Phase-dependent photoluminescence of non-symmetric 2,1,3-benzothiadiazole liquid crystals

In order to understand the effect of disubstitution on calamitic liquid crystals, a series of non-symmetric 2,1,3-benzothiadiazole compounds were synthesized and characterized. These specific molecular architectures without the C2 axis were prepared to investigate their mesomorphism and physical properties and to compare them with symmetric molecules. Their liquid crystalline behavior was studied by differential scanning calorimetry, polarized optical microscopy and X-ray diffraction. The thermal properties evidenced the influence of non-symmetric design on the formation of liquid crystalline phases. Photophysical studies were performed in solution and with films, where these materials displayed intense photoluminescence between 500–650 nm, high quantum yields (ΦF = 0.62 – 0.96) and strong solvatochromism. Photoluminescence was measured as a function of temperature, displaying a strong dependence on the phase.