Electronic structure methods are used to estimate differences in reaction barriers for transfer of an electron from singlet pi pi* excited 8-aminoguanine (A) or deprotonated 8-aminoguanine anion (A(-)) to a proximal thymine dimer site compared to barriers when pi pi* excited 8-oxoguanine (O) or deprotonated 8-oxoguanine (O-) serve as the electron donor. It is predicted that the barrier for photoexcited A should be lower than for photoexcited O, and the barrier for photoexcited A- should be lower than for photoexcited O-. Moreover, A, O-, and A(-) are predicted to have pi pi* excited states at energies near where O does, which allows them to be excited by photons low enough in energy to avoid exciting or ionizing any of DNA's bases. The origin of the differences in barriers is suggested to be the lower ionization potential of A compared to O and the lower electron detachment energy of A(-) compared to O-. Because O and O- have been experimentally shown to produce thymine dimer repair, it is proposed that A and A- are promising repair agents deserving experimental study.