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π–π stacking interactions and C–H⋯X (X = O, F) interactions formed by counteranions help to enhance the rigidity of these structures and further improve their luminescence quantum yields.

Five novel mononuclear [Cu(Bphen)(bdppmapy)]X complexes showing photoluminescence were synthesized. The same diphosphine ligand and diimine ligand and different Cu(I) salts were used in the one-pot synthesis of complexes 1–5. These complexes are listed as follows: [Cu(Bphen)(bdppmapy)]CF3SO3 (1), [Cu(Bphen)(bdppmapy)]BF4·0.268CH3OH (2), [Cu(Bphen)(bdppmapy)]ClO4 (3), [Cu(Bphen)(bdppmapy)]I·CH3OH (4) and [Cu(Bphen)(bdppmapy)]Br·2CH3OH (5) (Bphen = 4,7-diphenyl-1,10-phenanthroline, bdppmapy = N,N-bis((diphenylphosphino)methyl)-2-pyridinamine). IR, NMR, elemental analysis, single-crystal X-ray diffraction analysis, UV-vis, fluorescence spectroscopy and terahertz time-domain absorption spectroscopy (THz-TDS) were used to characterize 1–5. Their crystal structures have been elucidated by X-ray crystallography and their photophysical properties have been investigated in detail. These five complexes have a similar coordination center, while their space stacked structures are different, from a 0D dimeric structure to a 3D supramolecular structure. Photophysical studies and density functional theory calculations (DFT) show that the luminescence properties of these five complexes are mainly ascribed to metal-to-ligand charge transfer (MLCT). Among these five complexes, 1 emits luminescence with the highest quantum yield of 36.96% and a lifetime of 11.90 μs at ambient temperature. Different counter-anions lead to the distinction of QYs, maybe due to the influence of weak forces. Terahertz time-domain absorption spectroscopy was used to characterize these ligands and complexes in the range of 0.2–2.4 THz.

In this paper, a series of mononuclear/binuclear Cu(I) complexes, [CuI(dpq)(PPh3)2](CF3SO3)·CH3OH (1a), [CuI(dppz)(PPh3)2](CF3SO3)·CH3OH (1b), [CuI2(dpq)2(dppm)2](CF3SO3)2 (2a), [CuI2(dppz)2(dppm)2](CF3SO3)2 (2b), [CuI(dpq)(dppp)](CF3SO3)·CH3OH (3a), [CuI(dppz)(dppp)](CF3SO3)·CH3OH (3b), [CuI(dpq)(POP)](CF3SO3)·CH3OH (4a), [CuI(dppz)(POP)](CF3SO3)·CH3OH (4b), [CuI(dpq)(xantphos)](CF3SO3) (5a), and [CuI(dppz)(xantphos)](CF3SO3) (5b) {dppm = 1,1-bis(diphenylphosphino)methane; dppp = 1,3-bis(diphenylphosphino)propane; POP = bis[2-(diphenylphosphino)phenyl]ether; xantphos = 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene; dpq = pyrazino[2,3-f][1,10]-phenanthroline; dppz = dipyrido[3,2-a: 2′,3′-c]phenazine} have been synthesized and characterized by using IR, NMR, elemental analysis, terahertz (THz) time-domain absorption spectroscopy, UV-vis and fluorescence spectroscopy methods as well as single crystal X-ray diffraction analysis. The single crystal X-ray diffraction results indicated that the immediate geometry around each central Cu(I) in the above complexes is a distorted tetrahedron with the central metal atom being coordinated by the two phosphorus atoms of the phosphine ligands and two nitrogen atoms of the bidentate N-containing heterocyclic ligand moieties. It is found that complexes 1a–5a and 5b show photoluminescence in the solid state at room temperature with the highest quantum yield up to 0.5519, and the increased conjugation in the diimine ligands leads to emission reduction along with a red-shift in the emission maxima. Detailed photo-physical studies and density functional theory calculations (DFT) of these complexes have revealed that their lowest energy absorptions and emissions are ascribed to metal-to-ligand charge transfer (MLCT) excited states. The above results indicate that conjugation effects of N-heteroaromatic ligands play a significant role in the emission properties of mononuclear/binuclear Cu(I) complexes. For the first time, terahertz time-domain spectroscopy is applied for qualitatively understanding the photophysical properties of complexes, revealing that terahertz time-domain spectra are sensitive to the weak interaction between the ligands, especially the diimine ligands, and terahertz spectra are strongly correlated with photoluminescence quantum yields of the complexes.

Sixteen lanthanide–diphosphate complexes [LnL2(H2O)4Cl]Cl2 (Ln = La3+ for 1, Ln = Ce3+ for 2), [LnL2(H2O)4]Cl3·6H2O (Ln = Nd3+ for 3, Ln = Sm3+ for 4, Ln = Eu3+ for 5, Ln = Gd3+ for 6, Ln = Tb3+ for 7, Ln = Dy3+ for 8, Ln = Er3+ for 9), {[LaL2(H2O)4Cl]Cl2}2 (10), [PrL2(OH)2(H2O)Cl] [PrL2(H2O)4Cl]Cl2 (11), [LaL2(H2O)5Cl]Cl2·2H2O (12), [YbL2(H2O)3Cl]Cl2·H2O (13), [NdL2(H2O)3Cl]Cl2·3H2O (14), [HoL2(H2O)Cl2]Cl·H2O (15), [Sc2L2(H2O)4(OH)2]Cl4·4H2O·2CH3OH (16) (L = tetrakis(O-isopropyl)methylenediphosphonate) have been synthesized by the reaction of lanthanide chlorides and L ligand in the solvent of acetonitrile (with ethanol or DMF) at room temperature. The title complexes were characterized by IR, elemental analysis, single-crystal X-ray diffraction analysis, thermal analysis, 1HNMR and 31PNMR spectroscopy. Complexes 1–15 are mononuclear complexes and complex 16 is a binuclear cluster complex. Complex 12 is the intermediate of complex 1. Complexes 11–13 display a one-dimensional chain formed by hydrogen bonds and the structures of complexes 14, 16 can be simplified as two-dimensional mesh 63 topology formed by hydrogen bonds. In those lanthanide complexes, the lanthanide ion with an atomic number smaller than Pr element tends to form a nine-coordinated structure and that with the atomic number larger than Pr element tends to form an eight or lower number-coordinated structure. Pr element has two kinds of coordination situations, with coordination numbers of nine or eight. The terahertz (THz) time-domain spectra of these complexes were also studied.