Search

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 proton-transfer tautomerization reaction between 3(H) (I) and hydroxy (II) was determined to be 165 kJ·mol−1 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 πH→π*L and πH→π*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-atom-transfer 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. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Resonance Raman spectra were obtained for 2-nitrophenol in cyclohexane solution with excitation wavelengths in resonance with the charge-transfer (CT) proton transfer band absorption. These spectra indicate that the Franck-Condon region photodissociation dynamics have multidimensional character with motion along more than 15 normal modes: the nominal CCH bend+CC stretch ν12 (1326 cm-1), the nominal CCC bend ν23 (564 cm-1), the nominal CO stretch+NO stretch+CC stretch ν14 (1250 cm-1), the nominal CCH bend+CC stretch+COH bend ν15 (1190 cm-1); the nominal CCH bend+CC stretch ν17 (1134 cm-1), the nominal CCC bend+CC stretch ν22 (669 cm-1), the nominal CCN bend ν27 (290 cm-1), the nominal NO2 bend+CC stretch ν21 (820 cm-1), the nominal CCO bend+CNO bend ν25 (428 cm-1), the nominal CC stretch ν7 (1590 cm-1), the nominal NO stretch ν8 (1538 cm-1), the nominal CCC bend+NO2 bend ν20 (870 cm-1), the nominal CC stretch ν6 (1617 cm-1), the nominal COH bend+CC stretch ν11 (1382 cm-1), nominal CCH bend+CC stretch ν9 (1472 cm-1). A preliminary resonance Raman intensity analysis was done and the results for 2-nitrophenol were compared to previously reported results for nitrobenzene, p-nitroaniline, and 2-hydroxyacetophenone. The authors briefly discuss the differences and similarities in the CT-band absorption excitation of 2-nitrophenol relative to those of nitrobenzene, p-nitroaniline, and 2-hydroxyacetophenone. [ABSTRACT FROM AUTHOR]

The resonance Raman spectra were obtained for both 2-thiopyridone (2TP) and its proton-transfer tautomer 2-mercaptopyridine (2MP) in water solution. Density functional theory (DFT) calculations were carried out to help elucidate their ultraviolet electronic transitions and vibrational assignments of the resonance Raman spectra associated with their B-band absorptions. The nanosecond time-resolved resonance Raman spectroscopic experiment was carried out to further confirm the assignment that the transient species was the ground state 2MP. The different short-time structural dynamics were examined for both 2TP and 2MP in terms of their resonance Raman intensity patterns. The transition barriers between 2TP and 2MP for S0, T1, and S1states are determined by using (U)B3LYP-TD and CASSCF level of theory computations, respectively. The excited state proton transfer (ESPT) reaction mechanism is proposed and briefly discussed. [ABSTRACT FROM AUTHOR]