Photoresponsive liquid crystalline

N.S.S. Kumar, S. Abraham, K.V. Ratheesh, N. Tamaoki, S. Purumi, S. Das, Indane-1,3-Dione and cholesterol containing butadiene derivatives photoresponsive liquid crystalline glasses for imaging applications. J. Photochem. Photobiol. A Chem 207, 73-78 (2009)... 

Abstract The combination of nanomaterials and ordered deformable soft materials is emerging as an enabling system in nanoscience and nanotechnology. In this context, nanomaterial functionalized photoresponsive liquid crystalline polymers are very promising and versatile systems due to their dynamic function. Moreover, the unique characteristic of nanomaterials combined with the mechanical, self-organizing and stimuli-responsive properties of deformable liquid crystalline polymers opens up new and exciting possibilities. In this chapter, we present recent developments of photodeformable behaviors of liquid crystalline polymers functionalized with nanomaterials. The main emphasis revolves around how the physicochemical properties of different nanomaterials modulate the reversible photomechanical behaviors of liquid crystalline polymers and their potential application in devices such as optically controlled switches and soft actuators. 

In addition to investigating ferroelectric liquid crystalline conjugated polymers with dynamic switching functionahties under an electric field, our group has also developed photoresponsive liquid crystalline conjugated polymers with dynamic switching of linearly and circularly polarized luminescence. This was accomplished through the use of a photoisomerizable moiety in the polymer side chain. 

Another example of photoresponsive liquid crystalline material based on halogen bonding appeared recently [61]. The idea here was to extend the concept of photoinduced order-disorder phase transition (Fig. Ic) from conventional photoresponsive LCs to halogen-bonded supramolecular complexes. To do this, the authors complexed azopyridines (AzPy) and molecular dihalogens (Fig. 11) in a... 

Photochemical modulation of the helical screw sense and pitch of a cholesteric phase was achieved with the combination of a nematic liquid crystalline host and an optically active photoresponsive guest as illustrated in Scheme 25.[92] Doping of 4 -(pentyloxy)-4-biphenylcarbonitrile 41 with P-trans-17b (1 wt%) converts the nematic phase into a cholesteric phase. 

These azobenzene LCs display the liquid crystalline phase only when the azobenzene moiety is in the trans form, and no liquid crystalline phase at any temperature when the azobenzene moiety is in the cis form. In these azobenzene LC system, it was predicted that phase transition should be induced on essentially the same time-scale as the photochemical reaction of the photoresponsive moiety in each mesogen, if the photochemical reactions of a large number of mesogens were induced simultaneously by the use of a short laser pulse (Figure 7).1391 On the basis of such a new concept, the photoresponse of azobenzene LCs with the laser pulse was examined, and it was found that the N to I phase transition was induced in 200 xsJ39 40 This fast response, on the microsecond timescale, had been demonstrated for the first time in NLCs. From the viewpoint of application of LCs to photonic devices, such a fast response is quite encouraging. 

In conclusion regarding the results obtained with polymer-bound azobenzene chromophores, establishing liquid crystalline phases that combine order and flexibility in the side chain region of the polymer seems to be the best way to obtain materials with a strong photoresponse. This is because a high density of chromophores can be combined with sufficient flexibility that the chromophores still can be photoisomerized in the dense packing of an LBK film. When a low density of chromophores is acceptable, however, the chromophores can be diluted along the polymer chain to reduce their interaction and secure sufficient free volume. 

T. Kajiyama, H. Kikuchi, and K. Nakamura, Photoresponsive electrooptical effect of liquid crystalline polymer/low molecular weight liquid crystal composite system, Proc. SPIE 1911, 111-121 (1993). 

It is not necessary to carry out synthesis, if the triggering photochromic compound has good affinity to the polymer matrix. A mixture of the polyacrylate with BMAB which exhibits an excellent function as trigger is equally photoresponsive. While the monomer model compound (i.e. the acrylate before polymerization) does not provide a liquid crystalline phase, the polymer shows a clear nematic - isotropic transition at ca. 61 °C and the glass transition temperature at 24 °C as shown in Fig. 4. Tj j depends very much on the length of the alkyl spacer. In comparison with the... 

Moriyama M, Mizoshita N, Yokota T, Kishimoto K, Kato T. 2003. Photoresponsive anisotropic soft solids liquid crystalline physical gels based on a chiral photochromic gelator. Adv Mater 15 1335 1338. 

Yu HF, lyoda T, Okano K, Shishido A, Ikeda T. 2005a. Photoresponsive behavior and photochemical phase transition of amphiphilic diblock liquid crystalline copolymer. Mol Cryst Liq Cryst 443 191 199. 

H. Akiyama, V.A. Mallia, N. Tamaoki, Synthesis, liquid-crystalline properties, and photo-optical studies of photoresponsive oligomeric mesogens as dopants in a chiral glassy liquid crystal. Adv. Funct. Mater. 16, 477-484 (2006)... 

R. Thomas, Y. Yoshida, T. Akasaka, N. Tamaoki, Influence of a change in helical twisting power of photoresponsive chiral dopants on rotational manipulation of micro-objects on the surface of chiral nematic liquid crystalline films. Chem. Eur. J. 18, 12337-12348 (2012)... 

H.F. Yu, H. Liu, T. Kobayashi, Fabrication and photoresponse of supramolecular liquid-crystalline microparticles. ACS Appl. Mater. Interfaces 3, 1333-1340 (2011)... 

Dynamic Switching of Linearly and Circularly Polarized Luminescence of Liquid Crystalline Photoresponsive Conjugated Polymers... 

Here, we have designed and synthesized multifunctional poly(bithienylene-phenylene)s with either racemic (Poly-9) (M — 14,000) or chiral moieties ((/ )-/ (S)-Poly-lO (Mn = 10,000, 8,000, respectively), which exhibit fluorescence, liquid crystallinity, and photoresponsive properties (Fig. 11.20). The polymers are composed of a 7t-conjugated main chain, poly(bithienylene-phenylene), which acts as a fluorescence moiety and mesogen core, and photochromic DE moieties [71, 72] are linked with racemic or chiral alkyl groups in the side chains. The DE photoresponsive moiety isomerizes between its closed and open forms upon irradiation of UV and visible light, respectively. 

H. Hayasaka, K. Tamura, K. Akagi, Dynamic switching of linearly polarized emission in liquid crystallinity-embedded photoresponsive conjugated polymers. Macromolecules 41, 2341-2346 (2008)... 

Yu, H. Dong, C. Zhou, W. Kobayashi, T. Yang, H. Wrinkled liquid-crystalline microparticle-enhanced photoresponse of PDLC-like films by coupling with mechanical stretching. Small 2011, 7, 3039-3045. 

Beyer P, Krueger M, Giessehnann F, Zentel R (2007) Photoresponsive ferroelectric liquid-crystalline polymers. Adv Funct Mater 17(1) 109-114. doi 10.1002/Adfm.200600513... 

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