Twisted intramolecular charge transfer emission turn-on sensing towards picric acid.

A competent sensor of picric acid, 2-(4'-dimethylamino-2'-methoxyphenyl)-1H-imidazo[4,5-c]pyridine (DMAMPIP-c), has been reported. The sensor exhibits solvent assisted twisted intramolecular charge transfer (TICT) emission. The absorption, photoluminescence, and time-resolved photoluminescence spectra were recorded in various aprotic and protic solvents. DMAMPIP-c displays only dual emissions in methanol. But in other solvents, including protic solvents, the fluorophore exhibits single emission. In the presence of picric acid, TICT emission becomes significantly prominent in aprotic solvents as well. The sensor can exhibit not only a turn-off but also a turn-on emission in the presence of picric acid. It can be controlled solely by the excitation wavelength. This photophysical feature enables the detection of picric acid, with a low limit of detection (LOD) of 7.1 nM. DFT and TD-DFT calculations were incorporated to explore the experimental observations and also corroborate the experimental findings.