Dynamic Molecular Triplet Excitons Tune Lanthanide Emission Lifetime

Optical codes generated from the emission lifetimes of lanthanide complexes have received considerable attention for their potential application in multiplexed bioimaging and anti-counterfeiting. However, such tunable lifetimes are limited to short ranges (0.01-1 ms). Herein, we describe a method that extends the emission lifetime using dynamic molecular triplet excitons in aggregation systems composed of lanthanide complexes. To demonstrate the conceptual method, molecular crystals comprising lutetium (Lu³⁺) and luminescent lanthanide (europium: Eu³⁺ or terbium: Tb³⁺) complexes with two organic ligands (2,2,6,6-tetramethyl-3,5-heptanedionate and 2,7-bis(diphenylphosphoryl)phenanthrene) were prepared. These molecular crystals exhibited persistent emission via slow triplet exciton migration between the phenanthrene units. The extended degree of the lifetime could be controlled between 1 and 152 ms by ligand modifications. This proposed lifetime-tuning method should significantly expand the encoding capacity of lanthanide complexes.