Evidence for stepwise excited state double proton transfer process in quinolone–pyrazole triggered by methanol solvent

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Basing on the density functional theory and time-dependent density functional theory, we present a systematic theoretical investigation on the excited state double proton transfer process (ESDPT) of quinolone–pyrazole (QP) in methanol (MeOH). The theoretical results provide convincing evidence that ESDPT process takes place in QP-MeOH hydrogen bond (HB) complex. The analysis of the optimized geometry structures and non-covalent interactions adequately demonstrates that the strengthened intermolecular HBs make remarkable effect on the ESDPT process. Meanwhile, the frontier molecular orbitals have been delineated to understand the driving force of the ESDPT process. The changes of characteristic peaks in the infrared spectra further prove the occurrence of the ESDPT process. Combining with the analysis of constructed potential energy curves, the ESDPT mechanism for QP-MeOH complex is clearly clarified. Our studies not only shed light on the nature of ESDPT process of QP-MeOH, but also be helpful to design novel promising photoelectric materials.