Synthesis, photoluminescence and electrochemiluminescence of ruthenium(II) polypyridyl complexes based on bipyridine derivatives with carbazole moieties

Six complexes (1–6) with the type of [Ru(bpy)2L]X2 (1–3: L = L1–L3, X = Cl−; 4–6: L = L1–L3, X = PF6−) were synthesized based on 2,2′-bipyridine and three 2,2′-bipyridine derivatives L1, L2 and L3 (L1 = 5,5′-dibromo-2,2′-bipyridine, L2 = 5-bromo-5′-carbazolyl-2,2′-bipyridine, L3 = 5,5′-dicarbazolyl-2,2′-bipyridine). The complexes 1–6 were characterized by 1H NMR, MS(ESI) and IR spectra, along with the X-ray crystal structure analysis for 1, 5 and 6. Their photophysical properties and electrochemiluminescence (ECL) properties were investigated in detail. In the UV–Vis absorption spectra, all complexes 1–6 show strong intraligand (π → π∗) transitions and metal-ligand charge transfer (MLCT, dπ (Ru) → π∗) bands. Upon the excitation wavelengths at ∼508 nm, all complexes 1–6 exhibit typical MLCT emission of ruthenium(II) polypyridyl complexes. The introduction of carbazole moieties improves the MLCT absorption and emission intensity. The ruthenium(II) complexes 1–6 exhibit good electrochemiluminescence (ECL) properties in [Ru(bpy)2L]2+/tri-n-propylamine (TPrA) acetonitrile solution and the complexes with PF6− showed higher ECL emission intensity than that of the complexes with Cl− based on the same ligands.