Hydrogen bond induced twisted intramolecular charge transfer in 2-(4′-N,N-dimethylaminophenyl)imidazo[4,5-b]pyridine

Protic solvent induced dual fluorescence in 2-(4′-N,N-dimethylaminophenyl)imidazo[4,5-b]pyridine (DMAPIP-b) was studied by using steady-state and time resolved fluorescence measurements. The long wavelength emission is attributed to the formation of a twisted intramolecular charge transfer (TICT) state facilitated by H-bonding of the solvent with the pyridine nitrogen of DMAPIP-b. ab initio calculation predict that the molecule is planar in the ground state. Time resolved measurements suggest that an equilibrium is not established between the locally excited (LE) state and the TICT state. In an acidic medium the imidazole nitrogen is protonated and a single emission is observed.