Visible-light-driven bistable photoswitching with enhanced solid state NIR-fluorescence for multi-level optical storage

Photoswitchable near-infrared (NIR) fluorescence molecules have the characteristic of reversible NIR luminescence modulation, showing broad application prospects in advanced photonic applications such as optical storage and super-resolution fluorescence imaging. Herein, a visible-light-driven solid-state NIR fluorescent bistable molecular switch TDI-4(DTE-TPE) was constructed by covalently coupling aggregation-induced emissive tetraphenylethylene (TPE), photochromic dithienylethene (DTE) and NIR emissive terrylene diimide (TDI) into a single molecule. As the bulky TPE groups hinder the molecules from stacking, the open-form TDI-4(DTE-TPE) exhibits enhanced NIR in the solid state with a maximum emission wavelength of 786 nm, whose fluorescence intensity is 35 times higher than that of its precursor TDI powder. Upon 405 nm visible light irradiation, the open form converted into non-fluorescent closed form, accompanying a fluorescence quenching of >93%, arising from the electron-donating conjugation ability of the TPE group. This process is reversible under another longer wavelength irradiation with excellent fatigue resistance. Also, both the open and closed forms were stable at 85 degrees C and 85% humidity in air for more than 1000 h, showing great bistability and aging resistance. Benefitting from these, its PMMA film realizes multi-level optical information storage, which is a promising photonic storage medium.