A Study Of The Excited State Structural Dynamics Of Thioamides And Aromatic Diketones

Intramolecular hydrogen bonds, proton transfer reactions of thiocarbonyls andphoto-induced isomerization of aromatic diketones play an important role in thephotochemisty field. In this dissertation, we studied the excited state structural dyna-mics of dithiooxamide(DTO), amidinothiourea(ATR),1-phenyl-1,2-propanedione(PPD) and benzil (BZ) in various kinds of solutions (cyclohexane, methanol,acetonitrile and water) in the Franck-Condon region by the resonance Ramanspectroscopy. Combining with the DFT calculations, these compounds’ photochemicaland photophysical phenomena have have been investigated in detail. Mainconclusions are summarized as follows:(1) The absorption spectrum of DTO was obtained in methanol and acetonitrilesolvents. Combining with the TD-DFT theory calculated results, we assigned theA-band electronic absorptions as the�'*transitions. In the solvents, the maximumabsorption wavelength λmaxwas observed at~309nm by UV absorption experiments.Resonance Raman spectra of DTO were obtained covering five excitationwavelengths:282.4,299.1,309.1,319.9,341.5nm in the A-band absorption.According to the FT-Raman and FT-IR experiments, combining with DFTcalculations, we assigned the vibration spectra of DTO. The excited state structuraldynamics of DTO in the Franck-Condon region mainly occur along the C-C stretchingand-NH2rocking vibrational modes.(2) We have obtained the absorption spectrum of ATR in methanol, acetonitrileand water solutions. Combining with the TD-DFT calculations, we assigned theA-band electronic absorptions as the�'*transition. According to the FT-Ramanand FT-IR experiment, combined with DFT calculations, we have described andassigned the vibration spectra of ATR. The UV spectra in methanol and acetonitrileshowed obvious red shift compared with that in water. We obtained resonance Ramanspectra of ATR covering four excitation wavelengths in A-band absorption:252.7,266,273.9,282.4nm. The excited state structural dynamics of ATR in Franck-Condonregion mainly occur along the C=S stretching and C-N-C symmetry stretchingvibrational modes.(3) We have obtained the absorption spectrum of PPD in cyclohexane, methanol and acetonitrile solvents. Combining with the TD-DFT theory calculation results, weassigned the A-band electronic absorptions as the�'*transitions. Fromcyclohexane to methanol via acetonitrile solvents, the UV spectra showed a certainblue shift, which indicated the solvent may affect the electron transition of PPD. Weobtained the resonance Raman spectra of PPD covered five excitations in the A-bandelectronic absorption:239.5,245.9,252.7,266,273.9nm. According to the FT-Ramanand FT-IR experiment, combined with DFT calculations, we have described andassigned the vibration spectra of PPD. The�'*structural dynamics of PPD mainlyoccur along the C=O stretch, C-C stretch and ring C-H in plane bend vibrationalmodes.(4) The absorption spectrum of BZ in solvents of cyclohexane、methanol andacetonitrile are obtained. Combining with the TD-DFT computations, we assigned theA-band electronic absorptions as the�'*transitions. In these three solvents, theUV spectra were similar, and the maximum absorption wavelength λmaxwas all around252.7nm. We obtained the resonance Raman spectra of BZ covered four excitationsin the A-band electronic absorption:245.9,252.7,266,273.9nm. According to theFT-Raman and FT-IR experiment, combined with DFT calculations, we havedescribed and assigned the vibration spectra of BZ. The�'*structural dynamics ofBZ mainly occur along the C=O stretch and ring C-C symmetry stretch vibrationalmodes.