Amino donor-acceptor Stenhouse adducts as visible-light-responsive intrinsically emissive photoswitches for dynamic cellular imaging

Combining efficient photoswitching with emission into a single chromophore remains a major challenge, as the structural requirements for one function are often antagonistic to the other. Here, we report amino donor-acceptor Stenhouse adducts (aDASAs) as a new class of intrinsically emissive photoswitches that overcome this limitation. By introducing a sulfonamide at the C2 position, we interrupt the full isomerization pathway and impact isomer distribution ratios under irradiation, enabling single-wavelength visible-light photoswitching and fluorescence to coexist within the same thermodynamically favored chromophore. Optimizations yield compounds with red-shifted absorption, record photoluminescence quantum yields representing a six-fold improvement over previous donor-acceptor Stenhouse adducts, and enhanced stability in biologically relevant solvents. These new intrinsically emissive photoswitches correlate fluorescence intensity with switching equilibria, allowing reversible light-induced dimming that creates a fluorescence winking effect. Optimized aDASAs enable robust cytoplasmic visualization in both fixed and live human embryonic kidney (HEK293T) cell imaging, and repeated on/off fluorescence dimming occurs with minimal irreversible photobleaching in fixed cells and with little to no impact on cell viability. This shared-chromophore design provides precise spatiotemporal control for dynamic biological imaging and establishes aDASAs as potential lightresponsive probes for confocal and super-resolution microscopy.