Photoreactivity of Polymers with Regioisomeric Cinnamate Side Chains and Their Ability To Regulate Liquid Crystal Alignment

Abstract

Photoproduct distribution in films of cinnamate polymers was analyzed to reveal the contribution of both photoisomerization and photodimerization to LC alignment photoregulation. A polymethacrylate with o-cinnamate side chains displayed preferential formation of Z-isomer while the dimerization takes place more favorably for other polymers including poly(vinyl cinnamate). On the basis of the relationship between photoproduct distribution and liquid crystal photoalignment and on the reversibility of the photoinduced reorientation of a liquid crystal, it was concluded that the photoalignment results from the polarization photoisomerization of cinnamate residues in the same manner as that of photochromic moieties like azobenzenes, whereas the (2 + 2) photodimerization plays a role in enhancing the thermal stability of the homogeneous photoalignment.

Photo-alignment of Low-molecular Mass Nematic Liquid Crystals on Photochemically Bifunctional Chalcone-epoxy Film by Irradiation of a Linearly Polarized UV Light

“…16 If the optical anisotropy continue to increase under a continuous UV irradiation, LC alignment can be observed to quite stable. In order to overcome these problems, we designed and synthesized the photoreactive main chain oligomer bearing the chalcone group in the repeating unit and epoxy groups in the terminal ends.…”

“…Most of the photocrosslinkable side chain polymer bearing the cinnamates or chalcone group showed that the molecular orderness is reduced as the power of the UV light goes higher. 16,24 Although the irradiation continued longer subsequently, the order parameter of the chalcone-epoxy sample with photoinitiator decreased continuously to show high anisotropy.…”

Photochemistry of Polymethacrylates with Styrylpyridine Side Chains and Their Photocontrollability of Liquid Crystal Alignment.

“…For instance, linearly polarized UV irradiation of thin films of poly (vinyl cinnamate) generates uniaxially oriented homogeneous alignment of nematic LCs. [3][4][5][6][7] This technique is of practical significance because of the applicability to rubbing-free LC-aligning films, which are inevitable materials in the fabrication of LC display devices.…”

Room‐temperature processing of π‐conjugated oligomers into uniaxially oriented monodomain films on coumarin‐based photoalignment layers

“…To overcome the problems arising from rubbing, e.g., mechanical damage and the generation of dust and electrostatic charges, photoalignment induced by polarized UVirradiation has emerged as an attractive alternative. Three distinct material approaches have been demonstrated: axisselective degradation of polyimides, [22][23][24][25][26] cis-trans isomerization of azobenzenes, [27][28][29] and cycloaddition of cinnamates, [30][31][32][33][34] or coumarins. [35][36][37][38][39][40][41][42] Orientational order parameter values emulating those on rubbed polymer alignment layers have been realized via thermal annealing of films comprising p-conjugated polymers 43,44 and oligomers 39,40 on photoalignment layers.…”

“…A coumarincontaining polymer was chosen for its superior thermal and photochemical stability without complication from photoinduced isomerization. 31,35 Specific objectives are identified as follows: (i) solvent-vapor annealing of conjugated oligomers into uniaxially oriented monodomain films; (ii) elucidation of how vapor absorption affects the vapor annealing process; (iii) lyotropic nematic mesomorphism as the driving force for solvent-vapor annealing; (iv) effectiveness of solvent-vapor annealing on photoalignment layers versus rubbed polyimide alignment layers, and that of solvent-vapor annealing versus thermal annealing on rubbed polyimide alignment layers; and (v) demonstration of uniaxially oriented monodomain films on plastic substrates.…”