Correlation between Excited-State Intramolecular Proton Transfer and Electron Population on Proton Donor/Acceptor in 2-(2?-Hydroxyphenyl)oxazole Derivatives

Modulating the excited-state intramolecular proton transfer (ESIPT)reaction to achieve anticipant performance is always fascinating for chemists. However,feasible methods and a definite mechanism for tuning the ESIPT reaction remaininsufficient. In this work, we reported the feasibility of continuously modulating theESIPT dynamics in 2-(2 '-hydroxyphenyl)oxazole (HPO) derivatives with differentsubstitutions on the positions 5 and 5 ' of the core HPO through steady-state/transientspectroscopy and theoretical calculations. We found that the main factor affecting thetendency of the ESIPT reaction is the variation of electron population on proton donorand acceptor. An index Delta pdifwas proposed to evaluate the overall promotion effect onproton transfer caused by the variation of electron population on proton donor andacceptor, which shows high reliability in interpreting the ESIPT tendency. This method,for its capacity to quickly estimate the tendency of ESIPT, shows great potential in ESIPTmolecular design with chemical substitution of electron-donating/withdrawing moieties