A theoretical analysis of the intrinsic light-harvesting properties of xanthopterin

Belonging to the family of pterins, which are common chromophores in several bio-organisms, xanthopterin has been shown experimentally (Plotkin et al., 2010) to have the ability of acting as a light-harvesting molecule. In the present study, multiconfigurational second-order perturbation theory is used to determine the stability of distinct amino/imino and lactam/lactim tautomers and the absorption and emission spectroscopic characteristics, electron donor and acceptor properties and the electron and charge transfer efficiencies via π-stacking. The lactam–lactam form 3H5H (and in a lesser extent 1H5H) is predicted to have the most appropriate intrinsic characteristics for the light-harvesting properties of xanthopterin, since it is the most stable isomer predicted for the gas phase and estimated for polar environments, absorbs solar light at longer wave lengths, has relatively low donor properties and the presence of the keto groups, instead of enol, increases the efficiency for energy transfer through excimer-like interactions.