Novel Semiconducting Biomaterials Derived from a Proline Ester and Tetracyanoquinodimethane Identified by Handpicked Selection of Individual Crystals

Abstract

Complex mixtures of cation : anion stoichometries often result from the syntheses of tetracyanoquinodimethane (TCNQ) salts, and often these cannot be easily separated. In this study, the reaction of N,N-dimethyl-d-proline-methylester (Pro(CH3)3+) with LiTCNQ resulted in a mixture of crystals. Hand selection and characterisation of each crystal type by X-ray, infrared, Raman and electrochemistry has provided two stoichometries, 1 : 1 [Pro(CH3)3TCNQ] and 2 : 3 ([(Pro(CH3)3)2(TCNQ)3]). A detailed comparison of these structures is provided. The electrochemical method provides an exceptionally sensitive method of distinguishing differences in stoichiometry. The room temperature conductivity of the mixture is 3.1 × 10–2 S cm–1, which lies in the semiconducting range.