Tuning of energetics and reaction mechanism of water-assisted intramolecular proton transfer of 7-azaindole by external electric field applied in various directions: a TD-DFT study

Abstract

Ground- and excited-state intramolecular proton transfer reactions, as one of the most important processes in biological systems, have been utilized as the basis of artificially designed molecular photoswitch. Taking 7-azaindole as model of study, we report the electric field tuning of water-assisted proton transfer reactions in both the ground and excited states, by applying static electric fields along various directions. The electric fields applied in the direction (or those with component in the direction) of net proton transfer path have remarkable impact on the energetics of reaction, including tuning of thermodynamic and kinetic balance of tautomers, as well as red-/blueshifting the absorption and emission maxima. The electric fields applied in a direction perpendicular to the net proton transfer, although which have been found to play negligible roles in changing the energetics, tune the concerted double-proton transfer reactions from roughly synchronic to asynchronic. The electrostatic origins of such influences are analyzed. The findings of our (TD)-DFT calculations provide insights into fine tuning of both energetic and mechanistic aspects of reversible systems by electric field, and shed light on the nature of proton transfer in natural systems as well as designing novel electric optical switches.