Design Strategy for Ag(I)-Based Thermally Activated Delayed Fluorescence Reaching an Efficiency Breakthrough

Abstract

A design strategy for the development of Ag(I)-based materials for thermally activated delayed fluorescence (TADF) is presented. Although Ag(I) complexes usually do not show TADF, the designed material, Ag(dbp)(P2-nCB) [dbp = 2,9-di-n-butyl-1,10-phenanthroline, and P2-nCB = nido-carborane-bis(diphenylphosphine)], shows a TADF efficiency breakthrough exhibiting an emission decay time of τ(TADF) = 1.4 μs at a quantum yield of ΦPL = 100%. This is a consequence of three optimized parameters. (i) The strongly electron-donating negatively charged P2-nCB ligand destabilizes the 4d orbitals and leads to low-lying charge (CT) states of MLL′CT character, with L and L′ being the two different ligands, thus giving a small energy separation between the lowest singlet S1 and triplet T1 state of ΔE(S1–T1) = 650 cm–1 (80 meV). (ii) The allowedness of the S1 → S0 transition is more than 1 order of magnitude higher than those found for other TADF metal complexes, as shown experimentally and by time-dependent density functi...