Excited State Structural Dynamics Of Imidazole And Its Derivatives

The Photoinduction of Excited State Proton Transfer Reaction andCharge-Redistribution of Imidazole and its Imidazole derivatives, which has agreat role in biomacromolecule and luminescent materials. It is the reason that peoplehas done lots of research on photochemistry and photophysics. Of which thesecompound has been studied the dynamics information of biomacromolecule.The resonance Raman spectroscopy and quantum mechanical calculations wereused to study the short-time structural dynamics of imidazoles,4-formaldehydeImidazole(4FI),4-nitroimidazole(4NI) and2-nitroimidazole(2NI) respectively. Themain results were as follows:The vibrational spectra, UV absorption spectra and Resonance Raman spectrumof imidazole and its Imidazole derivatives were assigned. The results show that theA-band resonance Raman intensities of imidazole can be assigned to sixFranck-Condon active modes. The results also show that the A-band structuraldynamics of imidazole is predominantly along the N1H/C4H/C5H/C2H in-planebending reaction coordinate, which suggest that excited state proton or hydrogentransfer reaction takes place somewhere nearby the Franck-Condon region.By means of calculation method the vibrational spectra of dimer was assigned andthe dimers structure was aslo obtained. The results also show that the A-bandresonance Raman intensities of4-formaldehyde Imidazole can be assigned to twelveFranck-Condon active modes. In addition to the main vibration modes of imidazole,most importantly could be mainly reflected by the O6=O7sretch mode5and C4C5sretch mode6. It is predicted that the excited state structural dynamics of4FI ispredominantly along this modes reaction coordinate. CASSCF calculations werecarried out to determine the minimal singlet excitation energies and structures ofS1(nO*), S2(*), and conical intersection point S1(nO*)/S2(*). By means ofCASSCF calculations reveal that the deactivation channel via S2(*)/S1(nO*) for4FI is less efficiency and thus not considered as the major channel. In contrast to theexcited state structural dynamics of4FI is major via O=C6-C4=C5O—C6=C4—C5 mechanism.The results show that the A-band resonance Raman intensities of4-nitroimidazoleand2-nitroimidazole in methanol can be assigned to eleven Franck-Condon activemodes and six Franck-Condon active modes respectively. The ONO sretch mode8and the ONO scissor mode16is mainly reflected. The results show that the excitedstate structural dynamics of nitroimidazoles is predominantly along this modesreaction coordinate. CASSCF calculations were carried out to determine the minimalsinglet excitation energies and structures of S1(nO*), S2(*), and conicalintersection point S1(nO*)/S2(*)of4NI and2NI. The fluorescence spectrumtogether with those CASSCF calculations can reveal that the major decay channelinitiated from the S2(*) state is S2, FCâ†'S2, min()â†'S0radiation of4NI. While thesignificant difference between4NI and2NI in the short-time structural dynamics caninfer two dynamic channels, one channel could be via S1min()â†'S1/S0â†'S0and theother channel could be intersystem cross(ISC) with S1min(1)â†'S1/T1â†'T1(3...