Oligoaniline-Functionalized terpyridine ligands and their ruthenium(II) complexes: synthesis, spectroscopic property and redox behavior

Abstract

A series of oligoaniline-functionalized mono- and bis-topic terpyridine ligands, i.e. C₆H₅[N(R)C₆H₄]_nTPY (R = H, butyl, tert-butyloxycarbonyl; n = 1–4; TPY = 2,2′:6′,2″-terpyridyl) and TPYC₆H₄[N(R)C₆H₄]_mTPY (R = H, tert-butyloxycarbonyl; m = 2, 4), and the corresponding mono- and bis-nuclear ruthenium(II) complexes have been synthesized and verified. The spectroscopic results indicate that two kinds of π–π* transitions from TPY and oligoaniline fragments of ligands strongly shift to lower energy, and the metal-to-ligand charge-transfer transition (¹MLCT) bands of all obtained complexes are considerably red-shifted (Δλ_max = 22–64 nm) and their intensities become much more intense (approximately 4–6 times), compared with those of the reported complex [Ru(TPY)₂]²⁺. Moreover, the spectroscopic properties of the ligands and complexes with longer oligoaniline units (n = 3, 4) are markedly influenced by the external stimulus, such as the oxidation and proton acid doping. The characteristic absorption bands in the visual and near infrared (NIR) scales demonstrate the presence of various oxidized and doped states of the oligoaniline unit. All complexes show multiplicate redox processes based on metal center, oligoaniline and terpyridine units. The potential shifts suggest the donor and acceptor (D–A) interaction between the oligoaniline unit and the bis(terpyridine)–Ru²⁺ center.