Three-Dimensional Anisotropic Carrier Mobility and Structure–Property Relationships for [1]Benzothieno[3,2‑<i>b</i>][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 −COPhF 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

Impact of Edge-Core Structures and Substituent Effects on the Electronic and Charge-Transport Properties of Heteroaromatic Ring-Fused Oligomers

Herein, we systematically studied the electronic and conducting properties of the thiophene-fused polycyclic aromatic compounds and their analogues and discussed in detail the influences of edge-core structure, heteroatom substitution, and functionalization on their field-effect transistor properties and solid-state packing motifs. It was found that the influence of edge-core structure and heteroatom substitution on the electronic properties and reorganization energies of semiconducting materials mainly originates from the variations of the frontier molecular orbital charge distributions and the steric hindrance as well as the conjugate degree of compounds. Moreover, our results also showed that the fusion of benzene rings at the longitudinal end could effectively decrease energy barrier of charge injection and reorganization energies and change the molecular arrangement from herringbone packing to π stacking, which provides a promising way to functionalize organic semiconducting molecules