Surface-mediated dynamic cooperative motions in azobenzene polymer films

Azobenzene (1,2-diphenyldiazene in IUPAC name) is a widely studied simple rodlike photochromic molecule. The trans- (E) to cis- (Z) photoisomerization of this molecule was discovered long time (nearly 90 years) ago. Nevertheless, the allure and utilities of this molecule never get faded and does not surrender a leading position among many other organic photochromic molecules. New applications for photoswitching molecular and macromolecular systems are still being proposed extensively. When the azobenzene molecule is linked with liquid crystals (LCs) and polymer systems, a number of fascinating motility functions have been newly realized. This article overviews our research activities using azobenzene-containing monolayers and LC polymer films. The topics range surface photoalignment of LCs both from solid surface and free surface, photoalignment of hierarchical structures such as mesohybrids and block copolymers, photomechanical motions and morphological switching in block copolymer monolayers, high-density brushes of azobenzene side chain LC polymers (SCLCPs), photo-triggered mass migrations in azobenzene SCLCP films and polymer motions via Marangoni flow etc. Demonstrations of these dynamic photofunctions are expected to provide great opportunities toward practical smart applications. This account overviews our research activities using azobenzene-containing polymer monolayers and liquid crystalline (LC) materials undertaken over 35 years. The topics cover the surface photoalignment of LC materials both from solid surface and free surface, photoalignment of hierarchical structures, photomechanical motions and morphological switching in monolayers, phototriggered mass migrations etc. Dynamic photoresponsive systems are expected to provide wide opportunities toward practical smart applications.