Relationship between crystal structure and optical properties in light blue- and green-emitting crystal polymorphs of butyl group-substituted thiophene/phenylene co-oligomer: Fabrication of crystals and their lasing properties

Abstract

Light-blue (monoclinic) and green (orthorhombic) crystal polymorphs comprising a butyl group-substituted thiophene/phenylene co-oligomer, BP1T-Bu, were prepared by varying the crystal growth conditions with a solution-growth technique. The light-blue- and green-emitting crystals exhibited Fabry–Pérot lasing above the excitation density of 204 and 277 μJ/cm2 based on high group refractive indices and quality factors, respectively. The higher threshold in the green-emitting crystal originates from the lower absorption efficiency of the excitation light, in addition to the lower amount of absorption owing to the smaller thickness of the crystal.