Emerging Applications of TCNQ-Based Metal–Organic Semiconducting Materials

The discovery of TTF-TCNQ (TTF = tetrathiofulvalene and TCNQ = 7,7,8,8-tetracyanoquinodimethane), the first organic charge-transfer (CT) material based on TCNQ, sparked an explosion of research on the fabrication of semiconducting materials by combining TCNQ and its derivatives with other organic moieties, including NH₄⁺, R₄N⁺, amino acids, and amino acid esters. Some of these materials exhibit metal-like conductivity and superconductivity at low temperatures. Subsequent fundamental and technological advances occurred when metal cations (M⁺) replaced the organic moiety. These M⁺TCNQ^– metal–organic semiconducting CT materials or TCNQ-based salts have significantly contributed to the burgeoning field of organic and metal–organic electronics. However, until the late 2000s, the applications of these materials remained restricted to electronic devices. This review provides an overview of the wide applicability of TCNQ-based materials in applications beyond conventional electronics, including redox catalysis, photocatalysis, water splitting, ammonia production, sensing, superhydrophobic surfaces, iodine and lithium storage, desalination, sodium-ion and potassium-ion batteries, and biological applications. The review also outlines the challenges that must be addressed to realize the full potential of TCNQ-based materials across diverse application areas.