Molecular Cursor Caliper: A Fluorescent Sensor for Dicarboxylate Dianions

We report here the fluorescent sensing of both aromatic and linear saturated dicarboxylate anions (DC^2–) (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^2– 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.