Structural dynamics of 4‐pyrimidone in lower‐lying excited States

Abstract

The structural dynamics of 4-pyrimidone (4PMO) in the A-and B-band absorptions was studied by using the resonance Raman spectroscopy combined with quantum chemical calculations to better understand whether the excited state intramolecular proton-transfer (ESIPT) reaction occurs in Franck-Condon regions or not. The transition barrier for the ground state protontransfer tautomerization reaction between 3(H) (I) and hydroxy (II) was determined to be 165 kJÁmol À1 in vacuum on the basis of the B3LYP/6-311++G(d,2p) level of theory calculations. Two ultraviolet absorption bands of 4PMO were, respectively, assigned as p H !p* L and p H !p* L+1 transitions. The vibrational assignments were done on the basis of the Fourier transform (FT)-Raman and FT-infrared (IR) measurements, the density-functional theory computations and the normal mode analysis. The A-and B-band resonance Raman spectra of 4PMO were measured in water, methanol and acetonitrile. The structural dynamics of 4PMO was obtained through the analysis of the resonance Raman intensity pattern. We discuss the similarities in the structural dynamics of 4PMO and 2-thiopyrimidone (2TPM), and the results were used to correlate to the intramolecular hydrogen-atomtransfer process as observed by matrix-isolation IR experiments for 4PMO. A variety of NH/CH bend modes + C = O stretch mode mark the hydrogen-detachment-attachment or ESIPT reaction initiated in Franck-Condon region for 4PMO and 2TPM.

Solvent-dependent structural dynamics of 2(1H )-pyridinone in light absorbing S4 (ππ*) state

“…Resonance Raman spectroscopy has long been regarded as a powerful tool for exploring the ultrafast structural dynamics of various molecular systems in or near Franck–Condon region . Recently the excited state proton transfer (ESPT) or the excited state hydrogen atom detachment attachment (ESHDA) reaction dynamics has been studied by resonance Raman spectroscopy for 2‐hydroxyacetophenone (OHAP), 2‐hydroxybenzaldehyde, 2‐nitrophenol, 2‐thiopyridone, 4‐pyrimidone, and 2‐mercapto‐1‐methylimidazole . The results reveal that the Franck–Condon region structural dynamics of the ESPT or ESHDA model compounds are mostly along a variety number of the proton‐transfer related CO stretch, ring C―H/N―H bending, skeletal stretch, and bending coordinates, but without evolving substantial O―H stretch motion .…”

“…Recently the excited state proton transfer (ESPT) or the excited state hydrogen atom detachment attachment (ESHDA) reaction dynamics has been studied by resonance Raman spectroscopy for 2‐hydroxyacetophenone (OHAP), 2‐hydroxybenzaldehyde, 2‐nitrophenol, 2‐thiopyridone, 4‐pyrimidone, and 2‐mercapto‐1‐methylimidazole . The results reveal that the Franck–Condon region structural dynamics of the ESPT or ESHDA model compounds are mostly along a variety number of the proton‐transfer related CO stretch, ring C―H/N―H bending, skeletal stretch, and bending coordinates, but without evolving substantial O―H stretch motion . This is in a sharp contrast to the structural dynamics of photofragmentations, and/or non‐adiabatic internal conversions, which are in general dominated by the bond stretching coordinates.…”

Recent advances in linear and nonlinear Raman spectroscopy. Part VIII

“…He and coworkers studied the structural dynamics of 4‐pyrimidone (4PMO) in the A‐band and B‐band absorptions by using the resonance Raman spectroscopy combined with quantum chemistry calculations to better understand whether the excited state intramolecular proton‐transfer reaction occurs in Franck‐Condon regions or not . Jian et al .…”