Predictions of the electronic absorption and emission spectra of luciferin and oxyluciferins including solvation effects.

The ground and excited state properties of luciferin (LH(2)) and oxyluciferin (OxyLH(2)), the bioluminescent chemical in the firefly, have been characterized using the configuration interaction singles (CIS) and time dependent density functional (TDDFT) methods. The effects of solvation on the electronic absorption and emission spectra of luciferin and oxyluciferin are predicted with a self-consistent isodensity polarized continuum model of the solvent using both the configuration interaction singles model and time dependent density functional theory. The S(0)-->S(1) vertical excitation energies in the gas phase and in water are obtained with both methods. Optimizations of the excited state geometries permit the first predictions of the fluorescence spectra for these biologically important molecules. Shifts in both the absorption and emission spectra on proceeding from the gas phase to aqueous solution also are predicted.