Anion detection by aggregation-induced enhanced emission (AIEE) of urea-functionalized tetraphenylethylenes

Substituted tetraphenylethylenes (TPEs) have been prepared that feature four alkyl or aryl urea groups arrayed along the periphery. Exposure of these TPEs to monovalent anions (halide, carboxylate, nitrate, and azide) resulted in enhanced fluorescence emission attributed to aggregation of the TPE molecules via urea-anion hydrogen bonding. Emission enhancement correlated with anion basicity, with fluoride ion eliciting the largest fluorescence response. Increased fluorescence emission could also be detected visually in solutions viewed under UV light. This study demonstrates the feasibility of TPE-based fluorescent anion sensors/detectors, and it is envisioned that additional design modifications may afford anion-selective fluorescent sensors.