One-Photon Near-Infrared Sensitization of Well-Defined Yb(III) Surface Complexes for NIR-to-NIR Single Nanoparticle Imaging

Silica nanoparticles of 12 nm diameter were surface-doped with ca. 350 (TTF-dppz)Yb(III) surface species, containing bis(propylthio)tetrathiafulvenyl[ i ]dipyrido-[3,2- a:2′,3- c ]phenazine (TTF-dppz) as an antenna ligand through a surface organometallic chemistry approach. These nanoparticles absorb and emit in the NIR (λ abs = 750 nm, λ em = 983 and 1050 nm) with a lifetime (τ 1 ) of 2.8 μs, similarly to the corresponding Yb(III) molecular complex (λ abs = 750 nm, λ em = 975, 986, 1009, and 1020 nm with τ 1 = 6.93 μs). The silica materials were fully characterized using combined spectroscopic techniques (IR, NMR, UV–vis, luminescence and lifetime), molecular models and isostructural diamagnetic yttrium-containing materials for easier characterization by NMR spectroscopy. Having established the surface structures and photophysical properties of these nanoparticles, we transposed this methodology to larger silica particles with a diameter of ca. 100 nm. These larger nanoparticles have similar photophysical properties and contain ca. 30 000 chromophores, making possible one-photon NIR-to-NIR emission optical microscopy imaging of single nanoparticles.