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 ππ*state to the underlying nπ*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 ππ*and nπ*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 ππ* → nπ*decay. © 2009 Springer-Verlag.

*** IBB - CNR ***

Istituto per i Processi Chimico-Fisici, CNR, Area della Ricerca del CNR Via Moruzzi, 1, Pisa 56124, Italy

Dipartimento di Chimica and INSTM-Village, Università Federico II, via Cintia, Naples 80126, Italy

IBB-CNR, via Mezzocannone 16, Naples 80134, Italy

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