Photo-aligned ferroelectric liquid crystal displays based on azo-dye layers

doi:10.1016/j.displa.2004.04.003

Displays

Volume 25, Issue 1, May 2004, Pages 21-29

https://doi.org/10.1016/j.displa.2004.04.003 Get rights and content

Abstract

Photo-induced alignment of ferroelectric liquid crystals (FLCs) based on photochemical stable azo-dye films was studied. The alignment quality of FLC display depends mainly on an asymmetric boundary structure and preparation of photo-aligning/planar layers. The photo-aligned FLC display was optimized to obtain both a steadiness of multiplex operation and a high contrast ratio. A prototype of passively addressed 64×64 FLC display based on the photo-alignment technique has been developed with perfect bistable switching in the multiplex driving regime.

Introduction

Recently, photo-alignment technique has become an intense area of investigations in liquid crystal displays (LCD) research [1], [2], [3], [4]. Photo-alignment proves to possess important advantages in comparison with the traditional rubbing treatment, including [5], [6], [7], [8]:

(i)
avoiding of mechanical damage of the surface due to electrostatic charges and impurities;
(ii)
possibility to produce a structures with the required LC director azimuth within the selected areas of the cell, thus allowing sub-pixels to have different alignment to improve viewing angles.

The effect of photo-alignment is a direct consequence of the appearance of photo-induced optical anisotropy and absorption dichroism in thin amorphous films, formed by molecular units with anisotropic absorption properties [9]. In the new method, the anisotropic properties of a suitable polymer layer are induced by an exposure of a linear polarized UV radiation. The thin films of a polymer exhibiting photo-induced anisotropy can serve as aligning layers for LCD applications. Currently, there are several groups of materials suitable for this purpose, such as the polyvinylcinnamate, polyimide and liquid crystalline side-chain polymers. Historically, the photo-induced anisotropy recorded in the polyvinylcinnamate was first demonstrated in 1977 [9]. This material was then applied to align LC molecules, and very promising results have been obtained [10], [11]. However, homogenous alignment cannot be restored after a number of thermal cycles. The thermal stability and the compatibility with LCD manufacturing are the primary issues, which have to be resolved.

The second class of materials, which have successfully induced LC alignment, are the azo-dyes mixed with a polyimide [12] or polyvinylalcohol [13]. The thermal stability has been improved and become comparable to that of a rubbed polyimide film usually used as an aligning layer. Recently, the polyimide derivatives, cross-linked with the dyes, have shown impressive aligning quality [14], [15], [16]. Since these materials have the similar stable characteristics as polyimide, much research efforts have been undertaken in this direction. However, high exposure energy is usually required for the polyimide derivatives and some free radicals are generated by the photo-dissociation. The impact due to these free radicals to the LCD lifetime has not been fully understood. Moreover the polyimide materials are very sensitive to the UV exposure time and for sufficiently large exposure time the induced order parameter drastically decreases. In the early development of photo-alignment technique, the liquid crystalline side-chain polymers [17], [18] and photo-stable azo-dye polymer mixtures [19] had also drawn considerable attention.

Ferroelectric liquid crystals (FLC) are very sensitive to small particles that can induce nucleation centres for dislocations especially at a very small cell gaps (less than 2 μm). Such small cell gaps are necessary either for bistability or for improving the optical transmission of the LC cell. Moreover, buffing non-uniformity very often results in an appearance of large domains with opposite directors of FLC director [20]. The domain formation leads to a poor reproducibility in manufacturing of FLC display devices. A phenomenon of the bistability and multiplex mode degradation of FLC display, aligned with ordinary rubbing technique, has been already discovered many years ago [21]. To improve FLC alignment quality various kinds of aligning surfaces, including rubbed polyimide films [22], [23], [24], [25] and photo-aligning layers [26], [27], [28], [29], [30], [31] were used. Due to the advantages of photo-alignment technique, it looks very promising for FLC application.

Homogeneous, reproducible and steady FLC alignment is very important for FLC bistable switching. An azobenzene sulfuric dye SD-1 has been recently synthesized and successfully tested for the alignment of FLC displays [30]. A remarkable property of this azo-dye is a pure reorientation of molecular absorption oscillator perpendicular to UV light polarization without any photochemical transformations [32]. This property gives a good chance to provide a high photo-alignment quality of FLC using the azo-dye layer.

In this paper, we shall present our recent results on photo-alignment of the FLC. The quality of FLC alignment and the stability of bistable switching in multiplex operation of passively addressed FLC display are discussed in this paper. Optimization of photo-aligned FLC display was investigated, including the effects of substrate quality, aligning layer thickness and boundary conditions.

Section snippets

Mechanism of azo-dye SD-1 photo-alignment

The azobenzene sulfuric dye, used in the experiment is shown in Fig. 1. When the azo-dye molecules are optically pumped by a polarized light beam, the energy absorbed for the transformation is proportional to cos²θ, the angle θ characterizes the orientation of dye molecule with respect to the polarization vector of UV light. In other words, this probability distribution is non-uniform and has an angular dependence. Therefore, the azo-dye molecules that have their transition dipole moments

Photo-aligned FLC cell preparation

The azo-dye SD-1 dissolved in N,N-dimethylformamide (DMF) was spin-coated onto ITO substrates, and then exposed by a linearly polarized UV light with the wavelength of 365 nm and the intensity of 6 mW/cm². A boundary conditions asymmetry has been provided in order to avoid a competition in aligning action of solid surfaces of FLC cells. One ITO substrate was washed in DMF, providing a focal-conic, or planar degenerated alignment, where all directions in the plane of the substrate are

Conclusion

In this paper, photo-induced alignment for FLC displays based on the azo-dye films was investigated. The alignment quality of FLC display cells depended on the asymmetric boundary structure and treatment of ITO layer, including photo-aligning substrate and planar substrate. Asymmetric boundary conditions were necessary to avoid a competition in aligning action of solid surfaces of FLC cells. High exposure energy resulted in high-quality of photo-aligned SD-1 layer, and hence, perfect

Acknowledgements

This research was supported by the Hong KongGovernment Innovation and Technology Fund and Research Grants Council grant HKUST6102/03E.

References (36)

W.C Yip et al.
Displays—Technology and Applications
(2001)
V.G Chigrinov et al.
Proceedings of the SPIE
(2001)
Y Murakami et al.
Proceedings of the IDW'01 (Nagoya, Japan)
(2001)
M.O Neill et al.
Journal of Physics D—Applied Physics
(2000)
Y Tanaka et al.
SID'99 Digest (Santa Ana, USA)
(1999)
Y Iwamoto et al.
Proceedings of the IDW'01 (Nagoya, Japan)
(2001)
A Kumano
Journal of Photopolymer Science and Technology
(2001)
J Chen et al.
SID'99 Digest (Santa Ana, USA)
(1999)
E.D Kvasnikov et al.
Reports of USSR Academy of Sciences
(1979)
M Schadt et al.
Japanese Journal of Applied Physics
(1992)

A.G Dyadyusha et al.

JETP Letter

(1992)

W Gibbon et al.

Nature

(1991)

V.G Chigrinov et al.

Proceedings of the SPIE

(1998)

W.M Gibbons et al.

Proceedings of the SPIE

(1999)

M Nishikawa et al.

Japanese Journal of Applied Physics

(1999)

K Kumagai et al.

Japanese Journal of Applied Physics

(1999)

N Kawatsuki et al.

Japanese Journal of Applied Physics

(1997)

A.G Tereshchenko et al.

Optics and Spectroscopy

(1997)

Cited by (69)

pH-sensitive 4,(4-Nitrophenoxy)benzeneamine) derived azo dye: X-ray crystallographic, DFT and electrochemical studies
2020, Journal of Molecular Structure
A novel nitro terminated azo dye, (E)-3-((4-(4-nitrophenoxy)phenyl)diazenyl)-[1,1′-biphenyl]-4-ol (1), was produced by coupling biphenyl-4-ol with 4,(4-Nitrophenoxy)benzeneamine) and was characterized by various spectroscopic and XRD technique. The chemical structure of the compound (1) has a nitro terminal as an electron-withdrawing moiety (A), a biphenyl ring of coupling part as a proton-donating unit (D), and both groups are linked by an azo group connector. The stimulating pH-controlled absorption behavior of chemosensor was investigated using UV/VIS spectroscopic technique. It was observed that synthesized dye (1) has high sensitivity in pH range from 7.9 to 10.46 and could be applied as a selective ‘naked-eye’ colorimetric sensor for H⁺ ion concentration, as it exhibited a very strong hyperchromic shift in the absorption band from 399 nm to 521 nm with a significant color change from yellow to red. The sensitivity of chemosensor was observed to be fully reversible and rapid which enhance its chances of practical implicitly. Further, DFT simulations were performed using ADF-Modeling suite 2019, to get an idea of relevance with experiments. Additionally, redox behavior of the (1) dye was also investigated by employing cyclic voltammetry using 0.1M TBAP as supporting electrolyte. Cis–Trans conformational changes were analyzed to investigate the photoisomerization ability of the synthesized dye.
A superfast responsive and ultrathin self-constructed bilayer nanoarchitecture for automatic vertical orientation of liquid crystals
2020, Applied Materials Today
Citation Excerpt :
However, this method exhibits an unsatisfactory response time of dozens of milliseconds and requires an additional pretreatment process such as chemical solution deposition for monolayer formation prior to the display device assembly. The physical doping of the LC medium by alignment agents including nanoparticles or photochromic azo-dye has also been studied because it has been shown to generate planar or homeotropic orientation of LC molecules without pretreatment processes [21–37]. However, as most nanoparticles such as polyhedral oligomeric silsesquioxane, gold, and nickel typically exhibit a poor compatibility with mesogenic molecules and weak adsorption on electrode substrates, there are difficulties in addressing the severe aggregation issue of nanoparticles and realizing an enhanced electro-optical performance of those devices compared to the conventional alignment film [21–29].
Ultrathin bilayer nanoarchitectures are structurally and functionally tunable yet robust, which are hierarchical building blocks with a wide range of applications from flexible displays to wearable optoelectronic devices. Here, we report an unprecedented cost-effective fabrication strategy to construct an ultrathin, superfast responsive, and highly durable bilayer nanoarchitecture for automatic vertical arrangement of liquid crystals (LCs) by using the spontaneous and cooperative self-construction of small mesogenic amphiphiles. The self-constructed bilayer nanoarchitecture is achieved by the simple doping and subsequent in situ self-assembly of a small amount of mesogenic amphiphiles in the confined cell geometry. It is experimentally demonstrated that an ultrathin and rough bilayer nanoarchitecture with vertical nanopillar array formed by surficial hydrogen bonding and cooperative π–π interaction of mesogenic amphiphiles enables an automatic vertical orientation of LC molecules to be realized during self-construction process. In addition, this simple approach provides a superfast responsive and highly reliable nanoarchitecture with a greatly enhanced electro-optical switching performance compared to conventional polyimide alignment layer. The ultrafast response time of 1.5 ms, which is more than ten times faster than that obtained from a conventional alignment layer, and low voltage driving achieving about 33% energy savings are accomplished by our method.
Novel substituted aniline based heterocyclic dispersed azo dyes coupling with 5-methyl-2-(6-methyl-1, 3-benzothiazol-2-yl)-2, 4-dihydro-3H-pyrazol-3-one: Synthesis, structural, computational and biological studies
2020, Journal of Molecular Structure
Citation Excerpt :
Azo dyes are the important organic compounds that are mainly obtained from the synthetic origin and show a broad spectrum of colors [3]. In recent years, they have been extensively investigated due to their high technology industrial applications in the development of sensitized solar cells [4], liquid crystalline display [5], photo-sensitizers [6], inkjet printers [7], non-linear optical (NLO) materials [8] and coloring textiles [9]. More recently, azo molecules having heterocyclic moiety such as pyrazole, thiazole and benzothiazole have been used for various fields like nonlinear optics, Structure-Activity Relationship [SAR] and electrochemical applications [10–12].
In this study, we have synthesized four heterocyclic azo dyes by conventional diazo-coupling reaction between aniline derivatives with 5-methyl-2-(6-methyl-1,3-benzothiazol-2-yl)-2,4-dihydro-3H-pyrazol-3-one at lower temperatures and are characterized by physico-chemical techniques. The quantum chemical study was also employed to understand the chemical reactivity of the compounds by using B3LYP method in conjunction with 6–31G (d, p) basis set. The photochemical property of the dyes was studied and they showed higher intensity and good quantum yield with respect to the Rhodamine B. The azo dyes were screened for their antimycobacterial activity against M. tuberculosis and the results showed appreciable antitubercular activity. The anticancer activity of the compounds was studied against HCT116, A549, Jurkat and K562 and all the compounds could be able to inhibit the growth of the cancerous cells.
Synthesis, characterization and pharmacological evaluation of 2-aminothiazole incorporated azo dyes
2020, Journal of Molecular Structure
Citation Excerpt :
Additionally, azo dyes based on heterocyclic moiety are known for their excellent colouring properties, tinctorial strength, fastness, thermal stability. Further, this class of compounds also exhibits a prominent cell bathochromic effect than the dyes derived from simple aromatic systems [5–16]. Among the heterocyclic azo dyes, those containing thiazole nucleus fascinated the chemists because of its significance into in this field due to their exceptional pharmacological activities [17] such as inhibition of RNA, DNA, protein synthesis, antitumor [18], antihistamines [19,20], anti-inflammatory [21], schistosomicidal agents [22], anti-tuberculosis [23], antibacterial [24], insecticides [25] and production of drugs in chemotherapy [26,27].
Azo molecules (A1-A3) were prepared by reacting 2-aminothiazole with three different pyridone derivatives as coupling components, viz., 6-hydroxy-4-methyl-2-oxo-1,2-dihydropyridine-3-carbonitrile, 6-hydroxy-1,4-dimethyl-2-oxo-1,2-dihydropyridine-3-nitrile and 1-ethyl-6-hydroxy-4-methyl-2-oxo-1,2-dihydropyridine-3-carbonitrile via diazo-coupling reactions, under appropriate experimental conditions. The structural characteristics of the synthesized compounds were checked by different spectral techniques. The newly synthesized molecules were tested for their biological activities and the results of biological activity studies of the compounds prepared exhibited potential antimicrobial activity against the respective microorganisms. The synthesized azo dyes also demonstrated promising antimycobacterial activity screened against M. tuberculosis. All the compounds showed considerable cleavage efficiency against supercoiled pBR322 DNA. Further, the in silico molecular docking study was performed against E. coli 24 kDa domain and Cyp51 (cytochrome P450 14α-sterol demethylase) as target receptors. The binding energy of each studied compound was evaluated, and the data revealed that the compound A1 displayed higher binding affinity value and forms hydrogen bonds with the active amino acids.
6-Substituted benzothiazole based dispersed azo dyes having pyrazole moiety: Synthesis, characterization, electrochemical and DFT studies
2020, Journal of Molecular Structure
In the present work discusses synthesis, structural characterization and electrochemical investigation on some azo dyes derived from substituted benzothiazoles. The conventional diazo-coupling method was adopted to afford the heterocyclic azo dyes of benzothiazoles having pyrazole moiety. The obtained azo dyes were characterized by FT-IR, UV–visible, fluorescence, ¹HNMR and, mass spectrometric techniques. The quantum chemical studies (DFT) was also used to interpret the structural properties of the compounds by using B3LYP program at 6–311++ (d, p) basis set. Further, the cyclic voltammetry was used to study the electrochemical behavior of the synthesized azo dyes in 0.1 M H₂SO₄ solution on a glassy carbon electrode at different scan rates.
Characterization and absorption properties of newly synthesized mono azo dyes: Experimental and theoretical approach
2019, Journal of Molecular Structure
New mono azo dyes 5-amino-4-[4-(dimethylamino)phenyl]diazenyl]-pyrazol-3-ol (A) and 5-amino-4-[4-(dimethylamino)phenyl]diazenyl]-2-phenyl-pyrazol-3-one (B) are synthesized and their FT-IR, ¹H NMR and UV–Vis properties are measured. Computational quantum chemistry simulations based on Density Functional Theory (DFT) and Hartree-Fock (HF) by utilizing the basis set of 6-31G(d) are carried out to investigate the molecular structure and some spectroscopic properties, such as FT-IR, ¹H NMR,¹³C NMR and UV–Vis spectra and the frontier molecular orbitals of Compounds A and B. Potential energy distribution (PED) is used to determine the FT-IR vibrational modes of the mono azo compounds. The correlations between the measured and calculated vibrational frequencies are found to be in good agreement with each other. UV–Vis spectrum in different solvents are measured and supported by their ab-initio calculations. The frontier molecular analysis are considered to get the electronic properties of two molecules. A good agreement between the experiment and computation results indicates that DFT and HF methods are able to provide satisfactory results for structural, spectroscopic and electronic properties of mono azo dyes.

View all citing articles on Scopus

¹: On leave from P.N. Lebedev Physical Institute of Russian Academy of Sciences, Leninsky pr. 53, Moscow, 119924, Russia.

View full text

Photo-aligned ferroelectric liquid crystal displays based on azo-dye layers

Abstract

Introduction

Section snippets

Mechanism of azo-dye SD-1 photo-alignment

Photo-aligned FLC cell preparation

Conclusion

Acknowledgements

Displays—Technology and Applications

Proceedings of the SPIE

Proceedings of the IDW'01 (Nagoya, Japan)

Journal of Physics D—Applied Physics

SID'99 Digest (Santa Ana, USA)

Proceedings of the IDW'01 (Nagoya, Japan)

Journal of Photopolymer Science and Technology

SID'99 Digest (Santa Ana, USA)

Reports of USSR Academy of Sciences

Japanese Journal of Applied Physics

JETP Letter

Nature

Proceedings of the SPIE

Proceedings of the SPIE

Japanese Journal of Applied Physics

Japanese Journal of Applied Physics

Japanese Journal of Applied Physics

Optics and Spectroscopy