Vonika Ka-Man Au

High-efficiency green organic light-emitting devices utilizing phosphorescent bis-cyclometalated alkynylgold(III) complexes

A new phosphorescent material of cyclometalated alkynylgold(III) complex, [Au(2,5-F(2)C(6)H(3)-C∧N∧C)(C≡C-C(6)H(4)N(C(6)H(5))(2)-p)] (1) (2,5-F(2)C(6)H(3)-HC∧N∧CH = 2,6-diphenyl-4-(2,5-difluorophenyl)pyridine), has been synthesized, characterized, and its device performance investigated. This luminescent gold(III) complex was found to exhibit rich PL and EL properties and has been utilized as phosphorescent dopants of OLEDs. At an optimized dopant concentration of 4%, a device with a maximum external quantum efficiency (EQE) of 11.5%, corresponding to a current efficiency of 37.4 cd/A and a power efficiency of 26.2 lm/W, has been obtained. Such a high EQE is comparable to that of Ir(ppy)(3)-based devices. The present work suggests that the alkynylgold(III) complex is a promising phosphorescent material in terms of both efficiency and thermal stability, with the additional advantages of its relatively inexpensive cost and low toxicity.

Luminescent Cyclometalated N-Heterocyclic Carbene-Containing Organogold(III) Complexes: Synthesis, Characterization, Electrochemistry, and Photophysical Studies

A new class of luminescent mononuclear and dinuclear N-heterocyclic carbene-containing gold(III) complexes has been synthesized and characterized. The X-ray crystal structures of most of the complexes have also been determined. Electrochemical studies reveal a ligand-centered reduction originated from the RC--N--CR moieties with no oxidation waves. Interestingly, one of the dinuclear complexes exhibited two distinct reduction couples instead of one with the first reduction occurring at less cathodic potential, probably related to the splitting of the pi* orbital-based LUMO resulting from intramolecular pi-pi interaction. The electronic absorption and luminescence behaviors of the complexes have also been investigated. In dichloromethane solution at room temperature, the low-energy absorption bands are assigned as the intraligand pi-pi* transition, with mixing of a charge transfer character from the aryl ring to the pyridine moiety of the cyclometalating RC--N--CR ligand. The low-energy emission bands are ascribed to origins mainly derived from the intraligand pi-pi* states with an aryl to pyridine charge transfer character of the cyclometalating RC--N--CR ligand.

Luminescent Cyclometalated Dialkynylgold(III) Complexes of 2‐Phenylpyridine‐Type Derivatives with Readily Tunable Emission Properties

A novel class of luminescent dialkynylgold(III) complexes containing various phenylpyridine and phenylisoquinoline-type bidentate ligands has been successfully synthesized and characterized. The structures of some of them have also been determined by X-ray crystallography. Electrochemical studies demonstrate the presence of a ligand-centered reduction originating from the cyclometalating C^N ligand, whereas the first oxidation wave is associated with an alkynyl ligand-centered oxidation. The electronic absorption and photoluminescence properties of the complexes have also been investigated. In dichloromethane solution at room temperature, the low-energy absorption bands are assigned as the metal-perturbed π-π* intraligand (IL) transition of the cyclometalating C^N ligand, with mixing of charge-transfer character from the aryl ring to the pyridine or isoquinoline moieties of the cyclometalating C^N ligand. The low-energy emission bands of the complexes in fluid solution at room temperature are ascribed to originate from the metal-perturbed π-π* IL transition of the cyclometalatng C^N ligand. For complex 4 that contains an electron-rich amino substituent on the alkynyl ligand, a structureless emission band, instead of one with vibronic structures as in the other complexes, was observed, which was assigned as being derived from an excited state of a [π(C≡CC(6) H(4) NH(2) )→π*(C^N)] ligand-to-ligand charge-transfer (LLCT) transition.

Organic Memory Devices Based on a Bis-Cyclometalated Alkynylgold(III) Complex

A bis-cyclometalated alkynylgold(III) complex, [Au((t)BuC^N^C(t)Bu)(C≡C-C6H4N(C6H5)2-p)] ((t)BuHC^N^CH(t)Bu = 2,6-bis(4-tert-butylphenyl)pyridine), has been synthesized and characterized. The complex was found to exhibit rich photophysical and electrochemical properties. More interestingly, the complex has been employed in the fabrication of organic memory devices. The as-fabricated memory devices exhibited good performances with low operating voltage, high ON/OFF ratio, long retention time, and good stability.

Luminescent metallogels of bis-cyclometalated alkynylgold(III) complexes

A series of luminescent bis-cyclometalated alkynylgold(III) complexes have been synthesized and characterized. Some of the complexes have been demonstrated to exhibit gelation properties driven by π-π stacking and hydrophobic-hydrophobic interactions. The gelation properties have been investigated in detail through variable-temperature UV-vis absorption and emission studies, and the morphology of the gels has also been characterized by scanning electron microscopy and transmission electron microscopy.

Luminescence Color Switching of Supramolecular Assemblies of Discrete Molecular Decanuclear Gold(I) Sulfido Complexes

Significance Polynuclear gold(I) complexes have attracted enormous attention over the past decades owing to their intriguing luminescence behavior and their interesting structural and bonding properties, especially with regard to their propensity to form noncovalent short gold–gold contacts. Most works in polynuclear gold(I) clusters involve structural studies in the solid state, with less attention focused on supramolecular assembly in solution. Herein, discrete decanuclear gold(I) μ3-sulfido complexes with long alkyl chains are found to form supramolecular assemblies with different luminescence and morphologies that are tunable by solvent modulation. This has demonstrated the importance of the control and manipulation of intercluster assembly in influencing the photophysical properties and morphologies of the clusters. Such findings have not been previously reported in discrete molecular gold(I) systems. A series of discrete decanuclear gold(I) μ3-sulfido complexes with alkyl chains of various lengths on the aminodiphosphine ligands, [Au10{Ph2PN(CnH2n+1)PPh2}4(μ3-S)4](ClO4)2, has been synthesized and characterized. These complexes have been shown to form supramolecular nanoaggregate assemblies upon solvent modulation. The photoluminescence (PL) colors of the nanoaggregates can be switched from green to yellow to red by varying the solvent systems from which they are formed. The PL color variation was investigated and correlated with the nanostructured morphological transformation from the spherical shape to the cube as observed by transmission electron microscopy and scanning electron microscopy. Such variations in PL colors have not been observed in their analogous complexes with short alkyl chains, suggesting that the long alkyl chains would play a key role in governing the supramolecular nanoaggregate assembly and the emission properties of the decanuclear gold(I) sulfido complexes. The long hydrophobic alkyl chains are believed to induce the formation of supramolecular nanoaggregate assemblies with different morphologies and packing densities under different solvent systems, leading to a change in the extent of Au(I)–Au(I) interactions, rigidity, and emission properties.

Electrogenerated chemiluminescence of a bis-cyclometalated alkynylgold(iii) complex with irreversible oxidation using tri-n-propylamine as co-reactant.

Intense electrogenerated chemiluminescence of a bis-cyclometalated alkynylgold(iii) complex using tri-n-propylamine as a co-reactant at the fluorosurfactant-modified gold electrode has been observed for the first time.

Förster Resonance Energy Transfer Studies of Luminescent Gold Nanoparticles Functionalized with Ruthenium(II) and Rhenium(I) Complexes: Modulation via Esterase Hydrolysis

A number of ruthenium(II) and rhenium(I) bipyridine complexes functionalized with lipoic acid moieties have been synthesized and characterized. Functionalization of gold nanoparticles with these chromophoric ruthenium(II) and rhenium(I) complexes has resulted in interesting supramolecular assemblies with Förster resonance energy transfer (FRET) properties that could be modulated via esterase hydrolysis. The luminescence of the metal complex chromophores was turned on upon cleavage of the ester bond linkage by esterase to reduce the efficiency of FRET quenching. The prepared nanoassembly conjugates have been characterized by transmission electron microscopy (TEM), energy-dispersive X-ray analysis (EDX), Fourier transform infrared spectroscopy (FTIR), dynamic light scattering (DLS), UV-visible spectroscopy, and emission spectroscopy. The quenching mechanism has also been studied by transient absorption and time-resolved emission decay measurements. The FRET efficiencies were found to vary with the nature of the chromophores and the length of the spacer between the donor (transition metal complexes) and the acceptor (gold nanoparticles).

Synthesis, characterization and spectroscopic studies of luminescent L-valine modified alkynyl-based cyclometalated gold(III) complexes with gelation properties driven by π–π stacking, hydrogen bonding and hydrophobic–hydrophobic interactions

A series of luminescent L-valine modified alkynyl-based cyclometalated gold(III) complexes are synthesized and characterized. Through a balance of π–π stacking, hydrogen bonding and hydrophobic–hydrophobic interactions, organogelation of the gold(III) complexes is achieved in DMSO. The gelation properties of the complexes have been studied using scanning electron microscopy, transmission electron microscopy, X-ray powder diffraction, variable-temperature NMR, IR, UV-vis absorption and emission spectroscopy.

Luminescent Dinuclear Bis‐Cyclometalated Gold(III) Alkynyls and Their Solvent‐Dependent Morphologies through Supramolecular Self‐Assembly

A series of luminescent bis-cyclometalated gold(III) complexes containing bridging alkynyl ligands of different natures has been synthesised and characterised. The photophysical properties of the complexes have been investigated through electronic absorption spectroscopy and emission studies. The vibronic emission bands are found to originate from the triplet intraligand (IL) π-π* excited states of the bis-cyclometalating ligands with some mixing of 3 IL π-π* character of the alkynyl ligands. The electrochemical study of a nonsymmetric dinuclear complex shows two successive reduction processes originating from the reductions of the two different cyclometalating ligands. The complexes are found to undergo supramolecular self-assembly processes driven by π-π stacking and hydrophobic/hydrophilic interactions to give honeycomb nanostructures, as revealed from the SEM images. Solvent-dependent morphological transformations have also been observed, which have been studied by SEM and 1 H NMR spectroscopy.