Rubrene

Rubrene (5,6,11,12-tetraphenyltetracene) is the organic compound with the formula Template:Chem2. It is a red colored polycyclic aromatic hydrocarbon. Because of its distinctive optical and electrical properties, rubrene has been extensively studied. It has been used as a sensitiser in chemoluminescence and as a yellow light source in lightsticks.

Electronic properties

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. Single-crystal transistors can be prepared using crystalline rubrene, which is grown in a modified zone furnace on a temperature gradient. This technique, known as physical vapor transport, was introduced in 1998.

Rubrene holds the distinction of being the organic semiconductor with the highest carrier mobility, reaching 40 cm²/(V·s) for holes. This value was measured in OFETs prepared by peeling a thin layer of single-crystalline rubrene and transferring to a Si/SiO₂ substrate.

Crystal structure

Several polymorphs of rubrene are known. Crystals grown from vapor in vacuum can be monoclinic, triclinic, and orthorhombic motifs. Orthorhombic crystals (space group B_bam) are obtained in a closed system in a two-zone furnace at ambient pressure.

Synthesis

Rubrene is prepared by treating 1,1,3-Triphenyl-2-propyn-1-ol with thionyl chloride.

File:3-chloro-1,1,3-triphenylpropa-1,2-diene.png

The resulting chloroallene undergoes dimerization and dehydrochlorination to give rubrene.

File:Rubrene synthesis.png

Redox properties

Rubrene, like other polycyclic aromatic molecules, undergoes redox reactions in solution. It oxidizes and reduces reversibly at 0.95 V and −1.37 V, respectively vs SCE. When the cation and anion are co-generated in an electrochemical cell, they can combine with annihilation of their charges, but producing an excited rubrene molecule that emits at 540 nm. This phenomenon is called electrochemiluminescence.