Time-dependent blue shift of the fluorescence origin band of benzo[a]pyrene (BP)-derived BP-6-N7Ade adducts in glasses

We report unusual spectroscopic properties of the benzo[a]pyrene (BP)-deriv ed one-electron oxidation DNA adduct, BP-6-N7Ade, in glasses at low tempera tures. Time-resolved fluorescence emission and fluorescence excitation spec tra showed that the position of the origin bands shift to higher energies w ith longer delay lime of the observation window. A non-linear and time-depe ndent Stokes shift has been revealed. This effect has not been observed for any BP-derived diol-epoxide adduct. Such a blue-shift, in opposite directi on to the shift expected from solvation dynamics, has not been previously r eported. The experimental data are interpreted in terms of a distribution o f conformers and a matrix-induced frequency dependent dipole moment change across the inhomogeneously broadened absorption band.