Study Of The Photoinduced Dynamics Of P-cyanobenzaldehyde And Its Derivatives

The proton transfer, the photoinduced electron transfer reaction and energytransfer of aromatic carbonyl compounds act a very important role in chemistry,biology and materials science and other fields. In recent decades, people havebenzaldehyde and acetophenone as the representative of aromatic carbonylcompounds in photoinduced intersystem crossing, fluorescence, phosphorescence,isomerization, bond breaking and atomic transfer photophysical and photochemicalprocesses carried out a lot research.In this paper, the technology of Resonance Raman spectroscopy combinedwith density functional theory (DFT) calculations to study4-cyanobenzaldehyde,4-cyanoacetophenone,4-dimethylaminobenzaldehyde,4-dimethylaminoacetophenoneand their reaction dynamics in different solvents. we have acquired main conclusions as follows:(1) Resonance Raman spectra at six excitations covering the A-and B-bandabsorptions of4-cyanobenzaldehyde (p-CNB) were acquired. The electronicexcitations and the Franck-Condon region structural dynamics of p-CNB were studiedby using the resonance Raman spectroscopy and density functional theorycalculations. The A-band and B-band absorptions are assigned as Ï€*H-2â†'Ï€LandÏ€*H-1â†'Ï€Ltransitions respectively. The B-band resonance Raman spectra are assignedas13fundamentals, their21overtones and combination bands. The B-band resonanceRaman intensities of p-CNB are dominated by the ν6(C9-N10stretching),ν7(C7-O8stretching),ν8(C2-C3/C5-C6symmetric stretching),ν17(Ring CH in plane bend).Thisindicates that the structural dynamics of p-CNB are mainly along these reactioncoordinates. The conical intersection between S*1(nHÏ€L) and S*2(Ï€H-2Ï€L) state ofp-CNB was acquired.(2) We have obtained the electronic absorption spectrum of4-cyanoacetophenonein different solvents, which included cyclohexane, methanol and acetonitrile. Theabsorption spectrum contained A-band and B-band, under DFT calculations, theA-band and B-band were both assigned as the Ï€â†'Ï€*transitions. Resonance Ramanspectra in different wavelengths was acquired, while we obtain FT-IR, FT-Ramanspectra to assign vibrational modes of4-cyanoacetophenone. Resonance Raman intensities of4-cyanoacetophenone are dominated by the ν7(C9-N11stretching),ν8(C7-O10stretching), ν9(C5-C6/C3-C2symmetric stretching), ν18(C6-H15/C2-H12in plane bending), ν21(C8-H17in plane bending).This indicates that the S(ππ*) statestructural dynamics of4-cyanoacetophenone are mainly along these reactioncoordinates. It shows very similar that comparing with Resonance Raman spectra insame wavelength and in different solvents. That is to say that the Franck-Condonregion structural dynamics of4-cyanoacetophenone is less solvent-dependent nomatter whether the protic or the aprotic solvent is used.(3) We have obtained the electronic absorption spectrum of DMABA and DMAAPin different solvents, which included cyclohexane, methanol and acetonitrile. Theabsorption spectrum contained A-band and B-band, under DFT calculations, theA-band and B-band were both assigned as the Ï€â†'Ï€*transitions. While A-bandResonance Raman spectra of DMABA in cyclohexane solvent was acquired;Resonance Raman intensities of DMABA are dominated by the ν10(C11-O13stretching),ν11(C4H5/C1H2symmetric stretching), ν12(C1C6C5/C2C3C4asymmetricstretching), ν16(C15H16-18/C19H20-22unbrella stretching), ν26(Ring CH in planebend),ν31(Ring breath), ν32(Ring deformation). This indicates that the S(ππ*) statestructural dynamics of DMABA are mainly along these reaction coordinates.DMABAand DMAAP both exhibit dual fluorescence about1ππ*(LE)â†'S10andTICT(CT)â†'S0in polar solvent as acetonitrile.