Structural, Photophysical, and Distributed Feedback Lasing Characteristics of Furan-Substituted Thiophene/Phenylene Co-Oligomer Single Crystals

A furan derivative, 2-[1,1'-biphenyl]-4-yl-5-(5'-[1,1'-biphenyl]-4-yl-[2,2'-bithiophen]-5-yl)furan (BPFTT), was designed and synthesized and shown to have excellent optical and electronic characteristics. The synthesized compound exhibits a photoluminescence quantum yield (PLQY) of 28%. In addition, a field-effect transistor fabricated using this material in the active layer exhibits ambipolar mobilities of 0.54 (hole) and 0.03 (electron) cm² V^-1 s^-1. Single crystals with their natural crystal edges acting as Fabry-Pérot resonators exhibit dual gain narrowing phenomena with optical pumping thresholds as low as 15 μJ/cm². Introducing planar distributed feedback resonators reduces the threshold to 2.41 μJ/cm², with the <i>Q</i>-factor reaching 1.5 × 10⁴. The full width at half-maximum is measured to be 0.074 nm, which is an excellent value reported to date for any organic single-crystal laser.