The synthesis, electrochemistry, and photophysics of a series of square planar Pt(II) complexes are reported. The complexes have the general structure C(wedge)NPt(O(wedge)O),where C(wedge)N is a monoanionic cyclometalating ligand (e.g., 2-phenylpyridyl, 2-(2'-thienyl)pyridyl, 2-(4,6-difluorophenyl)pyridyl, etc.) and O(wedge)O is a beta-diketonato ligand. Reaction of K(2)PtCl(4) with a HC(wedge)N ligand precursor forms the chloride-bridged dimer, C(wedge)NPt(mu-Cl)(2)PtC(wedge)N, which is cleaved with beta-diketones such as acetyl acetone (acacH) and dipivaloylmethane (dpmH) to give the corresponding monomeric C(wedge)NPt(O(wedge)O) complex. The thpyPt(dpm) (thpy = 2-(2'-thienyl)pyridyl) complex has been characterized using X-ray crystallography. The bond lengths and angles for this complex are similar to those of related cyclometalated Pt complexes. There are two independent molecular dimers in the asymmetric unit, with intermolecular spacings of 3.45 and 3.56 A, consistent with moderate pi-pi interactions and no evident Pt-Pt interactions. Most of the C(wedge)NPt(O(wedge)O) complexes display a single reversible reduction wave between -1.9 and -2.6 V (vs Cp(2)Fe/Cp(2)Fe(+)), assigned to largely C(wedge)N ligand based reduction, and an irreversible oxidation, assigned to predominantly Pt based oxidation. DFT calculations were carried out on both the ground (singlet) and excited (triplet) states of these complexes. The HOMO levels are a mixture of Pt and ligand orbitals, while the LUMO is predominantly C(wedge)N ligand based. The emission characteristics of these complexes are governed by the nature of the organometallic cyclometalating ligand allowing the emission to be tuned throughout the visible spectrum. Twenty-three different C(wedge)N ligands have been examined, which gave emission lambda(max) values ranging from 456 to 600 nm. Well-resolved vibronic fine structure is observed in all of the emission spectra (room temperature and 77 K). Strong spin-orbit coupling of the platinum atom allows for the formally forbidden mixing of the (1)MLCT with the (3)MCLT and (3)pi-pi states. This mixing leads to high emission quantum efficiencies (0.02-0.25) and lifetimes on the order of microseconds for the platinum complexes.

We demonstrate that three Ir͑III͒ complexes used as principal dopants in organic electrophosphorescent diodes have very high photoluminescence quantum efficiency ͑ PL ͒ in a solid-state film. The green emitting complex, fac-tris͑2-phenylpyridinato͒iridium͑III͒ ͓Ir͑ppy͒ 3 ͔, the red-emitting bis͓2-͑2Ј-benzothienyl͒pyridinato-N , C 3 Ј͔ ͑acetylacetonato͒iridium͑III͒ ͓Btp 2 Ir͑acac͔͒, and the blue complex bis͓͑4 , 6-difluorophenyl͒pyridinato-N , C 2 ͔͑picolinato͒iridium͑III͒ ͑FIrpic͒ were prepared as codeposited films of varying concentration with 4,4 Ј-bis͑N-carbazolyl͒-2 , 2 Ј-biphenyl, a commonly used host material. The maximum PL values for Ir͑ppy͒ 3 , Btp 2 Ir͑acac͒, and FIrpic were, respectively, 97% ± 2% ͑at 1.5 mol%͒, 51% ±1% ͑at 1.4 mol%͒, and 78% ± 1% ͑at 15 mol%͒. Furthermore, we also observed that the maximum PL of FIrpic reached 99% ± 1% when doped into the high triplet energy host, m-bis͑N-carbazolyl͒benzene, at an optimal concentration of 1.2 mol%.

Solid-state self-quenching processes of highly efficient Ir(III) phosphorescent emitters are investigated by the measurement of thin film photoluminescence quantum efficiency and transient lifetime as a function of doping concentration in a host matrix. The radiative decay rate constant is found to be independent from the average distance between dopant molecules (R), and the concentration-quenching rate constant is shown to be dependent on R(-6). The quenching dependence on R strongly suggests that luminescent concentration quenching in a phosphorescent Ir(III) complex:host film is controlled by dipole-dipole deactivating interactions as described by the Förster energy transfer model.

Efficient white electrophosphorescence has been achieved with a single emissive dopant. The dopant in these white organic light emitting diodes (WOLEDs) emits simultaneously from monomer and aggregate states, leading to a broad spectrum and high quality white emission. The dopant molecules are based on a series of platinum(II) [2-(4,6-difluorophenyl)pyridinato-N,C 2 0 ] b-diketonates. All of the dopant complexes described herein have identical photophysics in dilute solution with structured blue monomer emission (l max ¼ 468, 500, 540 nm). A broad orange aggregate emission (l max % 580 nm) is also observed, when doped into OLED host materials. The intensity of the orange band increases relative to the blue monomer emission, as the doping level is increased. The ratio of monomer to aggregate emission can be controlled by the doping concentration, the degree of steric bulk on the dopant and by the choice of the host material. A doping concentration for which the monomer and excimer bands are approximately equal gives an emission spectrum closest to standard white illumination sources. WOLEDs have been fabricated with doped CBP and mCP luminescent layers (CBP ¼ N,N 0-dicarbazolyl-4,4 0-biphenyl, mCP ¼ N,N 0-dicarbazolyl-3,5-benzene). The best efficiencies and color stabilities were achieved when an electron/exciton blocking layer (EBL) is inserted into the structure, between the hole transporting layer and doped CBP or mCP layer. The material used for an EBL in these devices was fac-tris(1-phenylpyrazolato-N,C 2 0)iridium(III). The EBL material effectively prevents electrons and excitons from passing through the emissive layer into the hole transporting NPD layer. CBP based devices gave a peak external quantum efficiency of 3.3 AE 0.3% (7.3 AE 0.7 lm W À1) at 1 cd m À2 , and 2.3 AE 0.2% (5.2 AE 0.3 lm W À1) at 500 cd m À2. mCP based devices gave a peak external quantum efficiency of 6.4% (12.2 lm W À1 , 17.0 cd A À1), CIE coordinates of 0.36, 0.44 and a CRI of 67 at 1 cd m À2 (CIE ¼ Commission Internationale de l'Eclairage, CRI ¼ color rendering index). The efficiency of the mCP based device drops to 4.3 AE 0.5% (8.1 AE 0.6 lm W À1 , 11.3 cd A À1) at 500 cd m À2 , however, the CIE coordinates and CRI remain unchanged.

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