Nanoporous Films with Photoswitchable Absorption Kinetics Based on Polymerizable Columnar Discotic Liquid Crystals

A photoresponsive nanoporous polymer film has been produced from the templated self-assembly of a columnar liquid crystal containing azo units. A liquid crystalline complex of polymerizable azobenzoic acid and a tris-benzimidazolyl benzene template molecule was cross-linked via thiol-ene radical copolymerization with dodecanedithiol. Subsequent removal of the template yielded nanoporous polymer films with pores of approximately 1 nm in diameter. Both trans-cis and cis-trans photoisomerizations of azobenzoic acid took place in the porous films. At room temperature, the cis isomer was sufficiently long-lived to establish a difference in dye absorption kinetics of the two isomers. The cationic dye rhodamine 6G was bound to both isomers, but the rate of binding to films enriched in the cis isomer was 8 times faster.