Exploring hydrogen bond in the excited state leading toward intramolecular proton transfer: detailed analysis of the structure and charge density topology along the reaction path using QTAIM

Abstract

Excited state intramolecular proton transfer (ESIPT) reaction along the O-H[Symbol: see text][Symbol: see text][Symbol: see text][Symbol: see text]O hydrogen bond of o-hydroxy benzaldehyde (OHBA), methyl salicylate (MS) and salicylic acid (SA) was investigated by ab-initio quantum chemical calculation and theory of atoms and molecules (QTAIM) for the first time. Variation in several geometric as well as QTAIM parameters along the reaction coordinate was monitored in the fully relaxed excited state potential energy curve (PEC) obtained from intrinsic reaction coordinate (IRC) analysis. Although, the excited state barrier height for the forward reaction (∆E (0) (#) ) reduces substantially in all the systems, MS and SA do not show any obvious asymmetry for proton transfer. For MS and SA, the crossover of the bond index as well as the lengths of the participating bonds at the saddle point is assigned due to this symmetry in accordance with bond energy - bond order (BEBO) model, which does not hold true in OHBA both in the ground and excited states. Bond ellipticity, covalent and metallic character were examined for different structures along the reaction path within the QTAIM framework. The QTAIM analysis was found to be able to uniquely distinguish between the ground and excited states of the OHBA molecule as well as both determining the effects on the bonding character of adding different substituent groups and differentiating between the ESIPT reactions in the SA and MS molecules.

A QTAIM and stress tensor investigation of the torsion path of a light-driven fluorene molecular rotary motor

“…Fulfillment of this task is impossible without comprehensive understanding of the factors underlying the mechanism of action of these devices. In this regard, the methods of analyzing the total electronic density distributions ρ ( r ), such as the quantum theory of atoms in molecules QTAIM and stress tensor analysis methods, can provide complimentary information to the well established approaches analyzing the shape of the potential energy surfaces (PESs) of the ground and excited electronic states of the target compounds . Recently, some of us have developed QTAIM/stress tensor theory for use on the photoisomerization of the retinal chromophore and explored the implications of preferred direction of torsion − φ or + φ of the chromophore upon the photoexcitation …”

Structure, electronic, inclusion complex formation behavior and spectral properties of pillarplex

“…The ellipticity provides a measure of π and σ bond character. The larger values (>0.1) indicate a π character and lower values shows the existence of σ bond character [38]. Our AIM calculations show the existence of C-H⋯Metal and C-H⋯C intramolecular BCPs between the DAO and host molecule.…”

Synthesis, Spectral Studies and Quantum-Chemical Investigations on the Powerful Fluorophores: Imidazo[4,5-a]acridines

“…The RCP (ring critical point) is a point of minimum electron density within the ring surface and a maximum on the ring line [26,27]. Table 5 gives the information about electron density ρ RCP at the RCP and ∇ 2 ρ RCP of the chelate ring, produced by the intra-intermolecular interaction formation.…”