Molecular asterisks with a persulfurated benzene core are among the strongest organic phosphorescent emitters in the solid state

•A family of persulfurated molecular asterisks was synthesized and fully characterized.•They display very intense phosphorescence in the solid state and in a rigid matrix.•X-ray crystal structures were analyzed and compared to the emission properties.•Phosphorescent nanoparticles were obtained by a reprecipitation method.

A series of functionalized persulfurated benzene molecules were synthesized. Their photophysical properties and crystal structures were analyzed. All compounds are non-emitting in solution at room temperature, but in a sharp contrast, quantum yields can be very high (up to 100%) in the solid state at 298 K or in a rigid matrix at low temperatures. This is a consequence of a decrease of intramolecular rotations and motions, but conformational and rotamer issues along with substituent effects might also play a role. These compounds are among the rare examples of highly phosphorescent organic materials, due to a Crystallization Induced Phosphorescence or to an Aggregation Induced Phosphorescence. Compound 1 is among the most phosphorescent solid known to date. They thus represent an alternative to heavy metal ion-based triplet emitters in solid state.

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