Charge-Transfer-Mediated Mechanism Dominates Oxygen Quenching of Ligand-Protected Noble-Metal Cluster Photoluminescence

Abstract

Chemicals; synthesis of ligand-protected noble-metal clusters; electrospray ionization time-of-flight mass spectrometry; absorption and photoluminescence measurements; transient absorption spectroscopy; analysis of delayed fluorescence decay; procedure for determination of absorption edge; estimation of diffusion-limited rate constant (PDF)

Structurally Flexible Au–Cu Alloy Nanoclusters Enabling Efficient Triplet Sensitization and Photon Upconversion

“…For Au 2 Cu 6 , fluorescence (∼670 nm) and phosphorescence (∼810 nm) bands were discernibly separated, whereas for Au 4 Cu 4 , only a single broad band with a peak around 735 nm was observed (Figure b). The emission band of Au 4 Cu 4 was strongly quenched by molecular oxygen (Figure c), and the emission lifetime in Ar-degassed THF was 7.9 μs, which significantly reduced to 0.60 μs under air-saturated conditions . Thus, the emission of Au 4 Cu 4 mainly stems from phosphorescence from the triplet state.…”

“…In addition, NCs comprise plural heavy-metal elements (Au, Ag, Cu, etc.) with large spin–orbit coupling (SOC) constants, which allow rapid spin-flip and inevitably generate excited triplet states with high efficiency. − Owing to such an intrinsic triplet nature, NCs frequently exhibit relatively long excited-state lifetimes of several microseconds. Such photophysical properties render them highly desirable as photosensitizers that effectively promote photocatalysis, − singlet oxygen generation, − and photochemical upconversion (UC). − , …”

“…Additionally, they often contain toxic elements, such as Pb and Cd, which are problematic because they hinder the fabrication of ecofriendly materials. Recently, our group showed that NCs such as [PtAg 24 (DMBT) 18 ] 2– (DMBT = 2,4-dimethylbenzenethiolate); [Au 25 (PET) 5 (TPP) 10 Cl 2 ] 2+ (PET = 2-phenylethanethiolate; TPP = triphenylphosphine); [Ag x Au 25– x (PET) 5 (TPP) 10 Cl 2 ] 2+ ( x = 12, 13); [Au 13 (DPPE) 5 Cl 2 ] 3+ (Au 13 ; DPPE = 1,2-bis­(diphenylphosphino)­ethane); and Au 2 Cu 6 (S-Adm) 6 (TPP) 2 ( Au 2 Cu 6 ; S-Adm = 1-adamantanethiolate) can be utilized as new platforms for triplet sensitizers for TTA-UC. In addition to low toxicity, NCs possess advantages similar to those of semiconductor nanocrystals, such as the facile tunability of optoelectronic properties, surface functionalization by ligands, and a ubiquitous triplet nature.…”

“…Such photophysical properties render them highly desirable as photosensitizers that effectively promote photocatalysis, 26−30 singlet oxygen generation, 31−33 and photochemical upconversion (UC). [20][21][22][23]25 Photon UC based on triplet−triplet annihilation (TTA) is the sole mechanism that converts two low-energy photons into a high-energy one under low-intensity incoherent light irradiation. Therefore, TTA-UC is attracting significant attention as a promising photon energy management technique with a wide range of applications, including photovoltaics, 34,35 photocatalysis, 36 ultralow-power bioimaging, 37 oxygen sensing, 38 and optogenetics.…”

“…The emission band of Au 4 Cu 4 was strongly quenched by molecular oxygen (Figure 1c), and the emission lifetime in Ar-degassed THF was 7.9 μs, which significantly reduced to 0.60 μs under air-saturated conditions. 25 Thus, the emission of Au 4 Cu 4 mainly stems from phosphorescence from the triplet state. The emission quantum yield (Φ em ) obtained by the relative method (eq S2) was 0.32, so the phosphorescence quantum yield (Φ p ) should be greater than 0.32 because of the relationship of Φ em = Φ ISC Φ p .…”