Carbazole-Functionalized Dipicolinato LnIII Complexes Show Two-Photon Excitation and Viscosity-Sensitive Metal-Centered Emission.

EuIII and YbIII complexes with the carbazole-dipicolinato ligand dpaCbz2-, namely K3[Eu(dpaCbz)3] and K3[Yb(dpaCbz)3], were isolated. The EuIII complex displayed metal-centred emission upon one-photon excitation with a sensitized emission efficiency Φ L Ln of 1.8±0.3 %, corresponding to an intrinsic emission efficiency Φ Ln Ln of 46% and a sensitization efficiency of ηsens 3.9%, with an emission lifetime of the emissive state τ of 1.087±0.005 ms. The YbIII complex displayed Φ L Ln of 0.010±0.001 %, and a τ of 2.32±0.06 μs. The EuIII-centred emission was sensitized as well upon two-photon excitation and a two-photon absorption cross-section σ2PA of 63 GM at 750 nm was determined for the complex. The one- or two-photon sensitized emission intensity of the EuIII complex changes by more than two-fold when the solvent viscosity is varied in the range 0.5 - 200 cP and the emission is independent of dissolved oxygen. The YbIII complex displays a change in emission intensity as well. However, in this case, a dependence of the emission intensity on dissolved oxygen content was observed.