Biisoindolylidene solvatochromic fluorophores: Synthesis and photophysical properties

Environment-sensitive fluorescent probes are commonly utilized in various fields, including fluorescence sensing and imaging. This paper describes the synthesis and photophysical properties of a novel class of solvatochromic fluorophores that incorporate biisoindolylidene as the core backbone. This study investigates the structure-property relationships of these newly developed fluorophores. The central biisoindolylidene acts as an efficient electron acceptor, and by modifying the aryl ring substituent at the 3,3′ position, the photophysical properties of the fluorophores can be significantly enhanced, particularly in terms of photoluminescence quantum efficiency. Furthermore, when an electron-donor group replaces the aryl ring at the 3,3′ position, intriguing solvatochromic behavior is observed. This leads to a red-shift in the maximum emission wavelength and an increase in the Stokes shift with increasing solvent polarity. In solvent dimethyl sulfoxide (DMSO), the maximum emission wavelength can reach up to 750 nm, with a Stokes shift of approximately 150 nm. Finally, the potential application of the fluorophore in the detection of volatile acids is explored in a preliminary manner.