Quasi-reversible One-electron Reduction Research Articles

Competition between Cu-Br semi-coordinate bond and C-H∙∙∙Br, C-H∙∙∙S and S∙∙∙S interactions; new two thioalkylazothiophenol (SNS) copper (II) dimers [Cu(L)(µ-Br)

Two new copper dimers [Cu(L)(µ-Br)]2, HL = 2(RS)C6H4N = NC(COCH3)-SC6H5, where R = CH3 (1), C6H5 (2) were synthesized and characterized using a variety of physicochemical methods, including single crystal X-ray diffraction. The molecular structures of the two binuclear copper(II) complexes show that Cu∙∙∙Cu inter-nuclei distances are 3.662 \\AA and 3.392 \\AA in 1 and 2, respectively. Structural analysis of the two dimers supported by QTAIM analysis of electron density indicates the presence of competition between Cu∙∙∙Br semi-coordinate bond and CH∙∙∙Br and CH∙∙∙S hydrogen bonding interactions and S∙∙∙S chalcogen bonding interactions. In complex 1, CH∙∙∙Br and CH∙∙∙S hydrogen bonding interactions exist, in contrast, they are absent in 2. Cu∙∙∙Br semi-coordinate bonds are stronger in 2 as indicated by Cu∙∙∙Br bond distances; Cu∙∙∙Br bond distances are 2.955 and 2.858 Å in 1 and 2.746 Å in 2. There are two weaker S∙∙∙S interactions in 2 and one stronger interaction in 1 as indicated by S∙∙∙S interatomic distances. The two copper dimers and their ligands exhibited good anticancer efficacy against breast (MCF-7), lung (HCT115), and colon human (A549) cancer cell lines. Complex 1 demonstrated strong cancer cell death compared to complex 2. Additionally, the complexes exhibited higher activity than the ligands. Dimer 2 exhibits two quasi-reversible one-electron reduction waves at −0.05 V and −0.37 V. The comproportionating constant for forming the Cu(I/II) mixed-valence complex was 2.57 × 105. The absence of Intervalence transfer (IT) bands in the electronic absorption spectrum for the mixed-valence complex suggested that a single unpaired electron is localized on one copper center.

Primary amines as ligands and linkers in complexes of tripyrrindione radicals

Biopyrrin pigments, which result from the degradation of heme in biological settings, feature three or two pyrrole rings and characteristic pyrrolin-2-one termini. These scaffolds serve as redox-active ligands and electron reservoirs in coordination compounds. Tripyrrin-1,14-dione coordinates divalent transition metals as a dianionic ligand hosting a delocalized radical. Herein, we report the synthesis and characterization of palladium(II) and platinum(II) tripyrrindione complexes featuring a primary amine (i.e., aniline, tert-butylamine, 1,2-ethylenediamine) at the fourth coordination site within square planar geometries. Interligand hydrogen-bonding interactions are observed between the coordinated amine and the carbonyl groups on the tripyrrindione scaffold. Notably, 1,2-ethylenediamine is employed to link two Pt(II) tripyrrindione complexes. As revealed by optical absorption and electron paramagnetic resonance (EPR) spectroscopy, all resulting complexes present ligand-based radicals that are stable at room temperature and when exposed to air. Spin pairing through multicenter interactions leads to [Formula: see text]-dimerization of the tripyrrindione radicals and a decrease in the EPR signal at low temperatures. Electrochemical measurements indicate that the ligand system undergoes quasi-reversible one-electron oxidation and reduction, thus confirming the ability of tripyrrindione to form square planar complexes in three different redox states.

Square-Planar Heteroleptic Complexes of α-Diimine-NiII-Catecholate Type: Intramolecular Ligand-to-Ligand Charge Transfer.

Two heteroleptic NiII complexes combined the redox-active catecholate and 2,2′- bipyridine ligand platforms were synthesized to observe a photoinduced intramolecular ligand-to-ligand charge transfer (LL’CT, HOMOcatecholate → LUMOα-diimine). A molecular design of compound [NiII(3,6-Cat)(bipy)]∙CH3CN (1) on the base of bulky 3,6-di-tert-butyl-o-benzoquinone (3,6-DTBQ) was an annelation of the ligand with an electron donor glycol fragment, producing derivative [NiII(3,6-Catgly)(bipy)]∙CH2Cl2 (2), in order to influence the energy of LL’CT transition. A substantial longwave shift of the absorption peak was observed in the UV-Vis-NIR spectra of 2 compared with those in 1. In addition, the studied NiII derivatives demonstrated a pronounced negative solvatochromism, which was established using a broad set of solvents. The molecular geometry of both compounds can be ascribed as an insignificantly distorted square-planar type, and the π–π intermolecular stacking of the neighboring α-diimines is realized in a crystal packing. There is a lamellar crystal structure for complex 1, whereas the perpendicular T-motifs with the inter-stacks attractive π–π interactions form the packing of complex 2. The redox-active nature of ligand systems was clearly shown through the electrochemical study: a quasi-reversible one-electron reduction of 2,2′-bipyridine and two reversible successive one-electron oxidative conversations (“catecholate dianion—o-benzosemiquinonato radical anion—neutral o-benzoquinone”) were detected.

Proton reduction by phosphinidene-capped triiron clusters

Bis(phosphinidene)-capped triiron carbonyl clusters, including electron rich derivatives formed by substitution with chelating diphosphines, have been prepared and examined as proton reduction catalysts. Treatment of the known cluster [Fe3(CO)9(µ3-PPh)2] (1) with various diphosphines in refluxing THF (for 5, refluxing toluene) afforded the new clusters [Fe3(CO)7(µ3-PPh)2(κ2-dppb)] (2), [Fe3(CO)7(µ3-PPh)2(κ2-dppv)] (3), [Fe3(CO)7(µ3-PPh)2(κ2-dppe)] (4) and [Fe3(CO)7(µ3-PPh)2(µ-κ2-dppf)] (5) in moderate yields, together with small amounts of the corresponding [Fe3(CO)8(µ3-PPh)2(κ1-Ph2PxPPh2)] cluster (x = -C4H6-, -C2H2-, -C2H4-, -C3H6-, -C5H4FeC5H4-). The molecular structures of complexes 3 and 5 have been established by X-ray crystallography. Complexes 1–5 have been examined as proton reduction catalysts in the presence of p-toluenesulfonic acid (p-TsOH) in CH2Cl2. Cluster 1 exhibits two one-electron quasi-reversible reduction waves at –1.39 V (ΔE = 195 mV) and at –1.66 V (ΔE = 168 mV; potentials vs. Fc+/Fc). Upon addition of p-TsOH the unsubstituted cluster 1 shows a first catalytic wave at –1.57 V and two further proton reduction processes at –1.75 and –2.29 V, each with a good current response. The diphosphine-substituted derivatives of 1 are reduced at more negative potentials than the parent cluster 1. Clusters 2–4 each exhibit an oxidation at ca. +0.1 V and a reduction at ca. –1.6 V; for 4 conversion to a redox active successor species is seen upon both oxidation and reduction. Clusters 2–4 show catalytic waves in the presence of p-TsOH, with cluster 4 exhibiting the highest relative catalytic current (icat/i0 ≈ 57) in the presence of acid, albeit at a new third reduction process not observed for 2 and 3. Addition of the dppf ligand to the parent diphosphinidene cluster 1 gave cluster 5 which exhibited a single reduction process at –1.95 V and three oxidation processes, all at positive values as compared to 2–4. Cluster 5 showed only weak catalytic activity for proton reduction with p-TsOH. The bonding in 4 was investigated by DFT calculations, and the nature of the radical anion and dianion is discussed with respect to the electrochemical data.

Nickel(II) derivatives based on o-iminobenzoquinone-type ligands: Structural modifications, magnetism and electrochemical peculiarities

New bis-o-iminobenzosemiquinonato derivatives of nickel (imSQC(O)Ph)2Ni (1) and (imSQPh)2Ni (2) that are ligated by functionalized o-aminophenols H2LC(O)Ph and H2LPh, respectively, were synthesized. Complex 1 is distinguished by a square-planar geometry of N2O2 coordination core while the bis-o-iminobenzosemiquinonate 2 demonstrates a slight deviation from planarity. Both complexes 1 and 2 show the strong antiferromagnetic interactions between radical anion ligands as established by variable-temperature magnetic susceptibility measurements. Electrochemical behavior of 1 and 2 is represented by ligand-centered redox transitions: two quasi-reversible one-electron reduction processes and two-electron oxidation one. The salient peculiarity of cyclic voltammogram for 1 is an increase in number of redox waves owing to the quasi-reversible reduction of benzophenone fragments in ligands. Six-coordinated NiII derivative [(imQC(O)Ph)2Ni(H2O)2](OSO2CF3)2 (3) with two o-iminobenzoquinones as well as four-coordinated NiII species [(imSQC(O)Ph)Ni(APC(O)Ph)]CoCp2∙2.1toluene (4∙2.1toluene) including radical-anion and o-amidophenolate forms of redox-active ligand were prepared as products of oxidation and reduction of the initial 1, respectively, in accordance with the CV data. The value of effective magnetic moment (μeff) unambiguously indicates the high-spin state for nodal NiII ion in 3. Low-temperature EPR signal demonstrates rather the ligand-centered nature of unpaired electron in 4 that corresponds to the total doublet ground spin state (S = 1/2) for compound and diamagnetic low-spin (SNi = 0) configuration of the metal center.

Redox-Active Organoruthenium(II)– and Organoosmium(II)–Copper(II) Complexes, with an Amidrazone–Morpholine Hybrid and [CuICl2]− as Counteranion and Their Antiproliferative Activity

A novel proligand HLH has been prepared from 2-pyridinamidrazone and 6-(morpholinomethyl)pyridine-2-carboxaldehyde. Subsequently, starting from HLH and CuCl2·2H2O in the presence of triethylamine, a series of homo- and heterometallic complexes with [CuICl2]− as counteranion, namely mononuclear complex [CuIICl(HLOMe)][CuICl2] (1), dinuclear Ru(II)–Cu(II) complex [CuIIRuII(η6-p-cymene)Cl2(LH)][CuICl2]·1.5H2O (2·1.5H2O), Os(II)–Cu(II) complex [CuIIOsII(η6-p-cymene)Cl2(LH)][CuICl2]·H2O (3·H2O), and tetranuclear complex [CuII4(L1)2(L2)2Cl2]·5MeOH (4·5MeOH), where HLOMe, L1, and L2 are Schiff base ligands derived from HLH, were synthesized. The structures of metal complexes were established by X-ray diffraction. Complexes 1–3 demonstrated quasireversible one-electron reduction of Cu(II) in complex cations and one-electron oxidation of [CuICl2]− counterion, confirmed by UV–vis and EPR spectroelectrochemical measurements. They exhibited moderate antiproliferative activity against ovarian carcinoma and cervical ad...

The electrochemical reduction kinetics of oxygen in dimethylsulfoxide

The quasi-reversible one-electron reduction of oxygen in dimethylsulfoxide is reported for a range of electrode materials (C, Pt, Pd, and Au) and temperatures (293–343 K). Modelling was undertaken using Butler-Volmer and symmetric Marcus-Hush methods, with the former found to provide more reproducible results for this system, in agreement with previous reports of quasi-reversible systems. The reorganisation energy for the reaction was found to be ca. 1.0 eV, and the reaction confirmed to be predominantly outer-sphere. The observed standard electrochemical rate constant (k0) is ca. 5.7 times faster for C electrodes than Pt, despite having a lower electronic density of states.

Titanium thiosalicylate complexes: functional metalloligands for the construction of redox-active heterometallic architectures

The titanium complex [TiCp*(thiosal)(thiosalH)] (1) has been synthesised by reaction of [TiCp*Me3], Cp* = η5-C5Me5, with thiosalicylic acid (H2thiosal). Complex 1 reacts with [M(μ-OH)(COD)]2 (M = Rh, Ir) to yield the corresponding early-late heterobimetallic complexes [TiCp*(thiosal)2M(COD)] (M = Rh (2); Ir (3)). Carbon monoxide replaces the COD ligand in 2 and 3 leading to the respective dicarbonyl complexes [TiCp*(thiosal)2M(CO)2] (M = Rh (4); Ir (5)). Compound 4 reacts with PPh3 to yield the monocarbonyl derivative [TiCp*(thiosal)2Rh(CO)(PPh3)] (6). The reaction of compound 1 with LinBu yields the tetrametallic complex [{TiCp*(thiosal)2Li}2(THF)3(H2O)] (7). Compound 7 reacts with [RuCp*Cl(COD)] yielding the heterometallic complex [TiCp*(thiosal)2RuCp*] (8). The molecular structures of compounds 4, 5 and 7 have been studied by X-ray diffraction. From cyclic voltammetric (CV) and square wave voltammetric (SWV) experiments, we observed that attachment of the titanium moiety of precursor 1 to a late transition metal moiety through the sulfur atoms has a significant influence on the reduction behaviour of the Ti(iv) metal centre. Thus, monometallic 1 exhibits an irreversible reduction process at -1.15 V vs. SCE, whereas the CVs of heterobimetallic compounds 2-6 are characterized by the reversible or quasi-reversible one-electron reduction of the Ti(iv)/Ti(iii) system, suggesting a significant stabilization of the Ti(iii) reduced species. Likewise, substitution of the M(COD) diolefin fragment in 2 and 3 by the M(CO)2 carbonyl-containing moiety (in compounds 4 and 5) leads to a significant anodic shift in the titanium E1/2 reduction redox potentials.

Synthesis and Electrochemical Properties of Half-Sandwich Rhodium and Iridium Methyl Complexes

A series of complexes of the form [Cp(*)M(bpy)(CH3)]I was accessed by treatment of CpM(bpy) or Cp*M(bpy) with methyl iodide (M = Rh, Ir; Cp = cyclopentadienyl; Cp* = pentamethylcyclopentadienyl; bpy = 2,2′-bipyridyl). Solid state structures (X-ray diffraction) reveal the expected distorted octahedral geometry, with Cp or Cp* bound in the η5 mode and bpy bound in the typical κ2 mode. Electrochemical studies demonstrate that the Cp* complexes undergo a single, quasi-reversible one-electron reduction, whereas the Cp complexes undergo both a quasi-reversible one-electron reduction and a second, more negative, irreversible reduction. Electron paramagnetic resonance studies and comparisons between complexes of different metals suggest that the formulation of the singly reduced species is formally M(III) complexes with a bound bpy anion radical. The second reduction observed in the Cp complexes, on the other hand, results in cleavage of the M–C bond. Taken together, the results suggest that the compounds have st...

Electrochemical Capture and Release of CO2 in Aqueous Electrolytes Using an Organic Semiconductor Electrode.

Developing efficient methods for capture and controlled release of carbon dioxide is crucial to any carbon capture and utilization technology. Herein we present an approach using an organic semiconductor electrode to electrochemically capture dissolved CO2 in aqueous electrolytes. The process relies on electrochemical reduction of a thin film of a naphthalene bisimide derivative, 2,7-bis(4-(2-(2-ethylhexyl)thiazol-4-yl)phenyl)benzo[lmn][3,8]phenanthroline-1,3,6,8(2H,7H)-tetraone (NBIT). This molecule is specifically tailored to afford one-electron reversible and one-electron quasi-reversible reduction in aqueous conditions while not dissolving or degrading. The reduced NBIT reacts with CO2 to form a stable semicarbonate salt, which can be subsequently oxidized electrochemically to release CO2. The semicarbonate structure is confirmed by in situ IR spectroelectrochemistry. This process of capturing and releasing carbon dioxide can be realized in an oxygen-free environment under ambient pressure and temperature, with uptake efficiency for CO2 capture of ∼2.3 mmol g–1. This is on par with the best solution-phase amine chemical capture technologies available today.

Synthesis, Structure and Electrochemistry of Tetranuclear Oxygen-Centered Copper(II) Clusters with Acetylacetone and Benz-pyrazole Hydrolyzed Derivatives as Ligand

Two copper(II) clusters Cu(4)OCl(6)(pyrazole)4, 1, and Cu(4)OBr(6)(Br-pyrazole)4, 2, have been synthesized by reacting acetylacetone and benzohydrazide (1:1 ratio) with CuX(2) (X = Cl for 1 and X= Br for 2) in methanol solutions. The structures of both clusters have been established by X-ray crystallography. The clusters contain four Cu, one O, six μ(2)-X atoms, and four pyrazole ligands. The pyrazoles was prepared in situ by the reaction of acetylacetone with benzohydrazide in methanol under reflux. In 2, the methine hydrogens of the pyrazole ligands have been replaced by bromine atoms. The four copper atoms encapsulate the central O atom in a tetrahedral arrangement. All copper atoms are five-coordinate and have similar coordination environments with slightly distorted trigonal bipyramidal geometry. The cyclic voltammogram of the clusters 1 and 2 show a one-electron quasi-reversible reduction wave in the region 0.485 to 0.731 V, and a one-electron quasi-reversible oxidation wave in the region 0.767 to 0.898 V. In 1, one irreversible oxidative response is observed on the positive of side of the voltammogram at 1.512 V and this can be assigned to Cu(II) to Cu(III) oxidation.

Synthesis of mixed-ligand complexes of VO2+ and VO3+ incorporating hydrazone, 1,10-phenanthroline and 8-hydroxyquinoline

2-Aminobenzoylhydrazide (abh) reacts with equimolar amounts of either [VIVO(acac)2] or [VIVO(bzac)2] (where acac− and bzac− are the monoanionic forms of acetylacetone (Hacac) and benzoylacetone (Hbzac), respectively) in the presence of equimolar amounts of 1,10-phenanthroline (phen) to form the octahedral mixed-ligand complexes [VIVO(L1)(phen)] (1) and [VIVO(L2)(phen)] (2), where (L1)2− and (L2)2− are the dianionic forms of the 2-aminobenzoylhydrazone of acetylacetone (H2L1) and benzoylacetone (H2L2). Upon substituting phen by 8-hydroxyquinoline (Hhq), pentavalent [VVO(L1)(hq)] (3) and [VVO(L2)(hq)] (4) complexes were instead obtained. In the crystal structures of 3 and 4, the hydrazone ligands coordinate to the vanadium center through the enolic-O, one imine-N and amide-O in a mer geometry. The amine and the second imine nitrogen form intramolecular hydrogen bonds. Complexes 1 and 2 display quasi-reversible one-electron oxidation peaks near +0.60 V, while the pentavalent 3 and 4 exhibit quasi-reversible one-electron reduction peaks near −0.18 V versus Ag/AgCl in CH2Cl2 solution. EPR spectroscopic studies on 1 and 2 suggest that the unpaired electron is present in the dxy orbital. DFT studies for 3 indicate that the dxy orbital of vanadium is the main contributor to the LUMO.

1,6- and 1,7-Regioisomers of Highly Soluble Amino-Substituted Perylene Tetracarboxylic Dianhydrides: Synthesis, Optical and Electrochemical Properties.

1,6- and 1,7-regioisomers of diamino-substituted perylene tetracarboxylic dianhydrides (PTCDs) with different n-alkyl chain lengths (n = 6, 12 or 18) were synthesized and characterized by NMR spectroscopy and high-resolution mass spectrometry. These dyes are highly soluble in most organic solvents and even in nonpolar solvents, such as hexane. To the best of our knowledge, this is the first time the 1,6-diamino-substituted PTCDs (2a–2c) have been obtained in pure form. The regioisomers 1a–1c (1,7-) and 2a–2c (1,6-) exhibit significant differences in their optical characteristics. In addition to the longest wavelength absorption band at around 674 nm, 2a–2c exhibit another shoulder band at ca. 600 nm, and consequently, cover a large part of the visible region relative to those of 1a–1c. Upon excitation, 2a–2c also show larger dipole moment changes than those of 1a–1c; the dipole moments of all compounds have been estimated using Lippert–Mataga equation. Moreover, all the dyes show a unique charge transfer emission in the near-infrared region, of which the peak wavelengths exhibit strong solvatochromism. They all exhibit one irreversible one-electron oxidation and two quasi-reversible one-electron reductions in dichloromethane at modest potentials. Complementary density functional theory calculations performed on these chromophores are reported in order to rationalize their electronic structure and optical properties.

Synthesis and Characterization of Rare Earth Corrole-Phthalocyanine Heteroleptic Triple-Decker Complexes.

We recently reported the first example of a europium triple-decker tetrapyrrole with mixed corrole and phthalocyanine macrocycles and have now extended the synthetic method to prepare a series of rare earth corrole-phthalocyanine heteroleptic triple-decker complexes, which are characterized by spectroscopic and electrochemical methods. The examined complexes are represented as M2[Pc(OC4H9)8]2[Cor(ClPh)3], where Pc = phthalocyanine, Cor = corrole, and M is Pr(III), Nd(III), Sm(III), Eu(III), Gd(III), or Tb(III). The Y(III) derivative with OC4H9 Pc substituents was obtained in too low a yield to characterize, but for the purpose of comparison, Y2[Pc(OC5H11)8]2[Cor(ClPh)3] was synthesized and characterized in a similar manner. The molecular structure of Eu2[Pc(OC4H9)8]2[Cor(ClPh)3] was determined by single-crystal X-ray diffraction and showed the corrole to be the central macrocycle of the triple-decker unit with a phthalocyanine on each end. Each triple-decker complex undergoes up to eight reversible or quasireversible one-electron oxidations and reductions with E1/2 values being linearly related to the ionic radius of the central ions. The energy (E) of the main Q-band is also linearly related to the radius of the metal. Comparisons are made between the physicochemical properties of the newly synthesized mixed corrole-phthalocyanine complexes and previously characterized double- and triple-decker derivatives with phthalocyanine and/or porphyrin macrocycles.

Carbene supported dimer of heavier ketenimine analogue with p and si atoms.

A cyclic alkyl(amino) carbene (cAAC) stabilized dimer [(cAAC)Si(P-Tip)]2 (2) (Tip = 2,4,6-triisopropylphenyl) is reported. 2 can be considered as a dimer of the heavier ketenimine (R2C═C═N-R) analogue. The dark-red rod-shaped crystals of 2 were synthesized by reduction of the precursor, cAAC-dichlorosilylene-stabilized phosphinidene (cAAC)SiCl2→P-Tip with sodium napthalenide. The crystals of 2 are storable at room temperature for several months and stable up to 215 °C under an inert atmosphere. X-ray single-crystal diffraction revealed that 2 contains a cyclic nonplanar four-membered SiPSiP ring. Magnetic susceptibility measurements confirmed the singlet spin ground state of 2. Cyclic voltammetry of 2 showed a quasi-reversible one-electron reduction indicating the formation of the corresponding radical anion 2(•-), which was further characterized by EPR measurements in solution. The electronic structure and bonding of 2 and 2(•-) were studied by theoretical calculations. The experimentally obtained data are in good agreement with the calculated values.

Highly Soluble Monoamino-Substituted Perylene Tetracarboxylic Dianhydrides: Synthesis, Optical and Electrochemical Properties.

Three dialkylamino-substituted perylene tetracarboxylic dianhydrides with different n-alkyl chain lengths (n = 6, 12 or 18), 1a–1c, were synthesized under mild conditions in high yields and were characterized by 1H NMR, 13C NMR and high resolution mass spectroscopy. Their optical and electrochemical properties were measured using UV-Vis and emission spectroscopic techniques, as well as cyclic voltammetry (CV). This is the first time that the structures and the properties of monoamino-substituted perylene tetracarboxylic dianhydrides have been reported. These molecules show a deep green color in both solution and the solid state and are soluble in most organic solvents. They all show a unique charge transfer emission in the near-infrared region, and the associated peaks exhibit solvatochromism. The dipole moments of the compounds have been estimated using the Lippert-Mataga equation, and upon excitation, they show slightly larger dipole moment changes than those of corresponding perylene diimides, 2a–2c. Additionally, Compounds 1a–1c undergo two quasi-reversible one-electron oxidations and two quasi-reversible one-electron reductions in dichloromethane at modest potentials. Complementary density functional theory calculations performed on these chromophores are reported in order to gain more insight into their molecular structures and optical properties.

1,7-Bis-(N,N-dialkylamino)perylene Bisimides: Facile Synthesis and Characterization as Near-Infrared Fluorescent Dyes.

Three symmetric alkylamino-substituted perylene bisimides with different n-alkyl chain lengths (n = 6, 12, or 18), 1,7-bis-(N,N-dialkylamino)perylene bisimides (1a–1c), were synthesized under mild condition and were characterized by 1H NMR, 13C NMR and high resolution mass spectroscopy. Their optical and electrochemical properties were measured using UV-Vis and emission spectroscopic techniques as well as cyclic voltammetry (CV). These compounds show deep green color in both solution and solid state, and are highly soluble in dichloromethane and even in nonpolar solvents such as hexane. The shapes of the absorption spectra of 1a–1c in the solution and solid state were found to be almost the same, indicating that the long alkyl chains could efficiently prevent intermolecular contact and aggregation. They show a unique charge transfer emission in the near-infrared region, of which the peak wavelengths exhibit strong solvatochromism. The dipole moments of the molecules have been estimated using the Lippert–Mataga equation, and upon excitation, they show larger dipole moment changes than that of 1,7-diaminoperylene bisimide (2). Moreover, all the dyes exhibit two irreversible one-electron oxidations and two quasi-reversible one-electron reductions in dichloromethane at modest potentials. Complementary density functional theory calculations performed on these chromophores are reported in order to rationalize their electronic structure and optical properties.

Green Perylene Bisimide Dyes: Synthesis, Photophysical and Electrochemical Properties.

Three asymmetric amino-substituted perylene bisimide dyes with different n-alkyl chain lengths (n = 6, 12, or 18), 1-(N,N-dialkylamino)perylene bisimides (1a–1c), were synthesized under mild condition in high yields and were characterized by 1H NMR, 13C NMR (nuclear magnetic resonance), HRMS (High Resolution Mass Spectrometer), UV-Vis and fluorescence spectra, as well as cyclic voltammetry (CV). These molecules show intense green color in both solution and solid state and are highly soluble in dichloromethane and even in nonpolar solvents, such as hexane. The shapes of the absorption spectra of 1a–1c in solid state and in solution were found to be virtually the same, indicating that the long alkyl chains could efficiently prevent aggregation. They exhibit a unique charge transfer emission in the near-infrared region, of which the peak wavelengths show strong solvatochromism. The dipole moments of the compounds have been estimated using the Lippert-Mataga equation, and upon excitation, they show larger dipole moment changes than that of 1-aminoperylene bisimide (2). Furthermore, all of the compounds exhibit two quasi-reversible one-electron oxidations and two quasi-reversible one-electron reductions in dichloromethane at modest potentials. Complementary density functional theory (DFT) calculations performed on these dyes are reported in order to rationalize their molecular structures and electronic properties.

Synthesis and optical properties of novel asymmetric perylene bisimides

A novel series of asymmetric perylene bisimides, 1-amino-7-nitroperylene bisimides (1a–1c), was synthesized and fully characterized. These molecules undergo an excited-state intramolecular electron transfer reaction, resulting in a unique charge transfer emission in the near-infrared region, of which the peak wavelength exhibits strong solvatochromism. The dipole moments of these compounds have been estimated using the Lippert–Mataga equation, and upon excitation, the molecules show larger dipole moment changes than those of the symmetric 1,7-diaminoperylene bisimides (2a–2c). Furthermore, these dyes undergo two quasi-reversible one-electron oxidations and two quasi-reversible one-electron reductions in dichloromethane at modest potentials. They display good thermal stability and optical stability that can be used as stable near-infrared fluorescent dyes. Their spectroscopic properties in various conditions and complementary time-dependent density functional theory calculations are reported.

Yttrium and lanthanide complexes of β-dialdehydes: synthesis, characterization, luminescence and electrochemistry of coordination compounds with the conjugate base of bromomalonaldehyde.

Novel yttrium, europium and terbium coordination compounds having formulae [AsPh4][Ln(BrMA)4] (6LN), Ln(BrMA)3(bipyO2) (7Ln), Ln(NMA)3(phen) (8Ln) and Ln(NMA)3(terpy) (9Ln) (Ln = Y, Eu, Tb; BrMA = conjugate base of bromomalonaldehyde; bipyO2 = 2,2'-bipyridine-N,N'-dioxide; phen = 1,10-phenantroline; terpy = 2,2':6',2''-terpyridine) were synthesized and characterized by using spectroscopic and electrochemical techniques. Uncharged europium and, to a lesser extent, terbium complexes showed appreciable luminescence in the solid state upon excitation with UV light. Polymeric materials and ionic liquids containing BrMA and lanthanides were prepared and photoluminescence measurements were carried out. From an electrochemical point of view, europium(III) BrMA-complexes showed a quasi-reversible one-electron reduction process. The one electron transfer reaction Eu(III) to Eu(II) allowed the photoluminescence tuning of 8Eu deposited on the surface of a glassy carbon electrode.