Resolution of concerted versus sequential mechanisms in photo-induced double-proton transfer reaction in 7-azaindole H-bonded dimer

Resolution of concerted versus sequential mechanisms in photo-induced double-proton transfer reaction in 7-azaindole H-bonded dimer

^†Departamento de Química Física Aplicada, Universidad Autónoma de Madrid, Cantoblanco 28049, Madrid, Spain; and ^‡Institute of Molecular Biophysics and Department of Chemistry, Florida State University, Tallahassee, FL 32306-4380

Contributed by Michael Kasha

Abstract

The experimental and theoretical bases for a synchronous or concerted double-proton transfer in centro-symmetric H-bonded electronically excited molecular dimers are presented. The prototype model is the 7-azaindole dimer. New research offers confirmation of a concerted mechanism for excited-state biprotonic transfer. Recent femtosecond photoionization and coulombic explosion techniques have given rise to time-of-flight MS observations suggesting sequential two-step biprotonic transfer for the same dimer. We interpret the overall species observed in the time-of-flight experiments as explicable without conflict with the concerted mechanism of proton transfer.

Footnotes

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ABBREVIATIONS:

7-AI,

7-azaindole;

PT,

proton transfer;

RHF,

restricted Hartree-Fock;

HDF,

hybrid density functional;

TOF,

time of flight