A theoretical study of the electronic structure and charge transport properties of thieno[2,3-b]benzothiophene based derivatives

Abstract

The electronic structure and charge transport properties of thieno[2,3-b]benzothiophene (TBT) and its eight derivatives are investigated via density functional theory (DFT). The impact of different π-bridge spacers (1, the dimer of TBT; 2, vinyl; 3, phenyl; and 4, tetrafluorophenyl) and substituents (5, phenyl; 6, biphenyl; 7, naphthalenyl; and 8, benzothiophenyl) on the geometric structures, reorganization energy, absorption spectra, frontier orbitals, ionization potentials (IPs) and electron affinities (EAs) of all the compounds is explored to establish the relationship between the structure and properties. All the compounds show wide band gaps and low-lying HOMOs, and the IPs of all the TBT derivatives are higher than that of pentacene. The crystal packing interactions, transfer integrals and charge carrier mobilities of compounds 1, 2, 4 and 6 are also calculated. The calculated results demonstrated that these kinds of materials may exhibit good environmental stability and high charge mobility due to their large conjugated planar structure, close π-stacking arrangement, and multiple intermolecular interactions. For compounds 1 and 4, the predicted hole mobility is as high as 0.28 and 0.17 cm² V⁻¹ s⁻¹, respectively, indicating that both of them benefit hole transport, while compounds 2 and 6 exhibit balanced charge transport properties with the hole and electron mobilities of 0.012 and 0.013 cm² V⁻¹ s⁻¹, respectively, for compound 2. Compound 6 shows a relatively lower charge mobilities of 10⁻³ order of magnitude for both holes and electrons due to the larger reorganization energy and lower transfer integrals.