Luminescent 2,1,3-benzothiadiazole-based liquid crystalline compounds

A series of fluorescent 2,1,3-benzothiadiazole-based liquid crystals bearing a π-extended aromatic portion through CC triple bond was synthesized and characterized. The X-ray structure of the rigid core was performed. The mesomorphism and optical profile were evaluated. These compounds showed preferentially smectic C and nematic phases whose stability increase with the elongation of the π-extended aromatic portion. UV–vis spectra in solution displayed similar absorption patterns peaking around 410 and 470 nm (ε ∼ 6.0–9.0 × 104 mol−1 cm−1). Compounds exhibited fluorescence from green to red in solution (λemmax=500–610nm), and show large Stoke’s shifts (82–141 nm) and moderate fluorescence quantum yields (ΦF = 0.23–0.37). Only compound containing phenylpiperazine units displayed very low quantum yield (ΦF = 0.10).