Luminescent Gold Research Articles

Solvent Dependent Excited State Behaviors of Luminescent Gold(I)–Silver(I) Cluster with Hypercoordinated Carbon

Polynuclear Au(I) complexes continues to attract considerable attention because of their bright emissions in the visible wavelength, which hold promise in applications in luminescence, fluorescence sensing, and bioimaging. Despite various spectroscopic investigations on their steady state properties, detailed understanding of the origin of their emissions and excited state relaxations is still lacking. Here, we report femtosecond time-resolved transient absorption experiments combined with quantum chemical calculations on a brightly emissive [Au6Ag2(C)(dppy)6](BF4)4 cluster in different solvents. Global analysis on the transient absorption spectra based on a sequential model gives three spectral components: (1) excited state absorption (ESA) of 1MLCTAu state (τ = 1–3 ps); (2) ESA of 3MLCTAu state (τ = 11–40 ps), and (3) ESA of 3MLCTAg state (long-lived). By variation of the solvent’s polarity and hydrogen bonding ability, the relative population of the triplet MLCT states and the emission properties can b...

Decoupling the CO-Reduction Protocol to Generate Luminescent Au22(SR)18 Nanocluster

Development of efficient synthetic strategies for highly luminescent gold nanoclusters (Au NCs) requires a good understanding of their synthesis process and environmental factors involved which could affect their tailorability. In a recent study, we reported a new type of luminescent Au NCs featuring with the aggregation-induced emission (AIE) characteristic. This AIE-type luminescent Au NC has a molecular formula of Au22(SR)18 (SR denotes thiolate ligand), and it shows strong red emission at ∼665 nm with a high quantum yield of ∼8%. However, the formation process and reaction parameters that may affect the synthesis of Au22(SR)18 were not understood because of the lack of experimental evidence. Here, we revisit the synthetic protocol, a two-step carbon monoxide (CO) reduction method, to further understand the formation process of Au22(SR)18. First, we systematically investigate several reaction conditions (e.g., the solution pH and the duration of each step) that could affect the yield of red-emitting Au22(SR)18 in the protocol. Second, we use the time-course measurements of the optical properties (UV–vis absorption and photoemission) of the reaction solution to study the formation process of Au22(SR)18, which allows us to identify several key NC intermediates and makes possible the reconstruction of the formation process of red-emitting Au22(SR)18. Upon the basis of our experimental data, we propose a two-stage process for the growth of Au22(SR)18: (1) the reduction of Au(I)-thiolate complexes to form Au NCs with a narrow size distribution, which are subsequently focused to Au18(SR)14; and (2) a pH-induced aggregation of short Au(I)-thiolate complexes on Au18(SR)14, which are finally converted to Au22(SR)18. Our study suggests that the pH-induced aggregation of Au(I)-thiolate complexes on the in situ formed thiolated Au NCs could be an effective way to generate luminescent Au NCs with the AIE characteristic. This principle can also be used to synthesize other AIE-type metal NCs with strong luminescence.

Synthesis, luminescence and electrochemical properties of luminescent dinuclear mixed-valence gold complexes with alkynyl bridges

A series of luminescent dinuclear mixed-valence gold alkynyl complexes was synthesized. Their photophysical properties can be tuned by varying the nature of the alkynyl bridges, as supported by computational studies.

A luminescent double helical gold(i)–thiophenolate coordination polymer obtained by hydrothermal synthesis or by thermal solid-state amorphous-to-crystalline isomerization

The first structure of a luminescent gold thiolate coordination polymer, [Au(SPh)]n.

Metal-organic framework composites with luminescent gold(iii) complexes. Strongly emissive and long-lived excited states in open air and photo-catalysis.

The encapsulation of luminescent gold(iii) complexes by metal-organic frameworks (MOFs) lays the groundwork for new phosphorescent materials with activities that are not readily achieved by the host MOF materials or gold(iii) complexes alone. In this work, strong phosphorescence with lifetimes of up to ∼50 μs in open air at room temperature has been achieved by incorporation of cationic cyclometalated gold(iii) complexes into MOFs with anionic frameworks to form AuIII@MOFs. The AuIII@MOFs display solid state two-photon-induced phosphorescence. Photo-reduction of methyl viologen to the reduced radical was achieved inside AuIII@MOFs and in the presence of Et3N upon excitation at λ > 370 nm under ambient conditions. These AuIII@MOFs comprise a class of reusable and size-selective heterogeneous photo-catalysts for the aerobic oxidation of secondary amines to imines as well as five other reactions, including oxidative C-H functionalization under aerobic conditions.

A luminescent cyclometalated gold(iii)-avidin conjugate with a long-lived emissive excited state that binds to proteins and DNA and possesses anti-proliferation capacity.

Here we describe a luminescent cyclometalated Au(iii)-avidin conjugate that exhibits a 520 nm emission with a lifetime of 1.8 μs in PBS solution in open air. The conjugate stains proteins and DNA and can inhibit cancer cell proliferation.

Theoretical studies on the photophysical properties of luminescent pincer gold(iii) arylacetylide complexes: the role of π-conjugation at the C-deprotonated [C^N^C] ligand.

We have performed theoretical analyses of the photophysical properties of a series of cyclometalated gold(iii) arylacetylide complexes, [(C^N^C)AuIIIC[triple bond, length as m-dash]CPh-4-OMe], with different extents of π-conjugation at the doubly C-deprotonated [C^N^C] ligand via replacement of one of the phenyl moieties in the non-conjugated CH^N^C ligand (1) by a naphthalenyl (2) or a fluorenyl moiety (3-exo and 3-endo; HCH^N^CH = 2,6-diphenylpyridine). Conforming to the conventional wisdom that extended π-conjugation imposes rigidity on the structure of the 3IL(ππ*(C^N^C)) excited state (IL = intraligand), the calculated Huang-Rhys factors for the 3IL → S0 transition follow the order: 1 > 2 > 3-exo ∼ 3-endo, which corroborates qualitatively the experimental non-radiative decay rate constants, k nr: 1 ≫ 2 > 3-exo, but not 3-endo. Density Functional Theory (DFT) calculations revealed that there is an additional triplet excited state minimum of 3LLCT character (LLCT = ligand-to-ligand charge transfer; 3[π(C[triple bond, length as m-dash]CPh-4-OMe) → π*(C^N^C)]) for complexes 1 and 3-endo. This 3LLCT excited state, possessing a large out-of-plane torsional motion between the planes of the C^N^C and arylacetylide ligands, has a double minimum anharmonic potential energy surface along this torsional coordinate which leads to enhanced Franck-Condon overlap between the 3LLCT excited state and the ground state. Together with the larger spin-orbit coupling (SOC) and solvent reorganization energy for the 3LLCT → S0 transition compared with those for the 3IL → S0 transition, the calculated k nr values for the 3LLCT → S0 transition are more than 690- and 1500-fold greater than the corresponding 3IL → S0 transition for complexes 1 and 3-endo respectively. Importantly, when this 3LLCT → S0 decay channel is taken into consideration, the non-radiative decay rate constant k nr could be reproduced quantitatively and in the order of: 1 ≫ 3-endo, 2 > 3-exo. This challenges the common view that the facile non-radiative decay rate of transition metal complexes is due to the presence of a low-lying metal-centred 3dd or 3LMCT excited state (LMCT = ligand-to-metal charge transfer). By analysis of the relative order of MOs of the chromophoric [C^N^C] cyclometalated and arylacetylide ligands, one may discern why complexes 1 and 3-endo have a low-lying 3LLCT excited state while 3-exo does not.

A microwave-facilitated rapid synthesis of gold nanoclusters with tunable optical properties for sensing ions and fluorescent ink.

Luminescent glutathione-capped gold nanoclusters (GS-AuNCs) with tunable emissions have been efficiently synthesized by a solution-based microwave method.

Highly luminescent gold nanoparticles: effect of ruthenium distance for nanoprobes with enhanced lifetimes.

The photophysical properties of gold nanoparticles, AuNPs, with sizes of 13, 50 and 100 nm in diameter, coated with surface-active ruthenium complexes have been studied to investigate the effect of the distance of the ruthenium luminescent centre from the gold surface. Luminescence lifetimes of the three ruthenium probes, RuS1, RuS6 and RuS12, with different length spacer units between the surface active groups and the ruthenium centre were taken. The metal complexes were attached to AuNP13, AuNP50 and AuNP100 via thiol groups using a method of precoating the nanoparticles with a fluorinated surfactant. The luminescence lifetime of the longer spacer unit complex, RuS12, was enhanced by 70% upon attachment to the AuNP when compared to the increase of the short and medium linker unit complexes, RuS1 (20%) and (RuS6 40%) respectively. The effect of the surfactant in the lifetime increase of the ruthenium coated AuNPs was shown to be larger for the medium spacer probe, RuS6. There was no effect of the change of the size of the AuNPs from 13 to 50 or 100 nm.

Green synthesis, characterization and anticancer activity of luminescent gold nanoparticles capped with apo-α-lactalbumin

A green synthesis was developed to prepare protein coated gold nanoparticles (NPs) where apo-α-lactalbumin was used as reducing and stabilizing agent. The NPs are luminescent and non-toxic to normal cells but more toxic to MCF-7 cells over HeLa.

Luminescence enhancement in nanocomposite consisting of polyvinyl alcohol incorporated gold nanoparticles and Nile blue 690 perchlorate.

We have experimentally demonstrated that the emission of visible light from the polymer matrix doped with luminescent dye and gold nanoparticles (GNPs) can be enhanced with the use of surface plasmon coupling. GNPs can enhance the luminescence intensity of nearby luminescent dye because of the interactions between the dipole moments of the dye and the surface plasmon field of the GNPs. The electric charge on the GNPs and the distance between GNPs and luminescent dye molecules have a significant effect on the luminescence intensity, and this enhancement depends strongly upon the excitation wavelength of the pumping laser source. In particular, by matching the plasmon frequency of GNPs to the frequency of the laser light source we have observed a strong luminescence enhancement of the nanocomposite consisting of GNPs coupled with luminescent dye Nile blue 690 perchlorate. This ability of controlling luminescence can be beneficially used in developing contrast agents for highly sensitive and specific optical sensing and imaging. This opens new possibilities for plasmonic applications in the solar energy field.

Luminescent golden silk and fabric through in situ chemically coating pristine-silk with gold nanoclusters

Silk is an excellent natural material and has been used for a variety of applications. Modification of the pristine silk is usually needed depending on the intended purpose. The technical treatments involved in the modification not only should be easy, rapid, environmentally friendly, and cheap but should also retain the features of the pristine silk. Herein, we demonstrate that luminescent silk and fabric can be produced through nanotechnology. The surface of the natural silk fiber is chemically coated with luminescent gold nanoclusters (AuNCs) composed of tens to hundreds of Au atoms through a redox reaction between the protein-based silk and an Au salt precursor. The luminescent silk coated with AuNCs (called golden silk) possesses good optical properties, including a relatively long wavelength emission, high quantum yields, a long fluorescent lifetime, and photostability. Moreover, golden silk prepared this way has better mechanical properties than pristine silk, is better able to inhibit UV, and has lower toxicity in vitro. This work not only provides an effective strategy for in situ preparation of luminescent metal nanoclusters on a solid substrate but also paves the way for large-scale and industrialized production of novel silk-based materials or fabrics through nanotechnology.

Cluster linker approach: preparation of a luminescent porous framework with NbO topology by linking silver ions with gold(I) clusters.

A cluster-based luminescent porous metal-organic framework has been constructed through a "cluster linker" approach. The luminescent gold(I) cluster, prefunctionalized with pyrazinyl groups, was used as a cluster linker, similar to an organic linker, to connect silver ions in order to form a 3D framework. 1D channels with 1.1 nm diameter were observed in the framework. The cluster with its intrinsic luminescence was incorporated into a porous framework to give a luminescent bifunctional NbO net. This MOF shows solvatochromic behavior, and the interactions between solvent molecules and silver ions inside the channels account for the changes in absorption and emission spectra.

Cluster Linker Approach: Preparation of a Luminescent Porous Framework with NbO Topology by Linking Silver Ions with Gold(I) Clusters

AbstractA cluster‐based luminescent porous metal–organic framework has been constructed through a “cluster linker” approach. The luminescent gold(I) cluster, prefunctionalized with pyrazinyl groups, was used as a cluster linker, similar to an organic linker, to connect silver ions in order to form a 3D framework. 1D channels with 1.1 nm diameter were observed in the framework. The cluster with its intrinsic luminescence was incorporated into a porous framework to give a luminescent bifunctional NbO net. This MOF shows solvatochromic behavior, and the interactions between solvent molecules and silver ions inside the channels account for the changes in absorption and emission spectra.

Glutathione-coated luminescent gold nanoparticles: a surface ligand for minimizing serum protein adsorption.

Ultrasmall glutathione-coated luminescent gold nanoparticles (GS-AuNPs) are known for their high resistance to serum protein adsorption. Our studies show that these NPs can serve as surface ligands to significantly enhance the physiological stability and lower the serum protein adsorption of superparamagnetic iron oxide nanoparticles (SPIONs), in addition to rendering the NPs the luminescence property. After the incorporation of GS-AuNPs onto the surface of SPIONs to form the hybrid nanoparticles (HBNPs), these SPIONs’ protein adsorption was about 10-fold lower than those of the pure glutathione-coated SPIONs suggesting that GS-AuNPs are capable of providing a stealth effect against serum proteins.

Addition Reaction-Induced Cluster-to-Cluster Transformation: Controlled Self-Assembly of Luminescent Polynuclear Gold(I) μ3-Sulfido Clusters

Unprecedented addition reaction-induced gold(I) cluster-to-cluster transformation has been observed in the present work. Reaction of the chlorogold(I) precursor, [vdpp(AuCl)2] (vdpp = vinylidenebis(diphenylphosphine)) containing the diphosphine with unsaturated C═C bond, with H2S resulted in a series of polynuclear gold(I) μ3-sulfido clusters bearing Au(I)···Au(I) interactions; the identities of which have been fully characterized by NMR, electrospray-ionization mass spectrometry, elemental analysis, and single crystal X-ray diffraction analysis. Diverse research methods, including UV-vis absorption, (1)H NMR, and (31)P NMR spectroscopy, were employed to detect and monitor the transformation and assembly processes. Supported by single crystal structures, the existence of Au(I)···Au(I) bonding interactions sustains the diverse array of sophisticated polynuclear cluster structures and endues them with rich luminescence features.

Luminescent monocyclometalated cationic gold(III) complexes: synthesis, photophysical characterization and catalytic investigations.

Stable, luminescent, and cationic monocyclometalated gold(iii) monoaryl complexes of the type [(ppy)Au(FMes)(L)](+)[OTf](-) [L = 4-phenylpyridine (), quinoline (), 4-fluoroaniline (), P(OMe)3 (), PPh3 ()], bearing different ancillary ligands, synthesized starting from the precursor complex [(ppy)Au(FMes)(OH2)](+)[OTf](-) () are reported. The preliminary assignment of the structure of the complexes by various nuclear magnetic resonance spectroscopy techniques and elemental analysis has been further corroborated by single-crystal X-ray diffraction studies. The complexes exhibit room temperature phosphorescence in solution, in neat solids and in doped PMMA films. Detailed photophysical investigations of the complexes in solution, in neat solids and in PMMA films revealed the successful tuning of the emission quantum yield (ϕp) based on the electronic properties of the ancillary ligands. The catalytic photo-oxidation of benzylic amines to their corresponding imines using molecular oxygen as the oxidant was successfully achieved in the presence of the luminescent Au(iii) complexes. It is also established that the photocatalytic performance was strongly governed by the electronic properties of the ancillary ligands on the photosensitizer as well as by the steric bulk of the substrates.

A fluorescence detection of d-penicillamine based on Cu2+-induced fluorescence quenching system of protein-stabilized gold nanoclusters

In this contribution, a luminescent gold nanoclusters which were synthesized by bovine serum albumin as novel fluorescent probes were successfully utilized for the determination of d-penicillamine for the first time. Cupric ion was employed to quench the strong fluorescence of the gold nanoclusters, whereas the addition of d-penicillamine caused obvious restoration of fluorescence intensity of the Cu2+-gold nanoclusters system. Under optimum conditions, the increment in fluorescence intensity of Cu2+-gold nanoclusters system caused by d-penicillamine was linearly proportional to the concentration of d-penicillamine in the range of 2.0×10−5–2.39×10−4M. The detection limit for d-penicillamine was 5.4×10−6M. With the off–on fluorescence signal at 650nm approaching the near-infrared region, the present sensor for d-penicillamine detection had high sensitivity and low spectral interference. Furthermore, the novel gold nanoclusters-based fluorescent sensor has been applied to the determination of d-penicillamine in real biological samples with satisfactory results.

Fluorescence resonance energy transfer based immunosensing of human IgG by using quantum dot/GIgG-gold nanoparticles/IgG conjugation.

A novel immunosensor of human immune globulin (IgG) was fabricated based on the fluorescence transfer between luminescent semiconductor quantum dots (QDs) and gold nanoparticles (AuNPs). AuNPs and CdSe/ZnS QDs were respectively labeled with immune reaction pair:IgG and goat anti-human immunoglobulin (GIgG), by optimizing the conditions including pH value and protein amount. In the assembled QD-GIgG-IgG-AuNP fluorescence resonance energy transfer (FRET) immunocomplex system, the presence of AuNP-IgG directly reduced the fluorescence intensity of the GIgG conjugated QDs. As a result, the concentration of AuNP-IgG had a linear relationship with the fluorescence decrease in a range of 0-1.57 microg/mL. Furthermore, the mechanism of the QDs' fluorescence decay has also been discussed and attributed to the light-induced photobleaching. This novel sensing method achieves quantitative detection of trace proteins, suggesting the potential of biomolecule-AuNPs conjugation based analytical methods in further application.

Luminescent Gold(I) Alkynyl Clusters Stabilized by Flexible Diphosphine Ligands

Treatment of the homoleptic decanuclear compounds (AuC2R)10 with the cationic gold diphosphine complexes [Au2(PR′2-X-PR′2)2]2+ results in high-yield formation of the new family of hexanuclear clusters [Au6(C2R)4(PR′2-X-PR′2)2]2+ (PR′2-X-PR′2 = PPh2-(CH2)n-PPh2, n = 2 (1, R = diphenylmethanolyl), n = 3 (3, R = diphenylmethanolyl; 4, R = 1-cyclohexanolyl; 5, R = 2-borneolyl), 4 (6, R = 1-cyclohexanolyl); PR′2-X-PR′2 = PCy2-(CH2)2-PCy2 (2, R = diphenylmethanolyl); PR′2-X-PR′2 = 1,2-(PPh2-O)-C6H4 (7, R = diphenylmethanolyl); PR′2-X-PR′2 = (R,R)-DIOP (8, R = diphenylmethanolyl)). In the case of PPh2-(CH2)4-PPh2 phosphine and −C2C(OH)Ph2 alkynyl ligands an octanuclear cluster of a different structural type, [Au8(C2C(OH)Ph2)6(PPh2-(CH2)4-PPh2)2]2+ (9), was obtained. Complexes 1–3, 7, and 9 were studied by X-ray crystallography. NMR and ESI-MS spectroscopic investigations showed that all but two (2 and 9) compounds are fluxional in solution and demonstrate dissociative chemical equilibria between major and a few minor forms. All of these complexes are intensely emissive in the solid state at room temperature and demonstrate very high quantum yields from 0.61 to 1.0 with weak influence of the alkynyl substituents R′ and the diphosphine backbones on luminescence energies. Two crystalline forms of the cluster 2 (P21/n and P21 space groups) exhibit unexpectedly contrasting yellow and sky blue emission, maximized at 572 and 482 nm, respectively. Electronic structure calculations with density functional methods demonstrate that the transitions responsible for the highly effective phosphorescence are dominated by contributions from the Au and π-alkynyl orbitals.