Metal‐Free Synthesis of Hydroxybenzimidazole‐Derived ESIPT‐AIE Fluorophore Showing Time‐Dependent Emission: Synthesis, Computational Study, and Application in Esterase Sensing

Here, we present the design and synthesis of regio‐isomeric hydroxybenzimidazole‐dicyanophenyl‐vinyl (OH‐BIDCPV) molecules. Through detailed photophysical studies, we found that the ortho‐substituted hydroxybenzimidazole‐dicyanophenyl‐vinyl (o‐OH‐BIDCPV) exhibits a strong yellow fluorescence emission at 550 nm, attributed to excited‐state intramolecular proton transfer (ESIPT)‐coupled aggregation‐induced emission enhancement (AIEE) in both solid and solution phases. Interestingly, in solution, the 550 nm emission displays a time‐dependent enhancement, a relatively rare phenomenon in small molecules. Furthermore, we have utilized o‐OH‐BIDCPV to develop an activity‐based probe for detecting cellular esterase activity inside MCF‐7 breast cancer cells.