Viscosity-Responsive Electrochemiluminescence of Diphenylbenzofulvene Derivatives

The development of superior probes is highly desirable and valuable for viscosity measurement. Herein, we designed and reported a series of diphenylbenzofulvene (DPBF)-based organic luminophores according to the molecular regulation strategy. There are two free-rotating phenyl groups attached to the rigid fluorene skeleton in the DPBF, enabling its unique propeller-like noncoplanar chemical structure. Benefiting from this, DPBFs could feature outstanding PL and ECL emissions with intriguing aggregation-induced characteristics. Experimental and theoretical investigations revealed that substituent, spatial structure, and molecular orbital energy profoundly affected their luminescent behaviors. It was disclosed that fluoro-substituted DPBF(F)₂ with a smaller LUMO-HOMO band gap demonstrated the strongest ECL emission and was selected as the optimal ECL emitter. Finally, DPBF(F)₂ featured a linear response to the viscosity and VC content with lower limits of detection (LOD) of 5.69 μcP and 38.2 nM, respectively. This study represents the first example of the ECL probe toward viscosity and will be of great significance for both ECL application and viscosity measurement.