Lasing Operation under Long-Pulse Excitation in Solution-Processed Organic Gain Medium: Toward CW Lasing in Organic Semiconductors

High mechanical flexibility and wavelength tunability of organic semiconductor materials have propelled the development of organic semiconductor lasers (OSLs) as a complementary technology to current inorganic lasers. While excellent progress has been made across multiple aspects of OSLs, demonstration of long-pulse operation [quasi-continuous wave (qCW) or continuous wave (CW)] lasing has presented significant challenges due to the detrimental accumulation of triplets under long-pulse photoexcitation and substantial quenching of singlet excitons, arising from singlet-triplet annihilation (STA). In particular, qCW or CW lasing from solution-processed OSL materials has not been reported, and thus remains a long-thought objective in optoelectronic research. Using a novel bis(N-carbazolylstyryl)-9,9-dihexylfluorene (BSFCz), the first solution-processable organic laser dye demonstrating lasing oscillation in the long-pulse photoexcitation regime (up to 10 ms pulse width) with a low threshold (420 W cm⁻²), which in part can be attributed to its negligible spectral overlap between triplet excited-state absorption and laser emission, is herein reported. Temporal emission profiles below and above the lasing threshold also demonstrate that STA has a negligible effect on emission. These combined observations show BSFCz incur low losses due to triplet excited-states, leading to extremely small changes in lasing thresholds when moving from pulsed to qCW (>1 ms) excitation.