Phosphane tuning in heteroleptic [Cu(N^N)(P^P)]⁺complexes for light-emitting electrochemical cells

Abstract

The effects on photo-and electroluminescent properties of structurally modifying the bisphosphane in [Cu(N^N)(P^P)]+ complexes (N^N = bpy, 6-Mebpy, 6,6′-Me2bpy) are described.

Remote Modification of Bidentate Phosphane Ligands Controlling the Photonic Properties in Their Complexes: Enhanced Performance of [Cu(RN‐xantphos)(N^N)][PF6] in Light‐Emitting Electrochemical Cells

“…Solid‐state emission data were recorded for all the [Cu(HN‐xantphos)(N ^ N)][PF 6 ] and [Cu(BnN‐xantphos)(N ^ N)][PF 6 ] compounds (Table 2 and Figure 4b). For each series of compounds, the emission maximum blue‐shift on going from bpy to Mebpy to Me 2 bpy is consistent with earlier reports, [ 31 ] whereas the attachment of the benzyl group to the phenoxazine moiety of the P ^ P ligand causes a red‐shift ranging from 20 nm for [Cu(P ^ P)(bpy)][PF 6 ] to 2 nm for [Cu(P ^ P)(Me 2 bpy)][PF 6 ]. As expected from our previous investigations of [Cu(xantphos)(N ^ N][PF 6 ] complexes, [ 9,10,31 ] the presence of 6‐methyl or 6,6′‐dimethyl substituents in the bpy domain is beneficial in terms of PLQY and excited‐state lifetime (Table 2).…”

“…All the complexes show an irreversible reduction process (Table 1; Figure S10, Supporting Information) which moves to more negative potentials on going from bpy to Mebpy to Me 2 bpy. This trend was previously observed in series of related complexes, [ 31 ] and is consistent with the LUMO being located on the N ^ N ligand and increasing in energy with the number of Me groups (Figure 3). To investigate in more detail the oxidation processes, the dication and trication species of the [Cu(HN‐xantphos)(bpy)] + and [Cu(BnN‐xantphos)(bpy)] + were calculated theoretically.…”

“…Therefore, on the basis of both TD‐DFT and UDFT calculations, the 3 LLCT (HOMO→LUMO) triplet state does not play any special role in the phosphorescent emission of HN‐xantphos‐ and BnN‐xantphos complexes. It is also worth mentioning that, as previously discussed for xantphos‐containing complexes, [ 29,31 ] the partial oxidation of the copper atom in the T 1 state leads to the geometry of the complex in T 1 deviating from the tetrahedral geometry obtained for S 0 and rather tends to adopt a square‐planar coordination geometry. This geometrical relaxation is partially restricted by the presence of Me substituents in the 6 and 6′‐positions of the bpy ligand, [ 29,31 ] and the emission from T 1 blue‐shifts upon increasing the number of Me groups.…”

“…This is consistent with the description of the first triplet state previously discussed for complexes bearing the xantphos ligand. [ 10,29–31 ]…”

“…This trend follows those previously observed for related [Cu(P ^ P)(N ^ N)][PF 6 ] series. [ 31 ] Photoluminescence quantum yields (PLQYs) measured in deaerated solutions are lower than 2% and the compounds exhibit very short excited‐state lifetimes (Table 2).…”