The asymmetric dual-hydrogen-bond system TrySPy exhibiting ESIPT characteristics has attracted intramolecular double proton transfer (ESIDPT) mechanism under varying solvent polarities (cyclohexane, toluene, THF, acetonitrile) using density functional theory (DFT) and time-dependent DFT (TDDFT) methods. Through comparison of hydrogen bond-related parameters, we confirmed that dual hydrogen bonds of TrySPy are strengthened in the S1 state. Furthermore, we discovered opposite responses of the two hydrogen bonds to solvent polarity in the excited state: O1-H2···N3 strengthens while N4-H5···N6 weakens with increasing polarity. Frontier orbital analysis demonstrates dominant HOMO-LUMO transition (>97%) driving charge redistribution from proton donors to acceptors. Potential energy surface calculations identify the stepwise I → III → IV pathway as dominant for double proton transfer, but I → II as dominant for single proton transfer with O1-H2···N3 transfer exhibiting lower barriers than N4-H5···N6. Solvent polarity differentially modulates emission spectra, inducing redshift in native form fluorescence and blue shift in tautomer emission. This work establishes solvent polarity as a precise regulator for proton transfer dynamics in TrySPy, an asymmetric dual-hydrogen-bond system.
Shen et al. (Tue,) studied this question.