A Novel Near-Infrared Ytterbium Complex [Yb(DPPDA) 2 ](DIPEA) with Φ = 0.46% and τ obs = 105 μs.

The luminescent performances of near-infrared (NIR) lanthanide (Ln) complexes were restricted greatly by vibration quenching of X-H (X = C, N, O) oscillators, which are usually contained in ligands and solvents. Encapsulating Ln ³⁺ into a cavity of coordination atoms is a feasible method of alleviating this quenching effect. In this work, a novel ytterbium complex [Yb(DPPDA) ₂ ](DIPEA) coordinated with 4,7-diphenyl-1,10-phenanthroline-2,9-dicarboxylic acid (DPPDA) was synthesized and characterized by FT-IR, ESI-MS and elemental analysis. Under the excitation of 335 nm light, [Yb(DPPDA) ₂ ](DIPEA) showed two emission peaks at 975 and 1011 nm, respectively, which were assigned to the characteristic ² F _5/2 → ² F _7/2 transition of Yb ³⁺ . Meanwhile, this ytterbium complex exhibited a plausible absolute quantum yield of 0.46% and a luminescent lifetime of 105 μs in CD ₃ OD solution. In particular, its intrinsic quantum yield was calculated to be 12.5%, and this considerably high value was attributed to the near-zero solvent molecules bound to Yb ³⁺ and the absence of X-H oscillators in the first coordination sphere. Based on experimental results, we further proposed that the sensitized luminescence of [Yb(DPPDA) ₂ ](DIPEA) occurred via an internal redox mechanism instead of an energy transfer process.