Density functional theory description of excited-state intramolecular proton transfer

Enol to keto conversion in the lowest excited states of three different systems with similar OCCNN backbone structures is examined within density functional theory. Excited state proton transfer occurs both within the local spin density approximation and with gradient corrections. The latter approach provides an improved description of intramolecular hydrogen bonding and yield results in reasonable agreement with previous ab initio calculations for small model systems and with experiments for practical benzotriazole photostabilizers.