Excited-state relaxation paths of oxo/hydroxy and N9H/N7H tautomers of guanine: a CC2 theoretical study
We performed a theoretical investigation, at the CC2/aug-cc-pVDZ level, of the ring-deformation mechanisms of four guanine tautomers (oxo, hydroxy, N9H, and N7H). The study showed that the optimized conical intersections S-0/S-1 are accessible through the (1)pi pi* excited states of tautomers. The optimized conical intersections S-0/S-1, which show deformation at the pyrimidine ring, have high energies. This means that the relaxations of the (1)pi pi* excited states via internal conversion are disfavored. For two tautomers we found crossing points (1)pi pi*/(1)pi sigma* of the excited-state reaction paths, revealing the possibility of a population of the (1)pi sigma* excited state by the (1)pi pi* excited state.
guanine conical intersection excited state cc2 calculation excitation energy