Theoretical Study On The Redox Reactions Of Nitrogen-Containing Aromatic Compounds Modulated By Surface Plasmon

In recent years,Plasmon-enhanced photocatalytic reactions have become a very interesting and active direction of research.Under the excitation of a specific wavelength,the free electrons in the surface of gold or silver nanoparticles will oscillate in the presence of the external electromagnetic field.When the excitation frequency is consistent with the characteristic frequency of metal nanostructures,it creates a phenomenon known as surface plasmon resonance(SPR).Surface plasmon resonance has a variety of promoting effects on surface reactions,due to its unique properties.So,plasmon-enhanced heterogenous catalysis has recently come into focus as a promising technique for high performance solar energy conversion.A large number of literatures have reported that the aromatic molecules adsorbed on the metal surface or the metal electrode,the Raman signal will be significantly enhanced.However,the mechanism of SERS is still not clear.For the enhancement of Raman signal,scientists generally hold two views: chemical enhancement mechanism and electromagnetic field enhancement mechanism.A thorough research has been studied for the electromagnetic field enhancement mechanism.However,the chemical enhancement mechanism is limited to the charge transfer while ignoring the chemical effect of surface plasmon polaritons.In this paper,we take the chemical effect of surface plasmon polaritons as the starting point.The study was carried out from two aspects,such as plasmon enhanced Raman spectroscopy(PERS)and plasmon enhanced chemical reaction(PECR).The relevant contents and results are listed as followes:(1)We simulated the normal Raman and surface Raman spectra of PNA and assigned all vibrational modes by the DFT.Then,we studied that the reaction routes of PNA in the air and in the solution.Our calculated results demonstrated that PNA can be converted to p,p’-diaminoazobenzene(DAAB)and p,p’-dinitroazobenzene(DNAB)through a reductive coupling reaction in the solution and in the absence of air and a catalysed oxidative coupling reaction at the presence of oxygen in the air,respectively.(2)Surface-enhanced Raman spectroscopy and density functional theory are performed to study the photocatalytic polymerization of p-dinitrobenzene(DNB)and p-phenylenediamine(PDA)to the corresponding azo-like oligomers on silver surfaces.Research contents includ that the simulated normal Raman and surface Raman spectra of target molecule and corresponding experimental spectra.Furthermore,the reaction mechanisms of DNB and PDA are also discussed.Experimental and theoretical results suggest that DNB and PDA can convert to the corresponding N-N oligomers through a reductive reaction in the solution and an oxidative coupling reaction at the air,respectively.(3)Density of functional(DFT)calculations are performed to explore the trans-cis isomerization of azobenzene and stilbene mediated by Ag NPs under the dark field and the irradiation of light,respectively.We calculated the potential energy surface of trans-cis isomerization of azobenzene and stilbene and the molecular orbitals and Low-lying charge transfer transitions of azobenzene-Ag22 and stilbene-Ag22.The results indicate that hole oxide the trans-azobenzene(trans-stilbene)is the most likely pathway for Ag NPs mediated azobenzene(stilbene)trans-cis isomerization.This work not only helps us to understand the reason that the Raman signal of the target molecule is enhanced when they adsorbed on the surface of the metal,but also provides a new green method for producing azobenzene compounds.In addition,the study on azobenzene and stilbene can further help us to make them applied in optical molecular switch.