The Experimental And Theoretical Studies Of Raman Spectra Of Benzothiazolinethione Compounds And P-Aminothiolphenol On Gold

The thiol(thione) molecules,especially aromatic compounds,have been widely used both in fundmental and in practical studies,such as the electrode surface modification and functionalization,nanoparticals synthesis,the probe for the SERS mechanism studies, corrosion inhibitor and the minerals flotation,etc.In this dissertation,the binding capacities with metals,the properties of clusters and solvent effect of the aromatic thiol(thione) compounds for both practical and theoretical consideration are investigated by combining Raman spectroscopy and density function theory(DFT).The main results and conclusions of the dissertation are listed as follows:â… .Raman spectra and theory study of benzothiazolinethione CompoundsThe stable forms of benzothiazoline-2-thione(BTT) and its derivatives(FBTT,DBTT, CMBTT,NTT) were confirmed in different states by Raman spectroscopy and DFT calculation results.The three possible reaction pathways in the proton transfer processes between the thione and the thiol tautomer were investigated.We also compared the binding capacity of the stable thione forms with gold surface.The adsorption behavior of DBTT on gold surface was deduced by SERS together with potential energy distribution (PED) analysis.1.It revealed that the four derivatives exhibited stable conformation of benzothiazoline-2-thione(BTT) form not only in gas,solid and solution but also on gold surfaces.Namely,the tautomeric preference of the BTT molecule was not influenced by the inclusion of substitute groups in benzene ring.The substitute groups have changed some geometric parameters and the charge distribution on atoms in benzothiazoline cycle.2.The three possible reaction pathways were investigated:(a) intramolecular proton transfer;(b) water-assisted intermolecular transfer and(c) methanol-assisted intermolecular transfer.The process(a) has higher activation energies because of the formation of four-membered ring transition complex,while the processes(b) and(c) have relatively lower activation due to six-membered ring hydrogen-bonded complex. It is likely that the hydrogen bonds formed in the clusters play an important role in the proton transfer processes in the later two reaction pathways.The solvent effects on the tautomerization reactions of BTT and its derivatives observed by the Onsager model did not significantly change the barrier height.The energies of DBTT have the major difference from others of the all effect factors.3.The reactive behaviors of BTT and its derivatives were discussed theoretically based on the chemical parameters such as the energies of HOMO,NBO charges and the binding energies with gold.The binding capability of the molecules with gold is in the sequence of DBTT≈NTT＞BTT≈CMBTT＞FBTT.The derivatives with the electron-donor substitutes in benzene ring were favorable to bind the metal for the p-Ï€conjugate effect.4.Based on the results of PEDs and SERS,we deduce the DBTT molecule is chemisorbed to the gold through both N and the exocyclic S atoms in its thione form and its molecular plane is perpendicular to the surface which is similarly as the adsorption configuration of BTT.â…¡.Spectroscopic electrochemistry and theory study of PATP on goldThe electrochemical behaviors of PATP on gold were investigated by electrochemical technique,SERS and quantum chemistry calculation.The pH-dependent configurations of PATP on gold and silver nanoparticals were also evaluated by SERS and DFT theory.Results are listed as follows.1.The self assembly monolayer(SAM) can inhibit the under potential deposition process of copper at a certain extent.The electrochemical transformation of PATP on gold electrode involves an electrochemical followed with chemical reaction in acidic solution.The surface-binding PATP was oxidized to a cation radical firstly,which interacted with the adjacent PATP molecules to form a surface-confined aniline dimer, 4'-mercapto-N-phenylquinone diimine(NPQD),through the head-to-tail coupling, which involves two electrons and two protons electrochemical kinetics.Following that, NPQD underwent the hydrolysis to yield 4'-mercapto-N-phenylquinone monoimine (NPQM).The above mechanism was confirmed by FT-SERS and DFT calculation results.2.We calculated the optimized geometry and Raman spectra by using the density functional method at the B3LYP/6-311++G^** level,which confined at the Cs point group symmetrical operation.The theoretical frequencies were scaled according to the scaled quantum mechanical(SQM) procedure.The result scaling factors are 0.884 for the N-H stretching modes,0.938 for the C-C,C-H,C-S and S-H stretching modes and 0.990 for other modes,such as ring in-plane deformation,ring out-of-plane deformation,C-H in-plane bending and C-H out-of-plane bending modes.The final harmonic vibrational wavenumbers and the potential energy distributions(PEDs) were derived by the Wilson's GF matrix method from the SQMF-DFT force field.The assignments of some bands relating to C-N,C-S,N-H modes have major difference by comparing the results from references.The simulated Raman spectrum is well accorded with the experimental.3.The pH-dependent SERS of PATP on gold and silver nanoparticals were studied by DFT theory.The optimized geometries,vibrational force fields and Raman intensities of possible Au(Ag)SC₆H₄NH₂ complexes in aromatic and quinonoidic states were calculated by using B3LYP method with 6-311+G^**(C,H,N,S)/LANL2DZ(Au,Ag) basis set.Based on the relative intensity and Raman shift of vibrational bands together with the PEDs results,the possible forms of PATP is existed in acidic solution with the aromatic structure and the quinonoidic one in alkaline solution on gold nanoparticals, while it keeps the quinonoidic state on silver nanoparticals independent of pH values of solution.