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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