Organic single-crystalline whispering-gallery mode microlasers with efficient optical gain activated via excited state intramolecular proton transfer luminogens.

A suitable energy level system of organic laser gain material is vital for the realization of organic solid-state lasers (OSSLs). In this work, it is experimentally demonstrated that the excited state intramolecular proton transfer (ESIPT) occurred within ∼1.4 ps in the singlet excited state (S₁*) of the organic dye 1,5-dihydroxyanthraquinone (1,5-DHAQ). An optimized energy level system is thereby constructed via the ESIPT process for efficient optical gain, and a deep red laser emission at ∼672 nm with a low threshold of 0.39 μJ is achieved based on the self-assembled square microdisks of 1,5-DHAQ, which simultaneously function as the high quality (Q ∼ 2033) whispering-gallery mode (WGM) cavity and efficient laser gain medium. Our work realizes the efficient WGM OSSL with a favored energy level system based on the ESIPT process, providing insight into the ESIPT lasing mechanism. The results would ultimately contribute to the development of organic coherent light sources. [ABSTRACT FROM AUTHOR]