Reversion of Alignment Direction in the Thermally Enhanced Photoorientation of Photo-Cross-Linkable Polymer Liquid Crystal Films

Abstract

Reversion of the in-plane reorientation direction of mesogenic groups has been observed for the first time in novel polymethacrylate liquid crystal (PLC) films substituted with a 4-methoxycinnamoyloxybiphenyl side group. The reversion was generated by irradiation with linearly polarized ultraviolet (LPUV) light and a subsequent annealing. Irradiation with LPUV light induces negative optical anisotropy of the films as a result of an axis-selective photoreaction of the side groups. The direction of the thermally enhanced reorientation is dependent on the degree of photoreaction and the distribution of photoproducts, while the induced orientational order in both directions, S, was larger than 0.5. The distribution of photoproducts in PLC films has been analyzed to elucidate their contribution to the thermally enhanced reorientation behavior. Initially upon photoreaction, thermal enhancement of the photoinduced negative optical anisotropy was observed. However, when the degree of photodimerization was 15% or greater, the direction of the thermally enhanced reorientation was found to be parallel to the polarization direction (E) of LPUV light. It is concluded that a small amount of photoproduct plays a role in the thermal amplification of the photoinduced negative optical anisotropy in a manner identical to that of PLC with azobenzene side groups. In contrast, photodimerized mesogenic groups generated reversion of the orientational direction and enhancement of positive optical anisotropy of the film through annealing.

Optical and Physical Applications of Photocontrollable Materials: Azobenzene-Containing and Liquid Crystalline Polymers

“…Ono and coworkers reported both optical properties and theoretical treatment [58,59]. The side-chain type LCP has a cinnamic moiety in its terminal region [60,61]. Under linearly-polarized UV light, the cinnamic parts parallel to the polarization were activated and crosslinked with similarly activated molecules.…”

“…For multiplexed recording with pure polarization modulation in a photocrosslinkable LCP, multiplexed diffraction of various polarizations was reported. Base on the recording mechanism of the photocrosslinkable LCP [60], each hologram retained the information without crosstalk [76,77].…”

“…It is also proposed that the photocrosslinkable liquid crystalline polymer [60,162] can be used as an alignment film for fabrication of photo-oriented mesoporous structures. In this method, the proposed alignment layer has sufficient tolerance to immersion in sol-gel reaction solutions, so that no additional intermediate layer is necessary [163].…”

Photoinduced mendable network polymer from poly(butylene adipate) end-functionalized with cinnamoyl groups

“…12,13 Although various applications including photolithography 9 and the fabrication of liquid crystals 14 have been examined, there are only a few reports on photoinduced mendable materials using photodimerization. 15,16 Chung et al 15 developed a photomendable polymer using cinnamate dimer.…”

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.…”