Microsecond Lifetimes Research Articles

Delayed Fluorescence of Dyes Sensitized by Eu3+ Chelate Nanoparticles

Dye-doped nanoparticles of Eu3+ chelate complexes with naphtoyltrifluoroacetone and 1,10-phenanthroline were synthesized using two different reprecipitation techniques. The nanoparticles were characterized by atomic force microscopy, absorption spectroscopy, steady-state, and time-resolved fluorescence spectroscopy. Fluorescent spectroscopy of chelate nanoparticles doped with Oxazine 170 and Nile blue dyes indicates that a single dye molecule efficiently quenches luminescence of more than a hundred chelates. The Eu3+ chelates have a significantly longer luminescence lifetime than organic dyes, which leads to the appearance of delayed dyes fluorescence with microsecond lifetimes. The fluorescence brightness of dye-doped chelate nanoparticles was determined to be 50 times higher than that of a single Rhodamine 6G molecule. The combination of high fluorescence brightness and long fluorescence lifetime of the dye-doped chelate nanoparticles is promising for time-gated applications.

Synthesis, characterization and luminescent properties of three-coordinate copper(I) halide complexes containing diphenylamino monodentate phosphine ligand

Three-coordinate copper halide complexes with a bidentate phosphine ligand have received much attention. Here, a series of three-coordinate dinuclear copper halide complexes containing a diphenylamino monodentate phosphine ligand, [CuX(dpnp)]2 (dpnp = N-[2-(diphenylphosphino)-4,5-dimethylphenyl]-N-phenylaniline, X = I (1), Br (2) and Cl (3)), were synthesized, and their molecular structures and photophysical properties were investigated. The structural analysis reveals that two copper(I) centers are bridged by two halogen ligands to form a dinuclear structure with a four-membered Cu2X2 ring. Crystal structures of 1–3 contain 1-D supramolecular arrays constructed by intermolecular C–H⋯π interactions. These complexes exhibit blue emission in the solid state at room temperature and have peak emission wavelengths at 483–487 nm with microsecond lifetimes (τ = 13.9–38.1 μs) and low emission quantum yields (<0.01%). The emission of complex 1 mainly originates from intraligand (IL) transition, whereas the emissions of complexes 2 and 3 are from a combination of MLCT, XLCT and IL transitions. The three complexes displayed good thermal stability.

Spatiotemporal Evolution of Coherent Elastic Strain Waves in a Single MoS2 Flake.

We use bright-field imaging in an ultrafast electron microscope to spatiotemporally map the evolution of photoexcited coherent strain waves in a single, micrometer-size flake of MoS2. Following in situ femtosecond photoexcitation, we observe individual wave trains emerge from discrete nanoscale morphological features and propagate in-plane along specific wave vectors at approximately the speed of sound (7 nm/ps). Over the span of several hundred picoseconds, the 50 GHz wave trains (20 ps periods) are observed to undergo phonon-phonon scattering and wave-train interference, resulting in a transition to larger-scale, incoherent structural dynamics. This incoherent motion further evolves into coherent nanomechanical oscillations over a few nanoseconds, ultimately leading to megahertz, whole-flake multimode resonances having microsecond lifetimes. These results provide insight into the low-frequency structural response of MoS2 to relatively coherent optical photoexcitation by elucidating the origin and the evolution of high-velocity, gigahertz strain waves.

Chromium(0), Molybdenum(0), and Tungsten(0) Isocyanide Complexes as Luminophores and Photosensitizers with Long-Lived Excited States.

Arylisocyanide complexes based on earth-abundant Group 6 d6 metals are interesting alternatives to photoactive complexes made from precious metals such as RuII , ReI , OsII , or IrIII . Some of these complexes have long-lived 3 MLCT excited states that exhibit luminescence with good quantum yields as well as nano- to microsecond lifetimes, and they are very strongly reducing. Recent studies have demonstrated that Cr0 , Mo0 , and W0 arylisocyanide complexes have great potential for applications in luminescent devices, photoredox catalysis, and dye-sensitized solar cells.

Structural, Electrochemical, and Photochemical Properties of Mono‐ and Digold(I) Complexes Containing Mesoionic Carbenes

Triazolylidenes are a prominent class of mesoionic carbenes (MICs) that are currently widely used in organometallic chemistry. Usually the metal complexes of such ligands are used as homogeneous catalysts even though they have vast potential in other branches of chemistry. We present here three related gold(I) complexes with MIC ligands: a neutral mononuclear chlorido complex [AuCl(MIC)], a cationic mononuclear complex containing two MIC ligands [Au(MIC)2]BF4, and a dicationic digold(I) complex containing two di‐MIC ligands [Au2(κ1,κ1,µ‐di‐MIC)2](BF4)2. The complexes were characterized by 1H and 13C{1H} NMR spectroscopy, mass spectrometry, and single‐crystal X‐ray diffraction. The gold(I) centers are linearly coordinated through either one MIC‐C and chlorido donors or through two MIC‐C donors. The triazolylidenes display a delocalized bonding situation within the ring. Additionally, a short Au–Au distance of about 3 Å is observed for the digold(I) complex. All complexes display reduction steps in their cyclic voltammograms, and these are assigned to the reduction of the MIC ligands, as opposed to the generation of gold(0). The complexes emit at ca. 500 nm, with lifetimes of several microseconds in deoxygenated solutions; the emission intensity and lifetime are strongly decreased by the presence of oxygen, supporting the triplet origin of the emissive state. The present results display the utility of MIC ligands for generating electro‐ and photoactive molecules.

Defect-Induced Band-Edge Reconstruction of a Bismuth-Halide Double Perovskite for Visible-Light Absorption.

Halide double perovskites have recently been developed as less toxic analogs of the lead perovskite solar-cell absorbers APbX3 (A = monovalent cation; X = Br or I). However, all known halide double perovskites have large bandgaps that afford weak visible-light absorption. The first halide double perovskite evaluated as an absorber, Cs2AgBiBr6 (1), has a bandgap of 1.95 eV. Here, we show that dilute alloying decreases 1's bandgap by ca. 0.5 eV. Importantly, time-resolved photoconductivity measurements reveal long-lived carriers with microsecond lifetimes in the alloyed material, which is very promising for photovoltaic applications. The alloyed perovskite described herein is the first double perovskite to show comparable bandgap energy and carrier lifetime to those of (CH3NH3)PbI3. By describing how energy- and symmetry-matched impurity orbitals, at low concentrations, dramatically alter 1's band edges, we open a potential pathway for the large and diverse family of halide double perovskites to compete with APbX3 absorbers.

Strongly Phosphorescent Transition Metal π-Complexes of Boron–Boron Triple Bonds

Herein are reported the first π-complexes of compounds with boron-boron triple bonds with transition metals, in this case CuI. Three different compounds were isolated that differ in the number of copper atoms bound to the BB unit. Metalation of the B-B triple bonds causes lengthening of the B-B and B-CNHC bonds, as well as large upfield shifts of the 11B NMR signals, suggesting greater orbital interactions between the boron and transition metal atoms than those observed with recently published diboryne/alkali metal cation complexes. In contrast to previously reported fluorescent copper(I) π-complexes of boron-boron double bonds, the Cun-π-diboryne compounds (n = 2, 3) show intense phosphorescence in the red to near-IR region from their triplet excited states, according to their microsecond lifetimes, with quantum yields of up to 58%. While the Cu diborene bond is dominated by electrostatic interactions, giving rise to S1 and T1 states of pure IL(π-π*) nature, DFT studies show that the CuI π-complexes of diborynes reported herein exhibit enhanced metal d orbital contributions to HOMO and HOMO-1, which results in S1 and T1 having significant MLCT character, enabling strong spin-orbit coupling for highly efficient intersystem-crossing S1 → Tn and phosphorescence T1 → S0.

Sodalite cages of EMT zeolite confined neutral molecular-like silver clusters

Stable luminescent silver clusters in nanosized EMT zeolite suspension were prepared and directly observed with high-resolution transmission electron microscopy (HRTEM). The luminescence of the Ag clusters remains stable in time due to their stabilization within the sodalite cages (0.7 nm) of the EMT zeolite nanocrystals. In addition to the experimental results, the first principle Density Functional Theory (DFT) computations showed that hydrated neutral clusters up to octamer (Ag8) with a diameter of 0.47 nm were stabilized in the sodalite cages of the EMT zeolite, trough binding of silver atom(s) to the zeolite oxygen(s). The silver clusters exhibit molecular-like emission properties (lem = 395 nm and t1/2 ≤ 1 ns) that are in a good agreement with the HRTEM and DFT results. The stabilization of charge silver species in the form of weakly interacting dimer or trimer was observed too, which was based on the microsecond lifetime of the emission band measured at 545 nm. The high stability combined with the luminescence properties of silver clusters in the EMT zeolite nanocrystals will be of great advantage for applications such as bio imaging and bio sensing.

Light and Heat Dually Responsive Luminescence in Organic Templated CdSO4-type Halogeno(cyano)cuprates with Disorder of Halogenide/Cyanide

Light and heat dually sensitive luminescent materials have promising applications such as light emitting diodes, bioimaging, and memories but are rather scarce due to simultaneous requirements of stimuli induced structural flexibility and the existence of multiple emissions. In continuation of our research interest in tunable photoluminescent materials with templated organic ligands, we report herein two isostructural organic templated CdSO4-topological halogeno(cyano)cuprates with disorder of halogenide and cyanide, formulated as [Me2DABCO]2Cu4Br5(CN)3 (1) and [Me2DABCO]2Cu4I4.5(CN)3.5 (2) (Me2DABCO = N,N′-dimethyl-1,4-diazabicyclo[2.2.2]octane). Both 1 and 2 show a very strong emission band upon photoexitation with microsecond lifetime and high quantum yield. With the increase of excitation wavelength, the strong main emission band in 1 is gradually red-shifted from 495 to 535 nm, seemingly breaking Kasha’s rule, and the strong main emission in 2 also significantly red-shifted. With the decrease of temp...

Phosphorescent 2-, 3- and 4-coordinate cyclic (alkyl)(amino)carbene (CAAC) Cu(i) complexes.

The photophysical properties of several Cu(i) complexes coordinated with cyclic (alkyl)(amino)carbene (CAAC) ligands were examined. All the compounds were found to be phosphorescent, regardless of whether they are 2-, 3- or 4-coordinated. Aggregate and excimer emission were observed from 2-coordinate CAAC-CuCl derivatives in methylcyclohexane solution. Emission from the complex 4-coordinated with a trispyrazolylborate ligand is red-shifted with respect to both the chloro-derivative and an analogous complex with an NHC ligand.

Cyclic Trinuclear Gold(I) Clusters with N,N and Unusual C,C Mixed-Ligand Bridges.

Three crystalline trinuclear gold(I) clusters, [Au3f2y] (1), [Au3fy2] (2), and [Au3y3] (3), where f = N,N'-bis(2,6-dimethylphenyl)methanimidamidate and y = dimethylendiphenylphosphinate, exhibit bridges from the N,N-formamidinate and/or from the ylide anion ligand whose P-methylene groups chelate in an unusual fashion, where the chelate CPC unit is perpendicular to the trigonal plane of the metal atoms. Assemblies 1 and 2 are the first gold(I) trinuclear clusters featuring mixed-ligand bridges from different N,N and C,C donors; 3 is a previously unknown homoleptic ylide anion cyclic trinuclear assembly. Formamidinate bridges in 1 and 2 connect gold(I) atoms at aurophilic distances of 3.084(2) and 3.0543(4) Å, whereas an out-of-plane (perpendicular) P-ylide anion bite produces AuI-AuI distances of as large as 3.900(2) Å in 3. The crystal space groups for 1 and 2 are triclinic P1̅ and that for 3 is monoclinic P21/c, with Z = 2 for 1 and 2 and Z = 4 for 3. Compounds are synthesized under Schlenk conditions at -20 °C in toluene by reacting the proper ratios of the gold(I) formamidinate [Au2f2] with the phosphorus ylide [Hy] under basic conditions (KOH), followed by extraction with ether. This synthesis also produces a dinuclear cation, [Au2f(Hy)2]+, previously reported by our group. A neutral mixed-ligand dinuclear complex, [Au2fy], was not observed. Under UV light, 1 and 2 display a bright-green luminescence at room temperature and in frozen methyltetrahydrofuran solutions under liquid nitrogen, with microsecond lifetimes. All three complexes 1-3 are characterized by their X-ray crystal structures, 1H NMR, IR, UV-visible, and luminescence spectroscopies, and elemental analysis.

Photophysical and Electrochemical Characterization of BODIPY-Containing Dyads Comparing the Influence of an A-D-A versus D-A Motif on Excited-State Photophysics.

A complete photophysical characterization of organic molecules designed for use as molecular materials is critical in the design and construction of devices such as organic photovoltaics (OPV). The nature of a molecule's excited state will be altered in molecules employing the same chromophoric units but possessing different molecular architectures. For this reason, we examine the photophysical reactions of two BODIPY-based D-A and A-D-A molecules, where D is the donor and A is the acceptor. A BODIPY (4,4'-difluoro-4-bora-3a,4a-diaza-s-indacene) moiety serves as the A component and is connected through the meso position using a 3-hexylthiophene linker to a N-(2-ethylhexyl)dithieno[3,2-b:2',3'-d]pyrrole (DTP), which serves as the D component. An A-D-A motif is compared to its corresponding D-A dyad counterpart. We show a potential advantage to the A-D-A motif over the D-A motif in creating longer-lived excited states. Transient absorption (TA) spectroscopy is used to characterize the photophysical evolution of each molecule's excited state. Global analysis of TA data using singular value decomposition and target analysis is performed to identify decay-associated difference spectra (DADS). The DADS reveal the spectral features associated with charge-transfer excited states that evolve with different dynamics. A-D-A possess slightly longer excited-state lifetimes, 42 ps nonradiative decay, and 4.64 ns radiative decay compared to those of D-A, 24 ps nonradiative decay, and 3.95 ns radiative decay. A longer lived A-D-A component is observed with microsecond lifetimes, representing a small fraction of the total photophyscial product. Steady-state and time-resolved photoluminescence augment the insights from TA, while electrochemistry and spectroelectrochemistry are employed to identify the nature of the excited state. Density functional theory supports the observed electronic and electrochemical properties of the D-A and A-D-A molecules. These results form a complete picture of the electronic and photophysical properties of D-A and A-D-A and provide contextualization for structure-function relationships between molecules and OPV devices.

Synthesis, characterization and luminescent properties of three-coordinate copper(I) halide complexes containing 2-(diphenylphosphino)biphenyl

Highly emissive three-coordinate copper halide complexes with a bidentate phosphine ligand have attracted attention. Here, a series of three-coordinate mono- and dinuclear copper halide complexes, [CuI(dpbp)2] (1) and [CuX(dpbp)]2 (dpbp = 2-(diphenylphosphino)biphenyl, X = Br (2), Cl (3)), were synthesized, and their molecular structures and photophysical properties were investigated. In the solid state, these complexes exhibit green photoluminescence with microsecond lifetimes (λmax = 515–538 nm; τ = 11.8–19.1 μs) at 298 K. The emission of the complexes originates from the (σ + X) → π* transition. All three complexes displayed good thermal stability.

Fluorination of Cyclometalated Iridium β-Ketoiminate and β-Diketiminate Complexes: Extreme Redox Tuning and Ligand-Centered Excited States

In this work we describe a series of bis-cyclometalated iridium complexes with ancillary β-ketoiminate (acNac) and β-diketiminate (NacNac) ligands, prepared by a general synthetic route. Fluorination of these ligands by introducing CF3 substituents onto the ligand backbone and/or N-aryl substituent(s) leads to pronounced changes in the redox properties and photophysical properties. All of the complexes show a reversible IrIV/IrIII redox couple that is sensitive to the degree of fluorination on the ancillary ligand. Introduction of CF3 groups at the 3- and 5-positions of the N-aryl substituent shifts the potential positive by ca. 50–70 mV per CF3 group, whereas fluorination of the acNac or NacNac backbone induces larger shifts of ca. 200–300 mV per CF3 group. Fluorination of the NacNac backbone gives rise to substantially altered excited-state properties. Complexes with backbone CF3 groups luminesce in the red and near-infrared regions out of an excited state that is predominately a π → π* NacNac-centered triplet state. A preponderance of evidence supports the assignment of this low-energy feature, including minimal dependence of this emission feature on the identity of the cyclometalating ligand, pronounced vibronic structure, and microsecond lifetimes. These results demonstrate that acNac and NacNac ancillary ligands can engender cyclometalated iridium complexes with desirable and readily tailorable redox and optical properties, motivating continued application of this important ligand class to the design of phosphorescent organometallic molecules.

Lipophilic phosphorescent gold(I) clusters as selective probes for visualization of lipid droplets by two-photon microscopy

Abstract The development of organelle-specific phosphorescent multiphoton probes is a rapidly growing area in biomedical imaging. Phosphorescent properties allow spectral or time-resolved discrimination from autofluorescence, while the use of two-photon microscopy provides higher spatial resolution as well as deeper penetration into the sample compared to conventional microscopies. The main challenge in this area is the design of probes that combine a complex of desired properties. Here we present investigation of the phosphorescent homoleptic alkynyl gold(I) cluster, (AuC 2 R) 10 (R − 2,6-dimethyl-4-heptanol), which combines nonlinear optical properties with selectivity to lipid droplets of adipocytes and other cells. This label reveals high two-photon absorption and emission cross-sections in hexane, good solubility in triglycerides (vegetable oil) and microsecond lifetimes both in solution and in biological tissues. These features make it a promising probe for multiphoton bioimaging as demonstrated by successful visualization of various adipose tissues (subcutaneous fat, visceral adipose tissue, adipose tissue of mesentery) of different animals (pigeon, chicken, mouse) as well as lipid droplets in Hep G2 cells. The complex demonstrates high selectivity to lipid droplets in animal tissues and cells. The probe lifetimes in microsecond domain made possible its visualization using phosphorescent lifetime imaging (PLIM) techniques.

(Invited) Silicon Quantum Dots: From Single-Dot Studies to Highly Luminescent Ensembles

The luminescent properties of nanoscale silicon were demonstrated in 1990 triggering the interest in Si nanostructures for optical emission. While the luminescence was quite strong even at room temperature, the micro-second long PL lifetimes revealed an inherited indirect bandgap from bulk Si. The luminescence mechanism was heavily debated whether quantum confinement really played a role or the emission would be due entirely from surface states. Many studies have confirmed the quantum confinement model but it has also been shown that the emission can be widely tuned by changing the surface passivation or by adding different ligands to the shell. The physics of the emission was however obscured by inhomogeneous line broadening due to the large size dispersion of the emitting entities in porous silicon or in matrices containing silicon nanocrystals. This called for single-dot spectroscopy studies as demonstrated for single molecules and later for nanocrystals of direct bandgap semiconductors. In this talk I will start by reviewing our work on PL emission and spectroscopy of individual Si quantum dots. These were initially fabricated using electron-beam lithography, plasma etching and oxidation resulting in micron spaced Si quantum dots that could be individually distinguished in an optical microscope. More recently we have also looked at more “randomly” spaced Si nanocrystals as well as colloidal nanocrystals dispersed on a wafer. These single-dot studies have revealed many of the phenomena observed for the II-VI nanocrystals such as on/off intermittency (blinking), spectral diffusion and narrow linewidth. Indeed, the linewidth at low temperatures was found to be ~250 µeV, limited by system resolution while the room temperature homogenous linewidth was shown to depend on the surface passivation and ligand shell. Recently, we have also performed absorption measurements of single nanocrystals revealing several distinct absorption levels above the fundamental bandgap that can be compared to theoretical calculations. Finally, in a collaboration with the group of Prof Veinot at the Univ. of Alberta, we have examined colloidal dispersions of Si nanocrystals fabricated from HSQ (hydrogen silsesquioxane). Recent data show very high quantum yields approaching 70 % for these nanocrystals. Lifetime measurements suggest that near 100 % internal quantum efficiency can be reached paving the way for many applications.

Insight into the Amino-Type Excited-State Intramolecular Proton Transfer Cycle Using N-Tosyl Derivatives of 2-(2'-Aminophenyl)benzothiazole.

Studies have been carried out to gain insight in to an overall excited-state proton transfer cycle for a series of N-tosyl derivatives of 2-(2'-aminophenyl)benzothiazole. The results indicate that followed by ultrafast (<150 fs) excited-state intramolecular proton transfer (ESIPT), the titled compounds undergo rotational isomerization along the C1-C1' bond. For the model compound 2-(2'-tosylaminophenyl)benzothiazole (PBT-NHTs) the subsequent cis-trans isomerization process in both triplet and ground states are probed by nanosecond transient absorption (TA) and two-step laser-induced fluorescence (TSLIF) spectroscopy. Both TA and TSLIF results indicate the existence of a long-lived trans-tautomer species in the ground state with a lifetime of few microseconds. The experimental results correlate well with the theoretical approach, which suggests that PBT-NHTs proton transfer tautomer generated in the excited state undergoes intramolecular C1-C1' rotation to ∼100° between benzothiazole and phenyl moieties in which the energetics for the S1 and T1 states are nearly identical. As a result, the intersystem crossing between S1 and T1 states serves as a fast deactivation pathway for the excited-state cis-tautomer to channel into both cis- and trans-tautomer in their respective T1 states, followed by the dominant T1-S0 radiationless deactivation to populate the trans-tautomer in the ground state. The trans-tautomer species in the S0 state proceeds with intermolecular double proton transfer to regenerate the cis-normal form. An overall proton-transfer cycle describing the amino-type ESIPT and the subsequent isomerization processes is thus depicted in detail.

Synthesis, crystal structure and photophysical study of luminescent three-coordinate cuprous bromide complexes based on pyrazole derivatives

The 1 : 2 M-ratio reaction between cuprous bromide and pyrazole derivatives in toluene results in mononuclear Cu(I) complexes [CuBr(pyrazole)2]. The complexes have been characterized by 1H NMR spectroscopy and elemental analysis. The molecular structure, established by single-crystal X-ray diffraction, features a trigonal planar geometry around copper, with monodentate pyrazole derivatives. All the Cu(I) complexes are luminescent in the solid state at ambient temperature. Intense blue or blue-green emission in the solid state is observed for these complexes, with the maxima ranging from 431 to 493 nm. The observed photoluminescence could be ascribed to the metal-to-ligand charge-transfer excited states, probably mixed with some halide-to-ligand character. The microsecond lifetime scale of the complexes implies that these transitions arise from the triplet excited states.

Cancer Cell Imaging Using in Situ Generated Gold Nanoclusters.

In situ generated fluorescent gold nanoclusters (Au-NCs) are used for bio-imaging of three human cancer cells, namely, lung (A549), breast (MCF7), and colon (HCT116), by confocal microscopy. The amount of Au-NCs in non-cancer cells (WI38 and MCF10A) is 20-40 times less than those in the corresponding cancer cells. The presence of a larger amount of glutathione (GSH) capped Au-NCs in the cancer cell is ascribed to a higher glutathione level in cancer cells. The Au-NCs exhibit fluorescence maxima at 490-530 nm inside the cancer cells. The fluorescence maxima and matrix-assisted laser desorption ionization (MALDI) mass spectrometry suggest that the fluorescent Au-NCs consist of GSH capped clusters with a core structure (Au8-13). Time-resolved confocal microscopy indicates a nanosecond (1-3 ns) lifetime of the Au-NCs inside the cells. This rules out the formation of aggregated Au-thiolate complexes, which typically exhibit microsecond (≈1000 ns) lifetimes. Fluorescence correlation spectroscopy (FCS) in live cells indicates that the size of the Au-NCs is ≈1-2 nm. For in situ generation, we used a conjugate consisting of a room-temperature ionic liquid (RTIL, [pmim][Br]) and HAuCl4. Cytotoxicity studies indicate that the conjugate, [pmim][AuCl4], is non-toxic for both cancer and non-cancer cells.

A Hybrid DNA-Templated Gold Nanocluster For Enhanced Enzymatic Reduction of Oxygen.

We report the synthesis and characterization of a new DNA-templated gold nanocluster (AuNC) of ∼1 nm in diameter and possessing ∼7 Au atoms. When integrated with bilirubin oxidase (BOD) and single walled carbon nanotubes (SWNTs), the AuNC acts as an enhancer of electron transfer (ET) and lowers the overpotential of electrocatalytic oxygen reduction reaction (ORR) by ∼15 mV as compared to the enzyme alone. In addition, the presence of AuNC causes significant enhancements in the electrocatalytic current densities at the electrode. Control experiments show that such enhancement of ORR by the AuNC is specific to nanoclusters and not to plasmonic gold particles. Rotating ring disk electrode (RRDE) measurements confirm 4e(-) reduction of O2 to H2O with minimal production of H2O2, suggesting that the presence of AuNC does not perturb the mechanism of ORR catalyzed by the enzyme. This unique role of the AuNC as enhancer of ET at the enzyme-electrode interface makes it a potential candidate for the development of cathodes in enzymatic fuel cells, which often suffer from poor electronic communication between the electrode surface and the enzyme active site. Finally, the AuNC displays phosphorescence with large Stokes shift and microsecond lifetime.