Phosphorescent Platinum(II) Complexes Derived from Multifunctional Chromophores: Synthesis, Structures, Photophysics, and Electroluminescence

The synthesis and structural, photophysical, electrochemical, and electroluminescent properties of a novel class of
trifunctional Pt(II) cyclometalated complexes are reported in which the hole-transporting triarylamine, electron-transporting oxadiazole, and electroluminescent metal components are integrated into a single molecule. These
neutral metal chelates display good thermal stability (>250 °C under N2) and morphological stability. All of them
exhibit intense ligand-centered fluorescence and phosphorescence in fluid solutions at room temperature, but the
emission spectra become largely dominated by triplet emission bands in CH2Cl2 glass at 77 K. Substituents with
different electronic properties were introduced into the bipolar cyclometalating ligands to fine-tune the absorption
and emissive characteristics of the compounds, and the results were correlated with theoretical calculations using
density functional theory. A comparison of the photophysics and electrochemistry of our multifunctional systems to
those only derived from each of the constituent components was also made and discussed. These Pt complexes
can be vacuum-sublimed and applied as emissive dopants for the fabrication of vapor-deposited electrophosphorescent
organic light-emitting devices (OLEDs), which generally exhibit good device performance with efficiencies up to
3.6%, 11.0 cd A-1, and 5.8 lm W-1. While the electroluminescence energy resembles that recorded in fluid solutions
for these Pt emitters, these monochromatic OLEDs can emit tunable colors by varying the aryl ring substituents
and the level of doping. Saliently, single dopant white-light electroluminescence, triggered by the simultaneous
fluorescence/phosphorescence emission of the metal complexes and a variation of applied driving voltages, has
also been realized based on some of these multifunctional complexes with peak electrophosphorescence efficiencies
of 6.8 cd A-1 and 2.6%.