Transient IR spectroscopy and ab initio calculations on ESIPT in 3-hydroxyflavone solvated in acetonitrile

Abstract

Femtosecond polarization resolved UV/Vis and mid-infrared spectroscopy was used to thoroughly identify and characterize the relevant elementary chemical and physical processes in the photocycle of 3-hydroxyflavone (3-HF) in solution. In one set of experiments with the polar aprotic solvent acetonitrile-d(3), for the first time excited state intramolecular proton transfer (ESIPT), vibrational cooling/relaxation and rotational diffusion could be separated, and furthermore mid IR vibrational spectra of 3-HF excited states in solution phase were obtained. UV/Vis transient absorption data yield the time constant τ(Rot) = 22 ps for rotational diffusion and the time constant τ(VR) = 8.5 ps for vibrational cooling/relaxation in the tautomer excited state (S(1)'). Biphasic ESIPT with τ < 120 fs and τ = 2.4 ps as well as slow ground state recovery with τ > 500 ps was found. The time resolved mid IR data yield a time constant of ≈3.4 ps for the slow ESIPT step as well as the vibrational frequencies of S(0,) S(1)' and, in particular those of the short lived excited state S(1). Via quantum chemical calculations, structural parameters of these states are obtained. Various models were used, namely for the isolated molecule, aggregates with solvent as well as a polarizable continuum, that allow us to correlate the two ESIPT components with two mechanisms. Results are compared to those from previously published gas-phase experiments and indicate that the observed slow ESIPT is mediated by solute-solvent interaction via a hydrogen bond with the hydroxyl group of 3-HF.

Supramolecular Inclusion‐Assisted Disruption of Probe‐Solvent Network

“…Flavonols, a class of ESIPT responsive flavonoids, are present in wide varieties of fruits and vegetables and have immense therapeutic importance ,. 3‐Hydroxyflavone (3HF), an ESIPT prone probe and the backbone of the flavonols, has been studied extensively in homogeneous as well as in microheterogeneous environments both experimentally and theoretically . Only recently we have proposed, for the first time, that 3HF is not solvated in protic solvents in a symmetrical pattern.…”

Ultrafast proton release reaction and primary photochemistry of phycocyanobilin in solution observed with fs-time-resolved mid-IR and UV/Vis spectroscopy

“…However, the identification of the proposed processes in the visible and near-IR spectral region is difficult due to their complex influence on the TA properties and the overlapping absorption spectra of the ground state species. Thus, for a more detailed characterization of the primary photoinduced processes of PCB, in this work we performed fs-TA measurements in the mid-IR spectral region, which monitors structural changes and is sensitive to protonation processes and intermolecular interactions [33][34][35][36][37][38]. The measurements are complemented by DFT calculations for the basic ground state structures (Fig.…”

A combined IR/IR and IR/UV spectroscopy study on the proton transfer coordinate of isolated 3-hydroxychromone in the electronic ground and excited state

“…Thus a substituent on the chromone unit as the phenyl group in 3-HF might even promote a faster ESPT since it hinders specific solute-solvent interactions enabling the pathway via the stabilised trans structure. 50,51 Further theoretical investigations on the structure and reactivity of 3-HC are presented in ref. 32 and 52-54. In order to achieve more information on the structure and reactivity of isolated 3-HC and defined aggregates with water we present in this paper the first molecular beam investigations of 3-HC including mass selected IR spectroscopy for the electronic ground state (IR/R2PI method) and the electronically excited state (UV/IR/UV method).…”