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.