Factors that influence the energy transfer pathways in luminescent lanthanide Schiff base complexes

In the past decades, lanthanide(III) complexes from the Schiff base ligands have received attention for their marvelous luminescence properties. Accordingly, their complexes have been used in a variety of applications in optical, biological and environmental fields. In this review, the structural and sensitization aspects of the lanthanide(III) Schiff base complexes have been investigated. The factors that induce their luminescence properties through efficient energy transfer pathways have been discussed thoroughly, such as (1) metal’s geometry, (2) ligand’s design and the preferred binding modes, (3) temperature and (4) molecular aggregation. In addition, the nature of the low-lying excited triplet state initiated from (1) intra-ligand charge transfer, ILCT, (2) ligand to metal charge transfer, LMCT, (3) ligand–ligand interaction, LLI, or (4) mixed d-f or f-f excited states in a single molecule, have also been discussed in detail.