Silica sol-gel glasses incorporating dual-luminescent Yb quinolinolato complex: Processing, emission and photosensitising properties of the 'antenna' ligand

The [Yb(5,7ClQ)₂(H5,7ClQ)₂Cl] (1) complex, that exhibits dual-luminescence in the visible (ligand-centered) and in the NIR (Yb-centered), has been incorporated into a silica sol-gel glass obtaining 1-doped glassy material which is optically transparent and homogeneous and with good mechanical properties. The doped sol-gel glass can be considered a "solid state solution" and photophysical studies demonstrate that the emissive properties of the dopant complex are preserved in the silica matrix. Observed NIR decay times fall in the μs range and are likely limited by "second-sphere" matrix interactions. The ligand-to-metal energy transfer mechanism occurs on ultrafast timescale and involves ligand triplet states. The sensitization efficiency of the antenna quinolinolato ligand toward Yb³⁺ is estimated to be as high as ∼80%. The Yb natural radiative lifetime observed for 1 in MeCN-EtOH solution (τ_rad = 438 μs) is the shortest reported so far for ytterbium complexes.