Full Quantum Dynamics of Complex Chemical System——Modelling Excited State Proton Transfer

Abstract

Non-equilibrium dynamics of chemical and biological systems generally take place inchemical reactions and biological functions. Proton transfer is fundamental and ubiquitous whose mechanisms provide basic insights for more complex processes. Excited state proton transfer reaction (ESIPT) is the ideal model system for studying proton transfer mechanism because its dynamics can be controlled and tracked by light. As the general challenge faced in studying non-equilibrium proton transfer, complex quantum interactions among multiple degrees of freedom causes that the field does not have well-established theory at present. In this dissertation, we combine complex system methodology and theory of open quantum system to model ESIPT and provide mechanistic understanding. We construct an effective Hamiltonian of open quantum dynamics to simulate the quantum interplay of electron, proton, molecular skeleton, solvent, and light. It precisely quantifies the time-resolved spectroscopies of two single-site molecules, which reveals the deterministic motion and interaction could be protonic-electronic transition induced by proton-electron vibronic coupling, rather than semiclassical skeleton deformation assisting ballistic proton delivery as thought before. The vibronic coupling interaction can cause resonant electron-proton oscillation that determines the oscillatory pattern of time-resolved spectroscopy. The same model framework is applied to a double-site molecule, which suggests that the experimental symmetry-dependent isotope effect could be from quantum interference between two reaction channels. The next step will be prediction and validation to confirm these novel mechanisms and keep on developing ESIPT effective Hamiltonian which can be useful to the broader field of condensed phase chemical dynamics.