Regioisomeric AIE-active luminogens with a substituent aldehyde group for controllable and reversible photochromic behavior and sensitive fluorescence detection of hydrogen sulfite

The three isomeric tetraarylethylene derivativesDPDT-o-CHO,DPDT-m-CHOandDPDT-p-CHOhave been designed and synthesized, based on a 1,1-diphenyl-2,2-(2-dithiophen) ethylene (DPDT) core doubly bonded to the phenyl group with anortho-/meta-/para-aldehyde substituent for unique aggregation-induced emission (AIE)-active luminescences. They exhibited remarkable photochromic behaviors based on the UV-light induced photocyclization reaction, including fluorescence enhancement in solution and emission quenching in the solid state. Moreover, the positions of the substituent aldehyde group exert distinct influence on their molecular conformation and spatial arrangement, resulting in distinct photoresponse. Interestingly, the solid-state ofmeta-substituted isomerDPDT-m-CHOundergoes a fast reversible photo-switch with a high colorimetric contrast and exhibited a rewritable process on filter paper, which highlight the advantage of these AIE-active photochromic molecules in various practical applications. In addition, owing to the reaction of the aldehyde group with hydrogen sulfite (HSO₃⁻) to generate ionic adducts triggering the disaggregation process, the three AIE-active luminogens were capable of exhibiting a “turn-off” fluorescence response to hydrogen sulfite in high water content. Our work provides a general method to design aldehyde group functionalized regioisomeric AIE luminogens with photochromic features by the controllable UV-light induced photocyclization reaction and fluorescence quenching by reverse chemical reaction-based disaggregation, indicating the prospective applications of these luminogens in information security and specific fluorescence sensing.