Site-Selective Photoinduced Electron Transfer of Excited-State Intermolecular Hydrogen-Bonded Cluster in Solution.

In this work, the electronic excited states of hypoxanthine in solution such as water and acetonitrile are investigated by the time-dependent density functional theory (TDDFT) method. We demonstrated for the first time that the intermolecular excited-state electron transfer (ESET) from solvents to the hypoxanthine through excited-state intermolecular hydrogen-bonds cluster exhibits obvious site-selectivity. Excited-state electron transfer could only occur at the N7 site of hypoxanthine molecule in water solution, while that is the N9 site in acetonitrile. Potential energy surfaces for different electronic states of hypoxanthine with and without the influence of the excited-state hydrogen bonding cluster are also discussed. Site-selective ESET is proposed to induce the internal conversion of hypoxanthine from S2 state to S1 at a conical intersection, which is responsible for the ultrashort lifetime of hypoxanthine in excited state in solution. These results pave a novel way to understand the photophysical and photochemical behaviors of DNA bases and their derivatives in solution phase. [ABSTRACT FROM AUTHOR]