Theoretical investigations of spectroscopy and excited state dynamics of adenine

A set of harmonic potential surfaces have been obtained at the CASSCF/6-311+G∗∗ level for the ground, n–π∗, and π–π∗ states of 9H-adenine. They have been used to analyze experimental R2PI and resonance fluorescence spectra and the excited state lifetimes of adenine. A tentative plausible assignment has been proposed, which takes into account a strong coupling between these electronic states. Using the potential surfaces, the excess energy dependence of the excited state lifetimes of adenine has been interpreted, and the lifetime of the n–π∗ state at the band origin has also been estimated to be in the order of 10 ns.