The luminescence properties of multinuclear platinum complexes

Platinum(II) complexes featuring conjugated aromatic ligands are widely studied in the context of luminescence. Many such compounds have been discovered that display intense phosphorescence from triplet excited states, offering potential applicability to numerous areas of contemporary interest, including as phosphors for light-emitting devices and imaging agents in cell biology. Aside from the large number of mononuclear Pt(II) complexes that have been reported in the context of luminescence, there are several examples of multinuclear systems – ones that incorporate two or more Pt(II) ions or Pt(II) in combination with other platinum group metal ions. The introduction of a second metal ion can lead to very different luminescence properties compared to the mononuclear analogues. This review aims to provide an overview of some of the key features of multinuclear Pt(II) complexes and their luminescence. It proves to be convenient to subdivide the examples into three classes, according to whether or not there are significant intramolecular interfacial interactions between the square-planar units. In some cases (Class A), for example with aromatic bridging ligands, the units are rigidly held apart from one another and no such intramolecular interactions are possible. In some such complexes, however, the presence of a second metal ion can nevertheless lead to very different properties compared to mononuclear analogues. In particular, recent work has shown that large red shifts in absorption and emission can be accompanied by an increase in the phosphorescence radiative rate constant, offering a way to efficient red and near-infrared emitters. In Class B, on the other hand, the planar Pt(II) units are rigidly held in a conformation that facilitates interfacial interactions. In many cases they involve overlap of Pt 5dz2 and 6pz orbitals, leading to the generation of low-energy 3MMLCT excited states similar to those seen in aggregates of mononuclear Pt(II) complexes. Finally, complexes in Class C – of which there are very many and we cover only a selection of examples – are those in which there is some flexibility in the linkers between the Pt(II) units. They may display dual emission both from excited states that resemble those of the isolated units, and from lower-energy excited states similar to aggregates or excimers, owing to the ability of the Pt(II) moieties to approach one another in the appropriate conformation

Mono and dinuclear iridium(iii) complexes featuring bis-tridentate coordination and Schiff-base bridging ligands: the beneficial effect of a second metal ion on luminescence

The synthesis and photophysical properties of a set of iridium(III) complexes featuring tridentate N^N^O-coordinating ligands are described, of generic structure [Ir(N^C^N-dpyx)(N^N^O-Ln)]+ (n = 1 to 4) (dpyx = 1,3-dipyridyl-4,6-dimethylbenzene). The proligands HLn are Schiff bases synthesised by condensation of salicylaldehydes with N-methyl-hydrazinopyridines: they are able to coordinate to the Ir(III) via lateral pyridine-N and phenolate-O− atoms and a central hydrazone-N atom; the four examples differ in the substitution pattern within the phenolate ring. The bis-tridentate coordination is confirmed by X-ray diffraction. The complexes are phosphorescent in solution at ambient temperature, with higher quantum yields and longer lifetimes than those of structurally related bis-cyclometallated complexes with an N^N^C-coordinating ligand. Related proligands H2L5 and H2L6 have been prepared from 4,6-bis(1-methyl-hydrazino)pyrimidine. They feature a central pyrimidine and two N^N^O units. They are shown to bind as ditopic, bis-tridentate ligands with two iridium(III) ions, leading to unprecedented dinuclear complexes of the form [{Ir(N^C^N)}2(O^N^N–N^N^O-Ln)]2+ (n = 5, 6; N^C^N = dpyx or 1,3-dipyridyl-4,6-difluoro-benzene), with an intramolecular Ir⋯Ir distance of around 6 Å determined crystallographically. Mononuclear analogues [Ir(N^C^N-dpyx)(N^N^O-HLn)]+ have also been isolated. The dinuclear complexes display a well-defined and unusually intense lowest-energy absorption band in the visible region, around 480 nm. They emit much more efficiently than their mononuclear counterparts, even though the emission wavelengths are comparable. Their superior performance appears to be due to an enhancement in the radiative rate constant, affirming conclusions drawn from recent related studies of dinuclear Ir(III) and Pt(II) complexes with ditopic, pyrimidine-based cyclometallating ligands

Platinum(II) Complexes of Tridentate ‐Coordinating Ligands Based on Imides, Amides, and Hydrazides: Synthesis and Luminescence Properties

Five Pt(II) complexes are described in which the metal ion is bound to anionic urn:x-wiley:14341948:media:ejic202000879:ejic202000879-math-0003 ‐coordinating ligands. The central, deprotonated N atom is derived from an imide Ar−C(=O)−NH−C(=O)−Ar {PtL1–2Cl; Ar=pyridine or pyrimidine}, an amide py−C(=O)−NH−CH2−py {PtL3Cl}, or a hydrazide py−C(=O)−NH−N=CH−py {PtL4Cl}. The imide complexes PtL1–2Cl show no significant emission in solution but are modestly bright green/yellow phosphors in the solid state. PtL3Cl is weakly phosphorescent. PtL4Cl is formed as a mixture of isomers, bound through either the amido or imino nitrogen, the latter converting to the former upon absorption of light. Remarkably, the imino form displays fluorescence in solution, λ0,0=535 nm, whereas the amido shows phosphorescence, λ0,0=624 nm, τ=440 ns. It is highly unusual for two isomeric compounds to display emission from states of different spin multiplicity. The amido‐bound PtL4Cl can act as a bidentate urn:x-wiley:14341948:media:ejic202000879:ejic202000879-math-0004 ‐coordinating ligand, demonstrated by the formation of bimetallic complexes with iridium(III) or ruthenium(II)

Die Faktorenanalyse als Instrument der empirischen Regionalforschung Eine kritische Einfuehrung in ein statistisches Verfahren

SIGLETIB: RN 4768 (59) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Enantiopure cycloplatinated pentahelicenic N-heterocyclic carbenic complexes that display long-lived circularly polarized phosphorescence

The preparation of the first enantiopure cycloplatinated complexes bearing a bidentate, helicenic N-heterocyclic carbene and a diketonate ancillary ligand is presented, along with their structural and spectroscopic characterization based on both experimental and computational studies. The systems exhibit long-lived circularly polarized phosphorescence in solution and in doped films at room temperature, and also in a frozen glass at 77 K, with dissymmetry factor glum values ≥10−3 in the former and around 10−2 in the latter

A Series of [Co(Mabiq)Cl_2–<i>n</i>] (<i>n</i> = 0, 1, 2) Compounds and Evidence for the Elusive Bimetallic Form

The synthesis and characterization of a series of cobalt compounds, coordinated by the redox-active macrocyclic biquinazoline ligand, Mabiq [2–4:6–8-bis­(3,3,4,4-tetramethyldihydropyrrolo)-10–15-(2,2′-biquinazolino)-[15]-1,3,5,8,10,14-hexaene-1,3,7,9,11,14-N₆], is presented. The series includes the monometallic Co­(Mabiq)­Cl₂ (<b>1</b>), Co­(Mabiq)Cl (<b>2</b>), and Co­(Mabiq) (<b>4</b>), with formal metal oxidation states of 3+ → 1+. A binuclear cobaltous compound, Co₂(Mabiq)­Cl₃ (<b>3</b>), also was obtained, providing the first evidence for the ability of the Mabiq ligand to coordinate two metal ions. The electronic structures of the paramagnetic <b>2</b> and <b>3</b> were examined by electron paramagnetic resonance spectroscopy and magnetic susceptibility studies. The Co^II ion that resides in the N₄-macrocylic cavity of <b>2</b> and <b>3</b> adopts a low-spin <i>S</i> = ¹/₂ configuration. The bypirimidine functionality in <b>3</b> additionally coordinates a high-spin <i>S</i> = ³/₂ cobaltous ion in a tetrahedral environment. The two metal ions in <b>3</b> are weakly coupled by magnetometry. The square-planar, low-valent <b>4</b> offers one of a limited number of examples of structurally characterized N₄-macrocyclic Co^I compounds. Spectroscopic and density functional theory computational data suggest that a Co^II(Mabiq^•) description may be a reasonable alternative to the Co^I formalism for this compound

An external quantum efficiency of &gt;20% from solution-processed poly(dendrimer) organic light-emitting diodes

Controlling the orientation of the emissive dipole has led to a renaissance of organic light-emitting diode (OLED) research, with external quantum efficiencies (EQEs) of >30% being reported for phosphorescent emitters. These highly efficient OLEDs are generally manufactured using evaporative methods and are comprised of small-molecule heteroleptic phosphorescent iridium(III) complexes blended with a host and additional layers to balance charge injection and transport. Large area OLEDs for lighting and display applications would benefit from low-cost solution processing, provided that high EQEs could be achieved. Here, we show that poly(dendrimer)s consisting of a non-conjugated polymer backbone with iridium(III) complexes forming the cores of first-generation dendrimer side chains can be co-deposited with a host by solution processing to give highly efficient devices. Simple bilayer devices comprising the emissive layer and an electron transport layer gave an EQE of >20% at luminances of up to ≈300 cd/m, showing that polymer engineering can enable alignment of the emissive dipole of solution-processed phosphorescent materials