A series of cyclometalated diruthenium complexes with a redox-active amine bridge were synthesized. Depending on the terminal ligands of the ruthenium components and the substituent on the amine unit, the one-electron-oxidized state can be either in the form of a weakly or strongly coupled mixed-valence diruthenium complex, a fully charge-delocalized three-center system, or a bridge-biased electrophore. This transition among different electronic forms was supported by electrochemistry, near-infrared absorption, electron paramagnetic resonance, and density functional theory analysis.

The construction of well-controlled porous materials is very challenging. Herein, we report the successful preparation of structurally defined porous membranes based on hexakistriphenylamine metallacycles through electropolymerization. The newly designed porous materials were characterized by the typical cyclic voltammograms, XPS, SEM, and TEM investigations. Further investigations revealed that the metallacycle-based polymer films displayed a good size-selective molecular-sieving behavior.

Six cyclometalated diruthenium complexes bridged by 3,3′,5,5′-tetra(pyrid-2-yl)biphenyl have been prepared, in which 1²⁺, 3²⁺, and 5²⁺ are symmetric complexes with different terminal ligands [2,6-bis(N-methylbenzimidazolyl)pyridine (Mebip), 4′-tolyl-2,2′:6′,2″-terpyridine (ttpy), and trimethyl-4,4′,4″-tricarboxylate-2,2′:6′,2″-terpyridine (Me₃tctpy), respectively]. Three other complexes with mixed terminal ligands (Mebip-Me₃tctpy for 6²⁺; Mebip-ttpy for 7²⁺; ttpy-Me₃tctpy for 8²⁺) are structurally nonsymmetric. These complexes display two consecutive Ru(III/II) redox couples between 0.20 and 0.90 V vs. Ag/AgCl, with the potential splitting ranging from 150 (for 5²⁺) to 280 mV (for 6²⁺). The mixed-valent states of these complexes have been generated by stepwise electrolysis. The symmetric complexes show intervalence charge transfer (IVCT) transitions at similar energy (E_op ≈ 5750 cm^–1), with the electronic coupling parameter V_ab of 1240, 1220, and 970 cm^–1 for 1³⁺, 3³⁺, and 5³⁺, respectively. The nonsymmetric series show significantly different E_op (7600, 5850, and 6650 cm^–1 for 6³⁺, 7³⁺, and 8³⁺, respectively) but V_ab values that were comparable to that of 1³⁺. DFT and TDDFT calculations have been performed to complement these experimental results.

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 Ru^III/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.

A diruthenium complex with a redox-active amine bridge has been designed, synthesized, and studied by single-crystal X-ray analysis and DFT and TDDFT calculations. It shows three well-separated redox processes with exclusive near-infrared (NIR) absorbance at each redox state. The electropolymerized film of a related vinyl-functionalized complex displays multistate NIR electrochromism with low operational potential, good contrast ratio, and long retention time. Flip-flop, flip-flap-flop, and ternary memories have been realized by using the obtained film (ca. 15–20 nm thick) with three electrochemical inputs and three NIR optical outputs that each displays three levels of signal intensity.

A diruthenium complex with a redox-active amine bridge has been designed, synthesized, and studied by single-crystal X-ray analysis and DFT and TDDFT calculations. It shows three well-separated redox processes with exclusive near-infrared (NIR) absorbance at each redox state. The electropolymerized film of a related vinyl-functionalized complex displays multistate NIR electrochromism with low operational potential, good contrast ratio, and long retention time. Flip-flop, flip-flap-flop, and ternary memories have been realized by using the obtained film (ca. 15–20 nm thick) with three electrochemical inputs and three NIR optical outputs that each displays three levels of signal intensity.

A common bridging ligand, 3,3′,5,5′-tetrakis(N-methylbenzimidazol-2-yl)biphenyl, and four terpyridine terminal ligands with various substituents (amine, tolyl, nitro, and ester groups) have been used to synthesize ten cyclometalated diruthenium complexes 1²⁺–10²⁺. Among them, compounds 1²⁺–6²⁺ are redox nonsymmetric, and others are symmetric. These complexes show two Ru^III/II processes and an intervalence charge transfer (IVCT) transition in the one-electron oxidized state. The potential separation (ΔE) of 1²⁺–10²⁺ has been correlated to the energy difference ΔG⁰, the energy of the IVCT band E_op, and the ground-state delocalization coefficient α². Time-dependent (TD)DFT calculations suggest that the absorptions in the visible region of 1²⁺–6²⁺ are mainly associated with the metal-to-ligand charge-transfer transitions from both ruthenium ions and to both terminal ligands and the bridging ligand. However, the energies of these transitions vary significantly. DFT calculations have been performed on 1²⁺–6²⁺ and 1³⁺–6³⁺ to give information on the electronic structures and spin populations of the mixed-valent compounds. The TDDFT-predicted IVCT excitations reproduce well the experimental trends in transition energies. In addition, three monoruthenium complexes have been synthesized for a comparison study.

Nine cyclometalated ruthenium complexes with a redox-active diphenylamine unit in the para position to the RuC 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.

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.

Six bis-tridentate and two tris-bidentate cyclometalated ruthenium complexes with a 1,2,3-triazole-containing ligand have been prepared and characterized. Single-crystal X-ray analyses of complexes [(MeOptpy)Ru(Budtab)](PF₆) and [(Mebip)Ru(Budtab)](PF₆) are presented, where MeOptpy is 4′-p-methoxyphenyl-2,2′:6′,2′′-terpyridine, Budtab is the 2-deprotonated form of 1,3-di(N-n-butyl-1,2,3-triazol-4-yl)benzene, and Mebip is bis(N-methyl-benzimidazolyl)pyridine. The electronic properties of these complexes are probed by spectroscopic and electrochemical analyses. Time-dependent density functional theory calculations have been performed to assist the assignment of the absorption spectra.

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.

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⁺.

A new bridging ligand, 2,3-di(2-pyridyl)-5-phenylpyrazine (dpppzH), has been synthesized. This ligand was designed so that it could bind two metals through a NN-CNN-type coordination mode. The reaction of dpppzH with cis-[(bpy)₂RuCl₂] (bpy=2,2′-bipyridine) affords monoruthenium complex [(bpy)₂Ru(dpppzH)]²⁺ (12+) in 64 % yield, in which dpppzH behaves as a NN bidentate ligand. The asymmetric biruthenium complex [(bpy)₂Ru(dpppz)Ru(Mebip)]³⁺ (23+) was prepared from complex 12+ and [(Mebip)RuCl₃] (Mebip=bis(N-methylbenzimidazolyl)pyridine), in which one hydrogen atom on the phenyl ring of dpppzH is lost and the bridging ligand binds to the second ruthenium atom in a CNN tridentate fashion. In addition, the RuPt heterobimetallic complex [(bpy)₂Ru(dpppz)Pt(CCPh)]²⁺ (42+) has been prepared from complex 12+, in which the bridging ligand binds to the platinum atom through a CNN binding mode. The electronic properties of these complexes have been probed by using electrochemical and spectroscopic techniques and studied by theoretical calculations. Complex 12+ is emissive at room temperature, with an emission λ_max=695 nm. No emission was detected for complex 23+ at room temperature in MeCN, whereas complex 42+ displayed an emission at about 750 nm. The emission properties of these complexes are compared to those of previously reported Ru and RuPt bimetallic complexes with a related ligand, 2,3-di(2-pyridyl)-5,6-diphenylpyrazine.

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, ΔE_1/2 (E_1/2(Ru^II/III)−E_1/2(Fc^0/+)), decreased slightly with increasing solvent donocity. The mixed-valent states of these complexes have been generated by electrolysis 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, E_op, and ΔE_1/2 of four mixed-valent complexes in a given solvent.

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.

The electronic coupling between two amine redox sites bridged through the 5,5′-positions of the [Re(CO)₃Cl]-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.