Dicopper(I) Paddle-Wheel Complexes with Thermally Activated Delayed Fluorescence Adjusted by Ancillary Ligands

A suite of paddle-wheel shaped [Cu₂(PymPPh₂)₃(L_an)](PF₆)₂ complexes showing efficient thermally activated delayed fluorescence (TADF) has been synthesized. In these complexes, Cu(I) ions are P,N-bridged by three diphenyl(2-pyrimidyl)phosphine (PymPPh₂, L) ligands in a "head-to-tail" fashion, and one or both metals are also capped by the ancillary ligand (L_an = MeOH, Me₂CO, MeCN, PhCN). At ambient temperature, the solid complexes emit TADF with the quantum yield of up to 85% and the lifetimes of from 9.6 to 27 μs. The ancillary ligands, whose orbitals negligibly contribute to the radiative ¹(M + L + L_an)LCT state, remarkably adjust emission energies and ΔE(S₁-T₁) energy splitting magnitudes of the emitters obtained. Thus, depending on structure and/or number of the L_an molecules, the emission maxima vary from 500 to 563 nm, and the ΔE(S₁-T₁) gaps range 550-1100 cm^-1. Such tunable TADF characteristics coupled with the excellent solubility and air-stability make the complexes presented to be promising TADF materials.