A computational investigation on the intramolecular hydrogen bonding interaction and excited state intramolecular proton transfer process in 2-quinolin-2-yl-phenol

In the present work, we report computational investigation on the photophysics of 2-quinolin-2-yl-phenol (2Q2P) which can function as the basic unit responsive to excited state intramolecular proton transfer (ESIPT) reaction in the polymer framework composed of polyquinoline derivatives. The operation of ESIPT in 2Q2P has been most critically addressed on the lexicon of potential energy surface (PES) across the reaction coordinate and cross-validated from frontier molecular orbital (MO) analysis. Evolution of other geometrical parameters during the course of the ESIPT process in 2Q2P has been crucial to delve into the mechanistic details of the process. Major emphasis of the work is rendered on the analysis of the intramolecular hydrogen bonding (IMHB) interaction in 2Q2P explored by calculation of electron density ρ(r) and the Laplacian ∇2ρ(r) at the bond critical point (BCP) using Atoms-In-Molecule (AIM) theory. Topological features, energy densities provided by AIM theory are calculated with ρ(r) for a number of intramolecular H-bond distances. The results suggest that at equilibrium geometry the IMHB interaction in the system (2Q2P) develops certain characteristics typical of covalent interaction. Integrated AIM properties have been applied to delve into the phenomenon of resonance-assisted hydrogen bonding (RAHB). The inter-correlation between aromaticity and RAHB is also discussed in this context.