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 S-1 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 Catalan, del Valle and Kasha who based their findings on ground-state calculations and stationary experiments. (C) 2000 Elsevier :Science B.V. All rights reserved.