As a widely-used sunscreen compound, the caffeic acid (CA) shows the strong UV absorption, while the photoinduced reaction mechanisms behind its photoprotection ability are not fully understood. We try to investigate the photoinduced internal conversion dynamics of CA in order to explore the photoprotectiodn mechanism. The most stable CA isomer is selected to examine its nonadiabatic dynamics using the on-the-fly surface hopping simulations at the semi-empirical level of electronic-structure theory. The dynamics starting from different electronic states are simulated to explore the dependence of the photoinduced reaction channels on the excitation wavelengths. Several S1/S0 conical intersections, driven by the H-atom detachments and the ring deformations, have been found to be responsible for the nonadiabatic decay of the CA. The simulation results show that the branching ratio towards these intersections are modified by the light with different excitation energies. This provides the valuable information for the understanding of the photoprotection mechanism of the CA compound.
The analysis of the leading active molecular motions in the on-the-fly trajectory surface hopping simulation provides the essential information to understand the geometric evolution in nonadiabatic dynamics. When the ring...
The analysis of the leading active molecular motions in the on-the-fly trajectory surface hopping stimulation provides the essential information to understand the geometrical evolution in nonadiabatic dynamics. When the ring deformation is involved, the identification of the key active coordinates becomes challenging. A "hierarchical" protocol based on the dimensionality reduction method and clustering approaches is proposed for the automatic analysis of the ring deformation in the nonadiabatic molecular dynamics. The representative system keto isocytosine is taken as the prototype to illustrate this protocol. The results indicate that the current hierarchical analysis protocol is a powerful way to clearly clarify both of the major and minor active molecular motions of the ring distortion in nonadiabatic dynamics.
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