Excellent Blue Emissive Neutral Cu(I) Complexes: Structural Analysis, Thermochromic Luminescent Properties, and Terahertz Spectrum Research

Abstract

Herein, we report six neutral Cu(I) halide complexes based on [CuX(BIM)(P^P)] (P^P, diphosphine ligands; BIM, 1-butylimmidazole) with intense blue emission. When diphosphine ligands (POP, bis(2-(diphenylphosphino)phenyl)ether; Xantphos (4,5-bis(diphenylphosphino)-9,9-dimethylxanthene)), BIM and CuX (X = I, Br, Cl) were mixed in solution, pure and high yield products were obtained. Single crystal X-ray diffraction showed that each complex was of copper-centered tetrahedral structure. Different weak interactions in the molecules, such as hydrogen bonds, π−π stacking, and C−H•••π, make them exhibit various stacking modes like 1D, 2D, or 3D. Photoluminescent spectra showed various emissions from 444 to 480 nm with excellent quantum yields from 38.8% (6) to 92.3% (2). Interestingly, after heating complex 1-CH 2 Cl 2 at 60 °C, the emission exhibited a hypochromatic shift to 458 nm from the original 470 nm at room temperature. Complex 4-CH 2 Cl 2 showed an opposite bathochromic shift from 444 to 470 nm. Differential scanning calorimetry (DSC) and powder X-ray diffraction (PXRD) characterizations illustrated that the emission change was the result of the solvent (CH 2 Cl 2 ) loss from the pores of the structures. While they were put under a dichloromethane atmosphere, they demonstrate reversible luminescence reduction. Further research was carried out to prove the effect of pore solvent on terminal luminescence by synthesizing complex 4-THF (tetrahydrofuran). It showed a similar structure as complex 4-CH 2 Cl 2 but with different emission at 472 nm. Terahertz (THz) time domain spectra were applied to explore the relationship between structure and emission. After heating, the spectrum of complex 4-CH 2 Cl 2 changed a lot compared to the original and was dramatically similar to 4-THF. This inviting discovery suggests that the loss of solvent promotes the conversion of complex 4-CH 2 Cl 2 to a new crystal phase, which is more closed to 4-THF. THz technology provides a new measure to analyze molecules, especially for materials without crystal structure information.

Construction and characterization of an inorganic–organic hybrid copper(i) iodide coordination polymer with semiconducting luminescence

“…The single band blue emission can be assigned to the mixture of high-lying metal-to-ligand charge transfer (MLCT) and halogen-to-ligand charge transfer (XLCT) excited states. 57–62…”

Synthesis and luminescent properties of three excellent yellow emissive Cu(i) complexes based on the diphosphine ligand and the diimine ligand

“…The phosphorus ligand used in this study is the same as that in previous work, namely POP. 38 However, the nitrogen ligands differ, resulting in significant differences in the luminescent properties. Based on theoretical investigations, we found that the LUMO of the complexes are primarily composed of the nitrogen ligands, while the HOMO-6 and HOMO-3 are composed of the metal, halogen atoms, and phosphorus ligands.…”

“…Following our previous work, we retained the rigid ligand POP that contributes to luminescence, to ensure that the complexes in this work also have a high quantum yield similar to that of the previous work. 38 The nitrogen ligand has been replaced with bipy, the elevation of the LUMO energy has resulted in a decrease in the HOMO-6–LUMO (for 1 and 2 ) and HOMO-3–LUMO (for 3 ) energy gaps, resulting in a redshift in the emission position of the complexes from blue to yellow light emission. Furthermore, we investigated the influence of weak interactions for the complexes on the luminescent properties.…”