Opposites Attract: Organic Charge Transfer Salts

Abstract

A laboratory experiment is described that introduces second-year undergraduate organic chemistry students to organic electronic materials. The discovery of metallic conductivity in the charge transfer salt tetrathiafulvalene tetracyanoquinodimethane (TTF–TCNQ) is a landmark result in the history of organic electronics. The charge transfer interaction is not only relevant to real-world applications, it also has pedagogical value related to understanding redox chemistry, aromaticity, and conjugation. In this laboratory experiment, students carry out a solution phase synthesis of TTF–TCNQ from the molecular precursors TTF and TCNQ. The product is characterized by infrared spectroscopy. Characteristic changes in absorption frequency are correlated with increased aromatic character and observable lengthening of the nitrile bond. In an optional extension, students experimentally verify the great difference in conductivity between the charge transfer salt and the neutral parent components.

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

“…To confirm the synthesis of these materials, further characterization was undertaken. The FTIR spectrum of TTF‐TCNQ (Figure a) is consistent with previous studies and shows signature bands at =3092 and 3073 cm −1 [υ(C−H) region], which are at higher wavenumbers than the bands corresponding to neutral TTF at =3064 cm −1 and neutral TCNQ at =3053 cm −1 . The characteristic band at =2202 cm −1 [υ(C≡N) region] is also different from the band observed at =2221 cm −1 for neutral TCNQ.…”

Ethynylated Acene Synthesis and Photophysics for an Organic Chemistry Laboratory Course

“…The mention of small molecule organic chromophores in the chemical education literature has mostly been limited to the analysis of molecular photophysics and/or reaction kinetics − and generally does not include the preparation of conjugated small molecules in combination with photophysical analysis. When considering the variety of substitution, elimination, and coupling reactions that meet the requirements for air- and water-free techniques, most of the reactions with low molecular weight species do not yield colorful products. − Although UV–vis analysis could be performed on many of these phenyl, styrenyl, biphenyl, etc.…”

A new platform for development of photosystem I based thin films with superior photocurrent: TCNQ charge transfer salts derived from ZIF-8

“…Specically, certain organic complexes have high enough electronic conductivities to be considered fully organic metals, such as the well-known TTF-TCNQ salt. 41 Herein, inspired by our successful encapsulation of PSI in ZIF-8 (PSI@ZIF-8) 42 we report the use of PSI@ZIF-8 composites as starting scaffolding materials to drive the constituent cations (namely, Zn 2+ or the imidazole ion, H 2 mim + ) from ZIF-8 towards subsequent formation of charge transfer complexes with TCNQ. While it has recently been demonstrated that a copper-based MOF can undergo ligand substitution to form CuTCNQ, 43 our work enables a transformation in an aqueous environment amenable to a host of biological materials rather than an organic solvent-a heretofore unachievable task.…”