Elaborating the excited state behavior of 2-(4-N,N-dimethylaminophenyl)-imidazo[4,5-c]pyridine coupling with methanol solvent

We present a theoretical investigation about the excited state dynamical mechanism of 2-(4-N,N-dimethylaminophenyl)-imidazo[4,5-c]pyridine (DMAPIP-c). Within the framework of density functional theory and time-dependent density functional theory methods, we reasonably repeat the experimental electronic spectra, which further confirm the theoretical level used in this work is feasible. Given the best complex model, 3 methanol (MeOH) solvent molecules should be connected with DMAPIP-c forming DMAPIP-c-MeOH complex in both ground state and excited state. Exploring the changes about bond lengths and bond angles involved in hydrogen bond wires, we find the O7-H8<bold>N</bold>9 one should be largely strengthened in the S-1 state, which plays an important role in facilitating the excited state intermolecular proton transfer (ESIPT) process. In addition, the analyses about infrared vibrational spectra also confirm this conclusion. The redistribution about charges distinguished via frontier molecular orbitals based on the photoexcitation, we do find tendency of ESIPT reaction due to the most charges located around N9 atom in the lowest unoccupied molecular orbital. Based on constructing the potential energy curves of both S-0 and S-1 states, we not only confirm that the ESIPT process should firstly occur along with hydrogen bond wire O7-H8<bold>N</bold>9, but also find a low potential energy barrier 8.898kcal/mol supports the ESIPT reaction in the S-1 state forming DMAPIP-c-MeOH-PT configuration. Subsequently, DMAPIP-c-MeOH-PT could twist its dimethylamino moiety with a lower barrier 3.475kcal/mol forming DMAPIP-c-MeOH-PT-TICT structure. Our work not only successfully explains previous experimental work but also paves the way for the further applications about DMAPIP-c sensor in future.