Synthesis and characterization of methoxy- or cyano-substituted thiophene/phenylene co-oligomers for lasing application.

As new candidates of thiophene/phenylene co-oligomer (TPCO) species, 5,5''-bis(4'-methoxy-[1,1'-biphenyl]-4-yl)-2,2':5',2''-terthiophene (BP3T-OMe) and 4',4'''-([2,2':5',2''-terthiophene]-5,5''-diyl)bis(([1,1'-biphenyl]-4-carbonitrile)) (BP3T-CN) were synthesized for lasing applications. Although most unsubstituted TPCO species crystallize in monoclinic form, BP3T-OMe and BP3T-CN crystallized in orthorhombic and triclinic forms, respectively. Since the unsubstituted species, 5,5''-bis(4-biphenylyl)-2,2':5',2''-terthiophene (BP3T), shows unique and superior lasing performance in single crystals, the newly synthesized BP3T-OMe and BP3T-CN have possibilities to show different or improved optoelectronic characteristics. Amplified spontaneous emission (ASE) and optically pumped lasing were observed from both of the single crystals based on their well-shaped crystalline cavity and high group refractive index values of 3.7-5.3 for excellent light confinement. The lasing threshold for the BP3T-OMe crystal was lower than that for the BP3T-CN crystal, which was attributed to their different molecular orientation, standing in the former and inclining in the latter.