Keith Man-Chung Wong

Luminescent metallogels of platinum(II) terpyridyl complexes: interplay of metal⋯metal, π–π and hydrophobic–hydrophobic interactions on gel formation

A series of platinum(II) terpyridyl complexes has been demonstrated to show gelation properties driven by Pt...Pt and pi-pi interactions in addition to hydrophobic-hydrophobic interactions; counter-anions have been found to affect strongly the colour of the metallogel.

Supramolecular self-assembly of amphiphilic anionic platinum(II) complexes: A correlation between spectroscopic and morphological properties

A new class of amphiphilic anionic platinum(II) bzimpy complexes has been demonstrated to show aggregation in water through Pt···Pt and π-π stacking interactions. An interesting aggregation-partial deaggregation-aggregation process and a morphological transformation from vesicles to nanofibers have been demonstrated. These changes can be systematically controlled by the variation of solvent composition and could readily be probed by UV-vis absorption, emission, NMR, transmission electron microscopy, and even with our naked eyes.

Single-stranded nucleic acid-induced helical self-assembly of alkynylplatinum(II) terpyridyl complexes

Single-stranded nucleic acids, which carry multiple negative charges in an aqueous medium at near neutral pH, are found to induce the aggregation and self-assembly of the positively charged alkynylplatinum(II) terpyridyl complexes via electrostatic binding of the platinum complexes to the single-stranded nucleic acids, as revealed by the appearance of new UV-vis absorption and emission bands upon addition of single-stranded nucleic acids to a buffer solution of the complex. Changes in the intensity and pattern of circular dichroism (CD) spectroscopy are also observed, many of which are consistent with the assembly of the platinum complexes into helical structures, via metal⋯metal and π⋯π stacking interactions. The induced spectroscopic property changes are found to depend on the structural properties of the nucleic acids.

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.

Molecular design of luminescent dinuclear gold(I) thiolate complexes: From fundamentals to chemosensing

Abstract A number of dinuclear gold(I) phosphine thiolates have been synthesized and characterized. Detailed spectroscopic and luminescence studies have provided a fundamental understanding on their spectroscopic origins, which serves as the basis for the design of versatile spectrochemical and luminescence chemosensors as well as molecular optoelectronic ‘on-off’ switching devices based on the switching on and off of weak metal⋯metal interactions using the dinuclear gold(I) phosphine thiolate as the basic building block. The binding characteristics have been studied by both UV–vis and emission spectroscopic measurements, and the identities of the ion-bound species have been confirmed by electrospray-ionization mass spectrometric studies.

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.

Synthesis, photophysics and binding studies of Pt(II) alkynyl terpyridine complexes with crown ether pendant. Potential luminescent sensors for metal ions

Two crown ether-containing platinum(II) alkynyl terpyridine complexes, [Pt(tpy)(CC-benzo-15-crown-5)]OTf (1) and [Pt(tpy)(CC-N-phenylaza-15-crown-5)]OTf (2) (tpy = 2,2′:6′,2″-terpyridine), have been synthesized and characterized. UV-vis spectrophotometric, emission and 1H NMR titration methods were employed to investigate their ion-binding properties. Complex 1 was found to show luminescence enhancement upon binding of Mg2+ and Ca2+ ions to its crown cavity.

Dendritic Luminescent Gold(III) Complexes for Highly Efficient Solution-Processable Organic Light-Emitting Devices†

Emission control: carbazole-based dendritic alkynylgold(III) complexes have been evaluated as phosphorescent emitters in organic light-emitting devices. The energy as well as the bathochromic shift of the emissions can be tuned effectively through a control of the dendrimer generation. The optimized devices show high current and external quantum efficiencies of up to 24.0 cd A(-1) and 7.8 %, respectively.

Luminescent Molecular Rods - Transition-Metal Alkynyl Complexes

A number of transition-metal complexes have been reported to exhibit rich luminescence, usually originating from phosphorescence. Such luminescence properties of the triplet excited state with a large Stokes shift, long lifetime, high luminescence quantum yield as well as lower excitation energy, are envisaged to serve as an ideal candidate in the area of potential applications for chemosensors, dye-sensitized solar cells, flat panel displays, optics, new materials and biological sciences. Organic alkynes (poly-ynes), with extended or conjugatedπ-systems and rigid structure with linear geometry, have become a significant research area due to their novel electronic and physical properties and their potential applications in nanotechnology. Owing to the presence of unsaturated sp-hybridized carbon atoms, the alkynyl unit can serve as a versatile building block in the construction of alkynyl transition-metal complexes, not only throughσ-bonding but also viaπ-bonding interactions. By incorporation of linear alkynyl groups into luminescent transition-metal complexes, the alkynyl moiety with goodσ-donor,π-donor andπ-acceptor abilities is envisaged to tune or perturb the emission behaviors, including emission energy (color), intensity and lifetime by its role as an auxiliary ligand as well as to govern the emission origin from its direct involvement. This review summarizes recent efforts on the synthesis of luminescent rod-like alkynyl complexes with different classes of transition metals and details the effects of the introduction of alkynyl groups on the luminescence properties of the complexes.

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.