Ruthenium-tris(bipyridine) complexes with multiple redox-active amine substituents: tuning of spin density distribution and deep-red to NIR electrochromism and electrofluorochromism.

In response to the application of low electrochemical potentials, ruthenium-tris(bipyridine) complexes decorated with multiple electron-rich and redox-active amine substituents show reversible absorption and emission spectral changes in the deep-red to NIR region. The number of amine substituents strongly affects the electrochemical and spectroscopic properties and the spin density distributions of the complex in the one-electron-oxidized state.

Combined Experimental and Computational Study of Pyren-2,7-diyl-Bridged Diruthenium Complexes with Various Terminal Ligands.

Cyclometalated diruthenium complexes 1(PF6)2-5(PF6)2 bridged by 1,3,6,8-tetra(pyrid-2-yl)-pyrene have been prepared, with the terminal ligand bis(N-methylbenzimidazolyl)pyridine (1(PF6)2), 4'-di-(p-methoxyphenyl)amino-2,2':6',2″-terpyridine (2(PF6)2), 4'-p-methoxyphenyl-2,2':6',2″-terpyridine (3(PF6)2), 2,2':6',2″-terpyridine (4(PF6)2), and trimethyl-4,4',4″-tricarboxylate-2,2':6',2″-terpyridine (5(PF6)2). The single-crystal X-ray structure of 4(PF6)2 is presented. These complexes show two stepwise anodic redox pairs, and the potentials progressively increase from 1(PF6)2 to 5(PF6)2. Complexes 1(PF6)2-4(PF6)2 have comparable electrochemical potential splitting of 200-210 mV, while complex 5(PF6)2 has a splitting of 170 mV. Upon one-electron oxidation by chemical oxidation or electrolysis, the resulting mixed-valent complexes 1(3+)-5(3+) display broad and intense absorptions between 1000 and 3000 nm. Complexes 1(3+) and 2(3+) show the presence of a higher-energy shoulder band in addition to the main near-infrared absorption band. This shoulder band is less distinguished for 3(3+)-5(3+). Three-state theory has been used to explain this difference. The one-electron oxidized forms, 1(3+)-5(3+), exhibit rhombic EPR signals at 77 K with the isotropic g values in the range of 2.18-2.24. Density functional theory (DFT) and time-dependent DFT (TDDFT) computations have been performed on 1(2+)-5(2+) to characterize their electronic structures and rationalize the absorption spectra in a wide energy range. DFT computations on 1(3+)-5(3+) show that both ruthenium ions and the bridging ligand have comparable spin densities. TDDFT computations on 1(3+) and 4(3+) have been performed to complement the experimental results.

Metal chelation-assisted amine-amine electronic coupling through the 4,4'-positions of 2,2'-bipyridine.

A redox-active diamine ligand, 4,4'-bis(di-p-anisylamino)-2,2'-bipyridine (NNbpy), has been prepared. Electrochemical and spectroscopic studies suggest that little electronic coupling is present between two amine groups in NNbpy. After chelation with Ru(bpy)2 (bpy is 2,2'-bipyridine), the resulting complex displays two N(•+/0) processes at +1.02 and +1.16 V versus Ag/AgCl. In the mixed-valent state, rich near-infrared absorptions have been observed, which are believed to consist of multiple metal-to-ligand charge transfer and intervalence charge transfer transitions in the low-energy region. These results suggest that the amine-amine electronic coupling has been enhanced by chelation with Ru(bpy)2. In contrast, no efficient electronic coupling can be realized by chelation with Ir(ppy)2 (ppy is 2'-phenylpyridine) or Re(CO)3Cl. A ruthenium ion-mediated electron transfer mechanism, instead of through-space coupling, has been proposed to explain this phenomenon. For the purpose of comparison, a monoamine-substituted bpy ligand and corresponding Ru(bpy)2 complex have been synthesized and studied. In addition, EPR, DFT, and TDDFT studies have been performed to complement the experimental results.

Strongly coupled cyclometalated ruthenium-triarylamine hybrids: tuning electrochemical properties, intervalence charge transfer, and spin distribution by substituent effects.

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.

Oligotriarylamines with a pyrene core: a multicenter strategy for enhancing radical cation and dication stability and tuning spin distribution.

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 CH2 Cl2 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 2(2+) -6(2+) , 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 2(2+) -4(2+) have a triplet ground state, whereas 5(2+) and 6(2+) have a singlet ground state. The dication of 1,3-disubstituted diamine 4 exhibits a strong EPR signal.

Near-infrared electrochromism in electropolymerized metallopolymeric films of a phen-1,4-diyl-bridged diruthenium complex.

A phen-1,4-diyl-bridged tris-bidentate diruthenium complex 3(PF6)2, [Ru2(dpb)(vbpy)4](PF6)2, has been designed and prepared, where dpb is 1,4-di(pyrid-2-yl)benzene and vbpy is 5-vinyl-2,2'-bipyridine. Upon reductive electropolymerization, metallopolymeric thin films of this complex have been deposited on platinum and ITO glass electrode surfaces. These films display two well-separated redox couples at +0.16 and +0.60 V versus Ag/AgCl. In the mixed-valent state, these films display intense intervalence charge transfer absorptions around 1300 nm. The electrochromic behavior at this wavelength has been examined by spectroelectrochemical measurements and double-potential-step chronoamperometry. A highest optical contrast ratio of 41% at 1300 nm with a coloration efficiency of 200 cm(2)/C has been achieved. The electrochromic behavior is highly dependent on the surface coverage. The highest contrast ratio was obtained with a film of 6.0 × 10(-9) mol/cm(2). In addition, a monoruthenium complex 2(PF6), [Ru(dpb)(vbpy)2](PF6), has been prepared and electropolymerized for a comparison study.

Organic-inorganic mixed-valence systems with strongly-coupled triarylamine and cyclometalated osmium.

Organic-inorganic mixed-valence systems with strongly-coupled triarylamine and cyclometalated osmium have been developed. They display two well-separated redox couples at low potentials. Each of the three readily accessible oxidation states can be distinguished by the absorbance at three different wavelengths.

Reductive electropolymerization of bis-tridentate ruthenium complexes with 5,5''-divinyl-4'-tolyl-2,2':6',2''-terpyridine.

Four bis-tridentate ruthenium complexes with 5,5''-divinyl-4'-tolyl-2,2':6',2''-terpyridine (dvtpy) have been synthesized. Among them, 3(PF6) ([(dvtpy)Ru(Mebib)](PF6)) and 4(PF6) ([(dvtpy)Ru(dpb)](PF6)) are cyclometalated, and 5(PF6)2 ([(dvtpy)Ru(Mebip)](PF6)2) and 6(PF6)2 ([(dvtpy)Ru(tpy)](PF6)2) are noncyclometalated, where Mebib is 2-deprotonated-1,3-bis(N-methylbenzimidazolyl)benzene, dpb is 2-deprotonated-1,3-di(2-pyridyl)benzene, Mebip is 2,6-bis(N-methylbenzimidazolyl)pyridine, and tpy is 2,2':6',2''-terpyridine, respectively. Reductive electropolymerization of these complexes and copolymerization of 4(PF6) and 5(PF6)2 proceeded smoothly, both on glassy carbon and ITO glass electrodes, to afford stable metallopolymeric films with well-defined redox processes. On the basis of the monomer structures, electrochemical properties, and polymerization mechanism, the polymer chains of these materials are supposed to be composed of organic frameworks with the metal ions laterally chelated to the main backbones. The polymeric films on ITO surfaces display promising electrochromism in the visible region with good reversibility and moderate contrast ratio. Besides, the apparent diffusion constants of films of 3(PF6)­6(PF6)2 were measured by potential step chronoamperometry and the typical surface morphology of poly-5(PF6)2/ITO film was studied using SEM.

A combined experimental and computational study of linear ruthenium(II) coordination oligomers with end-capping organic redox sites: insight into the light absorption and charge delocalization.

Two series of linear ruthenium coordination oligomers, [(Ntpy)Ru(n)(tppz)(n-1)(tpy)](2n+) (mono-Ntpy series, n = 1-3) and [(Ntpy)2Ru(n)(tppz)(n-1)](2n+) (bis-Ntpy series, n = 1-3) have been prepared, where Ntpy is the capping ligand 4'-di-p-anisylamino-2,2':6',2''-terpyridine, tppz is tetra-2-pyridylpyrazine, and tpy is 2,2':6',2''-terpyridine. The electrochemical measurements evidence oxidation events from both the amine segments and the metal centers and reduction waves from tppz and the capping ligands. Both series complexes display much enhanced light absorption with respect to model complexes without terminal amine units. Density functional theory (DFT) calculations have been performed on both series and time-dependent DFT (TD-DFT) calculations have been performed on the bis-Ntpy-series compounds (n = 1-4) to characterize their electronic structures and excited states and predict the electronic properties of long-chain polymers. Upon one-electron oxidation, the mono-Ntpy-series monoruthenium and diruthenium complexes display N(+)-localized transitions and metal-to-nitrogen charge-transfer (MNCT) transitions in the near-infrared (NIR) region. DFT and TD-DFT computations on the one-electron-oxidized forms of the mono-Ntpy-series compounds (n = 1-4) provide insight into the nature of the MNCT transitions and the degree of charge delocalization.

In situ switching layer-by-layer assembly: one-pot rapid layer assembly via alternation of reductive and oxidative electropolymerization.

In situ one-pot rapid layer-by-layer assembly of polymeric films as an active layer of a photoactive device via alternation of reductive and oxidative electropolymerization has been demonstrated. This novel fabrication without moving or changing experimental gears would be a powerful strategy to develop automated layer-by-layer machines.

A bis(terpyridine)ruthenium complex with three redox-active amine sites: electrochemical, optical, and computational studies.

Two ruthenium complexes, [Ru(NN)(ttpy)](2+) and [Ru(NN)(daatpy)](2+), have been designed and prepared, where NN is bis(amine) ligand 4'-tolyl-5,5"-bis(di-p-anisylamino)-2,2':6',2"-terpyridine, ttpy is 4'-tolyl-2,2':6',2"-terpyridine, and daatpy is 4'-di-p-anisylamino-2,2':6',2"-terpyridine. Complex [Ru(NN)(daatpy)](2+) contains three redox-active amine groups and has been characterized by single-crystal X-ray analysis. These two complexes display much-enhanced light absorption capabilities with respect to the prototype compound [Ru(tpy)(2)](2+) (tpy = 2,2':6',2"-terpyridine), which has been rationalized on the basis of time-dependent density functional theory calculations. Electrochemical and optical studies showed that there was little electronic coupling between two amine sites in complex [Ru(NN)(ttpy)](2+). On the other hand, a ligand-to-ligand (N → N'(•+)) charge-transfer band has been observed at 1430 nm for singly and doubly oxidized forms of [Ru(NN)(daatpy)](2+), and an electronic coupling parameter of 1000 cm(-1) was derived using the Hush formula. This band is interpreted as a charge transfer from the neutral amine of the daatpy ligand to oxidized aminium units in the NN ligand.

Electronic coupling between two amine redox sites through the 5,5'-positions of metal-chelating 2,2'-bipyridines.

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)(3)Cl], 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.

Near-IR electrochromism in electropolymerized films of a biscyclometalated ruthenium complex bridged by 1,2,4,5-tetra(2-pyridyl)benzene.

Reductive electropolymerization of the biscyclometalated ruthenium complex [(vtpy)Ru(tpb)Ru(vtpy)](2+) [vtpy = 4'-vinyl-2,2':6',2″-terpyridine; tpb = 1,2,4,5-tetra(2-pyridyl)benzene] proceeded smoothly on electrode surfaces. Thanks to the strong electron coupling between the ruthenium centers of the individual monomeric units and strong intervalence charge-transfer absorption in the mixed valence state, the produced adherent metallopolymeric films exhibited near-IR electrochromism with tricolor switching, good contrast ratio (40% at 1165 nm), short response time, low-switching voltage, and long memory time.

[Re(CO)3Cl]-chelation-mediated electronic coupling between two amine redox sites through the 5,5'-positions of 2,2'-bipyridine.

The electronic coupling between two amine redox sites bridged through the 5,5'-positions of the [Re(CO)(3)Cl]-chelated 2,2'-bipyridine was studied by the electrochemical, spectroscopic, and EPR analysis. Interestingly, multiple near-infrared bands were observed in this new organic mixed-valent system. The results are interpreted with the aid of DFT and TDDFT calculations.

Synthesis of vinyl-substituted polypyridyl ligands through Suzuki-Miyaura cross-coupling of potassium vinyltrifluoroborate with bromopolypyridines.

Suzuki-Miyauru cross-coupling of bromopolypyridines with potassium vinyltrifluoroborate affords vinyl-substituted polypyridyl ligands in moderate to good yields. This reaction allows simple and practical syntheses of numerous vinyl-substituted polypyridines, such as 4'-vinyl-2,2':6',2''-terpyridine, 5,5'-divinyl-2,2'-bipyridine, and 4,4'-divinyl-2,2'-bipyridine. In addition, a new ruthenium complex, [Ru(5,5'-divinyl-2,2'-bipyridine)(3)](2+), was synthesized and found to undergo reductive electropolymerization smoothly.