H‑Aggregates Granting Crystallization-Induced Emissive Behavior and Ultralong Phosphorescence from a Pure Organic Molecule

Solid-state
luminescent materials with long lifetimes are the subject
of ever-growing interest from both a scientific and a technological
point of view. However, when dealing with organic compounds, the achievement
of highly efficient materials is limited by aggregation-caused quenching
(ACQ) phenomena on one side and by ultrafast deactivation of the excited
states on the other. Here, we report on a simple organic molecule,
namely, cyclic triimidazole (C9H6N6), 1, showing crystallization-induced emissive (CIE)
behavior and, in particular, ultralong phosphorescence due to strong
coupling in H-aggregated molecules. Our experimental data reveal that
luminescence lifetimes up to 1 s, which are several orders of magnitude
longer than those of conventional organic fluorophores, can be realized
under ambient conditions, thus expanding the class of organic materials
for phosphorescence applications.