have established a breadth of TCNQ-based charge-transfer complexes, each with unique properties. While growing recognition of TCNQ-based materials has led to a number of fabrication strategies including electrochemical, vapor deposition, and wet chemical routes; the applicability of these materials has until recently been severely restricted to electronics. [21][22][23][24][25][26] A unique subset of this group of materials is MTCNQ ionic charge transfer complexes, wherein M corresponds to a transition metal cation (CuTCNQ and AgTCNQ are the most extensively studied) and TCNQ is an anion. [1][2][3][4][5][6][7][8] The presence of transition metal in these metal-organic charge transfer complexes offers a unique opportunity to combine their inherent organic semiconducting properties with the well-established applications of metals in catalysis, sensing, and biology. In recent years, our group and others have shown the potential of these materials beyond electronics, such that CuTCNQ and its metal composites were found as outstanding catalysts for electron transfer and dye degradation reactions; [1][2][3]5] CuTCNQ/ZnO heterojunctions as a humidity sensor; [27] CuTCNQ nanoarrays as pressure sensors; [28] KTCNQ, NaTCNQ, and LiTCNQ as highly specific NO x /H 2 gas sensors; [29,30] and AgTCNQ as antimicrobial agents. [31] These emerging applications of MTCNQ materials now warrant new developments in the current fabrication strategies such that obtained materials are best suited for the targeted application.For CuTCNQ, the current wet chemical fabrication strategy employs a Cu foil (Cu 0 ) as a source of metal, which is immersed in a TCNQ 0 solution dissolved in acetonitrile (MeCN). [1][2][3]32] A spontaneous redox reaction leads to crystallization of phase I CuTCNQ [i.e., Cu + TCNQ − ] microrods vertically aligned on the surface of the Cu foil. [21] A limitation of this approach is that the length of the CuTCNQ microrods is typically restricted to ≈10-15 µm. This is primarily because the as-synthesized CuTCNQ concomitantly dissolves into Cu + and TCNQ − ions on prolonged exposure to MeCN. [32] The concurrent dissolution/ crystallization of CuTCNQ does not allow the growth of these materials beyond certain dimensions. [32] In addition to dissolution, a physicochemical change occurs through which the original conductive phase I CuTCNQ (4.8 × 10 −3 S cm −1 ) transforms A new bisolvent approach is introduced to overcome the limitation of wet chemical routes of a semiconducting phase I CuTCNQ (7,7,8,8-tetracyanoquinodimethane) synthesis, which currently does not allow these materials to be grown beyond certain dimensions (10-15 µm). The use of water as a cosolvent during acetonitrile-mediated conventional synthesis of CuTCNQ allows a dynamic control over its crystallization and dissolution process through favorably shifting the reaction equilibrium. This enables CuTCNQ structures of unique morphologies with secondary growth, alongside dimensions exceeding 100 µm to be produced. These new morphologies of phase I CuTCNQ show re...

Vipul Bansal and co‐workers overcome the challenge in fabricating large dimension Cu(7,7,8,8‐tetracyanoquinodimethane) (CuTCNQ) metal‐organic semiconductors in article number https://doi.org/10.1002/admi.201700097. The use of water‐acetonitrile bisolvent mixture instead of acetonitrile in conventional synthesis allows a dynamic control over the reaction equilibrium. This favours CuTCNQ crystallization and enables growth of highly redox active CuTCNQ structures exceeding 100 μm in length.