Spectroscopic And Theoretical Study On The Excited State Proton Transfer Of 3-substituted 1,2,4-triazoles And Imidazoles

We select 3-amino-5-mercapto-1,2,4-triazole(AMT),2-mercaptoimidazole(MIZ),and 3-nitro-1H-1,2,4-triazole(NT)to investigate their structures,solvent effect,and excited-state decay channels through UV-Vis absorption,resonance Raman experiments,and density functional theoretical and time-dependent density functional theoretical(TD-DFT)calculations.It illustrates how to control the excited state structural dynamics in the Franck-Condon region by the polarity and hydrogen bonding of solvent and as well as substituted groups.The innovative idea is that the sites of the the structure of clusters are confirmed between nitrogen heterocyclic and the solvent molecules.The triplet states are characterized by transient absorption spectroscopic experiments.The main conclusions are as follow:1.The ground AMT and MIZ thione structures are confirmed in crystal and solvents by FT-Raman and FT-IR combining with DFT calculations.3-NT is 1H isomer in crystal and solvents.The maximum UV-Vis absorption bands of the three molecules are assigned to ???*transition in acetonitrile,methanol,and water combining with TD-DFT calculations.The structures are perturbed significantly by the polarity and hydrogen bond interaction of solvents.2.According to the UV-Vis absorption spectra,we obtain the resonance Raman spectra of AMT in water and methanol at 239,245,252,266 and 273 nm,MIZ in acetonitrile,methanol,and water at 245,252,266 and 273 nm,and NT in acetonitrile,methanol,and water at 217,223,245,252,266,and 273 nm excitation wavelengths.Comparing the spectra of AMT in methanol and water at the same wavelengths,the hydrogen bonding sites between solvents and AMT locate at-N4H11…O and H9N7H8…O.The resonance Raman spectra indicate that high-energy exciting light can weaken the bending vibration and increase the stretching vibration of the triazole ring.In methanol and water,v8(N2C3/N4C3 strech+H11N4C3/H8N7C3 bend)is relatively enhanced,while v10(N1C5 strech+H6N1N2 bend)weaken in water but increase in methanol.The reaction coordinates of AMT in the Franck-Condon region mainly along the:N4C3 stretch.We calculate the structure of the MIZ-solvent cluster,then compare it with resonance Raman spectra,which indicates that MIZ(H2O)cluster can be greatly stabilized via cyclic S…HO and OH…N bonding in H2O.Comparing the resonance Raman spectra of MIZ at different wavelengths,high-energy exciting light can weaken the bending vibration intensity and increase the stretching vibration intensity of the imidazole ring,but in methanol and water,the bending vibration near the S atom side(H7N3C2+H10N1C2)increase,which indicates that MIZ has changed from a planar structure to a non-planar structure.The reaction coordinates of MIZ in the Franck-Condon region mainly along the:N1C2N3 bend.Comparing the resonance Raman spectra of NT at different wavelengths,it is shown that the high-energy exciting light can increase stretching vibration and weaken bending vibration of NT.The reaction coordinates of NT in the Franck-Condon region mainly along the:N2C3/N4C5/N1N2 stretch+H10N1N2 bend.3.TD-DFT calculate the decay channels of AMT/MIZ from Sn states.AMT:(1)S2?S1?S1T2?S1min/T2min?T1.(2)S2?S2min?T2?T1.MIZ:(1)S3?S2?S1?S1T2?S1 min/T2min?T1.