Lanthanide(III) dendrimer complexes based on diphenylquinoxaline derivatives for photonic amplification
A series of novel lanthanide(III) complexes (Ln=Gd, Er, Yb) based on dendritic diphenylquinoxaline (DPQ) ligands was designed and synthesized with the aim of enhancing the luminescence intensity of Er3+ and Yb3+ ions for photonic applications. The diphenyl-quinoxaline ligand was introduced as a photon antenna for efficient light harvesting and subsequent energy transfer onto the Ln(3+) ions. The dendritic complexes showed strong near-IR emission at 981 (Yb3+) and 1,530 (Er3+) nm, which was sensitized through energy transfer from the excited states of the diphenyl-quinoxaline ligands. The near-IR emission intensity of the lanthanide ions in second-generation [Ln(G2-DPQ-COO)(3)(terpy)] complexes was significantly enhanced, due to the light-harvesting effect, with respect to [Ln(G1-DPQ-COO)(3)(terpy)]. However, increasing the size of the dendron in [Ln(G3-DPQ-COO)(3)(terpy)] was found to be detrimental to the emission efficiency. This may be attributed to the twisted structure of the dendritic ligand and suggests that conformational effects should be taken into consideration when designing ligands for photonic amplification.