Synthesis and characterization of novel luminescent liquid crystalline compounds based on 2,1,3-benzoxadiazole

Light-emitting molecules exhibiting luminescence have been attracting scientific interest because of their potential applications in electronic devices.1 Luminescent liquid crystals (LLC) are of great interest, since their self-organizing properties can be exploited to achieve linearly polarized for emissive.2 Here we present the synthesis and characterization of LLCs based on 2,1,3-benzoxadiazole (5a-f). The 4,7-dibromo-2,1,3-benzoxadiazole 3 was prepared by the reaction of 2-nitroaniline with sodium hypochlorite, reduction with triphenylphosphine and bromination using bromine. Acetylenes 4a-f were synthesized from aryl halides via palladium-catalyzed cross-coupling.3 The final step involved coupling between 3 and 4a-f to give 5a-f. The final compounds showed smectic C and nematic phases whose stability increased with the elongation of the alkyl portion. UV-vis spectra displayed absorption patterns peaking at around 439 and 451 nm ( ~ 2.0–5.8 x 104 mol-1cm-1). Compounds exhibited strong yellow photoluminescence in solution (542–567 nm) and high quantum yields (Φ F = 0.36-0.45).