Study Of The Photoinduced Dynamics Of Pyrazine Derivatives

Pyrazine derivatives are synthetic food spices, agricultural chemicals, pharmaceuticals,antistatic agents, textile finishing liquid other important raw materials and intermediates. In thecoffee and meat and other food flavoring component contains alkyl pyrazines can be widelyused in beverages and canned meat flavoring. Jellyfish body extracted from the fluorescentmaterial natural coelenterazine have an important role in bioassays. Pyrazine ring systemcontaining two nitrogen atoms, nitrogen-rich ring compound as an ideal structural unit.In this paper, the excited state reaction dynamics of2-methylpyrazine (2-MP),2-cyanopyrazine (2-CP),2-pyrazinecarboxylic acid (2-ACP) and5-methylpyrazine-2-carboxylicacid (2-MACP) in different solvents have been studied by the Resonance Raman spectra, andalso discussed the optical transformation mechanism of the photochemical reaction in microdynamics, combined with the density functional theory (DFT). Main contribution and results ofthe present work are summarized as follows.(1) We had obtained the electronic absorption spectra, the FT-IR, and the FT-Raman spectraof2-MP and assign vibrational modes through combining with DFT calculation and the A-bandof its absorption spectra were assigned to π π*. The Resonance Raman spectra were acquiredfor2-MP in water, methanol, acetonitrile and cyclohexane solvent under seven differentexcitation wavelengths. Assignment of Resonance Raman spectra in cyclohexane solvent with266.0nm excitation wavelength indicate that the Franck-Condon region of A-band excited statereaction dynamics of2-MP have multidimensional characters with motions predominantly alongC3H8/C6H10in-plane bend+C2C7stretch mode υ-113at1249cm, C3H8/C5H9/C6H10in-planebend mode υ16at1055cm-1, C3H8/C7H12in-plane bend+CH3rock mode υ-117at1018cm,C2C7stretch+C6in-plane bend mode υ19at827cm-1, pyrazine ring breathing mode υ20at638cm-1. In the B-band, the structure of reaction dynamics of2-MP have motions predominantlyalong C2C3/C5C6symmetric stretch mode υ6, C3H8/C5H9/C6H10in-plane bend mode υ16reaction coordinate. B-band and A-band main contribution of different vibrational modes thatA-band and B-band structure of the excited state reaction dynamics differ. (2) We had obtained the electronic absorption spectra, the FT-IR, and the FT-Ramanspectra of2-CP and assign vibrational modes through combining with DFT calculation and theA-band of its absorption spectra were assigned to π π*. The Resonance Raman spectra wereacquired for2-CP in water, methanol, acetonitrile and cyclohexane solvent under eight differentexcitation wavelengths. Assignment of Resonance Raman spectra in cyclohexane solvent with266.0nm excitation wavelength indicate that the Franck-Condon region of A-band excited statereaction dynamics of2-CP have multidimensional characters with motions predominantly alongC3H9/C5H10/C6H11in-plane bend mode υ7at1442cm-1, C2C7stretch+C3H9in-plane bendmode υ10at1222cm-1, C3H9/C5H10/C6H11in-plane bend mode υ13at1046cm-1, pyrazinering breathing mode υ14at1012cm-, pyrazine ring breathing mode υ15at804cm-1, N1/N4in-plane bend mode υ16at628cm-1. In the B-band, the structure of reaction dynamics of2-CPhave motions predominantly along C2C3/C5C6symmetric stretch mode υ5, pyrazine ringbreathing mode υ14reaction coordinate.(3) We had obtained the electronic absorption spectra and seven different wavelengthResonance Raman spectra in methanol, acetonitrile and water these three different polarsolvents of2-ACP. Optimized geometry and vibration frequency as well as the electronictransition energies for the ground state were calculated by the time dependent destiny functionaltheory of the Compound. The structure dynamics of2-ACP main along υ13(C3H10/O9H13in-plane bending), υ16(C5H11/C6H12in-plane bending), υ17(pyrazine ring breathing),υ18(pyrazine ring breathing), υ20(N1/N4in-plane bending) reaction coordinate. In methanolsolvent, υ8only appears in the A-band excitation wavelength, which shows A-band structuredynamics and B-band structure dynamics are different.(4) We had obtained the electronic absorption spectra and seven different wavelengthResonance Raman spectra in methanol, acetonitrile and water these three different polarsolvents of2-MACP. Optimized geometry and vibration frequency as well as the electronictransition energies for the ground state were calculated by the time dependent destiny functionaltheory of the Compound. The structure dynamics of2-MACP main along υ15(N1C6C5symmetric stretching+O9H13in-plane bending+H15C10H16scissoring), υ17(C3H11/C6H12in-plane bending+C5C10stretch), υ19(C3H11/O9H13in-plane bending), υ20(C3H11in-planebending+C7O9stretch), υ26(pyrazine ring breathing), υ30(N1/N4in-plane bending) reaction coordinate. We compared the Resonance Raman spectra of2-MACP in methanol solvent under217.8,228.7,252.7,266.0and282.4nm excitation wavelengths, in the B-band,30,26,20,19,17,15mode are strong, while in the A-band only26,8mode are strong. From the strengthand the number of active mode, we can conclude that the A-band structure dynamics and theB-band structure dynamics are significantly different.