To construct fluorescent vesicle-like structures showing reliable photoswitching capability, we designed a new type of sterically twisted trigonal compound by linking three carbazole-based azo arms to one central phenyl ring via esterification.

Abstract

Facile construction of light-responsive nano- and microstructured materials that can reliably switch between two states is a great challenge. In this study, to address two issues encountered during repeated photoswitching of azobenzene derivatives, namely, incomplete morphology recovery to the original assembled structures and the resulting degradation of their functions, a sterically bulky carbazole-based azo chromophore was designed in consideration of the balance of 1) twisted molecular geometry, 2) cis form with a sufficient lifetime, 3) complete cis-to-trans photoconversion, and 4) molecular assembly via less-ordered J-type aggregation. Without significant influence of solvent polarity, the trigonal compound predominantly assembles into hollow vesicle-like structures rather than solid spheres. Exposure to UV light results in 1) morphological conversion from vesicles with thin shells to disassembled objects, 2) marked red-shifts in absorption bands, and 3) an increase in fluorescence intensity. Conversely, switching to blue light allows for sufficient recovery to the original morphology and spectroscopic characteristics. Such reliable photoswitching was confirmed with excellent stability for over 10 cycles. Moreover, our further investigations demonstrate that the fluorescent vesicles can not only be used as simple optical information recording media, but the recorded information can also be deciphered by differences in color and emission characteristics.