Electronic structure of isoalloxazines in their ground and excited states

Electronic structures and transitions were calculated for a series of methyl derivatives of 10-methyl alloxazine using the time-dependent density-functional theory. Comparison of quantum chemical results to experimentally determined spectral and photophysical properties of these compounds indicates that these properties may be rationalised on the basis of the proximity effect, whereby two closely located n; p* and p; p* lowest excited states are vibronically coupled by out-of-plane modes. This theory allows explaining the substituent, temperature, and solvent dependence of the non-radiative decay rates, which affect the fluorescence lifetimes and quantum yields. q 2004 Elsevier B.V. All rights reserved