Cascaded Excited‐State Intramolecular Proton Transfer Towards Near‐Infrared Organic Lasers Beyond 850 nm

Near‐infrared (NIR) organic solid‐state lasers play an essential role in applications ranging from laser communication to infrared night vision, but progress in this area is restricted by the lack of effective excited‐state gain processes. Herein, we originally proposed and demonstrated the cascaded occurrence of excited‐state intramolecular proton transfer for constructing the completely new energy‐level systems. Cascading by the first ultrafast proton transfer of <430 fs and the subsequent irreversible second proton transfer of ca. 1.6 ps, the stepwise proton transfer process favors the true six‐level photophysical cycle, which supports efficient population inversion and thus NIR single‐mode lasing at 854 nm. This work realizes longest wavelength beyond 850 nm of organic single‐crystal lasing to date and originally exploits the cascaded excited‐state molecular proton transfer energy‐level systems for organic solid‐state lasers.