Excited-state hydrogen detachment and hydrogen transfer driven by repulsive 1πσ* states: A new paradigm for nonradiative decay in aromatic biomolecules

The combined results of ab initio electronic-structure calculations and spectroscopic investigations of jet-cooled molecules and clusters provide strong evidence of a surprisingly simple and general mechanistic picture of the nonradiative decay of biomolecules such as nucleic bases and aromatic amino acids. The key role in this picture is played by excited singlet states of πσ* character, which have repulsive potential-energy functions with respect to the stretching of OH or NH bonds. The 1πσ* potential-energy functions intersect not only the bound potential-energy functions of the 1ππ* excited states, but also that of the electronic ground state. Via predissociation of the 1ππ* states and a conical…