A suite of paddle-wheel shaped [Cu2(PymPPh2)3(Lan) n ]­(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 (Lan = 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 + Lan)­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 Lan 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.

The reduction of tetraphenyldiphosphine with two differently substituted samarocenes(II) proceeds via different pathways. With [SmCp* 2 (THF) 2 ] (Cp* = η 5 -C 5 Me 5 ), the reaction had been known to result in the THF ring-opening product, [SmCp* 2 (O(CH 2 ) 4 PPh 2 )], 3, owing to the instability of phosphido complex [SmCp* 2 (PPh 2 )] in the presence of THF. Complex 3 crystallizes from apolar solvents as dimeric or polymeric polymorph with butoxo-phosphine bridging ligands in both cases. In contrast, the phosphide [SmCp″ 2 (PPh 2 )] (Cp′′ = η 5 -1,3-C 5 H 3 t Bu 2 ), 5, is not prone to ring-opening owing to insufficient space in the Sm coordination sphere for a THF ligand. Product 5 is inevitably accompanied by homoleptic complex [SmCp″ 3 ] 6 and dinuclear mixed-valent complex [Sm III Cp″ 2 (μ-PPh 2 ) 2 Sm II Cp″] 7 as the further products of redox transformations and ligand exchange. The formation of 5−7 is rationalized by a sequence of initial coordination of one or two {Sm II Cp″ 2 } fragments by P atoms and reductive elimination of PPh 2 • or Cp″• radicals. Further reaction with another equivalent of [SmCp″ 2 ] results in the trapping the radicals and formation of all three products.

A family of brightly luminescent dinuclear complexes of [Cu(μ-X)(N^N)] type (X = I or SCN) has been synthesized in 76-90% yields by the reaction of bis(2-pyridyl)phosphine oxides (N^N) with the corresponding Cu(i) salts. The X-ray diffraction study reveals that the CuI core of the [Cu(μ-I)(N^N)] complexes has either a butterfly- or rhomboid-shaped structure, while the eighth-membered [Cu()Cu] ring in the [Cu(SCN)(N^N)] complexes is nearly planar. In the solid state, these compounds exhibit a strong green-to-yellow emission (λ = 536-592 nm) with high PLQYs (up to 63%) and short lifetimes (1.9-10.0 μs). The combined photophysical and DFT study indicates that the ambient-temperature emission of the complexes obtained can be assigned to the thermally activated-delayed fluorescence (TADF) from the (M + X)LCT excited state, while at 77 K, phosphorescence from the(M + X)LCT state is likely observed.

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