Ligand Engineering in Lanthanide‐Titanium‐Oxo Clusters: Preventing Charge Transfer to Ti ^IV for High‐Efficiency Emission

Lanthanide-titanium-oxo clusters (LTOCs) exhibit promising luminescence potential owing to their unique core structures. In this study, the impact of ligand-to-metal charge transfer (LMCT, M = Ti^IV) is systematically elucidated on the luminescence of LTOCs through crystal structure analysis, theoretical calculations, and photophysical measurements. The results reveal that the existence of the LMCT state disrupts the normal energy transfer process, thereby causing the failure of photo-excitation in LTOCs. By strategically replacing LMCT-inducing ligands with non-LMCT counterparts in Eu₂Ti₄ and Eu₂Ti₆ clusters, the remarkable enhancement is achieved in luminescence intensity. This study provides valuable insights into the rational design of high-performance luminescent LTOCs, highlighting ligand coordination environments as a critical design factor in LTOCs.