Theoretical insights into elaborating and regulating excited state dynamics for the novel 6-cyano-2-(2′-hydroxyphenyl)imidazo[1,2a]pyridine system in polar and nonpolar solvents
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Given the importance of excited state relaxation in photochemical and photophysical behaviours, in this work, we mainly focus on the excited state dynamical behaviours for the novel 6-cyano-2-(2′-hydroxyphenyl)imidazo[1,2a]pyridine (6-CN-HPIP) system in different aprotic solvents. We find the ultrafast excited state intramolecular proton transfer (ESIPT) behaviour without potential energy barrier for 6-CN-HPIP in nonpolar solvents. Furthermore, we also explore the excited state intramolecular hydrogen bonding interactions and confirm the hydrogen bond O-HN of 6-CN-HPIP should be strengthened based photo-excitation process. It provides the possibility of ESIPT process. And the charge redistribution resulting from photo-excitation around hydrogen bonding moieties further reveals the ESIPT tendency for 6-CN-HPIP molecule. It is worth mentioning that the increased electronic densities around proton-acceptor moiety play important roles in attracting hydrogen proton, which directly promotes ESIPT reaction. Via constructing potential energy curves, we clarify the ESIPT dynamical process for 6-CN-HPIP system and present a novel mechanism that nonpolar aprotic solvents facilitate ESIPT behaviour for 6-CN-HPIP. We hope that novel applications and developments could be promoted for 6-CH-HPIP and its derivatives through regulating and controlling ESIPT behaviours in future.