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Bis-triarylamine 2 and cyclometalated diruthenium 6(PF6)2 with a linear trans, trans-urea bridge have been prepared, together with the bis-triarylamine 3 and cyclometalated diruthenium 8(PF6)2 with a folded cis, cis- N, N-dimethylurea bridge. The linear or folded conformations of these molecules are supported by single-crystal X-ray structures of 2, 3, and other related compounds. These compounds display two consecutive anodic redox waves (N .+/0 or RuIII/II processes) with a potential separation of 110-170 mV. This suggests that an efficient electronic coupling is present between two redox termini through the cross-conjugated urea bridge. The degree of electronic coupling has been investigated by using spectroelectrochemical measurements. Distinct intervalence charge-transfer (IVCT) transitions have been observed for mixed-valent (MV) compounds with a linear conformation. The IVCT transitions can also be identified for the folded MV compounds, albeit with a much weaker intensity. DFT results support that the electronic communication occurs by a through-bond and through-space pathway for the linear and folded compounds, respectively. The IVCT transitions of the MV compounds have been reproduced by TDDFT calculations. For the purpose of comparison, a bistriarylamine and a diruthenium complex with an imidazolidin-2-one bridge and a urea-containing mono-triarylamine and monoruthenium complex have been synthesized and studied. [ABSTRACT FROM AUTHOR]

Monoamine 1, diamines 2- 4, triamine 5, and tetraamine 6 have been synthesized by substituting dianisylamino groups at the 1-, 3-, 6-, and/or 8-positions of pyrene. Diamines 2- 4 differ in the positions of the amine substituents. No pyrene-pyrene interactions are evident in the single-crystal packing of 3, 4, and 6. With increasing numbers of amine substituents, the first oxidation potential decreases progressively from the mono- to the tetraamine. These compounds show intense charge-transfer (CT) emission in CH2Cl2 at around 530 nm with quantum yields of 48-68 %. Upon stepwise oxidation by electrolysis or chemical oxidation, these compounds were transformed into radical cations 1⋅+- 6⋅+ and dications 22+- 62+, which feature strong visible and near-infrared absorptions. Time-dependent density functional theory studies suggested the presence of localized transitions from the pyrene radical cation and aminium radical cation, intervalence CT, and CT between the pyrene and amine moieties. Spectroscopic studies indicated that these radical cations and dications have good stability. Triamine 5 and tetraamine 6 formed efficient CT complexes with tetracyanoquinodimethane in solution. The results of EPR spectroscopy and density functional theory calculations suggested that the dications 22+- 42+ have a triplet ground state, whereas 52+ and 62+ have a singlet ground state. The dication of 1,3-disubstituted diamine 4 exhibits a strong EPR signal. [ABSTRACT FROM AUTHOR]

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 (Me3tctpy)-were used to vary the electronic properties of these complexes. The derivative with an MeO-substituted amine unit and Me3tctpy 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. [ABSTRACT FROM AUTHOR]

Four heterodimetallic complexes [Ru(Fcdpb)(L)](PF6) (Fcdpb=2-deprotonated form of 1,3-di(2-pyridyl)-5-ferrocenylbenzene; L=2,6-bis-( N-methylbenzimidazolyl)-pyridine (Mebip), 2,2′:6′,2′′-terpyridine (tpy), 4-nitro-2,2′:6′,2′′-terpyridine (NO2tpy), and trimethyl-4,4′,4′′-tricarboxylate-2,2′:6′,2′′-terpyridine (Me3tctpy)) have been prepared. The electrochemical and spectroelectrochemical properties of these complexes have been examined in CH2Cl2, CH3NO2, CH3CN, and acetone. These complexes display two consecutive redox couples owing to the stepwise oxidation of the ferrocene (Fc) and ruthenium units, respectively. The potential difference, Δ E1/2 ( E1/2(RuII/III)− E1/2(Fc0/+)), decreased slightly with increasing solvent donocity. The mixed-valent states of these complexes have been generated by and the resulting intervalence charge-transfer (IVCT) bands have been analyzed by Hush theory. Good linear relationships exist between the energy of the IVCT band, Eop, and Δ E1/2 of four mixed-valent complexes in a given solvent. [ABSTRACT FROM AUTHOR]

Three bis-tridentate ferrocene-containing cyclometalated ruthenium complexes, [(Fcdpb)Ru(tpy)]+ ( 1+), [(Fctpy)Ru(dpb)]+ ( 2+), and [(Fcdpb)Ru(Fctpy)]+ ( 3+), have been prepared and characterized, where Fcdpb is the 2-deprotonated form of 1,3-di(2-pyridyl)-5-ferrocenylbenzene, tpy is 2,2′:6′,2'-terpyridine, dpb is the 2-deprotonated form of 1,3-di(2-pyridyl)benzene, and Fctpy is 4′-ferrocenyl-2,2′:6′,2'-terpyridine. Single crystals of compounds 2+ and 3+ have been studied by X-ray analysis. Complexes 1+ and 2+ displayed two anodic redox waves, whilst three well-separated redox couples were observed for compound 3+. A combined experimental and computational study suggested that the ferrocene unit on the Fcdpb moiety in compounds 1+ and 3+ was oxidized first. In contrast, the order of the oxidation of ruthenium and ferrocene in complex 2+ was reversed. Metal-to-metal-charge-transfer transitions (MM′CT) have been observed for the singly oxidized states 12+, 22+, and 32+ in the near-infrared region. Hush analysis showed that the metal-metal electronic couplings in compounds 12+ and 32+ were much stronger than those in compound 22+. [ABSTRACT FROM AUTHOR]

Electron delocalization of new mixed-valent (MV) systems with the aid of lateral metal chelation is reported. 2,2′-Bipyridine (bpy) derivatives with one or two appended di- p-anisylamino groups on the 5,5′-positions and a coordinated [Ru(bpy)2] (bpy=2,2′-bipyridine), [Re(CO)3Cl], or [Ir(ppy)2] (ppy=2-phenylpyridine) component were prepared. The single-crystal molecular structure of the bis-amine ligand without metal chelation is presented. The electronic properties of these complexes were studied and compared by electrochemical and spectroscopic techniques and DFT/TDDFT calculations. Compounds with two di- p-anisylamino groups were oxidized by a chemical or electrochemical method and monitored by near-infrared (NIR) absorption spectral changes. Marcus-Hush analysis of the resulting intervalence charge-transfer transitions indicated that electron coupling of these mixed-valent systems is enhanced by metal chelation and that the iridium complex has the largest coupling. TDDFT calculations were employed to interpret the NIR transitions of these MV systems. [ABSTRACT FROM AUTHOR]