Electronic Properties of New Organic Conductors Based on 2,7-Bis(methylthio)-1,6-dithiapyrene (MTDTPY) with TCNQ and p-Benzoquinone Derivatives

The electronic properties of charge-transfer (CT) complexes based on a new organic donor MTDTPY with TCNQ and p-benzoquinone derivatives (fluoranil (FLL), chloranil (CHL), bromanil (BRL), and DDQ) have been investigated by means of electrical conductivity, thermoelectric power, ESR, and band calculation. β-MTDTPY–TCNQ, MTDTPY–CHL, and MTDTPY–BRL show a metallic electrical conduction. MTDTPY–CHL and MTDTPY–BRL are the first organic metals among the CT complexes with p-benzoquinone derivatives. The metal–insulator (M-I) transition takes place around 110, 240, and 125 K for β-MTDTPY–TCNQ, MTDTPY–CHL, and MTDTPY–BRL, respectively. The sharp ESR linewidth and large anisotropy of the transfer integral for β-MTDTPY–TCNQ and MTDTPY–CHL suggest a one-dimensional electronic property. Thus, the M-I transition for these complexes is considered to be caused by a Peierls instability. MTDTPY–CHL undergoes a first-order phase transition in the semiconducting phase. This phase transition disappears by applying pressure.