Ru(II) polypyridine complexes: photophysics, photochemistry, eletrochemistry, and chemiluminescence

Before the 1960s, all anti-Stokes emissions, which were known to exist, involved emission energies in excess of excitation energies by only a few kT. They were linked to thermal population of energy states above excitation states by such an energy amount. It was the well-known case of anti-Stokes emission for the so-called thermal bands or in the Raman effect for the well-known anti-Stokes sidebands. Thermoluminescence, where traps are emptied by excitation energies of the order of kT, also constituted a field of anti-Stokes emission of its own. Superexcitation, i.e., raising an already excited electron to an even higher level by excited-state absorption (ESA), was also known but with very weak emissions. These types of well-known anti-Stokes processes have been reviewed in classical textbooks on luminescence.1 All fluorescence light emitters usually follow the well-known principle of the Stokes law which simply states that excitation photons are at a higher energy than emitted ones or, in other words, that output photon energy is weaker than input photon energy. This, in a sense, is an indirect statement that efficiency cannot be larger than 1. This principle is

Upconversion and Anti-Stokes Processes with f and d Ions in Solids

We describe the performance of an organic light-emitting device employing the green electrophosphorescent material, fac tris(2-phenylpyridine) iridium [Ir(ppy)3] doped into a 4,4′-N,N′-dicarbazole-biphenyl host. These devices exhibit peak external quantum and power efficiencies of 8.0% (28 cd/A) and 31 lm/W, respectively. At 100 cd/m2, the external quantum and power efficiencies are 7.5% (26 cd/A) and 19 lm/W at an operating voltage of 4.3 V. This performance can be explained by efficient transfer of both singlet and triplet excited states in the host to Ir(ppy)3, leading to a high internal efficiency. In addition, the short phosphorescent decay time of Ir(ppy)3 (<1 μs) reduces saturation of the phosphor at high drive currents, yielding a peak luminance of 100 000 cd/m2.

Very high-efficiency green organic light-emitting devices based on electrophosphorescence

The synthesis and photophysical study of a family of cyclometalated iridium(III) complexes are reported. The iridium complexes have two cyclometalated (C∧N) ligands and a single monoanionic, bidentate ancillary ligand (LX), i.e., C∧N2Ir(LX). The C∧N ligands can be any of a wide variety of organometallic ligands. The LX ligands used for this study were all β-diketonates, with the major emphasis placed on acetylacetonate (acac) complexes. The majority of the C∧N2Ir(acac) complexes phosphoresce with high quantum efficiencies (solution quantum yields, 0.1−0.6), and microsecond lifetimes (e.g., 1−14 μs). The strongly allowed phosphorescence in these complexes is the result of significant spin−orbit coupling of the Ir center. The lowest energy (emissive) excited state in these C∧N2Ir(acac) complexes is a mixture of 3MLCT and 3(π−π*) states. By choosing the appropriate C∧N ligand, C∧N2Ir(acac) complexes can be prepared which emit in any color from green to red. Simple, systematic changes in the C∧N ligands, whic...

Highly phosphorescent bis-cyclometalated iridium complexes: synthesis, photophysical characterization, and use in organic light emitting diodes.

Photophysics, photochemistry and solar energy conversion with tris(bipyridyl)ruthenium(II) and its analogues

The synthesis of the facial tris cyclometalated complexes fac-[Rh(ppy) 3 ] (ppyH=2-phenylpyridine), fac-[Ir-(ppy) 3 ], and fac-[Ir(thpy) 3 ] (thpyH=2-(2-thienyl)pyridine) by a generalized method is described. The conformation of the complexes is discussed on the basis of the 1 H NMR spectra, and for fac-[Ir(thpy) 3 ] the room-temperature crystal structure is presented: chemical formula C 27 H 18 N 3 S 3 Ir, cubic, space group Pa3, Z=8, a=16.872(4) A, V=4803(3) A 3 . The excited-state properties are investigated by absorption, luminescence, and luminescence line-narrowing spectroscopy in different media

Facial tris cyclometalated rhodium(3+) and iridium(3+) complexes: their synthesis, structure, and optical spectroscopic properties

The well-resolved absorption, excitation, and luminescence spectra of [Ir(ppy)2bpy]+ (ppyH = 2-phenylpyridine, bpy = 2,2'-bipyridine) in different media at cryogenic temperatures are presented. In solutions and glasses at ambient temperature the lowest energy excited state corresponds to an Ir - bpy charge-transfer excitation whereas in the crystalline host lattice [Rh(ppy)2bpy]PF6 the lowest excited state at 21 450 cm-1 is assigned to a 37r-r* excitation localized on the cyclometalating ppy- ligands. The next higher excited Ir - bpy charge-transfer state has shifted to 21 820 cm-', only 300 cm-I above the 3LC excited state. The close proximity of the 3LC and 3MLCT excited states and the large spin-orbit coupling constant of Ir3+ induce a strong mixing of charge-transfer character into the 3LC lowest excited states, resulting in increased oscillator strengths, reduced lifetimes, short axis polarized transitions, and a large zero-field splitting of 10-15 cm-1.

Evidence for strong mixing between the LC and MLCT excited states in bis(2-phenylpyridinato-C2,N')(2,2'-bipyridine)iridium(III)

The synthesis and high-resolution absorption and luminescence spectra at cryogenic temperatures of [Ir(thpy)[sub 2]bpy][sup +](thpyH = 2-(2-thienyl)pyridine, bpy = 2, 2'-bipyridine) are reported. In the crystalline host lattices [Rh(ppy)[sub 2]bpy]-PF[sub 6] and [Ir(ppy)[sub 2]bpy]PF[sub 6](ppyH = 2-phenylpyridine) the lowest excited states around 18,900 cm[sup [minus]1] correspond to spin-forbidden [sup 3][pi]-[pi]* transitions on the thpy[minus], whereas the next higher excited state is assigned to an Ir [yields] bpy charge-transfer transition at 21,700 cm[sup [minus]1]. This metal to ligand charge-transfer ([sup 3]MLCT) state is found to be strongly dependent on the surroundings. In liquid environments it can shift below the [sup 3][pi]-[pi]* state, which remains at about the same energy. Evidence for a mixing of charge-transfer character into the [sup 3][pi]-[pi]* excited states is provided by the measured oscillator strengths, the luminescence lifetimes, the vibronic structure, and by a comparison with the properties of analogous cyclometalated Rh[sup 3+] complexes.

Hans U. Guedel

Papers

Facial tris cyclometalated rhodium(3+) and iridium(3+) complexes: their synthesis, structure, and optical spectroscopic properties

Evidence for strong mixing between the LC and MLCT excited states in bis(2-phenylpyridinato-C2,N')(2,2'-bipyridine)iridium(III)

Synthesis and high-resolution optical spectroscopy of bis[2-(2-thienyl)pyridinato-C3,N'](2,2'-bipyridine)iridium(III)

The electronic spectrum of tris(2,2'-bipyridine)ruthenium(2+)

The electronic spectrum of tris(2,2'-bipyridine)iron(2+) and tris (2,2'-bipyridine)osmium(2+)