[epithermal]

Wikipedia:

Rubrene (5,6,11,12-tetraphenylnaphthacene) is a red colored polycyclic aromatic hydrocarbon. Rubrene is used as a sensitiser in chemoluminescence and as a yellow light source in lightsticks.

As an organic semiconductor, the major application of rubrene is in organic light-emitting diodes (OLEDs) and organic field-effect transistors, which are the core elements of flexible displays.

[Ernest_at_the_Beach]

Google turns up a number of references....including this one:

Role of synthesis for oxygen defect incorporation in crystalline rubrene

And a picture:

Packing of rubrene molecules (Carbon atoms in the tertacene backbone are coloured yellow for clarity).