Excited‐State Multiple Proton Transfer Depending on the Acidity and Basicity of Mediating Alcohols in 7‐Azaindole–( ROH )2 (R=H, CH 3) Complexes: A Theoretical Study

Long-range proton transfer plays an important role in many chemical and biological phenomena. It has recently been reported that the rate of excited-state multiple proton transfer depends on the acidity and basicity of mediating alcohols in the H-bonded wire. The excited-state triple proton transfer in 7-azaindole complexes through cyclic H-bonded wires was theoretically studied to investigate rates depending on the mediating alcohols. This study showed that the acidity and basicity of alcohols collectively functioned to assist proton transfers depending on the paths; the proton transfers of protolytic and solvolytic paths were assisted by the pull-behind effect and the push-ahead effect, respectively. Both proton-donating and accepting abilities of alcohols in the H-bonded wire can accumulate to help proton transfer, and the strong acidity and basicity of the alcohols with relatively small structural changes in the wire have larger impacts on reducing the activation energies than those of alcohols that trigger proton transfer.