Conformational Restriction-Induced Dual Visible Light-Switched Diarylethene Fluorochrome by Composite Films

Precise design of photoactive molecules that switch reversibly upon visible-light irradiation is beneficial to develop photosensitive intelligent luminescence materials applied in biological imaging and anticounterfeiting. Herein, we designed a photochromic molecular switch (DAE-BTS) that incorporated cleverly two photoactive groups i.e. diarylethene (DAE) and benzothiazole thiophene styrene (T-BTS) via a π-extended conjugation strategy. T-BTS was undoubtedly identified as a new photo/thermo-controlled molecular switch through some standard characterizations in this work. Interestingly, when T-BTS was connected to the DAE skeleton, its photo/thermos-isomerization activation was restrained. On the contrary, incorporation of two T-BTS sections into the DAE skeleton did not affect photochromism of DAE. Hence, DAE-BTS not only possessed photochromic distinguishing feature but also maintained aggregation-induced emission enhancement characteristic. Moreover, poly(methyl methacrylate) (PMMA) and polypropylene (PP) were first innovatively integrated to form a solid-state composite film, which can supply adaptive nanopores as accommodations for DAE-BTS. The resultant luminescence film DAE-BTS/PMMA–PP exhibited much stronger solid-state fluorescence than DAE-BTS in only PMMA or PP film. Crucially, the formation of the DAE-BTS/PMMA–PP film drove DAE-BTS from the free rotating state to the restricted rotating state. This conformation-constrained strategy further achieved visible light-induced cyclization reaction of the DAE, and then the solid-state fluorescence switch was reversibly controlled by dual visible light, which might be applied in light-recording and anticounterfeiting. The study provided theoretical guidance to accurately design and prepare visible-light-activated DAE derivatives in both directions and optically modulated photoluminescence materials with excellent performance.