Branched Oligophenylenes with Phenylene-Ethynylene Fragments as Anode Interfacial Layer for Solution Processed Optoelectronics

Two branched oligophenylenethynylenes with phenylene or biphenylene moieties as inter-nodal fragments are synthesized by the Sonogashira reaction for optoelectronic applications. The branching of polyphenylenethynylenes influences the electro-optical properties, but cannot be precisely controlled, while its determination is often hardly addressed. The optical investigation, supported by nuclear magnetic resonance (NMR) studies, of oligophenylenethynylenes and the properly synthesized model compounds is performed to get insights on the branching and related effect on the material performance. The proposed branched oligophenylenethynylenes are good ultraviolet emitters in solution, while in solid-state aggregation phenomena strongly affect emission properties. However, the interactions between pi-electrons on phenylene and ethynylene of neighboring molecules in films enhance intermolecular charge transport (hole mobility = 3.2 x 10(-3) cm(2) V(-1)s(-1)) making them optimal candidates as hole transport materials in optoelectronic devices. The insertion of the oligophenylenethynylene film as a hole transporting layer in multilayered solution processes blue, green, and red electroluminescent diodes, enhances OLEDs electro-optical properties.