Deepening Insights into Near-Infrared Excited-State Intramolecular Proton Transfer Lasing: The Charm of Resonance-Assisted Hydrogen Bonds

Excited-state intramolecular proton transfer (ESIPT)-active organic semiconductor materials, characterized by a or several resonance-assisted hydrogen bonds (RAHBs), are supposed to be ideal candidates for achieving high-performance near-infrared (NIR) lasers. However, according to the energy gap law, the development of ESIPT-active gain materials is still limited by the serious nonradiative decays. Herein, it is demonstrated that RAHBs can activate ESIPT lasing by inhibiting nonradiative decays. A new ESIPT-active material 1,5-dihydroxy-2,6-diphenylanthraquinone (DP-DHAQ) containing two centrosymmetric RAHBs is developed, which exhibits a approximate to 100-fold higher radiative decay rate (k(r) = 1.1 x 10(10) s(-1)) in doped polystyrene (PS) film than that of 1-hydroxy-5-methoxy-2,6-diphenylanthraquinone (DP-HMAQ) and 1,5-dimethoxy-2,6-diphenylanthraquinone (DP-DMAQ), in which one and two RAHBs are broken, respectively, by introducing methyl groups. Both DP-DHAQ and DP-HMAQ can form four-level systems based on the ESIPT processes, but only DP-DHAQ doped PS microspheres exhibit laser emission at 710 nm under the test conditions. It is worth mentioning that single-crystal microplates of DP-DHAQ can realize NIR laser emission at 725 nm. The results suggest that RAHBs can effectively activate the gain property of ESIPT-active materials, which deepens insights into NIR ESIPT lasing and provides a new proposal for the design of organic laser-active molecules.