Aggregation-Driven Thorough Cascaded Proton Transfer Process Targeting Ultralow-Threshold Near-Infrared Organic...

Near-infrared (NIR) organic solid-state lasers (OSSLs) are technologically crucial in lasing communication systems, yet they still suffer from the high threshold and low optical gain due to the limited exciton utilization rate. Excited-state double proton transfer (ESDPT) processes of organic gain materials offer promising gain mechanisms for NIR OSSLs due to the favored six-electronic-level energy systems and large red-shifted stimulated emission. Herein, we proposed a novel strategy aimed at modulating the ESDPT process through aggregation effect, where crystallization-enhanced thorough cascaded ESDPT process facilitates the exciton utilization rate and thus enables an ultralow lasing threshold. Impressively, the strong J-type coupling of 4260 cm^-1 in DDMC single-crystal microwires effectively stabilizes TB* level by lowering excited state energy, supporting a thorough ESDPT process. Consequently, all excited electrons decaying by radiative transitions participate in stimulated emission, enabling a high-gain six-level energy system with efficient population inversion density (∆N). Activated by this efficient energy-level system, the NIR single-crystal lasing at ∼870 nm was successfully realized with a record-low threshold of 486 nJ cm^-2. Our work elucidates the fundamental mechanism underlying aggregation effects on ESDPT gain materials, offering effective strategy to enhance the exciton utilization rate for low-threshold and high-gain NIR OSSLs, and even the electrically-pumped NIR OSSLs in the future.