Cyan-Emitting Cu(I) Complexes and Their Luminescent Metallopolymers

Abstract

Copper complexes have shown great versatility and a wide application range across the natural and life sciences, with a particular promise as organic light-emitting diodes. In this work, four novel heteroleptic Cu(I) complexes were designed in order to allow their integration in advanced materials such as metallopolymers. We herein present the synthesis and the electrochemical and photophysical characterisation of these Cu(I) complexes, in combination with ab initio calculations. The complexes present a bright cyan emission (λ_em ~ 505 nm) in their solid state, both as powder and as blends in a polymer matrix. The successful synthesis of metallopolymers embedding two of the novel complexes is shown. These copolymers were also found to be luminescent and their photophysical properties were compared to those of their polymer blends. The chemical nature of the polymer backbone contributes significantly to the photoluminescence quantum yield, paving a route for the strategic design of novel luminescent Cu(I)-based polymeric materials.

Keywords: RuAAC; functional copolymers; heteroleptic copper(I) complexes; light-emitting metallopolymers.

Figure 1

Structures of the copper(I) complexes that were investigated in this work. The structures can be classified as those bearing a hydroxyl group (5a, 5b) or a polymerisable unit (5c, 5d).

Scheme 1

Synthetic procedure for the preparation of the ligands 3a and 3b.

Figure 2

Structure of the ligands bearing a polymerisable unit. Ligand 4c has a styrenic functionality, while 4d has an acrylate unit.

Scheme 2

Synthetic procedure for the synthesis of the Cu(I) complexes.

Figure 3

Molecular structure of the Cu(I) complex in 5b (counteranion, lattice solvent and hydrogen atoms of the DPEPhos ligand omitted for clarity). Selected bond lengths (Å) and angle (°): Cu(1)-N(1) 2.112(3), Cu(1)-N(2) 2.048(4), Cu(1)-P(1) 2.2371(12), Cu(1)-P(2) 2.2459(12), N(1)-Cu(1)-N(2) 79.56(14).

Figure 4

(a,b) SEC of the styrenic and acrylate copolymers before (6c, 6d) and after complexation (7c, 7d), respectively.

Figure 5

UV–vis spectroscopy of complexes 5a (black curves); 5b (red curves); 5c (blue curves); and 5d (green curves) in DCM solutions at r.t. (a) Molar extinction coefficients (ε) in the UV–visible range of the electromagnetic spectrum—a zoom-in is shown in the inset; (b) emission of Ar-saturated solutions (concentration ~μM; λ_exc = 370 nm).

Figure 6

Isovalue contours calculated for the HOMO and LUMO of 5b (left), 5c (centre) and 5d (right). Hydrogen atoms are omitted for clarity. Red indicates the negative and blue the positive sign of the wave-function.

Figure 7

Cyclic voltammetry of Cu(I) complexes 5b (bottom), 5c (centre), 5d (top) in N,N-dimethylformamide (0.1 M TBAPF₆) at a scan rate of 100 mV/s.