Thermally activated delayed fluorescence emitters for efficient sensitization of europium(III)

We demonstrate for the first time a unique approach to efficiently sensitize lanthanides(III) using photosensitizer ligands that show thermally activated delayed fluorescence (TADF). TADF ligands have very small singlet (S₁) and triplet (T₁) excited state energy splitting and S₁/T₁ energy levels are in optimum energy to the acceptor level of Eu(III) to enable high energy transfer efficiency. The synthesized Eu(III) coordination polymers with TADF ligands showed bright red luminescence with an outstanding sensitization efficiency of 90-94% and Φ_tot of 79-85% in poly(methyl methacrylate) encapsulated films. This rational approach of efficiently sensitizing lanthanides with TADF ligands demonstrates their great potential for imaging and optical communications applications.