Exploring the possibilities of double proton transfer in hydrazides: A theoretical approach

Abstract

Hydrazides are known to exhibit keto-enol tautomerism upon photoexcitation. Theoretical aspects uncovering excited state intramolecular proton transfer (ESIPT) of N-acylsubstituted hydrazides with bithiophene core have been investigated. Geometrical aspects of the system are expected to undergo double proton translocation at its excited state. However, potential energy surface study for all the molecules reveals an impossible concurrent double proton translocation and to a greater extent dubious step-wise double proton translocation in the system. Potential energy scans reveal molecules possessing a lower forward barrier at its excited state in comparison with their ground state suggestive of possible excited state single proton transfer. Geometrical attributes and spectral analysis suggest the strengthening of intramolecular hydrogen bond (N?H???O) at its excited state, favoring single proton translocation. Theoretical estimation of electronic energy transition for all the conformers yields good correlation with the experimental figures with an energy overestimation <0.17 eV. © 2019 John Wiley & Sons, Ltd.