Toward Functional π-Conjugated Organophosphorus Materials: Design of Phosphole-Based Oligomers for Electroluminescent 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.