title: Strongly coupled cyclometalated ruthenium-triarylamine hybrids: tuning electrochemical properties, intervalence charge transfer, and spin distribution by substituent effects.
abstract: Nine cyclometalated ruthenium complexes with a redox-active diphenylamine unit in the para position to the RuC bond were prepared. MeO, Me, and Cl substituents on the diphenylamine unit and three types of auxiliary ligands-bis(N-methylbenzimidazolyl)pyridine (Mebip), 2,2':6',2''-terpyridine (tpy), and trimethyl-4,4',4''-tricarboxylate-2,2':6',2''-terpyridine (Me3 tctpy)--were used to vary the electronic properties of these complexes. The derivative with an MeO-substituted amine unit and Me3 tctpy ligand was studied by single-crystal X-ray analysis. All complexes display two well-separated redox waves in the potential region of +0.1 to +1.0 V versus Ag/AgCl, and the potential splitting ranges from 360 to 510 mV. Spectroelectrochemical measurements show that these complexes display electrochromism at low potentials and intense near-infrared (NIR) absorptions. In the one-electron oxidized form, the complex with the Cl-substituted amine unit and Mebip ligand shows a moderate ligand-to-metal charge transfer at 800 nm. The other eight complexes show asymmetric, narrow, and intense intervalence charge-transfer transitions in the NIR region, which are independent of the polarity of the solvent. The Mebip-containing complexes display rhombic or broad isotropic EPR signals, whereas the other seven complexes show relatively narrow isotropic EPR signals. In addition, DFT and time-dependent DFT studies were performed to gain insights into the spin distributions and NIR absorptions.
authors.affiliation: Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Photochemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190 (P. R. China).
authors.forename: Chang-Jiang
authors.initials: CJ
authors.lastname: Yao
authors.forename: Hai-Jing
authors.initials: HJ
authors.lastname: Nie
authors.forename: Wen-Wen
authors.initials: WW
authors.lastname: Yang
authors.forename: Jiang-Yang
authors.initials: JY
authors.lastname: Shao
authors.forename: Jiannian
authors.initials: J
authors.lastname: Yao
authors.forename: Yu-Wu
authors.initials: YW
authors.lastname: Zhong
keywords: charge transfer; electrochemistry; mixed-valent compounds; ruthenium; tridentate ligands