Triarylboron/Triarylamine-Functionalized 2,2′-Bipyridine Ligands and Their Copper(I) Complexes

Abstract

We report herein three new either −BMes₂ (Mes = mesityl) or −NPh₂ group-functionalized 2,2′-bipyridine ligands—4,4′-(p-BMes₂-phenyl-C≡C)₂-2,2′-bpy (BB-bpy), 4-(p-BMes₂-phenyl-C≡C)-4′-(p-NPh₂-phenyl-C≡C)-2,2′-bpy (BN-bpy), and 4,4′-(p- NPh₂-phenyl-C≡C)₂-2,2′-bpy (NN-bpy)—along with their heteroleptic copper(I) complexes Cu(L)(PPh₃)₂(BF₄) (L = BB-bpy, BN-bpy, and NN-bpy, respectively). The electron-donor and -acceptor units are connected to the bipyridine core via acetylene linkers. The incorporation of acetylene linkers decreases the dihedral angle between the bridging phenyl and pyridine rings, resulting in a nearly coplanar geometry of the ligands. All free ligands display temperature-dependent luminescence changes, which may be explained by the twisted intramolecular charge-transfer mechanism. Binding with Cu(I) results in significantly red-shifted emission maxima for the heteroleptic complexes Cu(NNbpy)(PPh₃)₂(BF₄) [Cu(NNbpy)] and Cu(BNbpy)(PPh₃)₂(BF₄) [Cu(BNbpy)] relative to those of the free ligands. The electronic and photophysical properties of all compounds were investigated by electrochemical, absorption, and emission spectroscopic analyses as well as density functional theory calculations.