Light-regulated crystal growth of π-conjugated luminophores in an azobenzene matrix

Control over the phase transition of functional molecules is a key to design stimuli-responsive materials. Although many efforts have been devoted toward controlling the phase transition of functional molecules by various stimuli such as temperature, solvent vapor, and mechanical stimuli, indirect control using other stimuli-responsive molecules has been hardly explored. Here we demonstrate the potential of this methodology by using a luminescent and a photoresponsive molecule. We prepare blend films composed of an oligo(p-phenylenevinylene) amphiphile showing intrinsic luminescent chromism through isotropic-to-crystalline phase transition and a photo-liquefiable azobenzene amphiphile. The two materials are designed to co-assemble on the molecular level by introducing identical alkyl and oligo(ethylene glycol) chains. The blend films exhibit a luminescence color change from orange to green upon rubbing and subsequent exposure to UV light. Structural analyses reveal that the crystallization of the luminescent amphiphile is regulated by the photoinduced isotropization of the azobenzene amphiphile.