Studies On Synthesis,proton Transfer And Spectra For 2-substituted Benzazole Compounds

Proton transfer and the tautomerization caused by proton transfer are among the most fundamentally important chemical or biological process, it is widely present in chemical reactions and play an important role in the the life events and biological evolution. So it is no questions that study on proton transfer have important implications. In this dissertation, the proton transfer reactions of a series of 2–substituted benzimidazole compound have been studied by the spectroscopic techniques and theoretical study. The principal results obtained are listed as follows:(1) 2-(3-Hydroxy-2-pyridyl)benzimidazole was synthesized and characterized well by NMR (¹H, ¹³C, COSY, HSQC, and HMBC), MS, IR, and UV techniques, together with X-ray single crystal diffraction throughly. The diffraction experiment confirmed the results of spectroscopic analysis and showed that the crystal belongs to triclinic, space group P21/c with unit cell parameters a=14.289(3) (A|°), b=10.618(2) (A|°), c=12.783(3) (A|°),β=93.51(3)o, V=1935.8(7) (A|°)³, and Z=8. The fluorescence spectrum indicates that there has been a double proton transfer in excited state. The results of density functional calculations provide a reasonable explanation on the experimental phenomena.(2) The excited-state intramolecular proton transfer (ESIPT) reaction of 2-(2-amino-3- pyridyl)-benzimidazole was studied at the TD B3LYP/6-31++G(d,p)//CIS/6-31G(d,p) level. The molecular geometries of 2-(2-amino-3-pyridyl)-benzimidazole were optimized and the viberationanalysis were carried out at the B3LYP/6-31G(d,p) level considering the model isolated. The emission spectra of the isomers of 2-(2-amino-3-pyridyl)-benzimidazole were calculated by means of the density functional theory. These results show that the dual fluorescence of 2-(2-amino-3-pyridyl)-benzimidazole is produced by its different tautomers, but not by the same isomer: the long wave length (500⁶00 nm) emission is from K tautomer, and the short wavelength band (350⁴50 nm) is produced by E1 and E2. The results of density functional calculations provide a reasonable explanation on the experimental phenomena.(3) 2-(3-Amino-2-pyridyl)-benzimidazole was synthesized and characterized well by NMR(¹H, ¹³C, COSY, HSQC, and HMBC), MS, IR, UV, together with X-ray singlecrystal diffraction throughly. The diffraction experiment confirmed the results of spectroscopic analysis and showed that the crystal belongs to triclinic, space group C12/c1 with unit cell parameter a=16.890(3) (A|°), b=7.9880(16) (A|°), c=14.747(3) (A|°),β=91.33(3)o, V=1991.6(7) (A|°)³, Z=8. The fluorescence spectrum indicated that there has been double proton transfer and single proton transfer in excitated statent. The fluorescence spectrum show that the polarity solvent is important to excited states intramolecular proton transfer.