Dinuclear Cyclometalated Pincer Nickel(II) Complexes with Metal-Metal-to-Ligand Charge Transfer Excited States and Near-Infrared Emission.

Facile non-radiative decay of low-lying metal-centered (MC) dd excited states has been well documented to pose a significant obstacle to the development of phosphorescent Ni complexes due to substantial structural distortions between the dd excited state and the ground state. Herein, we prepared a series of dinuclear Ni complexes by using strong σ-donating carbene-phenyl-carbene (C C C) pincer ligands, and prepared their dinuclear Pt and Pd analogues. Dinuclear Ni complexes bridged by formamidinate/α-carbolinato ligand exhibit short Ni-Ni distances of 2.

Chiral Iron Porphyrins Catalyze Enantioselective Intramolecular C(sp )-H Bond Amination Upon Visible-Light Irradiation.

Iron-catalyzed asymmetric amination of C(sp )-H bonds is appealing for synthetic applications due to the biocompatibility and high earth abundance of iron, but examples of such reactions are sparse. Herein we describe chiral iron complexes of meso- and β-substituted-porphyrins that can catalyze asymmetric intramolecular C(sp )-H amination of aryl and arylsulfonyl azides to afford chiral indolines (29 examples) and benzofused cyclic sulfonamides (17 examples), respectively, with up to 93 % ee (yield: up to 99 %) using 410 nm light under mild conditions. Mechanistic studies, including DFT calculations, for the reactions of arylsulfonyl azides reveal that the Fe(NSO Ar) intermediate generated in situ under photochemical conditions reacts with the C(sp )-H bond through a stepwise hydrogen atom transfer/radical rebound mechanism, with enantioselectivity arising from cooperative noncovalent interactions between the Fe(NSO Ar) unit and the peripheral substituents of the chiral porphyrin scaffold.

Oxidative C-O bond cleavage of dihydroxybenzenes and conversion of coordinated cyanide to carbon monoxide using a luminescent Os(VI) cyanonitrido complex.

The photoreactions of a luminescent osmium(VI) nitrido complex, [Os(N)(L)(CN)] (OsN, HL = 2-(2-hydroxy-5-nitrophenyl)benzoxazole), with catechol (HCat) and hydroquinone (HQ) lead to the cleavage of strong C-OH bonds ( 120 kcal mol) of the dihydroxybenzenes with concomitant conversion of the coordinated cyanide to carbon monoxide.

Conformational Engineering of Two-Coordinate Gold(I) Complexes: Regulation of Excited-State Dynamics for Efficient Delayed Fluorescence.

Carbene-Au-amide (CMA) type complexes, in which the amide and carbene ligands act as an electron donor (D) and acceptor (A), respectively, can exhibit strong delayed fluorescence (DF) from a ligand to ligand charge transfer (LLCT) excited state. Although the coplanar donor-acceptor (D-A) conformation has been suggested to be a crucial factor favoring radiative decay of the charge-transfer excited state, the geometric structural factor underpinning the excited-state mechanism of CMA complexes remains an open question. We herein develop a new class of carbene-Au-carbazolate complexes by introducing large aromatic substituents onto the carbazolate ligand, the presence of which are conceived to restrict the rotation of the Au-N bond and thus confine a twisted D-A conformation in both ground and excited states.

Self-Assembly of Molecular Trefoil Knots Featuring Pentadecanuclear Homoleptic Au -, Au /Ag -, or Au /Cu -Alkynyl Coordination.

Metal-free and metal-containing molecular trefoil knots are fascinating ensembles that are usually covalently assembled, the latter requiring the rational design of di- or multidentate/multipodal ligands as connectors. In this work, we describe the self-assembly of pentadecanuclear Au trefoil knots [Au (C≡CR) ] from monoalkynes HC≡CR (R=9,9-X -fluorenyl with X=nBu, n-hexyl) and [Au (THT)Cl]. Hetero-bimetallic counterparts [Au M (C≡CR) ] (M=Cu/Ag) were self-assembled by reactions of [Au (C≡CR) ] with [Cu(MeCN) ] /AgNO and HC≡CR.

Direct photo-induced reductive Heck cyclization of indoles for the efficient preparation of polycyclic indolinyl compounds.

The photo-induced cleavage of C(sp)-Cl bonds is an appealing synthetic tool in organic synthesis, but usually requires the use of high UV light, photocatalysts and/or photosensitizers. Herein is described a direct photo-induced chloroarene activation with UVA/blue LEDs that can be used in the reductive Heck cyclization of indoles and without the use of a photocatalyst or photosensitizer. The indole compounds examined display room-temperature phosphorescence.

Highly Efficient Thermally Activated Delayed Fluorescence from Pyrazine-Fused Carbene Au(I) Emitters.

Metal-based thermally activated delayed fluorescence (TADF) is conceived to inherit the advantages of both phosphorescent metal complexes and purely organic TADF compounds for high-performance electroluminescence. Herein a panel of new TADF Au(I) emitters has been designed and synthesized by using carbazole and pyrazine-fused nitrogen-heterocyclic carbene (NHC) as the donor and acceptor ligands, respectively. Single-crystal X-ray structures show linear molecular shape and coplanar arrangement of the donor and acceptor with small dihedral angles of <6.

Strong metal-metal Pauli repulsion leads to repulsive metallophilicity in closed-shell d and d organometallic complexes.

Metallophilicity is defined as the interaction among closed-shell metal centers, the origin of which remains controversial, particularly for the roles of spd orbital hybridization (mixing of the spd atomic orbitals of the metal atom in the molecular orbitals of metal complex) and the relativistic effect. Our studies reveal that at close M-M' distances in the X-ray crystal structures of d and d organometallic complexes, M-M' closed-shell interactions are repulsive in nature due to strong M-M' Pauli repulsion. The relativistic effect facilitates (n + 1)s-nd and (n + 1)p-nd orbital hybridization of the metal atom, where (n + 1)s-nd hybridization induces strong M-M' Pauli repulsion and repulsive M-M' orbital interaction, and (n + 1)p-nd hybridization suppresses M-M' Pauli repulsion.

Stable, High-Efficiency Voltage-Dependent Color-Tunable Organic Light-Emitting Diodes with a Single Tetradentate Platinum(II) Emitter Having Long Operational Lifetime.

Voltage-dependent, color-tunable organic light-emitting diodes (OLEDs) are appealing tools that can be used for the visualization of electronic output signal of sensors. Nonetheless, the literature-reported color-tunable OLEDs that have a simple single-cell device structure suffer from relatively low efficiency, pronounced efficiency roll-off, color-aging, and short operation lifetime, all of which limit their practical applications. Here, a novel co-host-in-double-emissive-layer (CHIDEL) device, designed to enhance the performance of color-tunable OLEDs with the use of a single tetradentate Pt[O N C N] emitter, is described.

C-H Activation by an Iron-Nitrido Bis-Pocket Porphyrin Species.

High-valent iron-nitrido species are nitrogen analogues of iron-oxo species which are versatile reagents for C-H oxidation. Nonetheless, C-H activation by iron-nitrido species has been scarcely explored, as this is often hampered by their instability and short lifetime in solutions. Herein, the hydrogen atom transfer (HAT) reactivity of an Fe porphyrin nitrido species (2 c) toward C-H substrates was studied in solutions at room temperature, which was achieved by nanosecond laser flash photolysis (LFP) of its Fe -azido precursor (1 c) supported by a bulky bis-pocket porphyrin ligand.

Luminescent tungsten(vi) complexes as photocatalysts for light-driven C-C and C-B bond formation reactions.

The realization of photocatalysis for practical synthetic application hinges on the development of inexpensive photocatalysts which can be prepared on a large scale. Herein an air-stable, visible-light-absorbing photoluminescent tungsten(vi) complex which can be conveniently prepared at the gram-scale is described. This complex could catalyse photochemical organic transformation reactions including borylation of aryl halides, such as aryl chloride, reductive coupling of benzyl bromides for C-C bond formation, reductive coupling of phenacyl bromides, and decarboxylative coupling of redox-active esters of alkyl carboxylic acid with high product yields and broad functional group tolerance.

Recent Advances in Metal-TADF Emitters and Their Application in Organic Light-Emitting Diodes.

In this contribution, recent advances in new classes of efficient metal-TADF complexes, especially those of Au(I), Au(III), and W(VI), and their application in OLEDs are reviewed. The high performance (EQE = 25%) and long device operational lifetime (LT = 5,280 h) achieved in an OLED with tetradentate Au(III) TADF emitter reflect the competitiveness of this class of emitters for use in OLEDs with practical interest. The high EQE of 15.

Iron porphyrin catalysed light driven C-H bond amination and alkene aziridination with organic azides.

Visible light driven nitrene transfer and insertion reactions of organic azides are an attractive strategy for the design of C-N bond formation reactions under mild reaction conditions, the challenge being lack of selectivity as a free nitrene reactive intermediate is usually involved. Herein is described an iron(iii) porphyrin catalysed sp C-H amination and alkene aziridination with selectivity by using organic azides as the nitrogen source under blue LED light (469 nm) irradiation. The photochemical reactions display chemo- and regio-selectivity and are effective for the late-stage functionalization of natural and bioactive compounds with complexity.

Controlling Metallophilic Interactions in Chiral Gold(I) Double Salts towards Excitation Wavelength-Tunable Circularly Polarized Luminescence.

Materials exhibiting excitation wavelength-dependent photoluminescence (Ex-De PL) in the visible region have potential applications in bioimaging, optoelectronics and anti-counterfeiting. Two multifunctional, chiral [Au(NHC) ][Au(CN) ] (NHC=(4R,5R)/(4S,5S)-1,3-dimethyl-4,5-diphenyl-4,5-dihydro-imidazolin-2-ylidene) complex double salts display Ex-De circularly polarized luminescence (CPL) in doped polymer films and in ground powder. Emission maxima can be dynamically tuned from 440 to 530 nm by changing the excitation wavelength.

Tetradentate Gold(III) Complexes as Thermally Activated Delayed Fluorescence (TADF) Emitters: Microwave-Assisted Synthesis and High-Performance OLEDs with Long Operational Lifetime.

Structurally robust tetradentate gold(III)-emitters have potent material applications but are rare and unprecedented for those displaying thermally activated delayed fluorescence (TADF). Herein, a novel synthetic route leading to the preparation of highly emissive, charge-neutral tetradentate [C^C^N^C] gold(III) complexes with 5-5-6-membered chelate rings has been developed through microwave-assisted C-H bond activation. These complexes show high thermal stability and with emission origin ( IL, ILCT, and TADF) tuned by varying the substituents of the C^C^N^C ligand.

High-Efficiency Solution-Processed Organic Light-Emitting Diodes with Tetradentate Platinum(II) Emitters.

The realization of high-efficiency solution-processed organic light-emitting diodes (OLEDs) using phosphorescent tetradentate Pt(II) emitters and bipolar organic hosts is demonstrated in this work. To investigate the effect of organic host on the platinum dopant, the performances of solution-processed Pt-OLEDs with various combinations between four tetradentate Pt(II) emitters, including two newly developed and and three bipolar organic hosts , , and , have been analyzed and compared. Among the tetradentate Pt(II) complexes studied in this work, exhibited the best electroluminescent performance attributable to its bulky molecular scaffold structure, high emission quantum yield, and good solubility in common organic solvents.

Thermally Stable Donor-Acceptor Type (Alkynyl)Gold(III) TADF Emitters Achieved EQEs and Luminance of up to 23.4% and 70 300 cd m in Vacuum-Deposited OLEDs.

Thermally stable, strongly luminescent gold-TADF emitters are the clue to realize practical applications of gold metal in next generation display and lighting technology, a scarce example of which is herein described. A series of donor-acceptor type cyclometalated gold(III) alkynyl complexes with some of them displaying highly efficient thermally activated delayed fluorescence (TADF) with Φ up to 88% in thin films and emission lifetimes of ≈1-2 µs at room temperature are developed. The emission color of these complexes is readily tunable from green to red by varying the donor unit and cyclometalating ligand.

Efficient acceptorless photo-dehydrogenation of alcohols and -heterocycles with binuclear platinum(ii) diphosphite complexes.

Although photoredox catalysis employing Ru(ii) and Ir(iii) complexes as photocatalysts has emerged as a versatile tool for oxidative C-H functionalization under mild conditions, the need for additional reagents acting as electron donor/scavenger for completing the catalytic cycle undermines the practicability of this approach. Herein we demonstrate that photo-induced oxidative C-H functionalization can be catalysed with high product yields under oxygen-free and acceptorless conditions inner-sphere atom abstraction by binuclear platinum(ii) diphosphite complexes. Both alcohols (51 examples), particularly the aliphatic ones, and saturated -heterocycles (24 examples) can be efficiently dehydrogenated under light irradiation at room temperature.

Visible-Light-Promoted Transition-Metal-Free Phosphinylation of Heteroaryl Halides in the Presence of Potassium tert-Butoxide.

A novel visible-light-promoted C-P bond formation reaction in the absence of both transition metal and photoredox catalysts is disclosed. By employing easily available and inexpensive heteroaryl chlorides/bromides as substrates, a variety of heteroaryl phosphine oxides were obtained in moderate to good yields. This strategy provides a simple and efficient route to heteroaryl phosphine oxides.

Counteranion- and Solvent-Mediated Chirality Transfer in the Supramolecular Polymerization of Luminescent Platinum(II) Complexes.

The chirality of supramolecular polymeric materials is subtly affected by a delicate balance among various non-covalent interactions, the details of which are inadequately understood. Now, a fine balance of intermolecular interactions, including closed-shell metal-metal, dispersive and electrostatic interactions, is used to direct the delicate orientation of monomeric building blocks, thereby achieving the successful preparation of different nanostructures with distinct supramolecular chirality. Moreover, kinetically trapped and thermodynamically stable aggregates were monitored over time in the supramolecular polymerization of cationic Pt complexes.

Metal-organic framework composites with luminescent pincer platinum(ii) complexes: MMLCT emission and photoinduced dehydrogenation catalysis.

Pincer platinum(ii) complexes are well documented to exhibit weak intermolecular interactions in the solid state and 77 K glassy solutions, leading to emissive triplet metal-metal-to-ligand charge transfer (MMLCT) excited states that often vanish in dilute solutions. In this work, metal-organic framework (MOF) materials are introduced to provide a "solid solution" environment for easy access to MMLCT excited states of pincer platinum(ii) complexes. Phosphorescent composites Pt@MOFs () with matrix-dependent monomers and oligomer emission properties were obtained.

The Metal-Metal-to-Ligand Charge Transfer Excited State and Supramolecular Polymerization of Luminescent Pincer Pd -Isocyanide Complexes.

Pincer Pd -isocyanide complexes are described that display intermolecular interactions and emissive MMLCT excited states in aggregation state(s) at room temperature. The intermolecular Pd -Pd and ligand-ligand interactions drive these complexes to undergo supramolecular polymerization in a living manner. Comprehensive spectroscopic studies reveal a pathway with a kinetic trap that can be modulated by changing the counteranion and metal atom.

Highly Luminescent Pincer Gold(III) Aryl Emitters: Thermally Activated Delayed Fluorescence and Solution-Processed OLEDs.

Herein are described the synthesis, photophysical properties and applications of a series of luminescent cyclometalated Au complexes having an auxiliary aryl ligand. These complexes show photoluminescence with emission quantum yields of up to 0.79 in solution and 0.

The interplay between fluorescence and phosphorescence with luminescent gold(i) and gold(iii) complexes bearing heterocyclic arylacetylide ligands.

The photophysical properties of a series of gold(i) [LAu(C[triple bond, length as m-dash]CR)] (L = PCy (), RNC (), NHC ()) and gold(iii) complexes [Au(C^N^C)(C[triple bond, length as m-dash]CR)] () bearing heterocyclic arylacetylide ligands with narrow band-gap are compared. The luminescence of both series are derived from an intraligand transition localized on the arylacetylide ligand (ππ*(C[triple bond, length as m-dash]CR)) but displayed prompt fluorescence ( = 2.7-12.