Three-dimensional diabatic models for the ππ* → nπ* excited-state decay of uracil derivatives in solution

Uracil and its derivatives strongly absorb UV light but photodamage is hampered through effective non-adiabatic decay channels. As a first step towards a quantum dynamical (QD) study of the decay route of the photoexcited pi pi* state to the underlying n pi* state, here we present our procedure to build a reliable reduced-dimensionality model of the decay process, and we discuss its theoretical foundation. We established the three most important nuclear coordinates for the decay process and we computed the S (1) and S (2) excited-state potential energy surfaces of Uracil and 5-fluoro-Uracil in acetonitrile and in water at TD-DFT level, describing the solvent in the frame of polarizable continuum model. Through a property-based diabatization we obtained the diabatic pi pi* and n pi* states' energies and coupling and we fitted them to analytical functions of the nuclear coordinates. We show how these diabatic models can be utilized for QD simulations of the pi pi* -> n pi* decay.