Dipolar switch of the proton phototransfer in the doubly hydrogen-bonded 7-azaindole dimer with C2h symmetry

Abstract

The potential loss of the C_2h symmetry in 7-azaindole dimer caused by the interaction with a polar molecule or environment was examined in a 10⁻⁴ M solution of this compound in 2-methylbutane containing 4 × 10⁻⁵ M 1-chlorobutane and in pure 1-chlorobutane at a low temperature, respectively, in the light of the proton phototransfer processes potentially undergone by the dimers. A scheme for the proton phototransfer in the dimer is proposed based on which the transfer involves two protons if the dimer possesses C_2h symmetry and a single one if such a symmetry is lost through complexing with a polar molecule or under the action of a polar environment. Based on the results, the proton transfers in 7-azaindole dimer take place via different mechanisms and the single-proton process is not an intermediate step in the formation of the tautomer dimer that results from the two-proton process.