Effect of the dangling aromatic ring on neutral luminescent bis(phosphine) Cu(i)/Ag(i) complexes with the asymmetric pyridyl-tetrazolate ligands

Abstract

A series of neutral luminescent bis(phosphine) Cu(I) complexes of pyridyl-tetrazolate ligands (L¹–L³) with the general formula [Cu^I(Lⁿ)(P^P)] (1–6) were synthesized, which have been well characterized by IR, UV/vis, CV, ¹H NMR and ³¹P NMR. For comparison, an Ag(I) complex [Ag^I(L²)(PPh₃)₂] (7) was also synthesized. The crystal structures of 2 and 7 have been further determined by X-ray crystallography. All these Cu(I) compounds show bright luminescence in the solid state with photoluminescence quantum yields (PLQYs) in the range of 25.8% to 85.0%. More interestingly, the Cu(I) complexes bearing an additional dangling aromatic ring on the diimine ligands exhibit enhanced luminescent performance in various solutions and their PLQYs are significantly higher than those of related Cu(I) complexes without steric protection. Compared with 1, the Cu(I) complexes with an additional dangling tetrazole moiety show a significant solvatochromic effect, which is uncommon for luminescent Cu(I) complexes. Moreover, [Cu^I(L²)(PPh₃)₂] (2) was further designed as an OLED material, which showed a high external quantum efficiency of 7.7%.