Photoswitchable Self-Assembly/Disassembly of Near-Infrared Fluorophores.

A new photoswitchable near-infrared fluorophore (TDI-4DTE) with a symmetric structure exhibited reversible photo-controllable self-assembly and disassembly. The modification of π-conjugated terrylenediimide with four dithienylethene groups not only induced photoswitchable near-infrared fluorescence, but also photoregulated reversible precipitation-dissolution with microscopic and macroscopic polymorphism. Upon 302 nm UV-light irradiation, a noticeable precipitation was observed within seconds. The precipitate was gradually dissolved again in half an hour upon visible light irradiation. Different microscopic morphologies of the precipitates, including nanoparticles, nanofibrils and nanosheets, were observed when altering the intensity of the 302 nm light irradiation, indicating the dynamic control process of self-assembly. Upon UV-light irradiation, TDI-4DTE nanosheets were also obtained as a solid polymeric film, whereas well-defined nanoribbons with molecular monolayer thickness formed at the oil/water interface with slower assembly dynamics.