Synthesis and characterization of polymerizable phosphorescent platinum(II) complexes for solution-processible organic light-emitting diodes

A norbornene-functionalized derivative of acetylacetone has been used to synthesize a series of new polymerizable norbornene-derivatized phosphorescent platinum complexes of the form Pt(C∧N)(O∧O*) where C∧N represents a cyclometalated ligand and O∧O* represents the functionalized acetylacetonate ligand. The complexes have been fully characterized, and the structures of three examples have been determined by X-ray diffraction. Solution absorption and luminescence spectra and electrochemical data are very similar to those for analogues without these polymerizable groups. A 9,9-dialkyl-2,7-di(carbazol-9-yl)fluorene material, in which one of the alkyl groups bears a norbornene group, has been synthesized and copolymerized with the Pt(C∧N)(O∧O*) complexes using Grubbs ruthenium catalysts, resulting in copolymers with broad molecular weight distributions. The copolymers have been used as lumophores in organic light-emitting diodes, thus demonstrating that platinum phosphors can be successfully integrated into the "hybrid" approach to organic light-emitting diodes, in which molecules with transport or luminescent properties are covalently attached to electronically inert polymer backbones to give solution-processible materials. Emission from aggregate states appears to play a similar role in these copolymers to that seen in vapor-deposited devices based on small phosphor and host molecules; in particular, considerable aggregate emission is observed when a phosphor with blue solution emission is used in the devices.