Pyrene-Capped Conjugated Amorphous Starbursts: Synthesis, Characterization, and Stable Lasing Properties in Ambient Atmosphere

A family of trigonal starburst conjugated molecules (TrFPy, TrFPy, and TrF2Py) composed of a truxene core and pyrene cappers with various bridge lengths is synthesized and characterized. The incorporation of pyrene cappers successfully depress the crystallization tendency, resulting in enhanced glassy temperature and improved morphological stability of the thin films. The high photoluminescence yield in neat films and excellent thermal stability render these pyrene-capped starbursts promising lasing optical gain media. Low amplified spontaneous emission (ASE) thresholds (E_th^ASE) of 180 nJ pulse^-1 and 101 nJ pulse^-1 were recorded for TrFPy and TrF2Py, respectively. One dimensional distributed feedback (1D DFB) lasers demonstrated lasing threshold of 9.3 kW/cm² and 7.3 kW/cm² for TrFPy (at 457 nm) and TrF2Py lasers (at 451 nm), respectively. The ASE performance of TrFPy and TrF2Py in an ambient condition was recorded with various annealing temperature (from 80 to 250 °C, 10 min). Surprisingly, TrFPy exhibited excellent ASE stability in an ambient condition, which is still detectable even after annealing at 250 °C for 10 min. The results suggest the pyrene-capped molecular design strategy is positive on improving the optical gain stability and meanwhile maintaining excellent lasing properties. Well-defined starburst conjugated macromolecules with pyrene moieties as end-capped groups are explored as the optical gain media for organic semiconductor lasers. The length of oligofluorene bridges between the truxene core and pyrene cappers is carefully tuned. The relationships between their morphology, thermal stability, and amplified spontaneous emission stability in an ambient condition are systematically investigated, suggesting that the pyrene-capped molecular design improves the optical gain stability.