Eddie Chung-Chin Cheng

Highlights on the recent advances in gold chemistry—a photophysical perspective

The presence of inter- and/or intra-molecular aurophilic interactions among the closed-shell gold(I) centres in various systems has been studied from various aspects, including synthetic, spectroscopic and theoretical approaches. The employment of different ligands can impose a significant influence on these factors and give rise to new complexes with interesting structural and photophysical properties. In this tutorial review, a number of recent examples are selected to illustrate the fascinating properties and chemistry, as well as versatility of gold(I) in these aspects and their potential applications to newcomers in this field. An emerging class of luminescent gold(III) complexes is also described.

Photochemistry and Photophysics of Coordination Compounds: Gold

Gold, in addition to its attractive historical monetary value, has attracted growing attention from the chemical perspective. A significant proportion of recent contributions has been associated with the luminescent behavior of gold compounds, some of which are associated with the presence of the weak closed-shell aurophilic interactions. In this review the photophysical properties of several classes of gold complexes in the oxidation states of + 1, + 2 and + 3 are discussed. Some of them also exhibit interesting photochemical properties. Such growth of attention has proven the potential application of gold complexes to serve as promising light-emitting molecular materials.

Selective ion probe for Mg2+ based on Au(I)···Au(I) interactions in a tripodal alkynylgold(I) complex with oligoether pendants

A simple but novel tripodal alkynylgold(I) complex with oligoether pendants has been synthesized and demonstrated to be a selective ion probe for Mg2+ based on Au(I)Au(I) interactions.

Design, Synthesis, Photophysics, and Anion‐Binding Studies of Bis(dicyclohexylphosphino)methane‐Containing Dinuclear Gold(I) Thiolate Complexes with Urea Receptors

A series of bis(dicyclohexylphosphino)methane (dcpm)-containing gold(I) thiolate complexes with urea receptors, 1-3, has been successfully designed and synthesized, and their photophysical and anion-binding properties have been studied. The linker between the thiolate and the urea group, and the electronic environment of the urea moiety, have been found to exert a great influence on the photophysical and anion-binding properties of the complexes. Complex 3 displays an intense long-lived orange-red luminescence at around 620 nm in the solid state and in the glass state at 77 K, which is considerably red shifted from the band seen in a solution of dichloromethane at room temperature, suggesting the presence of AuAu interactions. Upon introducing an electron-withdrawing NO(2) group, complex 1 was found to show high selectivity and sensitivity for F(-) through a drastic color change from yellow to red. The anion-binding constants of the complexes have been determined from electronic absorption and (1)H NMR spectroscopy titration studies and the data were found to fit well to a 1:1 binding model for the interactions between the complexes and the anions. Complexes 1 and 2 show the same anion selectivity trend of F(-) > AcO(-) > H(2)PO(4)(-) > Cl(-) approximately Br(-) approximately I(-), which is consistent with the trend in anion basicity. In addition, complex 1 has been shown to exhibit higher binding affinity for anions compared with those of complexes 2 and 3, probably due to the higher acidity of the urea moiety as a result of the introduction of the NO(2) group.

Unprecedented near-infrared (NIR) emission in diplatinum(III) (d7-d7) complexes at room temperature.

The synthesis and single-crystal X-ray structures of the first family of efficient NIR emitters with tunable emission energy based on dihalodiplatinum(III) (5d(7)-5d(7)) complexes of general formulae [Pt(2)(mu-C(6)H(3)-5-R-2-AsPh(2))(4)X(2)] (R = Me or CHMe(2); X = Cl, Br or I), together with that of their diplatinum(II) (5d(8)-5d(8)) precursors ([Pt(2)(mu-C(6)H(3)-5-R-2-AsPh(2))(4)]) and cyano counterparts (X = CN), are reported. The diplatinum(II) complexes with isopropyl groups are isolated initially as a mixture of two species, one being a half-lantern structure containing two bridging and two chelate C(6)H(3)-5-CHMe(2)-2-AsPh(2) ligands (1b) that exists in two crystalline modifications [d(Pt...Pt) = 3.4298(2) A and 4.3843(2) A]; the other is a full-lantern or paddle-wheel structure having four bridging C(6)H(3)-5-CHMe(2)-2-AsPh(2) ligands (2b) [d(Pt...Pt) = 2.94795(12) A]. Complete conversion of the isomers into 2b occurs in hot toluene. The Pt-Pt bond distances in the diplatinum(III) complexes are less than that in 2b and increase in the order X = Cl (3b) [2.6896(2) A] < Br (4b) [2.7526(3) A] < I (5b) [2.7927(7) A] approximately CN (6b) [2.7823(2), 2.7924(2) A for two independent molecules]. Comparison with the corresponding data for our previously reported series of complexes 3a-6a (R = Me) indicates that the Pt-Pt bond lengths obtained from single-crystal X-ray analysis are influenced both by the axial ligand and by intermolecular lattice effects. Like [Pt(2)(mu-pop)(4)](4-) [pop = pyrophosphite, (P(2)O(5)H(2))(2-)], the diplatinum(II) complexes [Pt(2)(mu-C(6)H(3)-5-R-2-AsPh(2))(4)] [R = Me (2a), CHMe(2) (2b)] display intense green phosphorescence, both as solids and in solution, and at room temperature and 77 K, with the emission maxima in the range 501-532 nm. In contrast to the reported dihalodiplatinum(III) complexes [Pt(2)(mu-pop)(4)X(2)](4-) that exhibit red luminescence only at 77 K in a glass or as a solid, complexes 3a-6a and 3b-6b are phosphorescent in the visible to near-infrared region at both room and low temperatures. The electronic spectra and photoemissive behavior are discussed on the basis of time-dependent density functional theory (TDDFT) calculations at the B3YLP level. The photoemissive states for the halide analogues 3a,b-5a,b involve a moderate to extensive mixing of XMMCT character and MC [d sigma-d sigma*] character, whereas the cyano complexes 6a and 6b are thought to involve relatively less mixing of the XMMCT character into the MC [d sigma-d sigma*] state.

Self-assembly of a neutral luminescent Au12 cluster with D2 symmetry

The preparation and characterization of luminescent neutral Au(12) shuttle-like complexes is reported which shows a cyclic framework consisting of twelve gold(i) ions arranged in a closed ring via non-covalent Au(i)Au(i) interactions to give a chiral D(2) symmetrical structure.

Design of luminescent sulfur-containing polynuclear gold(I) complexes for advanced nanomaterials and chemosensors

A series of high-nuclearity gold(I) sulfido complexes with bridging diphosphine ligands have been synthesized and isolated, with the general formulae of [Au10(μ-P^P)4(μ3-S)4]X2 and [Au12(μ-P^P)4(μ3-S)4]X4 (P^P = diphosphine; X = PF6 or ClO4). Intense green and orange emissions were observed upon excitation at λ > 350 nm both in the solid state and in solutions. The green emission has been attributed to originate from excited states derived from the metal-perturbed intraligand (IL) transition while the orange emission arises from the ligand-to-metal-metal bond charge-transfer (LMMCT; S(Au...Au) states. The switching on and off of the LMMCT emission in a series of dinuclear gold(I) thiolate complexes with crown ether pendants induced by ion-binding has been demonstrated, and this provides a new strategy for the design of luminescence signalling and chemosensing devices in optoelectronics and sensor technology.

Synthesis, characterization, and luminescence studies of discrete polynuclear gold(I) sulfido and selenido complexes with intramolecular aurophilic contacts.

The synthesis, characterization, and photophysical and photochemical properties of a family of high-nuclearity gold(I) chalcogenides, specifically, the gold(I) sulfido and selenido complexes containing different bridging diphosphine ligands with nuclearities of ten ([Au10{μ-Ph2PN(R)PPh2}4(μ3-E)4](2+)) and six ([Au6{μ-Ph2PN(R)PPh2}3(μ3-E)2](2+)), are reported. The X-ray crystal structures of the complex cations of Au10 and Au6 are found to be propeller-like structures and distorted cubane structures, respectively, with the presence of short intramolecular gold···gold distances. The complexes show intense green and/or orange phosphorescence upon photoexcitation in the solid state and in solution at ambient and low temperature. The emission properties are found to be strongly dependent on the nuclearities and the chalcogenido ligands, but are rather insensitive to the substituents on the bis(diphenylphosphino)amines. The emissions are tentatively assigned to originate from the excited states derived from the phosphine-centered intraligand (IL) transition or metal-centered (ds/dp) mixed with ligand-to-metal-metal charge transfer (LMMCT) (E→Au) transition. The photochemical properties of the complexes were also studied by transient absorption spectroscopy.

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.

Synthese eines neuen vielkernigen lumineszierenden Gold(I)-Sulfidokomplexes

Die Verbruckung von Gold(I)-zentren durch Bis(diphenylphosphanyl)methan(dppm)-Liganden sowie die Gegenwart aurophiler Schwefelzentren fuhren zur Bildung des vielkernigen Komplexkations [Au12(μ-dppm)6(μ3-S)4]4+ (siehe Bild) aus [Au2Cl2(dppm)] und H2S. Dieser Metalla-Makrobicyclus weist eine langlebige Lumineszenz im Mikrosekundenbereich auf.