Thermodynamically Stable Organic Dye Microcrystals for Highly Efficient Whispering-Gallery-Mode Lasing.

Organic laser dyes have the potential for advancing miniaturized laser technology because their vast molecular diversity offers infinite possibilities for laser design. However, it remains challenging to realize pure dye aggregate lasers due to intermolecular quenching. A universal chemical strategy for activating the optical gain in dye aggregates is highly desirable for the development of miniaturized dye lasers. Here, we propose a molecule-guided crystal engineering strategy to synthesize thermodynamically stable organic dye microcrystals capable of lasing efficiently. Multiple alkyl substituents are introduced on the organic dye molecule skeleton to transform the strong intermolecular interaction into multiple weak intermolecular interactions, which successfully activate the optical gain in dye single crystals. Different alkyl substituents lead to the formation of two kinds of microcrystals with distinct molecular packing modes and distinct geometries. Both kinds of organic dye microcrystals allow for efficient lasing. The hexagonal microcrystal with herringbone molecular packing combines large optical gain, strong cavity confinement, and high stability, which enables highly efficient and stable whispering-gallery-mode lasing. The molecule-guided crystal engineering strategy is universally applicable to diverse organic laser dye molecule skeletons and substituents, showing the potential for exploring organic microlasers with enhanced performance and functions.