Dicyanobenzothiadiazole Derivatives Possessing Switchable Dielectric Permittivities

Benzothiadiazoles are important electron acceptors and are frequently employed as electron-deficient components of donor-acceptor polymers. We report the effect of nitrile functionalities on the reactivity, steric hindrance, optoelectronic properties, and dielectric permittivity in dicyanobenzothioadiazole (DCNBT). Dielectric spectroscopy in the bulk and in solution assisted by DFT-calculations revealed that these molecules can be engineered to engender maximum values of the dipole moment and of dielectric permittivity due to the strong electron-withdrawing effect of the nitrile groups. The self-assembly in the bulk was investigated by X-ray scattering performed on single crystals, fibers (2D-WAXS), and thin films (GiWAXS). Combining these results, we found a switching of dielectric permittivity of the 4,7-alkylthienyl-substituted dicyanobenzothiadiazole at the transition from the liquid crystalline to the isotropic phase with values capable of competing with the best known rodlike liquid crystals.