A possible attributions of excited-state process for PIP and PIP-c system in methanol solvent

In this work, based on the DFT/TDDFT methods, we theoretically studied isomerides (2-phenylimidazo[4,5-b]pyridine (PIP) and 2-(phenyl)imidazo[4,5-c]pyridine (PIP-c)) about their excited state behavior in methanol solvents. Via comparing potential energy barriers, we deem that the single emission for these two systems should be attributed to the normal fluorescence mentioned in previous experiments if ESIPT could not occur. While if the potential barriers are suitable for ESIPT, the non-radiative path should be great mechanism in the excited state. Intersection and intersystem crossing could successfully explain the single fluorescence phenomenon for PIP and PIP-c system. AMS subject classifications: 65D18, 78M50, 74E40