Investigation into the molecular engineering of xanthene-derived AIE tunable fluorescent switching dyes: experimental and theoretical approaches

Dyes endowed with aggregation-induced emission (AIE) properties represent a very significant class of chromophores. Nonetheless, current AIE dyes have yet to possess a readily tunable fluorescence switching mechanism. Here, we delineate a structurally distinctive family of dyes, termed XD dyes, which exhibit AIE attributes. Notably, the novel XD dyes feature an intrinsic helical cyclization as a tunable fluorescence switch, conferring them with an advantage over conventional AIE fluorophores. Initially, the fluorescence of the XD dyes in water-tetrahydrofuran mixtures was investigated through spectral analysis as the volume of the aqueous component increased. Subsequently, particle size analysis, in conjunction with scanning electron microscopy (SEM), was employed to substantiate the aggregation propensity of the XD dyes. Of particular significance, XD-4 was observed for the first time to exhibit pronounced solid-state fluorescence, thereby corroborating the XD dyes’ capacity for robust fluorescence emission in the aggregated state. Moreover, alterations in optical properties and aggregation behavior of the XD dyes were elucidated theoretically through quantum chemical computations and molecular dynamics simulations. Critically, the calculated reorganization energy of XD-4 was reduced in an aqueous medium was reduced compared to the gas phase, providing further confirmation of its AIE nature. The unique AIE characteristics of the XD dyes were validated through the integration of experimental data and theoretical insights, offering novel perspectives for the advancement of high-performance fluorescent dyes and probes.