Tuning luminescence via transition metal-directed strategy in coordination polymers

Abstract

Six coordination polymers of transition metals, namely, Cu(bpy)(H₂L)₂ (1), Co(bpy)(H₂L)₂(H₂O)₂ (2), Mn(bpy)(H₂L)₂(H₂O)₂ (3), Ag(bpy)(H₂L) (4), Cd(bpy)(HL)(H₂O) (5), and [Zn(bpy)(HL)]·H₂O (6) (bpy = 4,4′-bipyridine, H₃L = 4-chloro-5-sulphamoylbenzoic acid), have been synthesized under hydrothermal conditions. Single crystal X-ray diffraction analysis reveals that these compounds exhibit 1D linear chains for 1–3 (2 and 3 are isomorphic), a 1D double chain for 4, a 2D square-grid sheet for 5 and a 3D window-shaped net for 6. Photoluminescent investigation shows that compounds 2–6 exhibit distinct tunable yellow-to-violet photoluminescence by varying the TMs. These five compounds show weak Co(II)-based yellow, intense Mn(II)-based blue, Ag(I)-based green, Cd(II)-based violet and Zn(II)-based violet luminescence upon irradiation with a standard UV lamp (λ_ex = 254 nm) at room temperature. However, the Cu(II)-based compound shows fluorescence quenching. Furthermore, the luminescent quantum yields (QYs) and lifetimes under UV irradiation of 2–6 as well as the H₃L and bpy ligands have been obtained.