Luminescent Neutral Cu(I) Complexes: Synthesis, Characterization and Application in Solution-Processed OLED

Abstract

Four novel neutral copper(I) compounds were prepared, based on the chelating phosphine bis(2-(diphenylphosphino)phenyl)ether, (DPEPhos), and a series of nitrogen-containing heterocycles as ancillary ligands. The optical properties can be tuned according to the ancillary ligand and their emissions at room temperature in aprotic solvent (CH 2 Cl 2 ) go from greenish blue to orange. Their photoluminescence in solid state is particularly attractive and make their employment in opto-electronic devices very appealing. In particular, the low-cost preparation method of solution-processed light emitting devices is suitable for copper(I) complexes. In order to choose a suitable device architecture, the electrochemical characteristics were investigated and the frontier orbitals values were determined. Preliminary results on solution-processed OLED are presented.Organic Light-Emitting Devices, OLEDs, have attracted attention for several years. Indeed their applications are various, 1-3 ranging from full color flat panel display and lighting (white light), to micro-led and polarized light. The low power dissipation and high performances make them of great interest and opportunities for mobile applications and bendable displays. In order to gain the maximum luminous efficiency in optoelectronic devices, phosphorescent emitters are known to be the best material to be employed in device fabrication, 4-6 since the singlets and triplets excited states are randomly populated upon electric excitation. Currently the phosphorescent compounds that allow to fabricate highly efficient devices, are mainly based on the transition metal complexes, such as Ir(III), Ru(II), Os(II) and Pt(II) complexes. 7 Nowadays the growing OLED technology and the increasing demand of highly efficient and low power consumption devices draw the interest and efforts of both academic and companies. The ambitious goal is to employ low cost, abundant materials, and for these reasons photoluminescent Cu(I) complexes have recently gained increasing attention. Moreover Cu ions are much less toxic than the other employed heavy metals. Generally, these complexes are characterized by the Cu(I) metal core tetracoordinated in a pseudotetrahedral geometry. 8 In its oxidative state +1, copper has the d-orbitals completely filled and the electronic distribution of the charge is almost symmetrically localized around the metal centre, which favors a tetrahedral disposition of the ligands. The electronic transition d-d are then avoided and the luminescence comes from the triplet metal-toligand charge-transfer ( 3 MLCT) states, as long as the empty π orbitals are easily accessible in the ligands. 9 For this reason, closed shell d 10 copper(I) complexes do not suffer from the deactivation of MLCT by metal centred (MC) transitions, as might be the case for Ru(II) or other d 6 metal complexes. 10 However, undesired non-radiative pathways are nevertheless favored by vibrational modes and distortions of the tetrahedral conformation, in the excited state, which can be caused by flatt...

Mononuclear and dinuclear heteroleptic Cu(I) complexes based on pyridyl-triazole and DPEPhos with long-lived excited-state lifetimes

“…The geometric parameters are comparable with the distances and angles reported for other mononuclear heteroleptic Cu(I) complexes. [49,50] 114.59 (5) Quantum chemical calculations at the density functional theory (DFT) level gave a structure in good agreement to the experimental one (see Table S2 and Fig. S12 in ESI).…”

“…5). [49][50][51] The increased emission might be due to the steric hindrance caused by the presence of the methyl group alpha to the N of the pyridine. The structural rigidity, in fact, leads to a lower reorganisation of the ligands around the excited Cu(I) core.…”

New Photosensitizers Based on Heteroleptic CuI Complexes and CO2 Photocatalytic Reduction with [NiII(cyclam)]Cl2

“…These transitions are assigned to charge transfer from the metal core to the diimine ligand. Compared to the absorption bands of previously reportedC u I complexes based on pyrid-2yl-triazoles, [21] the MLCT band is bathochromic shifted, allowing the complexes to absorb blue light (up to 450 nm). This is rationalised by the increased p-conjugation of the quinoline compared with the pyridine ring.…”

Selective Encapsulation and Enhancement of the Emission Properties of a Luminescent Cu(I) Complex in Mesoporous Silica

“…The hydrophobic Cu(I) complex, isolated as a yellow emissive powder, has been previously prepared in our laboratory . As some other organometallic copper(I) complexes, it tends to crystallize in different polymorphs.…”

“…The hydrophobic Cu(I) complex, isolated as a yellow emissive powder, has been previously prepared in our laboratory. [20] As some other organometallic copper(I) complexes, [21] [22] it tends to crystallize in different polymorphs. The two forms have been isolated by slow evaporation of EtOH leading to both yellow emitting crystals ‡ , Cu(I) yellow and blue-green emitting crystals, Cu(I) blue, and their single crystal X-ray structures was resolved ( Figure 1).…”