Biicosahedral Au25 clusters exhibit room-temperature phosphorescence from the excited triplet state with an intersystem crossing quantum yield of almost 100%. This property allows triplet sensitization and induces triplet fusion photon upconversion.

Scheme 2. Proposed relaxation of Ag 25 and PtAg 24 clusters. Core-toshell relaxation rate constant (1/3 CS! 1/3 SS) was assumed to be 10 11-10 12 s À1 , [24, 35] which was used to estimate the core ISC rate constant.

Photon upconversion (UC) from near‐infrared (NIR) to visible has been realized using singlet‐to‐triplet absorption of sensitizers, which are currently limited to osmium complexes and semiconductor nanocrystals. Motivated by the atomically precise tunability of electronic structure and photophysical properties of noble metal clusters, which often possess absorption bands that extend into the NIR region, we investigated MAg24(SR)18 (M=Ag, Pt; SR=2,4‐dimethylbenzenethiolate) clusters as a new NIR‐absorbing sensitizer for triplet–triplet annihilation UC. Combined with a blue light emitter, the NIR excitation (λex=785 nm) of Ag25(SR)18 results in no UC emission, while PtAg24(SR)18 exhibits strong UC emission. This enhancement is primarily due to a significant increase in the intersystem crossing quantum yield of the cluster associated with the spin–orbit coupling enhancement in the M@Ag12 core.

Clusterverbindungen In der Zuschrift auf S. 2858 berichten Masaaki Mitsui et al. über Pt‐dotierte Ag‐Cluster als neue NIR‐absorbierende Sensibilisatoren für die Photonen‐Aufkonvertierung. Pt‐Dotierung erhöht den Wirkungsquerschnitt des Intersystem‐Crossings im Cluster.

Cluster Compounds In their Communication on page 2822, Masaaki Mitsui et al. report on Pt‐doped Ag clusters as a new NIR‐absorbing sensitizer for photon upconversion. Pt doping significantly increases the intersystem crossing yield of the cluster.