Design of Janus triphenylene mesogens: Facile synthesis, mesomorphism, photoluminescence, and semiconductivity

Abstract

A new variety of non-symmetrical triphenylene-based discogens has been synthesized by intramolecular Scholl cyclodehydrogenation reaction of kinked terphenylenes using the FeCl3/MeNO2 couple as an efficient oxidant. The “Janus-like” tetrakis(alkoxy)triphenylene discogens containing electron-withdrawing groups, such as cyano-, chloro- and fluoro-substituents, or electron-donating moieties, such as carbazole, thiophene and naphthalene at the opposite of the alkylated side were prepared in good to high yields. Polarizing optical microscopy (POM), differential scanning calorimetry (DSC) and small-angle X-ray scattering (SAXS) investigations revealed that six of the 14 discogens synthesized exhibit a hexagonal columnar mesophase. These chromophores emit bright blue light from 350 nm to 500 nm in solution depending on the extension of their π-conjugation. In addition, all six columnar liquid crystals show non-dispersive time-of-flight photocurrent transportation, with charge carrier drift mobility in the range of 10−3 to 10−4 cm2 V−1 s−1, higher or in the same range as their symmetrical hexa(alkoxy)triphenylene parent compounds.