Thermo-Bistable Red and Sensitized Near-Infrared Photoswitches

Molecular photoswitching in the red and near-infrared (NIR) region is highly sought after for applications in biological systems, optoelectronic devices, and functional materials where low-energy light minimizes photodamage and enables deep-tissue penetration. However, developing photoswitches that simultaneously achieve long-wavelength responsiveness with robust thermal bistability and high quantum efficiency remains a formidable challenge. Here, we report an intrinsic thermo-bistable, red-light-responsive (605 nm/730 nm) photochromic motif based on a perylene bisimide (PBI) scaffold, which further enables an unprecedented sensitized NIR (808 nm/730 nm) photoisomerization through a triplet pathway. Rational side-chain engineering with aryl substituents of distinct aromaticity and electronic character finely tunes the transition-state energy barrier (ΔG^‡ = 45.07 kcal mol^-1), leading to exceptional thermal stability and a long-lived closed isomer. Further molecular engineering of PBI-based photoswitches also delivers high photoisomerization quantum yield, bright fluorescence, and near-quantitative photoconversion efficiency. This work provides a new photochromic motif that boosts the overall photochemical/thermal performances of molecular photoswitching at the red-light end, thereby enriching the structural and functional landscape of a high-performance photoswitching system. Demonstrations in dynamic cell-membrane imaging further highlight the potential of these PBI-based photoswitches as powerful photochemical platforms for advanced biomedical and optoelectronic applications.