Dichroic Dyes for Liquid Crystal Displays

362 Pages·1994·13.79 MB·English

by  Aleksandr V. Ivashchenko

DICHROIC DYES
for
LIQUID CRYSTAL
DISPLAYS
Alexander V. Ivashchenko
Boca Raton London New York
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Library of Congress Cataloging-in-Publication Data
Ivashchenko, A. V. (Aleksandr Vasil’evich)
Dichroic dyes for liquid crystal displays / by A. V. Ivashchenko.
p. cm.
Includes bibliographical references and index.
ISBN 0-8493-4886-2
1. Liquid crystal displays—Materials. 2. Dyes and dyeing—
Chemistry. I. Title.
TK7872.L56193 1994
621.3815’42—dc20 93-37241
A Library of Congress record exists under LC control number: 93037241
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PREFACE
The history of liquid crystalline materials (LCM) and displays based on them is not more
than 25 years old.1 It began in 1968 when Heilmeier, along with his co-workers, discov
ered the effect of dynamic light scattering in liquid crystals (LC),2 followed by other
findings, such as the S-and B-effects, the cholesteric-to-nematic phase change effect, the
twist and supertwist effects, the thennooptical effect, the effects in ferroelectric LC, and
the guest-host effect, which have found wide practical applications. Orientational,
electrooptical, and other effects are discussed in detail in a monograph,3 as well as in other
original papers and reviews.4•7 Owing to the efforts of a great number of scientists and
engineers, extensive progress both in the liquid crystal display (LCD) technology and in
the development of LCM for displays has been achieved within a relatively short period
of time.
Any LCM is a complex mixture of LC compounds and special additives possessing
a set of certain physicochemical properties imparting the desired electrooptical character
istics to LCDs. The problems related to the development of LCM with specified charac
teristics are discussed in detail. It should be noted that the design of LCM is a sophisti
cated creative process in which only joint efforts of chemists, physical chemists, physi
cists, and engineers can lead to success.
Of significant practical interest is the guest-host effect which in a number of cases
makes LCDs simpler, improves their reliability, and allows them to display color infor
mation. The development of high-voltage control circuits9 has led to a noticeable expan
sion of the possible applications of this effect. The guest-host LCDs represent a new
generation of electrooptical devices for displaying and processing information. The heart
of these devices is dichroic dyes (DD) incorporated in the LCM, enabling them to display
black-and-white or color information.
This book is geared to a wide range of researchers and engineers specializing in the
field of chemistry, physics, and applications of liquid crystals; those engaged in the
synthesis of dyes and development of novel LCMs; as well as those developing LC
systems for data display and processing. It is intended to be used as a guide in the wide
variety of the DD for LC currently available, to choose the correct DD for each specific
application, and to select an adequate route in engineering a new DD with the desired
properties. Results on the synthesis and properties of the DD obtained to date are
summarized (the appendices contain formulas and characteristics for about 3000 dichroic
dyes) and the problems to be solved are indicated. The book should also be useful for
organic chemists dealing with purpose-oriented synthesis of complex organic compounds
with preset properties.
The author would appreciate any comments or suggestions useful for future work.
The author is grateful to his numerous colleagues working in the field of dichroic dyes
and liquid crystals, especially Dr. V. G. Rumyantsev. Without their cooperative assis
tance it would have been impossible to write this book.
CONTENTS
Introduction .................................................................................................................... 1
Chapter 1
Types of Dichroic Dyes and Their Order Parameters ..................................................... 3
Chapter 2
Design of a Dichroic Dye Molecule ................................................................................ 7
Chapter 3
Dichroic Dyes ................................................................................................................. 15
I. Azomethines .................................................................................................... 15
IT. lndigoid and Thioindigoid Dyes ..................................................................... 16
TIL Merocyanine Dyes .......................................................................................... 17
IV. 1,3-Bis(dicyanomethylene)indans ................................................................... 19
V. Azulenes .......................................................................................................... 20
VI. Quinophthalonic Dyes ..................................................................................... 22
Vll. Perylene Dyes .................................................................................................. 23
Vlll. Phthaloperines ................................................................................................. 25
IX. Triphenodioxazines ......................................................................................... 28
X. Indolo[2,3-b ]quinoxalines ............................................................................... 28
XI. Imidazo[1,2-b]-1,2,4-triazines ......................................................................... 29
Xll. Tetrazines ........................................................................................................ 29
Xlll. L-Type Azo Dyes ............................................................................................ 30
A. Monoazodyes ............................................................................................ 31
B. Bisazodyes ................................................................................................. 36
C. Tris- and Polyazodyes .............................................................................. 45
D. Metal-Complexing Azo Dyes ................................................................... 50
XIV. T-Type Azo Dyes ............................................................................................ 53
XV. L,T-Type Azo Dyes ........................................................................................ 58
A. Preparation of L T-Type Azo Dyes ........................................................... 58
XVI. I-Type Azo Dyes ............................................................................................. 59
XVII. Benzo- and Naphthoquinones ......................................................................... 60
A. Preparation of Quinone Dyes ................................................................... 60
XVIIT. Anthraquinone Dyes ........................................................................................ 61
A. Electron Structure and Spectra of Anthraquinones .................................. 62
B. Mono- and Polyoxyanthraquinones .......................................................... 65
C. S-Substituted Mono- and Polymercaptoanthraquinones .......................... 68
D. S-Substituted Hydroxythioanthraquinones ............................................... 73
E. Aminoanthraquinones ............................................................................... 74
F. Aminohydroxyanthraquinones .................................................................. 87
G. S-Arylaminothioanthraquinones ............................................................... 98
H. S-Arylaminohydroxythioanthraquinones .................................................. 99
I. T-Type Anthraquinone Dyes .................................................................. 100
J. Anthrapyrimidinones .............................................................................. 109
K. Isotropic Anthraquinone Dyes ................................................................ 110
Chapter 4
Liquid Crystalline Materials ........................................................................................ 115
I. Introduction ................................................................................................... 115
IT. Dependence of the DD Order Parameter on the Nature of the
Liquid Crystal Matrix ................................................................................... 115
ill. Solubility of Dichroic Dyes in Liquid Crystals ........................................... 117
IV. Photo- and Electrochemical Stability of Dichroic Dyes .............................. 120
V. Liquid Crystalline Materials Incorporating Several Dichroic Dyes ............ 124
VI. Lurninophors and Fluorescent Dyes ............................................................. 128
Chapter 5
Electrooptical Effects and Color Displays Based on Them ........................................ 131
I. S-Effect: Splay of Nematic Liquid Crystal Molecules in an
Electric Field ................................................................................................. 131
II. B-Effect: Bend of Nematic Liquid Crystal Molecules in an
Electric Field ................................................................................................. 134
III. T-Effect: Unwinding of Nematic Liquid Crystal Molecules in an
Electric Field ................................................................................................. 135
IV. Electric Field-Induced Cholesteric-to-Nematic Transition .......................... 138
V. Thermal Addressing ...................................................................................... 141
Chapter 6
Commercial Dichroic Dyes and Liquid Crystalline Materials .................................... 145
References .................................................................................................................... 157
Appendices
Appendix 1. Bis( ary lidenearnino )anthraquinones .................................................... 165
Appendix 2. Merocyanine Dyes .............................................................................. 165
Appendix 3. Quinophthalonic Dyes ......................................................................... 166
Appendix 4. Perylene-3,9-Dicarboxylic Acid Esters .............................................. 169
Appendix 5. Phthaloperines ..................................................................................... 171
Appendix 6. Triphenodioxazines ............................................................................. 17 3
Appendix 7. Substituted Irnidazo[ 1, 2-b] -1 ,2,4-Triazines ........................................ 173
Appendix 8. 3,6-Disubstituted 1,2,4,5-Tetrazines ................................................... 174
Appendix 9. L-Type Monoazo Dyes ....................................................................... 174
Appendix 10. L-Type Bisazo Dyes ........................................................................... 193
Appendix 11. L-Type Trisazo Dyes .......................................................................... 215
Appendix 12. L-Type Tetra- and Pentaazo Dyes ...................................................... 223
Appendix 13. L-Type Metal Complexing Dyes ........................................................ 225
Appendix 14. T-Type Azo Dyes ................................................................................ 226
Appendix 15. L,T-Type Azo Dyes ............................................................................ 229
Appendix 16. 1-Type Azo Dyes ................................................................................. 229
Appendix 17. 4,8-Bis-(4-R-Anilino)-1,5-Naphthoquinones ...................................... 229
Appendix 18. L-Type Hydroxyanthraquinones ......................................................... 230
Appendix 19. L-Type Ary lthioanthraquinones .......................................................... 233
Appendix L-Type Arylthiohydroxyanthraquinones
200 ooooooooooooooooooooooooooooooooo 00000000000 242
Appendix L-Type Aminoanthraquinones
2lo oooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo 245
Appendix L-Type Aminohydroxyanthraquinones
220 oooooooooooooooooooo 000000 ooooooooooooooooooooo 271
Appendix L-Type Aminoary lthioanthraquinones
23 0 0 00 000 0 0 0 0 0 0 00 00 00 000 00000 00 000 0 0 0 0 0 00 0000 0 00 000 301
Appendix L-Type Aminoarylthiohydroxyanthraquinones
240 oooooooooooooooooooooooooooooooooo 319
Appendix T-Type Anthraquinone Dyes
25o oooooooooooooooooooooooooOOooOOOOooooooooooooooooooooooooooooo 322
Appendix I-Type Anthraquinone Dyes
260 ooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo330
Appendix Composition of Hosts
270 ooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo336
Index ....
ooo .... o ........ o .. oooooooooooooooooooOooooooooooo• .......... oo .............. ooo ........ o .. ooooooooOOoOooooooooooooooooo339
INTRODUCTION
Since the discovery of the guest-host effect, 10 more than 3000 dichroic dyes (DD) related
to different classes of organic compounds have been synthesized and investigated, 11-13 a
methodology for designing DD molecules with specified properties has been developed,
and a great number of LC mixtures incorporating dichroic dyes has been studied_ This
extensive experimental material, available in numerous papers, patents, conference pro
ceedings, etc., lacks proper systematization.
In writing this book, the author has summarized the information available in the
scientific and patent literature based on his experience of many years in the field of
dichroic dyes, liquid crystalline materials, and their practical use. The book gives a
systematic presentation of issues pertaining to the development of dichroic dyes as
applied in electrooptical systems for displaying and processing data. Within this ap
proach, the first discussion explains the theory of the guest-host effect and methodology
of engineering DD molecules with specified characteristics, followed by an examination
of the properties of the DDs known to date, including the most interesting examples of
synthesis. The book then covers various aspects of designing LCM for guest-host devices,
and finally considers the available designs of guest-host LCDs. The characteristics of
dichroic dyes are presented in the appendices.
1

Chapter 1
Types of Dichroic Dyes and Their
Order Parameters
When a dye with geometric anisotropy is dissolved in a liquid crystal the dye molecules
tend to arrange in such a way that their long molecular axes align along the LC director,
ii (the direction of the predominant orientation of the LC long molecular axes). One of
the main criteria of the DD efficiency is the degree of ordering (or, in other words, the
order parameter), S, of the long-wave electron transition oscillator (LETO), responsible
for the color of the dye, with respect to n. S can be easily found from the electron
polarization spectra of the DD solution in LC using the following formula:
(1)
where D and D .L are optical densities of the aligned solution of DD in LC measured for
11
light polarizations parallel and normal to ii. As a rule, D and D .L are measured at the
11
maximum of the absorption band. Often, to characterize the DD efficiency, the dichroic
ratio N = D/D. L is used which is related to S as follows:
11
S == (N -1)/(N +2) (2)
If LETO coincides with the long geometrical axis x of the DD molecule (Figure 1a ), then
the value of S is equal to that of the geometrical ordering (SG) of the DD long molecular
axes in LC and can be found in the same way as the LC order parameter-3·14
(3)
where e is the angle between LETO (long axis) of an individual DD molecule and ii
averaged over all the DD molecules in the sample.
In the overwhelming majority of cases the DD LETO is polarized at an angle 13 relative
to the axis x (Figure 1b), hence the relationship between Sand sa can be given by11
(4)
Dependence of S on the angles 13 and e, and relationships between S and sa for such
dyes are presented in Figure 2. As can be seen from Figure 2b, for e = 0 the order
parameter decreases with 13. and S >0 for the angles in the range 0°:;; 13 < 54°44'8". The
dyes with S >0 are called DD of positive dichroism, or L-dyes (L =longitudinal). The L
dyes can be exemplified by 4-dialkylamino-4'-cyanoazobenzenes (Structure 1). The dyes
with S <0 (54°44'8" (< 13:;; 90°) are called DD of negative dichroism, or T-dyes (T =
transverse), for example, 3,6-disubstituted tetrazines (Structure 2).
Also known are dyes with s = 0 ([3 = 54°44'8" fore= 0, or 13 = 90° fore= 54°44'8'').
They are referred to as isotropic dyes, or !-dyes, because in the electron polarization spectra
3