Wide-Bite-Angle Diphosphine Ligands in Thermally Activated Delayed Fluorescent Copper(I) Complexes: Impact on the Performance of Electroluminescence Applications

Abstract

We report a series of seven cationic heteroleptic copper(I) complexes of the form [Cu(P^P)(dmphen)]BF 4 , where dmphen is 2,9-dimethyl-1,10-phenanthroline and P^P is a diphosphine chelate, in which the effect of the bite angle of the diphosphine ligand on the photophysical properties of the complexes was studied. Several of the complexes exhibit moderately high photoluminescence quantum yields in the solid state, with Φ PL of up to 35%, and in solution, with Φ PL of up to 98%. We were able to correlate the powder photoluminescence quantum yields with the % V bur of the P^P ligand. The most emissive complexes were used to fabricate both organic lightemitting diodes and light-emitting electrochemical cells (LECs), both of which showed moderate performance. Compared to the benchmark copper(I)-based LECs, [Cu(dnbp)(DPEPhos)] + (maximum external quantum efficiency, EQE max = 16%), complex 3 (EQE max = 1.85%) showed a much longer device lifetime (t 1/2 = 1.25 h and >16.5 h for [Cu(dnbp)(DPEPhos)] + and complex 3, respectively). The electrochemiluminescence (ECL) properties of several complexes were also studied, which, to the best of our knowledge, constitutes the first ECL study for heteroleptic copper(I) complexes. Notably, complexes exhibiting more reversible electrochemistry were associated with higher annihilation ECL as well as better performance in a LEC.

Closo- or Nido-Carborane Diphosphane as Responsible for Strong Thermochromism or Time Activated Delayed Fluorescence (TADF) in [Cu(N^N)(P^P)]0/+

“…The synthesis and study of heteroleptic copper complexes [Cu­(N^N)­(P^P)] n ( n = 0, 1) represents a growing field in the study of emissive coordination complexes. − One evident reason is the use of a cheaper metal (Cu) compared to those widely selected for the design of phosphors for emissive devices, such as Ir, Pt, or Au. Another relevant reason is related to their composition, which combines a diimine and a diphosphane.…”

Thermally activated delayed fluorescence in luminescent cationic copper(i) complexes

“…A similar analysis was performed by Zysman-Colman for [Cu(N^N)(P^P)] + complexes (10–16). 129 In their calculations of Δ E (S 1 –T 1 ) they considered the geometries of the ground state and the excited states to account for the effect of the flattening distortion. According to their results, the differences between Δ E (S 1 –T 1 ) values calculated using the ground state and the triplet excited state geometries were similar.…”

“…Interestingly, different P^P ligands were tested. 129 LEC devices were prepared using an ITO glass substrate coated with PEDOT:PSS (40 nm) hole injection layer. Abode this arrangement, the emissive layer composed of a mixture of the luminescent [Cu(dmp)(P^P)] + complex and LiBF 4 in a 9 : 1 molar ratio was spin-coated.…”

Mononuclear Copper(I) 3-(2-pyridyl)pyrazole Complexes: The Crucial Role of Phosphine on Photoluminescence

“…On the example of 100 heteroleptic copper(I) diimine complexes, they have demonstrated that a high value of V bur is a necessary but insufficient condition for high photoluminescence QY [42]. Quite recently, the effect of the bite angle of the diphosphine ligand on the photoluminescence of the [Cu(NˆN)(PˆP)] + (NˆN = neocuproine) has been studied by Zysman-Colman et al [43].…”

“…Based on the results obtained, we propose that the photophysical properties, especially photoluminescence QYs, of copper(I) complexes with Pyridine-pyrazoles and phosphines are affected by the steric effects of the ligands and the overall structural rigidity of complex, rather than by the donor ability of ligands. To our surprise, the role of the phosphine ligand has not been studied for the pyridine-pyrazole copper(I) complexes, even though the importance of the steric bulk has been demonstrated for bipyridine-containing analogs [42,43]. To confirm our hypothesis, we analyzed free volume around copper atoms in complexes 1-3 and in analogs [ Ph Pz Me PyCu(DPEPhos)]BF 4 that contain a Me substituent at the Py fragment and demonstrate comparable QY (71%) [40].…”