On the theoretical reports on 7-azaindole base-pair phototautomerization

In this Letter, we cite recent and previous reports on the phototautomerization of the 7-azaindole dimer (a widely used model for DNA base-pair tautomerization) in order to shed light on the molecular basis of its photodynamics. In agreement with quantum and dynamic calculations at the S1 state and with the results of femtosecond experiments from three independent groups using an array of ultrafast techniques, we conclude that the double proton transfer in the dimer occurs through a step-wise process. We emphatically contradict the conclusion of Catalلn, del Valle and Kasha who based their findings on ground-state calculations and stationary experiments.