Highly Emitting Neutral Dinuclear Rhenium Complexes as Phosphorescent Dopants for Electroluminescent Devices

A series of neutral, dinuclear, luminescent rhenium(I) complexes suitable for phosphorescent org. light emitting devices (OLEDs) is reported. These compds., of general formula [Re2(-Cl)2(CO)6(-1,2-diazine)], contain diazines bearing alkyl groups in one or in both the  positions. Their electrochem. and photophys. properties are presented, as well as a combined d. functional and time-dependent d. functional study of their geometry, relative stability and electronic structure. The complexes show intense green/yellow emissions in toluene soln. and in the solid state and some of the complexes possess high emission quantum yields ( = 0.18-0.22 for the derivs. with disubstituted diazines). In butyronitrile glass, at 77 K, due to the charge transfer character of the lowest (emitting) excited state, strong blue shift of the emission is obsd., accompanied by a strong increase in the lifetime values. The highest-performing emitting complex, contg. cyclopentapyridazine as ligand, is tested in a polymer-based light-emitting device, with poly(9-vinylcarbazole) as matrix, as well as in a device obtained by vacuum sublimation of the complex in the 2,7-bis(diphenylphosphine oxide)-9-(9-phenylcarbazol-3-yl)-9-phenylfluorene (PCF) matrix. This represents the first example of devices obtained with a rhenium complex which can be sublimed and is soln. processable. Furthermore, the emission is the bluest ever reported for electrogenerated luminescence for rhenium complexes.