Novel Erbium(III)-Encapsulated Complexes Based on pi-Extended Anthracene Ligands Bearing G3-Aryl-Ether Dendron: Synthesis and Photophysical Studies

Abstract

A series of inert and photo-stable Er(III)-encapsulated complexes based on pi-extended dendritic anthracene ligands bearing G3-aryl-ether dendron ([G3-AnX]-CO2H), which retain different pi-bridging systems, such as single (X=S), double (X=D) and triple (X=T) bonds was designed and synthesized to establish the structure-property relationship. The near infrared emission intensities of Er(III)-encapsulated complexes were enhanced dramatically by increasing the pi-conjugated extension of anthracene ligands. The time-resolved luminescence spectra show monoexponential decays with a lifetime of 2.0 similar to 2.4 ms for Er3+ ions in thin films, and calculated intrinsic quantum yields of Er3+ ions are in the range of 0.025 similar to 0.03%. As a result, all Er(Ill)-encapsulated dendrimer complexes exhibit the near IR emission with the following order: Er3+-[G3-AnD](3)(terpy) > Er3+-[G3-AnS](3)(terpy) approximate to Er3+-[G3-AnT](3)(terpy), because Er3+-[G3-AnD](3)(terpy) has a higher relatively spectral overlap J value and energy transfer efficiency. In addition, the lack of detectable phosphorescence and no significant spectral dependence of the pi-extended anthracene moieties on the solvent polarity support energy transfer from their singlet state to the central Er3+ ion taking place in Er3+-[G3-AnX](3)(terpy).