The photophysical properties of the adenine chromophore

The efficient nonradiative deactivation process of the excited adenine chromophore is studied in this paper. By comparing the photophysical properties and temperature dependence of several alkylated adenine derivatives, a mechanism for the thermally activated internal conversion process is suggested, Several alkylamino derivatives of adenine show dual fluorescence, and the solvent dependence of the excited states is investigated. It is concluded that the long wavelength emission originates from a CT state involving the alkylamino group and purine chromophore as donor and acceptor, respectively. The experimental observations are supported by quantum mechanical calculations, and the results are summarized into a model for the photophysical properties of the adenine chromophore. In this model, the two excited states associated with the dual emission from the alkylamino derivatives are populated from a common Franck-Condon state followed by independent decay to the ground state.