Material design for polymer/azobenzene liquid crystal/metal salt composite films possessing thermo‐ and photoresponsive ionic conductivity

Abstract

SYNOPSISVarious azobenzene derivatives and polymers were attempted as materials for thin composite films containing a polymer, a liquid crystal, and lithium perchlorate which can undergo ionic-conductivity switching induced by light or heat. Poly (vinyl chloride) -based composite films containing enantiotropic azobenzene liquid crystals 1 exhibited significant ionicconductivity change based on thermo-and photoinduced phase transitions of 1, the temperature dependence on the ionic conductivity reflecting the enantiotropic phase transition behavior of the liquid crystals. Marked, reversible ionic-conductivity switching on alternating irradiation of UV and visible lights was attained with the composite films containing 1, especially 1 ( n = 12). Incorporation of monotropic liquid crystals 3 to the composite films allowed bistability in the temperature dependence on the ionic conductivity. Employment of a polycarbonate resin and poly(methy1 methacrylate) as the polymer material of the composite films gave similar ionic-conductivity changes to the poly (vinyl chloride) composite films, whereas polyethyleneoxide brought about some different results in the photoinduced ionic-conductivity change.

Ionic conductivity probed in main chain liquid crystalline azobenzene polyesters

“…UV light irradiation resulted in an increase in the conductivity whereas visible light irradiation resulted in reduction in ionic conductivity . The range of switching observed for ionic conductivity values upon irradiation was similar to those reported in literature . The photoconductivity behavior of Poly(P4PTEG)/Li‐0.3 was in accordance with the observation from the absorption spectra recorded as a function of UV and visible irradiation steps which indicated reduction in aggregation.…”

“…34 The range of switching observed for ionic conductivity values upon irradiation was similar to those reported in literature. [32][33][34][35] The photoconductivity behavior of Poly(P4PTEG)/Li-0.3 was in accordance with the observation from the absorption spectra recorded as a function of UV and visible irradiation steps which indicated reduction in aggregation. The absorption spectra gave information regarding the state of aggregation of the azo segment brought about by the complexation of lithium ions to the connecting oligoethyleneoxy segments.…”

“…The structural design consisting of a rigid mesogen and flexible oxyethylene units is expected to lead to ion conductive LC materials. The utilization of the photoresponsive azobenzene as the rigid mesogen has the added advantage of providing a photoinduced ion‐conductive switching . Extensive research in the early 1990's by the group of Kimura et al addressed the effectiveness of a combination of materials like suitable polymer matrix for processability, LC molecule for thermal stimuli, azobenzene units for photostimuli, crown ether derivatives as ion conducting carriers and lithium salt for ionic conductivity for developing higher‐performing ionically conducting composite films.…”

“…The utilization of the photoresponsive azobenzene as the rigid mesogen has the added advantage of providing a photoinduced ion-conductive switching. [32][33][34][35] Extensive research in the early 1990's by the group of Kimura et al addressed the effectiveness of a combination of materials like suitable polymer matrix for processability, LC molecule for thermal stimuli, azobenzene units for photostimuli, crown ether derivatives as ion conducting carriers and lithium salt for ionic conductivity for developing higherperforming ionically conducting composite films. They also developed vinyl polymers having varying mole ratios of crowned azobenzene and mesogenic biphenyl moieties in the side chain as single polymeric photoresponsive ion conducting materials.…”

Application of Photoresponsive Polymers Carrying Crown Ether and Spirobenzopyran Side Chains to Photochemical Valve

“…We have been applying organic photochromic compounds to the photochemical switching of metal-ion complexation and ionic conduction, by combining a photochromism with metalion binding property of crown ether derivatives. [13][14][15][16][17][18][19][20][21][22][23][24][25] Nitrospirobenzopyran derivatives incorporating at the 8-position, which we call crowned spirobenzopyrans, undergo the photocontrol of metal-ion complexation by their crown ether moiety. 16 The crowned spirobenzopyran in the electrically neutral form can capture an alkali metal ion with its crown ether moiety, while its spirobenzopyran moiety isomerizes to the corresponding merocyanine form photochemically.…”