Near-unity NIR phosphorescent quantum yield from a room-temperature solvated metal nanocluster.

Metal nanoclusters have emerged as promising near-infrared (NIR)-emissive materials, but their room-temperature photoluminescence quantum yield (PLQY), especially in solution, is often low (<10%). We studied the photophysics of Au22(tBuPhC≡C)18 (Au22) and its alloy counterpart Au16Cu6(tBuPhC≡C)18 (Au16Cu6) (where tBu is tert-butyl and Ph is phenyl) and found that copper (Cu) doping suppressed the nonradiative decay (~60-fold less) and promoted intersystem crossing rate (~300-fold higher). The Au16Cu6 nanocluster exhibited >99% PLQY in deaerated solution at room temperature with an emission maximum at 720 nanometers tailing to 950 nanometers and 61% PLQY in the oxygen-saturated solution. The approach to achieve near-unity PLQY could enable the development of highly emissive metal cluster materials.

B-N Covalent Bond Embedded Double Hetero-[n]helicenes for Pure Red Narrowband Circularly Polarized Electroluminescence with High Efficiency and Stability.

Chiral B/N embedded multi-resonance (MR) emitters open a new paradigm of circularly polarized (CP) organic light-emitting diodes (OLEDs) owing to their unique narrowband spectra. However, pure-red CP-MR emitters and devices remain exclusive in literature. Herein, by introducing a B-N covalent bond to lower the electron-withdrawing ability of the para-positioned B-π-B motif, the first pair of pure-red double hetero-[n]helicenes (n = 6 and 7) CP-MR emitter peaking 617 nm with a small full-width at half-maximum of 38 nm and a high photoluminescence quantum yield of ≈100% in toluene is developed. The intense mirror-image CP light produced by the enantiomers is characterized by high photoluminescence dissymmetry factors (gPL ) of +1.40/-1.41 × 10-3 from their stable helicenes configuration. The corresponding devices using these enantiomers afford impressive CP electroluminescence dissymmetry factors (gEL ) of +1.91/-1.77 × 10-3 , maximum external quantum efficiencies of 36.6%/34.4% and Commission Internationale de I'Éclairage coordinates of (0.67, 0.33), exactly satisfying the red-color requirement specified by National Television Standards Committee (NTSC) standard. Notably a remarkable long LT95 (operational time to 95% of the initial luminance) of ≈400 h at an initial brightness of 10,000 cd m-2 is also observed for the same device, representing the most stable CP-OLED up to date.

Site-specific doping of silver atoms into a Au25 nanocluster as directed by ligand binding preferences.

For the first time site-specific doping of silver into a spherical Au25 nanocluster has been achieved in [Au19Ag6(MeOPhS)17(PPh3)6] (BF4)2 (Au19Ag6) through a dual-ligand coordination strategy. Single crystal X-ray structural analysis shows that the cluster has a distorted centered icosahedral Au@Au6Ag6 core of D 3 symmetry, in contrast to the I h Au@Au12 kernel in the well-known [Au25(SR)18]- (R = CH2CH2Ph). An interesting feature is the coexistence of [Au2(SPhOMe)3] dimeric staples and [P-Au-SPhOMe] semi-staples in the title cluster, due to the incorporation of PPh3. The observation of only one double-charged peak in ESI-TOF-MS confirms the ordered doping of silver atoms. Au19Ag6 is a 6e system showing a distinct absorption spectrum from [Au25(SR)18]-, that is, the HOMO-LUMO transition of Au19Ag6 is optically forbidden due to the P character of the superatomic frontier orbitals.

A 59-Electron Non-Magic-Number Gold Nanocluster Au99(C≡CR)40 Showing Unexpectedly High Stability.

An atomically resolved gold nanocluster Au99(C≡CC6H3-2,4-F2)40 (Au99) with an unusual 59 valence electrons has been synthesized. Single-crystal X-ray diffraction reveals that its Au79 kernel is a Au49 Marks decahedron capped by two Au15 units. The surface structure of Au99 consists of 20 linear Au(C≡CR)2 staples. Intercluster interactions are observed between these D5 symmetric clusters. The existence of an unpaired electron is verified by magnetic measurement. Interestingly, this open-shell gold cluster Au99 stays intact in toluene solution at 80 °C for more than a week, and it has good charging-discharging capability under electrochemical conditions. The compact ligand shell protection around the symmetric core accounts for the high stability. This work suggests that geometric factors may play a crucial role in determining the stability of a metal nanocluster, even though the cluster has an open-shell electronic structure.

Robust Gold Nanocluster Protected with Amidinates for Electrocatalytic CO2 Reduction.

The first all-amidinate-protected gold nanocluster [Au28 (Ph-form)12 ](OTf)2 (Ph-form=N,N'-diphenylformamidinate) (Au28 ) has been synthesized and structurally resolved. Single crystal X-ray diffraction reveals that Au28 has a compact Au4 @Au24 tetrahedral core-shell structure of T symmetry, which is fully protected by 12 bridging formamidinate ligands. This cluster is quite robust as indicated by the fact that it can stay intact in solution at 80 °C for 6 d. It exhibits excellent catalytic performance for the electroreduction of CO2 with 96.5 % Faradaic efficiency (FE) at -0.57 V and a maximum TOF of 1731 h-1 at -0.87 V. Its superior stability is also manifested in the fact that the supported catalyst Au28 /CNTs maintains stable potentials at ca. -0.69 V for 40 h with FE(CO)s>91 %. A superatomic electron configuration of 1S2 1P6 2S2 1D4 has been clarified by DFT computations, and the strong gold-ligand binding and geometric shell closure account for the superior stability of Au28 .

Structure Determination of Alkynyl-Protected Gold Nanocluster Au22 (t BuC≡C)18 and Its Thermochromic Luminescence.

An alkynyl-protected gold nanocluster, Au22 (t BuC≡C)18 (1), has been synthesized and its structure has been determined by single-crystal X-ray diffraction. The molecular structure consists of a Au13 cuboctahedron kernel and three [Au3 (t BuC≡C)4 ] trimeric staples. The cluster 1 has strong luminescence in the solid state with a 15 % quantum yield, and it displays interesting thermochromic luminescence as revealed by temperature-dependent emission spectra. The enhanced room-temperature emission is characterized as thermally activated delayed fluorescence.