Enlarging the π System of Phosphorescent (C^C*) Cyclometalated Platinum(II) NHC Complexes

Cyclometalated (C^C*)
platinum­(II) N-heterocyclic carbene (NHC) complexes
are emerging as a new class of phosphorescent emitters for the application
in organic light-emitting devices (OLEDs). We present the synthesis
of six new complexes of this class to investigate the influence of
extended π systems. Therefore, six different NHC ligands with
a varying number of additional phenyl substituents were used in combination
with the monoanionic acetylacetonate (acac) ligand to obtain complexes
of the general formula [(NHC)­Pt­(II)­(acac)]. The complexes were fully
characterized by standard techniques and advanced spectroscopic methods
(195Pt NMR). For all complexes the solid-state structure
determination revealed a square-planar coordination of the platinum
atom. Absorption and emission spectra were measured in thin amorphous
poly­(methyl methacrylate) films at room temperature. Four compounds
emit in the blue-green region of the visible spectrum with quantum
yields of up to 81%.