Organic chromophores as acceptors in Homometallic Yb Molecular Cluster Aggregates for Near-Infrared to Visible Linear Light Upconversion in Solution

A photoactive organic chromophore (Eosin Y) is here used as acceptor in an excited homometallic hexanuclear ytterbium molecular cluster-aggregate (MCA). This novel MCA can be easily prepared by hydrolysis of Yb(NO3)3 ⋅6·H2O in basic media (triethanolamine (H3teao) and triethylamine (tea)) in the presence of the organic chromophore (EOS). The 6[Yb6(Hteao)6(EOS)6] MCA, here termed (EOS-Yb)6 , displays near infrared (NIR) to visible (Vis) upconversion (UC) in solution via cooperative sensitization (CS). Specifically, upon excitation of (EOS-Yb) 6 MCA at 980 nm, a long-lived EOS emission (microseconds) is observed in the Vis, at room temperature (with a quantum yield value of 1.3x10-5 in DMSO-d6 at 8.04 W·cm‒2 ). The CS UC observed for (EOS-Yb)6 MCA increases with concentration and is nonsensitive to oxygen. (EOS-Yb)6 MCA not only benefits from easy synthetic reproducibility and allows for a long-lived UC emission of an organic chromophore, but also avoids the characteristic aggregation of xanthenic dyes, the need of deaerated environments for UC via triplet -triplet annihilation and mitigates the drawbacks of multiphoton excitation, allowing for continuous-wave (CW) NIR-activation.