Ultraviolet Organic Laser from Rhombus Microcrystal: Benefits of Single-Molecule Emission from Twisted Structure

Light-emitting molecular crystals
with efficient emission behavior
are crucial for fabricating low-threshold ultraviolet organic lasers.
Herein, we demonstrated a rhombus microcrystal from a fluorene-based
conjugated molecule (CL-1) with robust emission behavior for an ultraviolet
organic laser. Due to the synergistic effect of twisted intramolecular
conformation and weak π-interaction, the CL-1 single crystal
showed an extremely high photoluminescence quantum yield (PLQY) of
∼82%, due to their single-molecule excitonic behavior. Considering
the diverse noncovalent interactions, CL-1 molecules easily self-assembled
into the rhombus microcrystals. Finally, a low-threshold ultraviolet
organic laser was fabricated with a sharp emission at 379 nm, attributed
to the 0–1 vibration band of a single CL-1 molecule, also further
confirming the single twisted-molecule emission in crystal states.
Precisely controlling the intramolecular twisted structure and intermolecular
interaction of organic conjugated molecules is a precondition to obtain
robust ultraviolet emission for optoelectronic applications.