Dinuclear Ag(I) Complex Designed for Highly Efficient Thermally Activated Delayed Fluorescence

Abstract

The dinuclear Ag(I) complex has been designed to show thermally activated delayed fluorescence (TADF) of high efficiency. Strongly electron-donating terminal ligands are introduced to destabilize the d orbitals of the Ag⁺ ions. Consequently, the orbitals distinctly contribute to the HOMO, whereas the LUMO is localized on the bridging ligand. This ensures charge transfer character of the lowest excited singlet S₁ and triplet T₁ states. Accordingly, a small energy gap ΔE(S₁-T₁) is obtained, being essential for TADF behavior. Photophysical investigations show that at ambient temperature the complex exhibits TADF reaching a quantum yield of Φ_PL = 70% with the decay time of only τ = 1.9 μs, manifesting one of the fastest TADF decays observed so far. Such an outstanding TADF efficiency is based on a small value of ΔE(S₁-T₁) = 480 cm^-1 combined with a large transition rate of k(S₁ → S₀) = 2.2 × 10⁷ s^-1.