Novel semiconducting biomaterials derived from a proline ester and tetracyanoquinodimethane identified by handpicked selection of individual crystals

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(CH ₃) 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(CH ₃) ₃TCNQ] and 2:3 ([(Pro(CH ₃) 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 ^-2Scm ^-1, which lies in the semiconducting range.