Purely organic materials showing solid state room temperature phosphorescence (RTP) are receiving an ever growing interest due to their low toxicity, cost and environmental load compared to their organometallic counterparts.

A molecule consisting of a hexathio-benzene core and peripheral tolyl substituents exhibits outstanding phosphorescence properties in some environments favoring rigidity, in the solid state and in a solid matrix at 77 K, while no luminescence is recorded in solution at room temperature. This peculiar behavior is attributed to the restriction of bond rotation and conformational mobility of the tolylthio substituents, which slows down the non-radiative deactivation processes of the phosphorescent excited state. The solid material (powder) shows a very high phosphorescence quantum yield (80%), which, to the best of our knowledge, is the highest reported value for organic molecules. The photophysical investigation was accompanied by a detailed computational study disclosing the role of CH–π interactions. This molecule has been exploited toward luminescent organic nanocrystals and light-emitting diodes with a fully solution processable technology.