A Charge-transfer Phenomenon between 2,3,5,6-Tetrafluoro-7,7,8,8-tetracyanop-quinodimethane (F4TCNQ) and a Tetrathiafulvalene-based Self-assembled Monolayer Using an Indium-Tin Oxide Electrode

Abstract

Tetrathiafulvalene (TTF: C6H4S4) is a well-known two-electron donor molecule that is electrochemically active, showing two reversible redox cycles at E1/2 1 = 0.33 V and E1/2 2 = 0.71 V (vs SCE).1 It reacts with 7,7,8, to form an electrically conductive TTF-TCNQ chargetransfer (CT) complex with metallic conductivity at room temperature.2 Thereafter, many kinds of TTF-TCNQ-family CT complexes composed of, for example, ethylenedithio-tetrathiafulvalene (EDT-TTF) and 2, 3,5,7,8,, have followed. 3 In the early stage, the CT complexes in the form of a single crystal were investigated with respect to their bulk properties such as crystal structure, electrical conductivity, and optical properties. With many techniques such as LB-film, chemical vapor deposition (CVD), and self-assembled monolayers (SAM), having been applied in this research field, the properties of CT complexes with a mono-or multi-layer have been intensively investigated.4-6 Among these techniques, it is relatively easy to prepare SAM film and highly promising to construct such molecular architectures on metal and semiconductor surfaces.5 For example, a Au surface modified with a dodecanethiol chain with an EDT-TTF functional-group has already been reported. In the current work, a redox-active EDT-TTF group linked to a decanephosphonic acid (compound 5) was synthesized and used for the development of SAM on the surface of an electrically conductive indium-tin oxide (ITO) substrate. This surface-modified ITO (SM-ITO) was used to generate a CT salt with F4TCNQ by boiling, soaking, and electrochemical methods. The formation of the CT complex on the SM-ITO surface was confirmed by micro-Raman spectroscopic measurements, as well as cyclic voltammetry (CV) results. a Present address: Electronic Materials Division, Dongjin Semichem Co., Ltd., Korea. Experimental SectionMaterials. All synthetic reactions were carried out using dried glassware under an argon atmosphere overnight in an oven at 110 o C. Dichloromethane was dried over MgSO4, and triethyl phosphite (P(OEt) 3 ) was distilled prior to use. Tetrahydrofuran (THF) was freshly distilled over sodium benzophenone. Indiumtin oxide (ITO) film-coated glass plates from Samsung Corning Co., Ltd (sheet resistance: 8.5 ± 1.5 Ω/□, size: 35 × 10 mm 2 , transmission: 80.0 ~ 92.0%, flatness ≤ 400 Å) were used.Measurements. The reflection-absorption FT-IR spectra of SAM on ITO glass were measured on a Perkin Elmer Spectrum 100 spectrometer equipped with a specular reflectance attachment (PIKE Technol.). The spectroscopic measurements, viz. UV-vis, micro-Raman, FT-IR, FAB-mass and NMR spectroscopies, were carried out as described elsewhere. [8][9] Cyclic voltammetry (CV) measurements were carried out at room temperature with a CHI 620A Electrochemical Analyzer (CH Instruments Inc.) in CH2Cl2 solution (2 mL) containing 0.1 M n-Bu4N·PF6 as a supporting electrolyte, with a scan rate of 50 mV s -1 , the Ag/AgCl (sat. 3 M KCl) as a reference electrode, Pt-disk (ϕ = 2 mm) or ITO glass (A ≈ 7 mm 2 ) as a working electrode, an...

Aggregates Promote Efficient Charge Transfer Doping of Poly(3-hexylthiophene)

“…Comparison of P3HT/F 4 -TCNQ spectra with that of pristine F 4 -TCNQ (see Supporting Information) demonstrates that these spectral changes do not originate from the simple superposition of polymer and dopant lineshapes. , Closer inspection reveals more drastic changes in doped r-Re spectra at even small dopant loading that we attribute to facile polaron generation. It is also interesting to note that the Raman excitation wavelength is resonant with the F 4 -TCNQ anion absorption spectrum observed only in doped r-Re samples (Figure a).…”

Tetrathiafulvalene–7,7,8,8‐Tetracyanoquinodimethane and Tetrathiafulvalene–2,3,5,6‐Tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane Organic Charge‐Transfer Complexes: Reusable Catalysts for Electron‐Transfer Reactions

“…Interestingly, reports on the synthesis of TTF‐TCNQF 4 are remarkably scarce with no indication of the potential applicability of this material or indeed the morphology of the crystals that are created. However, the reaction of TCNQF 4 with TTF derivatives has been reported, although rarely, including the synthesis of [TTF(CH 2 OH) 4 ][TCNQF 4 ], which was found to be diamagnetic, and self‐assembled monolayers of [EDT‐TTF][TCNQF 4 ] (EDT=ethylenedithio) have also been prepared …”

Precise Orientational Control of Electroactive Units Using a Tripodal Triptycene Scaffold to Direct Noncovalent Pairing at the Single Molecular Level

“…Subsequently, the unimolecular conduction of covalently linked dyadic D-A molecules has been vigorously investigated . In the past, many D or A molecules containing a single tetrathiafulvalene (TTF), anthraquinone (AQ), or tetracyanoquinodimethane (TCNQ) moiety, which undergo changes in electronic properties through intermolecular interactions, have been developed − and successfully incorporated into SAMs. − The resulting monolayers were found to retain the properties particular to their bulk systems, including the formation of intermolecular D-A complexes, with increased conduction for both holes and electrons . We envisioned that the use of D and A systems within our triptycene-based scaffold would allow for the direct observation of the intermolecular conductive behavior.…”