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]-$CO_2H$), 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 $2.0{sim}2.4ms$ for $Er^{3+}$ ions in thin films, and calculated intrinsic quantum yields of $Er^{3+}$ ions are in the range of $0.025{sim}0.03%$. As a result, all Er(III)-encapsulated dendrimer complexes exhibit the near IR emission with the following order: $Er^{3+}-[G3-AnD]_3$(terpy) > $Er^{3+}-[G3-AnS]_3$(terpy) ${approx}$ $Er^{3+}-[G3-AnT]_3$(terpy), because $Er^{3+}-[G3-AnD]_3$(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 $Er^{3+}$ ion taking place in $Er^{3+}-[G3-AnX]_3$(terpy).