Advancing Beyond 800 Nm: Highly Stable Near-Infrared Thermally Activated Delayed Lasing Triggered by Excited-State Intramolecular Proton Transfer Process

Near-infrared (NIR) organic lasers have undergone rapid development in recent years, but still facing challenges in lowering the threshold and improving the stability. Herein, to overcome these challenges, a "two in one" strategy involving the integration of thermally activated delayed fluorescence (TADF) and excited-state intramolecular proton transfer (ESIPT) activity in a single molecule is proposed. Specifically, a donor-acceptor-donor type TADF material 2,6-bis[4-(diphenylamino)phenyl]-1,5-dihydroxyanthraquinone (TPA-DHAQ) with an ESIPT-active moiety as the acceptor, is designed and synthesized, based on which, a NIR organic laser at 820 nm with an exceptionally low threshold of 6.3 mu J cm(-2) can be realized. Benefiting from the synergistic effect of the TADF property and the ESIPT process, the resulting organic laser showed excellent stability by maintaining the laser intensity at approximate to 80% of the initial value after 580 min of continuous excitation. Finally, by modulating the size of the resonator, a single-mode NIR laser is successfully realized. This work provides a novel molecular design strategy for the development of new TADF gain materials to overcome the problem of high threshold and poor stability of conventional NIR organic lasers, and shed light on the future development of NIR organic lasers.