Reversible One-electron Oxidation Research Articles

Redox Non‐Innocence and Isomer‐Specific Oxidative Functionalization of Ruthenium‐Coordinated β‐Ketoiminate

This article deals with isomeric ruthenium complexes [RuIII (LR )2 (acac)] (S=1/2) involving unsymmetric β-ketoiminates (AcNac) (LR =R-AcNac, R=H (1), Cl (2), OMe (3); acac=acetylacetonate) [R=para-substituents (H, Cl, OMe) of N-bearing aryl group]. The isomeric identities of the complexes, cct (cis-cis-trans, blue, a), ctc (cis-trans-cis, green, b) and ccc (cis-cis-cis, pink, c) with respect to oxygen (acac), oxygen (L) and nitrogen (L) donors, respectively, were authenticated by their single-crystal X-ray structures and spectroscopic/electrochemical features. One-electron reversible oxidation and reduction processes of 1-3 led to the electronic formulations of [RuIII (L)(L⋅ )(acac)]+ and [RuII (L)2 (acac)]- for 1+ -3+ (S=1) and 1- -3- (S=0), respectively. The triplet state of 1+ -3+ was corroborated by its forbidden weak half-field signal near g≈4.0 at 4 K, revealing the non-innocent feature of L. Interestingly, among the three isomeric forms (a-c in 1-3), the ctc (b in 2 b or 3 b) isomer selectively underwent oxidative functionalization at the central β-carbon (C-H→C=O) of one of the L ligands in air, leading to the formation of diamagnetic [RuII (L)(L')(acac)] (L'=diketoimine) in 4/4'. Mechanistic aspects of the oxygenation process of AcNac in 2 b were also explored via kinetic and theoretical studies.

Synthesis, optical and electrochemical abilities of highly soluble poly(epoxy-ether)s bearing perylene bisimide units and their enhanced thermal properties by curing process

Three highly fluorescent poly(epoxy-ether) containing three different units at two imide functionalities of perylene bisimide unit (PER-EP1, PER-EP2 and PER-EP3) could be efficiently synthesized in high yields, and were characterized by FT-IR, 1H NMR and 13C NMR spectroscopic techniques. Their optical properties were measured using UV–vis and emission spectroscopic methods, as well as cyclic voltammetry (CV) to analyze their electrochemical abilities. They all showed emission in the visible region. Additionally, one reversible one-electron oxidation and two reversible one-electron reductions in acetonitrile took place for the synthesized poly(epoxy-ether)s. Dihydroxy compounds containing perylene units exhibited three absorption maxima (λmax) values of 458, 489 and 524 nm in DMF owing to presence of perylene units and highly conjugated framework of π bonds. For poly(epoxy-ether)s, the functional groups influenced the conjugated systems, giving rise to the absorption peaks to shift to longer wavelengths. Fluorescence spectra of the synthesized poly(epoxy-ether)s in DMF showed emission peaks in the wavelength range of green light, and the highest value of fluorescence quantum yield was 8.2% for PER-EP1 in comparison to standard fluorescein solution. Furthermore, morphological analysis demonstrated that the synthesized poly(epoxy-ether)s possessed well-organized microstructure particles despite the linkage of the perylene bisimide core. The prepared epoxy resins were cured with p-phenylenediamine as aromatic hardener. The resulting cured epoxy resins were analyzed for their thermal properties such as thermal stability, char yield, glass transition temperature (Tg), and flame retardancy. The morphology behaviour was performed by SEM analysis on poly(epoxy-ether)s.

Organometallic phthalazin-1(2H)-ones: Electrochemistry and advantage of solvothermal synthesis

o-Ferrocenylcarbonylbenzoic acid (η5-C5H5)Fe(η5-C5H4C(O)C6H4COOH) (I) and o-cymantrenylcarbonylbenzoic acid (II) were obtained from ferrocene or (η5-C5H5)Mn(CO)3, respectively, by the Friedel–Crafts reaction with phthalic anhydride. Methyl o-ferrocenylcarbonylbenzoate (η5-C5H5)Fe(η5-C5H4C(O)C6H4COOMe (III) and methyl o-cymantrenylcarbonylbenzoate (CO)3Mn(η5-C5H4C(O)C6H4COOMe) (IV) were synthesized from I and II, respectively using dimethyl carbonate (DMC) in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) to promote the methylation reaction. 4-Ferrocenylphthalazin-1(2H)-one (V) and 4-cymantrenylphthalazin-1(2H)-one (VI) were obtained by the interaction of hydrazine hydrate with I and II, respectively, by the prolonged reflux or convenient solvothermal synthesis. Cyclic voltammetry measurements showed that compounds III and V undergo reversible one-electron oxidation, localized presumably at the ferrocene unit. For III the irreversible one-electron oxidation is apparently associated with the oxidation of the benzoate fragment. All new compounds were characterized by spectroscopic methods and the molecular structures of II and III were determined by X-ray diffraction analysis.

Ferrocene appended naphthalimide derivatives: Synthesis, DNA binding, and in vitro cytotoxic activity

Three novel ferrocene appended naphthalimide derivatives (2a, 2b and 6) were synthesized and characterized by IR, 1H NMR and mass spectroscopies. In electrochemical experiments, all of the ferrocene appended naphthalimide derivatives exhibited reversible one-electron oxidation in CV curves. And the DNA binding ability of the compounds was studied by ethidium bromide displacement experiments and UV–visible spectrophotometry. The ferrocene appended naphthalimide derivative 6 also exhibited the highest DNA binding ability in all the tested compounds. According to the viscosity results, all of the synthesized compounds displayed the partial intercalation binding mode to DNA duplex. Bis-naphthalimide compound 5 was used as reference compound to evaluate the synergistic effect of the ferrocene group in ferrocene appended naphthalimide derivative 6. The cytotoxicity of the synthesized compounds against 4 different human cancer cell lines (EC109, BGC823, SGC 7901 and HepG2) was studied by MTT assay. The ferrocene appended bis-naphthalimide derivative 6 showed the best cytotoxicity against tested human cancer cells in all the synthesized naphthalimide derivatives and control drug amonafide. The uptake of naphthalimide derivative 6 was proved by laser confocal images. In addition, the DNA damage induced by naphthalimide derivative 6 was studied by comet assay.

Electronically Triggered Switchable Binding Modes of the C-Organonitroso (ArNO) Moiety on the {Ru(acac)2} Platform

This work evaluated the switchable binding profile of the biochemically relevant and redox non-innocent C-organonitroso (ArNO) moiety with the selective {Ru(acac)2} (acac = acetylacetonate) metal fragment as a function of external stimuli, including the solvent medium (EtOH versus toluene) and aryl substituents (C6H5, p-OMe-C6H4, and p-Cl-C6H4) in the framework of ArNO. In this context, the reaction of ArNO (Ar = C6H5 or p-OMe-C6H4) with the metal precursor RuII(acac)2(CH3CN)2 in polar protic EtOH led to the formation of monomeric [RuII(acac)2(ArNOo)2] (1a or 1b) with η1-N-bonded terminal ArNOo and double-ArNOo-bridged dimeric [(acac)2RuII(μ-ArNOo)2RuII(acac)2], 2a or 2b, respectively. On the other hand, the use of p-Cl-substituted ArNO selectively yielded the corresponding dimeric 2c. However, the use of nonpolar toluene resulted in monomeric 1 irrespective of the nature of aryl substituents in ArNO. Molecular identities, including the redox state of ArNOo in 1 and 2, were authenticated by their single-crystal X-ray structures as well as by solution spectral features. Though monomeric 1 exhibited reversible one-electron oxidation and reduction processes, leading to the electron paramagnetic resonance active [RuIII(acac)2(ArNOo)2]+ (1+; S = 1/2) and [RuII(acac)2(ArNO•-)(ArNOo)]- (1•-; S = 1/2), respectively, redox states of dimeric 2 were found to be unstable on the electrolysis time scale. Interestingly, monomeric 1 underwent transformation to dimeric 2 in the presence of a strong reducing agent, hydrazine hydrate, and the reverse process, i.e., conversion of dimeric 2 to 1, took place under the influence of external coordinating agent ArNO. The detailed experimental exploration, including kinetic investigations related to 1 → 2 and 2 → 1 transformations, revealed that the electronic aspects of ArNO (redox non-innocence of ArNOo/•-, π-accepting and coordinating features of ArNOo) had facilitated its switchable binding event in combination with the {Ru(acac)2} metal fragment.

Comparative Electrochemistry and Electrochromic Application of Novel Binuclear Double‐Decker Rare Earth Metal Phthalocyanines Bearing 4-(hydroxyethyl)phenoxy Moieties

In the present work, novel double-decker samarium(III), europium(III), and ytterbium (III) phthalocyanines (SmPc2, EuPc2, and YbPc2) bearing 4-(hydroxyethyl)phenoxy moieties have been synthesized and their electrochemical redox, spectroelectrochemical, and electrocolorimetric properties of the complexes have been inquired comparatively in two different non-aqueous solution. All complexes were observed to expose a series of usually reversible phthalocyanine ring-based one-electron reduction and oxidation processes. The effect of the size of rare earth metal ion was clearly reflected as the modest shift in half-wave potentials. Enriched electron transfer processes of the complexes and the interaction between the electrochemically generated anionic and cationic species caused distinct spectral and color changes, identified with in-situ spectroelectrochemical and in-situ electrocolorimetric measurements in solution medium. Spectroelectrochemical and electrocolorimetric measurements of the complexes were also performed in the solid state as the Langmuir-Blodgett film on an indium tin oxide glass in order to understand their technological applicability in electrochromic devices as color changing material. Comparative evaluation of these measurements suggested that Langmuir-Blodgett films of SmPc2 and EuPc illustrate highly reversible distinct color change from green to purple with satisfying electrochromic performance for electrochromic device applications.

A novel Nb2S4 complex with a dithiophosphinate ligand: Synthesis, structure and redox properties

A new diisobutyldithiophosphinate complex, [Nb2S4(S2PiBu2)4] (1), was obtained by a ligand substitution reaction using (Bu4N)4[Nb2S4(NCS)8] and NaS2PiBu2·3H2O. Its crystal structure has been determined. The NbNb distance is 2.9034(7) Å. The cyclic voltammogram (CV) of 1 in dichloromethane exhibits two successive chemically reversible one-electron oxidation waves at +0.55 and +1.10 V (versus Ag/AgCl) attributed to the NbIV/NbV couple. This is the first {Nb2S4} cluster that shows two reversible oxidations. The paramagnetic mixed-valence Nb(IV/V) product of the one-electron oxidation, [Nb2S4(S2PiBu2)4]+ (1+), was generated in situ. The EPR spectrum of 1+ in acetonitrile reveals a 19-line signal arising from the hyperfine interaction between the unpaired electron and two equivalent 93Nb nuclei with I = 9/2, indicating complete delocalization of the unpaired electron over both metal centers. DFT calculations have been performed for the complexes [Nb2S4(S2PMe2)4], [Nb2S4(S2P(OMe)2)4], [Nb2S4(S2CNMe2)4] and [Nb2S4(S2COMe)4] and their single and double oxidized species in order to explain the peculiarities of their redox behavior. The results show that the HOMOs responsible for oxidation have a predominantly metallic character in all cases, but they are significantly more high-lying for the dithiophosphinate and dithiocarbamate complexes, which explains their ability to be oxidized.

Highly Stable Active Materials for Nonaqueous Redox Flow Batteries

The commercialization of truly practical nonaqueous redox flow batteries (RFBs) requires the development of compounds that are extremely stable in at least two oxidation states. Moreover, ideal RFB catholyte materials should possess high oxidation potentials (>4 V vs. Li/Li+), while their anolyte counterparts should possess relatively low reduction potentials. A series of promising RFB anolytes based on p-phenylene-bridged bis(pyridinium) compounds has been prepared and characterized. These compounds are highly soluble in polar organic solvents and undergo a chemically reversible net two-electron reduction. Because the para orientation allows the formation of a quinoidal neutral species upon 2e- reduction, the reduction product is expected to display good stability. The synthesis, characterization, and electrochemical properties of several RFB catholytes based on phenothiazine-5,5-dioxide will also be described. These compounds exhibit chemically and electrochemically reversible one-electron oxidation at very high potentials (4.2-4.3 V vs. Li/Li+) in polar organic solvents. By attaching suitable ether functional groups, solubilities exceeding 2 M in propylene carbonate electrolytes can be achieved. Optical spectroscopy reveals that the radical cations produced by bulk electrolysis are extremely stable, undergoing minimal loss even after 1500 hours.

Enhancing the Visible-Light Absorption and Excited-State Properties of Cu(I) MLCT Excited States.

A computationally inspired Cu(I) metal-to-ligand charge transfer (MLCT) chromophore, [Cu(sbmpep)2]+ (sbmpep = 2,9-di(sec-butyl)-3,8-dimethyl-4,7-di(phenylethynyl)-1,10-phenanthroline), was synthesized in seven total steps, prepared from either dichloro- or dibromophenanthroline precursors. Complete synthesis, structural characterization, and electrochemistry, in addition to static and dynamic photophysical properties of [Cu(sbmpep)2]+, are reported on all relevant time scales. UV-Vis absorption spectroscopy revealed significant increases in oscillator strength along with a concomitant bathochromic shift in the MLCT absorption bands with respect to structurally related model complexes (ε = 16 500 M-1 cm-1 at 491 nm). Strong red photoluminescence (Φ = 2.7%, λmax = 687 nm) was observed from [Cu(sbmpep)2]+, which featured an average excited-state lifetime of 1.4 μs in deaerated dichloromethane. Cyclic and differential pulse voltammetry revealed ∼300 mV positive shifts in the measured one-electron reversible reduction and oxidation waves in relation to a Cu(I) model complex possessing identical structural elements without the π-conjugated 4,7-substituents. The excited-state redox potential of [Cu(sbmpep)2]+ was estimated to be -1.36 V, a notably powerful reductant for driving photoredox chemistry. The combination of conventional and ultrafast transient absorption and luminescence spectroscopy successfully map the excited-state dynamics of [Cu(sbmpep)2]+ from initial photoexcitation to the formation of the lowest-energy MLCT excited state and ultimately its relaxation to the ground state. This newly conceived molecule appears poised for photosensitization reactions involving energy and electron-transfer processes relevant to photochemical upconversion, photoredox catalysis, and solar fuels photochemistry.

Excited-State Processes of Cyclometalated Platinum(II) Charge-Transfer Dimers Bridged by Hydroxypyridines.

A series of four anti-disposed dinuclear platinum(II) complexes featuring metal-metal-to-ligand charge-transfer (MMLCT) excited states, bridged by either 2-hydroxy-6-methylpyridine or 2-hydroxy-6-phenylpyridine and cyclometalated with 7,8-benzoquinoline or 2-phenylpyridine, are presented. The 2-hydroxypyridine bridging ligands control intramolecular d8-d8 metal-metal σ interactions, affecting the frontier orbitals' electronic structure, resulting in marked changes to the ground- and excited-state properties of these complexes. Three of these molecules possess reversible one-electron oxidations in cyclic voltammetry experiments as a result of strong intramolecular metallophilic interactions. In this series of molecules, X-ray crystallography revealed Pt-Pt distances ranging between 2.815 and 2.878 Å; the former represents the shortest reported metal-metal distance for platinum(II) dimers possessing low-energy MMLCT transitions. All four molecules reported here display visible absorption bands beyond 500 nm and feature MMLCT-based red photoluminescence (PL) above 700 nm at room temperature with high PL quantum yields (up to 4%) and long excited-state lifetimes (up to 341 ns). The latter were recorded using both transient PL and transient absorption experiments that self-consistently yielded quantitatively identical excited-state lifetimes. The energy-gap law was successfully applied to this series of chromophores, documenting this behavior for the first time in molecules possessing MMLCT excited states. The combined data illustrate that entirely new classes of MMLCT chromophores can be envisioned using bridging pyridyl hydroxides in cooperation with various C^N cyclometalates to achieve photophysical properties suitable for excited-state electron- and energy-transfer chemistry.

High Potential Organic Materials for Battery Applications

Many organic heterocyclic compounds undergo reversible one-electron electrochemical oxidation. However, in order to function effectively as redox shuttles in lithium batteries, such materials must display such behavior at potentials exceeding 4.2 V vs Li/Li+, and designing compounds that meet this requirement yet remain stable in the cation radical form represents a significant challenge. We have developed two families of organic heterocycles suitable for battery applications; namely appropriately substituted carbazoles and phenothiazine 5,5-dioxides. We will describe the synthesis and characterization of these compounds, along with preliminary results of testing in lithium ion batteries and redox flow batteries. Figure 1

Pyrene Molecular Orbital Shuffle-Controlling Excited State and Redox Properties by Changing the Nature of the Frontier Orbitals.

We show that by judicious choice of substituents at the 2- and 7-positions of pyrene, the frontier orbital order of pyrene can be modified, giving enhanced control over the nature and properties of the photoexcited states and the redox potentials. Specifically, we introduced a julolidine-like moiety and Bmes2 (mes=2,4,6-Me3 C6 H2 ) as very strong donor (D) and acceptor (A), respectively, giving 2,7-D-π-D- and unsymmetric 2,7-D-π-A-pyrene derivatives, in which the donor destabilizes the HOMO-1 and the acceptor stabilizes the LUMO+1 of the pyrene core. Consequently, for 2,7-substituted pyrene derivatives, unusual properties are obtained. For example, very large bathochromic shifts were observed for all of our compounds, and unprecedented green light emission occurs for the D/D system. In addition, very high radiative rate constants in solution and in the solid state were recorded for the D-π-D- and D-π-A-substituted compounds. All compounds show reversible one-electron oxidations, and Jul2 Pyr exhibits a second oxidation, with the largest potential splitting (ΔE=440 mV) thus far reported for 2,7-substituted pyrenes. Spectroelectrochemical measurements confirm an unexpectedly strong coupling between the 2,7-substituents in our pyrene derivatives.

Formally Copper(III)-Alkylperoxo Complexes as Models of Possible Intermediates in Monooxygenase Enzymes.

Reaction of [NBu4][LCuIIOH] with excess ROOH (R = cumyl or tBu) yielded [NBu4][LCuIIOOR], the reversible one-electron oxidation of which generated novel species with [CuOOR]2+ cores (formally CuIIIOOR), identified by spectroscopy and theory for the case R = cumyl. This species reacts with weak O-H bonds in TEMPO-H and 4-dimethylaminophenol (NMe2PhOH), the latter yielding LCu(OPhNMe2), which was also prepared independently. With the identification of [CuOOR]2+ complexes, the first precedent for this core in enzymes is provided, with implications for copper monooxygenase mechanisms.

A Coordination Network with Ligand-Centered Redox Activity Based on facial-[CrIII (2-mercaptophenolato)3 ]3- Metalloligands.

The design of redox-active metal-organic frameworks and coordination networks (CNs), which exhibit metal- and/or ligand-centered redox activity, has recently received increased attention. In this study, the redox-active metalloligand (RML) [Me4 N]3 fac-[CrIII (mp)3 ] (1) (mp=2-mercaptophenolato) was synthesized and characterized by single-crystal X-ray diffraction analysis, and its reversible ligand-centered one-electron oxidation was examined by cyclic voltammetry and spectroelectrochemical measurements. Since complex 1 contains O/S coordination sites in three directions, complexation with K+ ions led to the formation of the two-dimensional honeycomb sheet-structured [K3 fac-{CrIII (mp)3 }(H2 O)6 ]n (2⋅6 H2 O), which is the first example of a redox-active CN constructed from a RML with o-disubstituted benzene ligands. Herein, we unambiguously demonstrate the ligand-centered redox activity of the RML within the CN 2⋅6 H2 O in the solid state.

Molybdenum Dithiolene Complexes: Trinuclear Mixed-Valence Complexes and Geometrical Isomers of Dinuclear Complexes

Abstract The reaction of an oxygen- and sulfur-bridged incomplete cubane-type molybdenum complex [Mo3(µ3-S)(µ-S)2(µ-O)(dtp)3(µ-dtp)(CH3CN)] (3) (dtp, diethyl dithiophosphate) with methyl propiolate (HC≡CCOOCH3, MP) and phenyl acetylene (HC≡CC6H5, PA) yields trinuclear mixed-valence Mo3(IV, V, V) complexes [Mo3(O)2(µ3-S)(µ3-SCH=C(COOCH3)S)(dtp)3(µ-OAc)] (3MP) and [Mo3(O)2(µ3-S)(µ3-SCH=C(C6H5)S)(dtp)3(µ-OAc)] (3PA), respectively, and also dinuclear Mo2(V, V) complexes [Mo2(O)2(µ-S)(µ-SCH=C(COOCH3)S)(dtp)2] (2aMP and 2bMP (a geometrical isomer of 2aMP)) and [Mo2(O)2(µ-S)(µ-SCH=C(C6H5)S)(dtp)2] (2aPA and 2bPA (a geometrical isomer of 2aPA)), respectively. The origin of the geometrical isomerism of the dimers comes from the unsymmetric nature of the acetylene derivatives. All of the structures were determined by X-ray crystallography, which revealed that each complex has two carbon-sulfur (µ-S) bonds arising from the adduct formation reaction between complex 3 and an acetylene derivative MP or PA. 1H NMR spectroscopy has proven that the dinuclear complexes are formed via the trinuclear complexes. The XPS spectra of 3MP show that the peaks of Mo 3d3/2 and Mo 3d5/2 are clearly split into two in the ratio of two to one, respectively, while those of 3 show no splitting, which indicates that 3MP is a mixed-valence complex with Mo3(IV, V, V) oxidation states. Cyclic voltammograms of 3MP and 3PA show chemically reversible one-electron oxidation processes at E1/2 = 0.21 V and E1/2 = 0.15 V vs. Ag/Ag+, respectively, and irreversible reduction peaks at −0.92 V and −1.00 V vs. Ag/Ag+, respectively. The dinuclear complexes, especially 2aPA and 2bPA having phenyl groups, are photosensitive to give their isomeric counter parts.

Coordinating Tectons. Experimental and Computational Infrared Data as Tools To Identify Conformational Isomers and Explore Electronic Structures of 4-Ethynyl-2,2′-bipyridine Complexes

4-Ethynyl-2,2′-bipyridyl-substituted ruthenium alkynyl complexes have been prepared and used to access a range of binuclear homometallic ruthenium and heterometallic ruthenium–rhenium complexes. These have been characterized by a variety of spectroscopic and single-crystal X-ray diffraction experiments. The IR spectra of a number of these ruthenium alkynyls display multiple ν(C≡C) bands in the IR spectra, which are rationalized in terms of putative conformational isomers, whose calculated infrared stretching frequencies are comparable to those obtained experimentally. The mononuclear alkynyl ruthenium complexes undergo reversible one-electron oxidations centered largely on the alkynyl ligands, as inferred from the significant shift in ν(C≡C) frequency on oxidation, while the binuclear complex [Ru{C≡C-4-bpy-κ2-N,N′-RuClCp}(dppe)Cp*]+ undergoes initial oxidation at the very electron rich {RuCl(bpy)Cp} fragment, causing only a small change in ν(C≡C). A combination of IR and UV–vis spectroelectrochemical expe...

3-Phenothiazinyl propiolates – Fluorescent electrophores by Sonogashira coupling of ethyl propiolate

Fluorescent ethyl 3-phenothiazinyl propiolates with reversible Nernstian oxidation potentials were efficiently synthesized by an improved Sonogashira coupling of aryl iodides and ethyl propiolate. The versatility of this modified alkynylation was illustrated by 13 ethyl 3-arylpropiolates in mostly excellent yields with a broad substrate scope. In addition to reversible one-electron oxidations, the title compounds reveal large Stokes shifts, high fluorescence quantum yields, and solvatochromic emission. The photophysical characteristics were corroborated and rationalized by DFT and TD-DFT calculations.

Microwave-Mediated Synthesis of Bulky Lanthanide Porphyrin-Phthalocyanine Triple-Deckers: Electrochemical and Magnetic Properties.

Five heteroleptic lanthanide porphyrin-bis-phthalocyanine triple-decker complexes with bulky peripheral groups were prepared via microwave-assisted synthesis and characterized in terms of their spectroscopic, electrochemical, and magnetic properties. These compounds, which were easily obtained under our preparative conditions, would normally not be accessible in large quantities using conventional synthetic methods, as a result of the low yield resulting from steric congestion of bulky groups on the periphery of the phthalocyanine and porphyrin ligands. The electrochemically investigated triple-decker derivatives undergo four reversible one-electron oxidations and three reversible one-electron reductions. The sites of oxidation and reduction were assigned on the basis of redox potentials and UV-vis spectral changes during electron-transfer processes monitored by thin-layer spectroelectrochemistry, in conjunction with assignments of electronic absorption bands of the neutral compounds. Magnetic susceptibility measurements on two derivatives containing TbIII and DyIII metal ions reveal the presence of ferromagnetic interactions, probably resulting from magnetic dipolar interactions. The TbIII derivative shows SMM behavior under an applied field of 0.1 T, where the direct and Orbach process can be determined, resulting in an energy barrier of Ueff = 132.0 K. However, Cole-Cole plots reveal the presence of two relaxation processes, the second of which takes place at higher frequencies, with the data conforming to a 1/t ∝ T7 relation, thus suggesting that it can be assigned to a Raman process. Attempts were made to form two-dimensional (2D) self-assembled networks on a highly oriented pyrolytic graphite (HOPG) surface but were unsuccessful due to bulky peripheral groups on the two Pc macrocycles.

Bis(diarylethenyl)-thiophenes, -bithiophenes, and -terthiophenes: a new series of electrochromic systems that exhibit a fluorescence response

2,5-Bis(diarylethenyl)thiophenes (1) and their bithiophene (2) and terthiophene (3) homologues were designed as a new series of violene/cyanine-hybrid-type electrochromic materials. Alkoxyphenyl and dialkylaminophenyl groups are used as the aryl group in the cyanine parts of 1/2/3O and 1/2/3N, respectively, which emit fluorescence in the neutral state but not in the oxidized state. Voltammetric analyses of 18 newly prepared electron donors show that they all undergo two reversible one-electron oxidations. Redox potentials, UV–vis spectral features, and fluorescence quantum yields are important parameters for characterizing the present electrochromic behavior with a fluorescence response, and can be finely tuned by changing aryl groups in the cyanine part, the number of thiophene rings in the violene part, and the alkyl-chain length of the alkoxyphenyl or diaklylaminophenyl groups (R = CH3, C8H17, C16H33), which makes this a versatile platform for the design of novel electrochromic materials.

Ru-Os dyads based on a mixed bipyridine-terpyridine bridging ligand: modulation of the rate of energy transfer and pH-induced luminescence switching in the infrared domain.

A series of heterobimetallic complexes of compositions [(bpy/phen)2Ru(dipy-Hbzim-tpy)Os (tpy-PhCH3/H2pbbzim)]4+ (bpy = 2,2'-bipyridine, phen = 1,10-phenanthroline, tpy-PhCH3 = 4'-(4-methylphenyl)-2,2':6',2''-terpyridine and H2pbbzim = 2,6-bis(benzimidazole-2-yl)pyridine)), derived from a heteroditopic bpy-tpy bridging ligand, were synthesized and thoroughly characterized in this work. The heterometallic complexes exhibit two successive one-electron reversible metal-centered oxidations corresponding to OsII/OsIII at lower potential and RuII/RuIII at higher potential. All the four dyads exhibit very intense, ligand centered absorption bands in the UV region and moderately intense MLCT bands in the visible region. The dyads also show intense infrared emission with the emission maximum spanning between 734 nm and 775 nm with reasonably long room temperature lifetimes varying between 30 ns and 104 ns. Both steady state and time resolved luminescence spectroscopic investigations indicate that efficient and fast intramolecular energy transfer from the 3MLCT state of the Ru(ii) center to the Os-center takes place in all the four dyads. In addition, the rate of energy transfer was found to depend on the terminal ligand on the Os-site. Due to the presence of a number of imidazole NH protons in the dyads, significant modulation of both the ground and excited state properties of the complexes was made possible by varying the pH of the solution. By varying the terminal ligand, pH-induced "on-off", "off-off-on" and "on-off-on" emission switching of the complexes was nicely demonstrated in the infrared region.