Ferrocene-Based\nOrganic Semiconductors: Evaluating\nIntermolecular Transfer Integrals and Transistor Properties

Ferrocene, with its unique redox properties and stability,\noffers\npromising potential for use in semiconductor layers of organic transistors.\nHowever, it has not previously been applied due to its high vapor\npressure and inability to form thin films. We have successfully fabricated\nthin-film transistors by introducing appropriate substituents into\nferrocene and increasing the molecular weight, thereby suppressing\nits sublimation properties. Based on the crystal structures at room\ntemperature, we have calculated the intermolecular transfer integrals\nusing density functional theory. We have evaluated the carrier-path\nanisotropy (dimensionality of the electronic structure), as well as\nthin-film transistor properties. Ferrocene derivatives having small\nsubstituents such as phenyl groups form herringbone-like molecular\narrangements, realizing two-dimensional carrier paths. In contrast,\nferrocene derivatives with bulky substituents such as anthryl groups\nform one-dimensional uniform stacks, though the transfer integrals\nof all ferrocene derivatives are relatively small below 10 meV. Our\nevaluation have confirmed the switching of the drain currents in the\nforward-back scan of the gate voltage during transistor operations,\nindicating that the reversible redox property of Fc/Fc<sup>+</sup> in the ferrocene units are realized even in the solid state.