potentials for optical changes upon reduction and oxidation, respectively.17 Figure 5 13 Relative luminance as a function of applied potential and L*a*b* color coordinates and photography at redox extremes of SprayDOTTMRed 252 in 0.1 M TBAP/PC -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 20 30 40 50 60 70 Relative Luminance (% Y)Potential ( V vs. Fc/Fc + ) L*=60 a*=49 b*= 5 L*=87 a*= -1 b*= 2

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121 Figure 5 14 Relative luminance as a function of applied potential and L*a*b* color coordinates and photography at redox extremes of SprayDOTTMGreen 179 in 0.1 M TBAP/PC. Figure 5 15 Relative luminance as a function of applied potential and L*a*b* color coordinates and photography at redox extremes of SprayDOTTMBlue 153 in 0.1 M TBAP/PC. -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 20 30 40 50 60 70 Relative Luminance (% Y)Potential ( V vs. Fc/Fc + ) L*= 57 a*= -15 b*= -5 L*=84 a*= -3 b*= -8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 20 30 40 50 60 70 Relative Luminance (% Y)Potential ( V vs. Fc/Fc + ) L*= 57 a*= -21 b*= -36 L*= 84 a*= -4 b*= -2

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122 5.2 Dual Absorptive/Transmissive Window ECDs After the completion of the optical characterizations, the behaviors of the polymers were studied in standard dual absorptive/transmissve window type ECDs. The schematic and the construction details of the devices are given in Chapters 1 and 2. EC polymers were sprayed onto ITO/glass electrodes and dried under vacuum. A layer of PTMA s pray on ITO/glass was followed by a spray of PTMA/PMMA solution until the film becomes opaque white. Once placed in the electrolyte, the film becomes transmissive. Film thicknesses were set to balance the number of redox sites on the cathodically coloring and noncolor changing film couples. All the electroactive films were conditioned by potential cycling. Cathodically coloring red, green and blue polymer films were doped (bleached) and PTMA/PMMA films were reduced prior to the device assembly to start with an initial charge balance. Cathodically coloring films were coated with a TBAP/PC gel electrolyte and sandwiched with the counter electrodes, ITO/PTMA/PMMA. Devices were encapsulated by paraffin wax and the results obtained from these separate appli cations of the films let us set the baseline properties and foresee their behavior in more complicated systems. Spectroelectrochemical and colorimetric studies were conducted to acquire the optical characteristics of the window devices. The spectroelectr ochemical data for these Red,. Green and B lue ECDs are shown in Figures 5 16 to 5 18 with the photographs of the associated colors. When the devices were negatively biased to their colored states, SprayDOTTMRed 252/PTMA device appears red (absorbing mainly at 532 nm) and has L*, a*, b* coordinates of 58,38,6, respectively, SprayDOTTMGreen 179/PTMA device appears green (absorbing at 443nm and 643 nm) and has L*, a*, b* coordinates of 45, 13, 1, respectively, and SprayDOTTMBlue 153/PTMA device appears blu e (absorbing at 398 nm and 652 nm) and has L*, a*, b* coordinates of 55, 18, 35, respectively. When the bias was reversed, devices switched to their transmissive states,

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123 SprayDOTTMRed 252/PTMA device maintains a yellow hue and has L*, a*, b* coordinates of 81, 2,3, respectively, SprayDOTTM-Green 179/PTMA device maintains a blue hue and has L*, a*, b* coordinates of 69, 4, 10, respectively, and SprayDOTTM-Blue 153/PTMA device maintains a blue hue and has L*, a*, b* coordinates of 80, 3, 5, respectively. Even though the dual ECDs showed good contrast and saturated colors their limited stabilities hindered the efficiency of the devices. Figure 5 16 SprayDOTTM-Red 252/PTMA Window ECD. UV -vis NIR spectra and the L*a*b* color coordinates with the associate d photographs at the redox extremes. Figure 5 17 SprayDOTTM-Green 179 /PTMA Window ECD. UV -vis NIR spectra and the L*a*b* color coordinates with the associated photographs at the redox extremes. 400 600 800 1000 1200 1400 1600 0.0 0.2 0.4 0.6 0.8 1.0 Absorbance (a.u.)wavelength (nm) L*= 58 a*= 38 b *= 6 L*= 81 a*= -2 b *= 3 1.5 V 400 600 800 1000 1200 1400 1600 0.0 0.2 0.4 0.6 0.8 1.0 1.2 Absorbance (a.u.)wavelength (nm) L*= 45 a*= -13 b *= -1 L*= 69 a*= -4 b *= -10 2 V

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124 Figure 5 18 SprayDOTTM-Blue 153 /PTMA Window ECD. UV -vis NIR spectra and the L*a*b* color coordinates with the associated photographs at the redox extremes. 5.3 RGB Color Space 5-Electrode ECD The RGB 5 ECD reported here consists of three working electrodes and two counter electrodes whose potentials are co ntrolled separately as demonstrated by th e schematic diagram in Figure 5 19. ITO/glass was chosen as the electrode material for the outermost electrodes, working electrode 1 and working electrode 3, in order to establish a strong foundation for the multi -layered device. Inner electrodes were constructed using porous PETE/PEDOT:PSS/Au as detailed in Chapter 4. Electrochromic polymers which are red (SprayDOTTMRed 252) and green (SprayDOTTMGreen 179) at their neutral states were sprayed on to ITO/glass el ectrodes and named working electrodes 1 and 3, respectively. Electrochromic polymer which is blue (SprayDOTTMBlue 153) at its neutral state was sprayed on PETE/PEDOT:PSS/Au electrode and named working electrode 2. PTMA/PMMA the non-electrochromic, elect roactive, transparent polymer blend, was sprayed on the porous PETE/PEDOT:PSS/Au electrode and treated as detailed in Chapter 4 to be utilized as counter electrodes 1 and 2. Counter electrodes 1 and 2 were sandwiched in between the working electrodes 1, 2 and 3 and maintained the charge 400 600 800 1000 1200 1400 1600 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 Absorbance (a.u.)wavelength (nm) L*= 55 a *= -18 b *= -35 L*= 80 a *= -3 b *= -5 2 V

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125 balance in the device. The electrode layers were separated by the TBAP/PC gel electrolyte, which utilizes the charge transport. The device was encapsulated with a paraffin wax. The potential control of the 5 electrode de vice was facilitated by a potentioastat and a bipotentiostat. Spectroelectrochemical and colorimetric data were obta ined from the device (Figures 5 20 to 5 21). When the green and blue films were doped to their transmissive states (at +2.5 V each) and t he red film was neutralized at its colored state (at 2.5 V) the device appears red absorbing mainly at 532 nm (Figure 5 20 (a)). When the red and blue films were doped to their transmissive states and the green film was neutralized at its colored state t he device appears green absorbing mainly at two bands of 434 and 647 nm (Figure 5 20 (b)). When the red and green films were doped to their transmissive states and the blue film was neutralized at its colored state the device appears blue absorbing at two bands of 398 and 634 nm (Figure 520 (c)). The photographs with the associated color coordinates and the chromaticity diagram of the thrichromat ic states are shown in Figure 5 22. The blue triangle represents the color gamut of RGB 5 ECD and the black triangle represents the color gamut for CRT display. The chromaticity coordinates far from the spectral locus on chromaticity diagram indicates the low purity of the colors we achieved from the device. The device appeared red with L*, a* and b* values of 32, 20 and 1, respectively, appeared green with L*, a* and b* values of 42, 6 and 1, respectively, and appeared blue with L*, a* and b* values of 37, 11 and 23, respectively. Pure and more saturated colors could be achieved by further optimization of the counter electrode which adds a blue hue to the overall device because of the reflectance of PEDOT:PSS and Au. In addition to that, polymer structures could be tailored further towards obtaining more saturated colors. The color purity (saturation) de creases from a single EC film to dual ECD and to RGB 5 -

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126 ECD as shown by the the changes in a* and b* values in Table 5 1. It is promising since the change from single layer film to multi -electrode devices is not drastic. Figure 5 19 Schematic of the RGB 5 ECD Figure 5 20 UV vis -NIR spectra of the individual colors obtained from the RGB 5 ECD, (a) red, (b) green and (c) blue. WE 1 WE 3 CE 1 CE 2 WE 1 WE 3 WE 2 CE 1 CE 2 Pot. Bipot CE R E WE2 WE3 WE1 CE R E 400 600 800 1000 1200 1400 1600 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 a b c c b Absorbance (a.u.)wavelength (nm) a

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127 Figure 5 21 L*a*b* color coordinates and photography of the RGB 5 ECD. CIE chromaticity diagram with chromaticity coordinates shown for the RGB 5 ECD (blue triangle) and the CRT phosphors (black triangle). Table 5 1 Change in a*/b* values from a single EC film to multi -electrode devices a*/b* Red Green Blue Film 49/5 15/ 5 21/ 36 Dual ECD 38/6 13/ 1 18/ 35 RGB 5 ECD 20/1 6/ 1 11/ 23 5.4 Conclusions and Future Perspectives Entire range of colors to be used in display applications is accessible if we have three primary colors. In this project, three primaries, SprayDOTTMRed 252, SprayDOTTMGreen 179 and SprayDOTTMBlue 153, were utilized in the RGB 5-ECD. The display device consisted of five electrodes of which three have red, green and blue electrochromic polymers sprayed on them. Highly conductive, transmissive and porous counter electrode, PETE/PEDOT:PSS/Au an d noncolor changing, electroactive PTMA was used as a counter electrode material to supply charge and prevent early degradation. In this device red, green and blue electrodes are stacked 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 .y x .700 nm 400 nm. L*= 32 a*= 20 b*= 1 L*= 42 a*= -6 b*= -1 L*= 37 a*= -11 b*= -23

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128 on top of each other. The separate control of three primary colors allowed the generation of a RGB color spaces through one single pixel. Today display technology uses red, green and blue phosphors on adjacent pixels. When viewed from a proper distance the mixing of all these regular sequence of red, green and blue strip es or rectangles gives an impression of white. By varying the intensity of light at each pixel different colors can be achieved. In the second part of this project conductive, transparent electrodes will be patterned to regular sequences of dots, rectang les or stripes and they will sprayed with red, green and blue polymers. Separate control of three primary colors and their intensities will generate full RGB color space. The methodologies used by our group in the past can be revisited to utilize pattern ing and printing techniques into RGB 5 ECD application. In order to access all the colors along the visible spectrum, Red, Orange, Yellow, Green, Blue, Indigo and Violet, different primaries must be utilized. These primaries are red, blue and yellow. Ha ving red and blue to transmissive switching EC polymers available, this goal could be achieved by sysnthesis of yellow to transmissive switching EC polymer.

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134 BIOGRAPHICAL SKETCH Ece Unur was born in 1979 in Bursa, Turkey, to Havva an d Irfan Unur. She has a younger brother, Lutfu and an older sister, Necibe. She started school in Bursa, and then moved to a boarding school in Istanbul. She stayed there for seven years. She started college in Ankara at Middle East Technical Universit y in 1998. She got her B.S. in chemistry in 2002 and the next year she received her M.Sc. in chemistry and her double major B.S. in chemical engineering. In August 2003 she moved to Gainesville, Florida to pursue a Ph.D. degree and joined the Reynolds G roup.