Linking topology in oligocarbazoles (see figure) has a strong influence on their electronic properties. 3(6),9′‐linked oligocarbazoles exhibit unusual suppression of electronic coupling between units, leading to localized excited states and very small reduction of triplet energies (compared to the monomer). Coupled with their excellent morphological stability, this makes them suitable as host materials for blue electrophosphorescence devices.

The photophysical, electrochemical, and optoelectronic properties of conjugated systems incorporating dibenzophosphole or phosphole moieties are described. Dibenzophosphole derivatives are not suitable materials for OLEDs due to their weak photoluminescence (PL) in the solid state and the instability of the devices. Variation of the substitution pattern of phospholes and chemical modification of their P atoms afford thermally stable derivatives, which are photo- and electroluminescent. Comparison of the optical properties of solution and thin film of thioxophospholes shows that these compounds do not form aggregates in the solid state. This property, which is also supported by an X-ray diffraction study of three novel derivatives, results in an enhancement of the fluorescence quantum yields in the solid state. In contrast, (phosphole)gold(I) complexes exhibit a broad emission in thin film, which is due to the formation of aggregates. Single- and multilayer OLEDs using these P derivatives as the emissive layer have been fabricated. The emission color of these devices and their performances vary with the nature of the P material. Interestingly, di(2-thienyl)thiooxophosphole is an efficient host for the red dopant DCJTB, and devices using the gold complexes have broad emission spectra.

Blue electrophosphorescence in organic light‐emitting diodes (OLEDs) is enhanced by the use of 3,6‐bis(triphenylsilyl)carbazole (see figure). This carbazole derivative with sterically bulky and large‐gap triphenylsilyl groups is an electrochemically and morphologically stable efficient host material for blue electrophosphorescence. When utilized in OLEDs, high efficiencies of up to 16 %, 30.6 cd A–1, and 26.7 lm W–1 are achieved.