A novel type of cyclic P,N-ligands, pyridyl containing phospholanes, has been synthesized in a moderate yield by the reaction of primary phosphines with 1,4-dichlorobutane in a superbasic medium. A series of homo tetranuclear octahedral Cu₄I₄L₂, dinuclear tetrahedral Cu₂I₂L₃, and dinuclear “head-to-tail” Cu₂I₂L₂ luminescent complexes with these ligands were obtained. All the compounds were characterized using a range of spectroscopic and computational techniques, and in the case of some Cu₄I₄L₂ and Cu₂I₂L₃ complexes, by single crystal X-ray diffraction. The structural diversity of the obtained complexes was reflected in their photophysical properties: phosphorescence spectra of the compounds display emission in broad spectral range of 471–615 nm. TD-DFT computations allow the assignment of a single emission band around 550 nm for Cu₂I₂L₃ complexes and 471 nm for Cu₂I₂L₂ complex to a vertical triplet–singlet transition from a metal-to-ligand and halide-to-ligand charge-transfer ³(M + X)LCT excited state, whereas a second band at around 600 nm in the spectra of octahedral Cu₄I₄L₂ complexes was assigned predominantly to Cu₄I₄ cluster-centered (³CC) excited state.

The series of chelating phosphine ligands, which contain bidentate P² (bis[(2-diphenylphosphino)phenyl] ether, DPEphos; 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene, Xantphos; 1,2-bis(diphenylphosphino)benzene, dppb), tridentate P³ (bis(2-diphenylphosphinophenyl)phenylphosphine), and tetradentate P⁴ (tris(2-diphenylphosphino)phenylphosphine) ligands, was used for the preparation of the corresponding dinuclear [M(μ₂-SCN)P²]₂ (M = Cu, 1, 3, 5; M = Ag, 2, 4, 6) and mononuclear [CuNCS(P³/P⁴)] (7, 9) and [AgSCN(P³/P⁴)] (8, 10) complexes. The reactions of P⁴ with silver salts in a 1:2 molar ratio produce tetranuclear clusters [Ag₂(μ₃-SCN)(t-SCN)(P⁴)]₂ (11) and [Ag₂(μ₃-SCN)(P⁴)]₂²⁺ (12). Complexes 7–11 bearing terminally coordinated SCN ligands were efficiently converted into derivatives 13–17 with the weakly coordinating ^–SCN:B(C₆F₅)₃ isothiocyanatoborate ligand. Compounds 1 and 5–17 exhibit thermally activated delayed fluorescence (TADF) behavior in the solid state. The excited states of thiocyanate species are dominated by the ligand to ligand SCN → π(phosphine) charge transfer transitions mixed with a variable contribution of MLCT. The boronation of SCN groups changes the nature of both the S₁ and T₁ states to (L + M)LCT d,p(M, P) → π(phosphine). The localization of the excited states on the aromatic systems of the phosphine ligands determines a wide range of luminescence energies achieved for the title complexes (λ_em varies from 448 nm for 1 to 630 nm for 10c). The emission of compounds 10 and 15, based on the P⁴ ligand, strongly depends on the solid-state packing (λ_em = 505 and 625 nm for two crystalline forms of 15), which affects structural reorganizations accompanying the formation of electronically excited states.

Organometallics featuring acyclic diaminocarbene ligands have recently emerged as powerful emitters for use in electroluminescent technologies.