Modulating the energy transfer processes via XPh3 (X = Si, Ge, Sn) substitution in luminescent Eu3+ β-diketonate complexes

Abstract

A series of novel Eu³⁺ complexes with group 14 element-containing β-diketone ligands were synthesized and their photoluminescence properties were studied in detail. The introduction of electron-donating XPh₃ groups (X = Si, Ge, Sn) into the phenyl ring of the well-known BTFA β-diketone ligand was found to lower the energy of the ligand triplet excited state T₁. Along the Si–Ge–Sn series, this results in a progressively reduced energy gap between the excited triplet state T₁ and ligand-to-metal charge transfer (LMCT) states. This provides an efficient channel for quenching the ligand excitation via the LMCT channel. As a result, a gradual decrease in the overall luminescence quantum yield is observed, identifying the Si-based derivative as the most efficient luminescent complex among substituted derivatives. The experimental findings were supported by theoretical calculations using the TD-DFT method.