Molecular Cursor Caliper: A Fluorescent Sensor for Dicarboxylate Dianions

We report here the fluorescent sensing of both aromatic and linear saturated dicarboxylate anions (DC) (as their tetrabutylammonium salts) with different lengths and shapes in acetonitrile using a single fluorescent probe, i.e., the bis-calix[4]pyrrole-appended 9,14-diphenyl-9,14-dihydrodibenzo[a,c]phenazine (DPAC-bisC4P) incorporating a vibration-induced emission (VIE) phenazine core. Fluorescence titration studies revealed that treating DPAC-bisC4P with dicarboxylate guests capable of forming pseudomacrocyclic host-guest complexes via multiple hydrogen-bonding interactions between the dicarboxylates and calix[4]pyrrole moieties led to a blue-shift in the emission of the phenazine core. The binding-based fluorescence-tuning features of DPAC-bisC4P allow the underlying binding events and inferred structural changes to be monitored in the form of different chromaticity outputs. The analyte-induced differences in the fluorescence response to DC cover a wide range within the chromaticity diagram and can be visualized readily. The present system thus functions as a rudimentary dicarboxylate anion sensor. It highlights the potential benefits associated with combining a tunable VIE core with noncovalent binding interactions and thus sets the stage for the development of new fluorescent chemosensors where a single chemical entity responds to different analytes with a high level of tunability.