Efficient optical waveguiding and lasing in needle crystals of thiophene/phenylene co-oligomers grown in solution

Abstract

Needle organic single crystals of light-emitting π-conjugated compounds are superior platforms for photonic circuits. Thiophene/phenylene co-oligomers have been ideal laser media, however, a facile crystal growth method that controls crystal morphologies and optical waveguiding characteristics has not yet been developed. Here, 2,5-bis(4′-cyanobiphenyl-4-yl)thiophene (BP1T-CN) and 5,5′-bis(4′-cyanobiphenyl-4-yl)-2,2′-bithiophene (BP2T-CN) are crystallized with needle morphologies in solution. The attenuation coefficients estimated via spatially resolved PL measurements were 0.012 ± 0.006 μm−1 for a BP1T-CN crystal and 0.027 ± 0.003 μm−1 for a BP2T-CN crystal. Furthermore, both exhibited lasing in a Fabry–Pérot mode via self-cavity effects.