Three-Dimensional Anisotropic Carrier Mobility and Structure–Property Relationships for [1]Benzothieno[3,2-b][1]benzothiophene Derivatives: A Theoretical Study

Through the Marcus electron-transfer theory combined with the random walk technique for the charge-carrier diffusion process, we simulated the three-dimensional (3D) distributions of hole and electron mobilities for [1]benzothieno[3,2- b ][1]benzothiophene ( BTBT ) and its derivatives. Our predicted mobility ranges agree well with the measured field-effect mobility of the BTBT derivatives. We further analyzed the charge-transfer mobility anisotropy of the studied compounds, and the optimum conducting-channel direction relative to the crystal axis was determined, which provides a reliable reference to assist in the performance optimization of field-effect transistors (FETs). Moreover, we analyzed in detail the influences of different substituents on the reorganization energies, ionization energies, electron affinities, frontier molecular orbital charge distributions, and solid-state packing motifs of the BTBT . It was found that the reorganization energies and energy barrier of charge injection effectively decreased with the fusion of the thiophene ring. However, the herringbone packing of BTBT is transformed to π stacking at a local site; as a result, the hole and electron mobilities of BTBT decreased slightly. In comparison, attaching electron-withdrawing − COPh F to BTBT not only increases the electron affinities significantly but also increases the electronic couplings and decreases the reorganization energy related to the electron transfer. It provides a promising way to design n-type or ambipolar organic semiconducting materials.