Electrochemical Synthesis of Silver-Tetracyanoquinodimethane Electrochemical Synthesis of Silver-Tetracyanoquinodimethane Nanorods at Agar Supported Water/1,2-Dichloroethane Interface Nanorods at Agar Supported Water/1,2-Dichloroethane Interface

: Silver-tetracyanoquinodimethane (AgTCNQ) is an important charge transfer salt due to its high conductivity and other electronic properties. In this communication, we report the synthesis of AgTCNQ at the liquid/liquid interface. Agar was used as a gelling agent to support water/1,2-dichloroethane (DCE) interface. Silver ions were transferred from the hydrogel into DCE phase, where they combined with TCNQ - to form AgTCNQ nanorods. The developed method can provide a new route for synthesis of functional materials based on the electrochemistry at the liquid/liquid interface.


Introduction
AgTCNQ has attracted significant interest during several decades due to its high conductivity, electrical switching properties and its applications in sensors and electronic s [1][2] .Different approaches to the synthesis of AgTCNQ have been reported, including the 野spontaneous electrolysis冶 in which metal silver reacts with dissolved TCNQ in organic solvents [3] , vacuum vapor deposition of TCNQ onto Ag metal films [4] , and reactions of TCNQ in organic solvent with metal precursors [5] .Electrochemical methodologies have been useful for studying the formation of nano-structured AgTCNQ crystals in acetonitrile, water and ionic liquids because they provide the means for precise control of the nucleation and growth processes [6][7][8][9] .Nevertheless, questions remain open about the mechanism of the AgTCNQ formation process.Both silver and silver salts can react with TCNQ/TCNQ -spontaneously, which makes it difficult to distinguish the direct chemical precipitation from electrocrystallization of AgTCNQ.
To exclude the direct chemical precipitation and focus on the electrochemically induced crystallization, one can take advantage of the hydrophilicity of Ag + and hydrophobicity of TCNQ.This can be achieved by conducting AgTCNQ synthesis at the interface between two immiscible electrolyte solutions (ITIES), e.g., the interface between a hydrogel and 1,2-dichloroethane (DCE).The immiscible water/organic interface can also hinder the diffusion of reactants, thus, reducing the overall reaction rate.
This approach was previously used to synthesize nanoparticles and further modify their surface [6][7] .
When electrolytes are introduced into each phase, the water/oil interface can be polarized to induce charge transfer reactions [8][9] , including the ion transfer of Ag + [10] .Electrosynthesis can involve either ion transfer or electron transfer across the ITIES.An ex-Electrochemical Synthesis of Silver-Tetracyanoquinodimethane Nanorods at Agar Supported Water/1,2-Dichloroethane Interface Li Huang 1,2 , Yixian Wang 3 , Michael V. Mirkin 3 , Bin Ren 1,2 , Dongping Zhan 1,2* ample of the fo rmer approach is the oxidation of cis-cyclooctene in DCE by MnO 4 -, which involved phase transfer catalysis [11] .Oxidation of 4-methylanisole by Ce 4+ at the water/DCE interface involved interfacial electron transfer [12] .
In this communication, we present a new electrosynthetic method based on ion transfer at the agar hydrogel/DCE interface.When the interface is polarized, Ag + gets transferred from the aqueous gel to DCE phase, where it reacts with TCNQ -(the product of the TCNQ reduction by TPBCl -) to form AgTCNQ nanorods.

Results and Discussion
This 野EC冶-type mechanism with a rapid subsequent crystallization reaction (2) can explain the observed irreversible ion transfer wave (curve 3 in Fig. 2).
The only species in Cell 3 that can reduce TCNQ to TCNQ -is TPBCl -, which is relatively easy to oxidize [13] .
The morphology of electrochemically induced crystalline AgTCNQ nanorods was characterized by scanning electron microscopy (SEM).The SEM images (Fig. 3) reveal high-aspect ratio of AgTCNQ nanorods.The surface is essentially smooth, and the rod diameter is in the 200 ~500 nm range, while its length is up to ~5 滋m.EDS results further confirmed the elemental composition of the product.It can be observed obviously that there exist carbon, nitrogen and silver with a weight ratio of 36:44:20.
Since EDS reflects the local surface components of the objects, the EDS results are not in accordance with the stoichiometric ratio.To confirm the composition of the nanorods, Raman spectra of Agar, TCNQ powder and the synthesized nanorods were collected and shown in Fig. 4. Comparing to TCNQ, AgTCNQ has a red-shift peak at 1386 cm -1 and a weak peak at 1603 cm -1 , which are in accordance with the previously reported results [9] .All the above results show that the AgTCNQ nanorods were obtained through the electrochemical method at liquid/liquid interface.
The investigation of the experimental factors that determine the size and shape of the AgTCNQ nanorods and the characterization of their electronic and photonic properties are in currently progress.

Conclusions
We developed a novel method for synthesizing TCNQ-based conductive salt by electrochemistry at the ITIES.Metal ions were transferred from the aqueous hydrogel to organic phase containing a hydrophobic anion and combined with TCNQ - therein to form AgTCNQ nanorods.This approach can be used to produce charge-transfer complexes, which have potential applications in electronic and photonic microdevices.

2
Fig. 1 Electrosynthesis of AgTCNQ at the liquid/liquid interface.A. Schematic diagram of the electrochemical cell.B. Scheme of the mechanism of the electrochemically induced crystallization of AgTCNQ at the water/DCE interface.

Fig. 2
Fig. 2 shows three ion transfer voltammograms obtained at the hydrogel/DCE interface.The background voltammogram (curve 1) obtained in Cell 1 Ag|100 mmol 窑L -1 Na 2 SO 4 ||5 mmol 窑L -1 BTPPATPBCl|AgTPBCl|Ag (Cell 1) shows that no ion-transfer occurred within the polarization window with no Ag + ions added to the aqueous phase.The addition of TCNQ to DCE did not result in appearance of any additional voltammetric wave (not shown).This could be expected because TCNQ is a neutral molecule and there was no electron donor in water phase.In contrast, reversible voltammograms of Ag + transfer (curve 2) were obtained in Cell 2. Ag|1 mmol 窑L -1 Ag 2 SO 4 + 100 mmol 窑L -1 Na 2 SO 4 || 5 mmol 窑L -1 BTPPATPBCl| AgTPBCl|Ag (Cell 2)The presence of a hydrophobic anion, TPBCl -, facilitates the transfer of Ag + to organic phase.A similar wave of Ag + transfer to organic phase (curve 3) was recorded in Cell 3 after TCNQ was added to DCE solution.Ag|1 mmol 窑L -1 Ag 2 SO 4 + 100 mmol 窑L -1 Na 2 SO 4 || 5 mmol 窑L -1 BTPPATPBCl + 10 mmol 窑L -1 TCNQ| AgTPBCl|Ag (Cell 3) However, the reverse wave corresponding to the silver transfer back to the aqueous phase has completely disappeared, and solid substance precipitated at the hydrogel/DCE interface.The disappearance of the reverse transfer wave and the observed precipitation can be attributed to the interfacial crystallization of AgTCNQ that follows the ion transfer reaction: