Studies On Plasmon Enhanced Photo-induced Charge Transfer Reaction Of AgTCNQF₄with Raman Spectroscopy

In the last decades, Metal-organic charge-transfer complex MTCNQ (M=Cu,Ag; TCNQ=7,7,8,8-tetracyanoquinodimethane) have gained worldwide attentionsfor their electrical and optical properties. This kind of charge transfer complexes isendowed with the electrical and optical bistable switching as well as photochromismproperties, which make it became a candidater in electrical switching, photoelectricmemory storage and field emission devices. Many methods, such as solution process,vapor–solid chemical reaction, two-phase method, electrodeposition andphotocrystallization, have been applied to the synthesize in different morphologies ofmicro-/nanomaterials. At the same time, the corresponding crystal structures andgrowth mechanisms have received an abundance of attention. More research onMTCNQ and its fluorinated derivative TCNQF4(TCNQF4=2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane) are focused on applyingprospect. Although, a number of literatres about optical, electrical aspects ofMTCNQF4have been reported, there has yet to fully understand on the basis issue forlight or electricity induced MTCNQ(F4) chemical transformation. To the best of ourknowledge, external light stimulations to induced AgTCNQF4charge transfer havenever reported.Redox levels of TCNQF4system are neutral TCNQF4, TCNQF4-monoanion andTCNQF42-dianion, respectively. The transformation among the redox levels not onlyby electron gain or loss but also by external stimulations，such as, light, electricity and heat. In this work, we have investigated photo-induced metal-organic charge-transfercomplexes AgTCNQF4charge transfer reaction, and used the LSPR property ofAu/Ag nanoparticles to alter and control the charge transfer reaction. Thischaracterization of photo-induced charge transfer reaction by the means of Ramantechnique. Main content as follows:1. The Studies on Raman Spectra of TCNQF4, AgTCNQF4and Ag2TCNQF4.In order to understand what will happen when the laser radiated on the surface ofAgTCNQF4. It is a previous question to identify the Raman spectra of redox levels ofTCNQF4(TCNQF4，AgTCNQF4and Ag2TCNQF4). First, we took TCNQF4-andTCNQF42-as models to compute the Raman spectra of AgTCNQF4and Ag2TCNQF4,respectively. Combine with the theoretical calculation, the TCNQF4, AgTCNQF4andAg2TCNQF4Raman spectra which come from experimental were further accurateidentification. This work provides a materials spectroscopy basis for the studies ofphoto-induced AgTCNQF4charge transfer reaction.2. Photo-induced AgTCNQF4charge transfer and its electrical switchingbehaviorIn order to investigate whether and how charge transfer occurs at thephoto-induced AgTCNQF4, we carried out the resonanse raman spectra of AgTCNQF4microarray varying excitation wavelength. The threshold wavelength ofphoto-induced AgTCNQF4charge transfer is514nm. And the transformation trendtoward Ag2TCNQF4. As the excitation wavelength get shorter, the degree of chargetransfer continued to accelerate. These transformations from AgTCNQF4toAg2TCNQF4occur derive from photoinduced blue band system electron transition aswell as photothermy. Conductive-AFM experiments proved the reversible electricalbistable switching of AgTCNQF4microrods array.3. Studies on Plasmon enhanced Photo-Induced Charge Transfer Reaction inAgTCNQF4with Raman spectroscopy.Noble metal nanoparticles LSPR possess the function of light electrical andthermal processor, which play a importent role in photochemical teactions. The core of the studies is that the photo-induced AgTCNQF4charge transfer reaction beenenhanced and controled by the SPR enhanced or SPR-mediated catalysis. First, theAuNPs@AgTCNQF4nanocomposite material was synthesized via galvanicreplacement reaction (the reaction of AgTCNQF4microrods array and KAuCl4acetonitrile solution). Then, Using λex=532nm laser induced undecoratedAgTCNQF4and AuNPs@AgTCNQF4microrods. The Raman data show that thephenomenon of photo-induced charge transfer happening on AgTCNQF4in presenceof AuNPs. The rate and the degree of charge transfer occurring on AgTCNQF4aredepended on the excitation wavelength, the irradiation time, excitation intensity andthe coverage density of Au NPs. This study proposes a possible way to synthesizeAg2TCNQF4controllably through plasmon enhanced photochemical reaction.4. The synthesis of AgNPs-AgTCNQF4and its photo-induced charge transferreaction.As described in the previous chapter that the nanocomposite material ofAuNPs@AgTCNQF4via the galvanic replacement reaction consumed manyprecursors of AgTCNQF4, and the rate of charge transfer was relatively low. So, wemade a improvement in synthetic method of MNPs-AgTCNQF4. we designed andsynthesized a small-size AgNPs-AgTCNQF4nanorods via a one-pot, no-damage, andsynchronous synthesis method in aqueous phase. Similarily, Under the λex=532nmlaser irradiation, the small-size AgNPs-AgTCNQF4nanorods shown a relatively fasterphoto-induced charge transfer from the monoanion of TCNQF4to dianion. When thereactant ratio of AgNP colloid and TCNQF4microemulsion is1:1, the reaction timefor completing the photo-induced charge transfer reaction is120s. As the load ofAgNPs increased, photoinduced charge transfer reaction rate was accelerated. Hardlyhad the laser start irradiated when the photo-induced AgTCNQF4charge transferreaction was completed. The quick response abilities of small-sizeAgNPs-AgTCNQF4nanorods to the visible light, which make them became anoutstanding candidate for optical memory storage.