Effect of heteroatom exchange (S/Se) in the mesomorphism and physical properties of benzochalcogenodiazole-based liquid crystals

In order to investigate the effect on the structure-property relationship by the exchange of sulfur atom by selenium, a new series of fluorescent calamitic liquid crystals based on 4,7-disubstituted-2,1,3-benzoselenadiazole was successfully synthesized and characterized. The mesomorphic properties were studied by differential scanning calorimetry, polarized optical microscopy and X-ray diffraction. Thermal properties have evidenced the influence of changing sulfur by selenium atom in the formation of liquid crystalline phases and mesomorphism range. Photophysical studies were performed in chloroform solution, where these compounds displayed strong orange luminescent under UV light, with relevant quantum yields (ΦF = 0.14–0.16) and greater solvatochromic dependence. Electrochemical studies showed oxidation and reduction patterns similar to 2,1,3-benzothiadiazoles analogues, however presenting lower band gap.