Phototriggered aggregation-induced emission enhancement with color modulation in <i>N</i> -substituted diarylmaleimide- <i>S</i> , <i>S</i> , <i>S′</i> , <i>S′</i> -tetraoxide derivatives

Abstract Diarylethenes (DAEs), a class of photochromic compounds, exhibit excellent fatigue resistance and thermal stability, and their photochemical properties can be tuned through modification of the ethene or aryl moieties, making them attractive photoresponsive materials. We focused on diarylmaleimide (DAM)-S,S,S′,S′-tetraoxide derivatives as switchable, highly polar fluorescent DAE derivatives. To increase polarity compared with the previously reported DAM 1 and its S,S,S′,S′-tetraoxide derivative 2, we designed 5 bearing a triethylene glycol substituent and its S,S,S′,S′-tetraoxide derivative 6, and synthesized N-H maleimide analogs 3 and 4 as references. 3 and 5 showed reversible photochromism under 436- and 550-nm irradiation with weak fluorescence quenching, whereas 4 and 6 exhibited partial two-way photoisomerization in ethanol, switchable to one-way depending on solvent polarity. Photochemical properties in aqueous systems were examined in water/ethanol mixtures. In 75% water/ethanol, the closed-ring form formed aggregates emitting fluorescence distinct from the solution state, enabling color switching. Among 2, 4, and 6, 6 formed the largest and fastest-growing aggregates and displayed blue-shifted aggregation-induced emission enhancement (AIEE). To the best our knowledge, this is the first report that DAM-S,S,S′, S′-tetraoxide derivatives exhibiting AIEE with distinct emission colors between solution and aggregate states. These findings provide new insight into designing multi-color, multi-state photoresponsive materials. AIEE has attracted significant attention for applications in bioimaging, chemical sensing, and organic electronics, and the present results further suggest potential in these areas.