Deep-red and near-infrared organic lasers based on centrosymmetric molecules with excited-state intramolecular double proton transfer activity

Organic lasers that emit light in the deep-red and near-infrared (NIR) region are of essential importance in laser communication, night vision, bioimaging, and information-secured displays but are still challenging because of the lack of proper gain materials. Herein, a new molecular design strategy that operates by merging two excited-state intramolecular proton transfer-active molecules into one excited-state double proton transfer (ESDPT)-active molecule was demonstrated. Based on this new strategy, three new materials were designed and synthesized with two groups of intramolecular resonance-assisted hydrogen bonds, in which the ESDPT process was proven to proceed smoothly based on theoretical calculations and experimental results of steady-state and transient spectra. Benefiting from the effective six-level system constructed by the ESDPT process, all newly designed materials showed low threshold laser emissions at approximately 720 nm when doped in PS microspheres, which in turn proved the existence of the second proton transfer process. More importantly, our well-developed NIR organic lasers showed high laser stability, which can maintain high laser intensity after 12000 pulse lasing, which is essential in practical applications. This work provides a simple and effective method for the development of NIR organic gain materials and demonstrates the ESDPT mechanism for NIR lasing.