Tervalent conducting polymers with tailor-made work functions: Preparation, characterization, and applications as cathodes in electroluminescent devices

A series of conducting polymers have been prepared through thermal polymeri zation of transition-metal diimine complexes. The as-polymerized material i s electrochemically converted into its formally zerovalent form. Due to the proximity of the half-wave potentials of the formal 1+/0 and 0/1 - couples , there is substantial disproportionation of the redox sites at room temper ature, resulting in a conductive tervalent mixed-valent material. The redox processes that give rise to this mixed-valent material are predominantly l igand-based, and therefore are highly sensitive to substitution on the liga nd periphery. Solution redox chemistry of the monomer can be used to accura tely predict the work, function of the corresponding zerovalent conducting polymer, which has been verified by ultraviolet photoelectron spectroscopy. Many of these materials have especially low work functions (<3.6 eV) makin g them appropriate materials to use as cathode materials in organic light-e mitting devices (OLEDs). Working examples of tris(8-hydroxyquinoline)alumin um(III)-based OLEDs have been fabricated using one of these polymers as a c athode.