Dianionic Species Research Articles

Reduction-Induced Self-Propelled Oscillatory Motion of Perylenediimides on Water.

The emergence of macroscopic self-propelled oscillatory motion based on molecular design has attracted continual attention in relation to autonomous systems in living organisms. Herein, a series of perylenediimides (PDIs) with various imide side chains was prepared to explore the impact of molecular design and alignment on the self-propelled motion at the air-water interface. When placed on an aqueous solution containing a reductant, a solid disk of neutral PDI was reduced to form the water-soluble, surface-active PDI dianion species, which induces a surface tension gradient in the vicinity of the disk for self-propelled motion. We found that centimeter-scale oscillatory motion could be elicited by controlling the supply rate of PDI dianion species through the reductant concentration and the structure of the imide side chains. Furthermore, we found that the onset and speed of the self-propelled motion could be changed by the crystallinity of PDI at the water surface. This design principle using π-conjugated molecules and their self-assemblies could advance self-propelled, non-equilibrium systems powered by chemical energy.

Reduction‐Induced Self‐Propelled Oscillatory Motion of Perylenediimides on Water

AbstractThe emergence of macroscopic self‐propelled oscillatory motion based on molecular design has attracted continual attention in relation to autonomous systems in living organisms. Herein, a series of perylenediimides (PDIs) with various imide side chains was prepared to explore the impact of molecular design and alignment on the self‐propelled motion at the air‐water interface. When placed on an aqueous solution containing a reductant, a solid disk of neutral PDI was reduced to form the water‐soluble, surface‐active PDI dianion species, which induces a surface tension gradient in the vicinity of the disk for self‐propelled motion. We found that centimeter‐scale oscillatory motion could be elicited by controlling the supply rate of PDI dianion species through the reductant concentration and the structure of the imide side chains. Furthermore, we found that the onset and speed of the self‐propelled motion could be changed by the crystallinity of PDI at the water surface. This design principle using π‐conjugated molecules and their self‐assemblies could advance self‐propelled, non‐equilibrium systems powered by chemical energy.

Tuning Structure and Properties of a Ferromagnetic Organic Semiconductor via a Magnetic Field-Modified Reduction Process

The development of novel synthesis and assembly strategies is critical to achieving a ferromagnetic organic semiconductor with high Curie temperature. In this study, we report a high magnetic field (HMF)-modified solvothermal approach for the reduction in neutral perylene diimide (PDI) into the dianion species to prepare the PDI magnets comprising radical anions after subsequent oxidation processes. The PDI materials, assembled from the dianion solution by an HMF-modified reduction, exhibit a smaller crystallite size and an enlarged distance of the π-π stacking in the PDI aggregates. Furthermore, the PDI magnets obtained from the process under a 9T field reveal weakened ferromagnetism and the rapid degradation of electrical conductivity compared to those prepared without a magnetic field. Based on spectral and structural characterizations, such performance deterioration originates from the enhanced instability of the radical anions exposed to air, as well as the decreased crystallinity for the radical PDIs synthesized from the HMF-modified reduction process. This work demonstrates that magnetic fields offer an effective way in the material synthesis process to manipulate the structure and magnetic properties of the radical-based organic magnets.

Longitudinal Extension of Double π-Helix Enables Near-Infrared Amplified Dissymmetry and Chiroptical Response.

Near-infrared (NIR) circularly polarized light absorbing or emitting holds great promise for highly sensitive and precise bioimaging, biosensing, and photodetectors. Aiming at designing NIR chiral molecular systems with amplified dissymmetry and robust chiroptical response, herein, we present a series of double π-helical dimers with longitudinally extended π-entwined substructures via Ullmann or Yamamoto homocoupling reactions. Circular dichroism (CD) spectra revealed an approximate linear bathochromic shift with the rising number of naphthalene subunits, indicating a red to NIR chiroptical response. Particularly, the terrylene diimide-entwined dimers exhibited the strongest CD intensities, with the maximal |Δε| reaching up to 393 M-1 cm-1 at 666 nm for th-TDI[2]; and a record-high chiroptical response (|ΔΔε|) between the neutral and dianionic species of 520 M-1 cm-1 at 833 nm for th-TDI[2]Cl was achieved upon further reduction to its dianionic state. Time-dependent density functional theory (TDDFT) calculations suggested that the pronounced intensification of the CD spectra originated from a simultaneous enhancement of both electric (μ) and magnetic (m) transition dipole moments, ultimately leading to an overall increase in the rotatory strength (R). Notably, the circularly polarized luminescence (CPL) brightness (BCPL) reached 77 M-1 cm-1 for th-TDI[2]Cl, among the highest values reported for NIR-CPL emitters. Furthermore, all chiral dianions exhibited excellent air stability under ambient conditions with half-life times of up to 10 days in N-methylpyrrolidone (NMP), which is significant for future biological applications and chiroptic switches.

Indenoannulated Tridecacyclene: An All-Carbon Seven-Stage Redox-Amphoter.

We disclose an indenoannulated tridecacyclene comprising a central cyclooctatetraene moiety with multiple adjacent pentagonal rings which is accessible in a concise synthetic sequence. The saddle-shaped geometry of the non-benzenoid polycyclic scaffold and its unique packing behavior in the solid state were characterized by X-ray crystallography. In electrochemical studies, the compound undergoes seven reversible redox events comprising five reductions and two oxidations. The dicationic and dianionic species obtained by chemical oxidation and reduction, respectively, were characterized spectroscopically in solution. Density functional theory calculations were applied to provide insights into aromaticity evolution in the respective charged species, highlighting the beneficial effect of the non-benzenoid moieties on charge stabilization.

Aza-Diphosphido-Bridged Di-Iron Complexes Related to the [FeFe]-Hydrogenases

The reaction of the dianionic species [Fe2(CO)6(μ-PPh)2]2− with tBuN(CH2Cl)2 gives the di-iron carbonyl aza-diphosphido-bridged complex [Fe2(CO)6(µ-{P(Ph)CH2}2NtBu)] (1). Attempts to prepare 1 by click-chemistry by reacting [Fe2(CO)6(μ-PHPh)2] with CH2O and tBuNH2 afforded a bis-phosphido compound [Fe2(CO)6(µ-P(Ph)CH2NHtBu)2] (2) which exists as two, syn and anti, isolable isomers depending on the relative orientation of the groups carried by the phosphorus atoms. In the presence of HBF4.Et2O, in dichloromethane, 1 leads to the stabilized ammonium species [Fe2(CO)6(µ-{P(Ph)CH2}2NHtBu)](BF4) (3). The derivatives 1–3 were characterized by IR and 1H, 31P-{1H} NMR spectroscopies. Their structures in a solid state were determined by X-ray diffraction analyses, which accord with their spectroscopic characteristics.

N-Aryloxide-Amidinate Thorium Complexes.

An N-aryloxide-amidine ligand (1), [ONNO] ligand, integrating phenoxide (PhO-) and amidine ligands through methylene linkers, was employed in actinide chemistry. Upon reaction of the deprotonated ligand with ThCl4(DME)2 in ether, the corresponding dimer complex 2 was obtained. Upon treatment of 2 with KCp* (Cp* = Cp(Me)5) in tetrahydrofuran, the corresponding {[ONNO]ThIVCp*(LiCl)}2 (4) was obtained. In complex 2, the two ArO- arms bonded from the same ligand to different ThIV centers. In contrast, both ArO- arms coordinated to the same metal center in 4. Notably, when a mixture of 2 and bipyridine was treated with one or two equiv of KC8, the [ONNO]ThIV-bipyridyl•̅ radical dimer complex (5) and [ONNO]ThIV-bipyridyl2- dianionic dimer species (6) were obtained, respectively.

Stabilizing an exotic dianionic tetrazine bridge in a Ln2 metallocene.

The unique electronic nature of the 1,2,4,5-tetrazine or s-tetrazine (tz) ring has sparked tremendous scientific interest over the last few years. Tetrazines have found numerous applications, and their ability to coordinate to metal ions has opened the possibility of exploring their chemistry in both molecular systems and extended networks. The rich redox chemistry of s-tetrazines allows them to exchange electrons and switch between their dihydro (H2tz), neutral (tz), and radical (tz˙-) forms. Previous reports in the literature have observed electrochemically that a second electron can potentially be stored in the tetrazinyl ring and form a dianionic species. However, due to its extremely reactive nature, this has not been isolated before. Herein, the combination of strictly anhydrous and inert conditions, strong reducing agents, non-acidic solvents and most importantly blocking the accessibility of the nitrogen atoms by coordinating them to lanthanide ions allowed for the stabilization of a dianionic tetrazine in a lanthanocene complex. Three dinuclear metallocene complexes are reported, [(Cp*2Ln)2(tz˙-)(THF)2](BPh4) (Ln = Y (1-Y); Cp* = pentamethylcyclopentadienyl; THF = tetrahydrofuran) and [(Cp*2Ln)2(tz2-)(THF)2]·2THF (Ln = Gd (2-Gd), or Y (2-Y)), which utilize the unsubstituted tz as the ligand. In 1-Ln, the tz ligand is reduced to the radical anion (tz˙-), while in 2-Ln, the tz ligand is in the -2 charge state. These complexes are the first structurally and physically characterized complexes bearing the dianion radical of an s-tetrazine. Detailed structural analysis, ab initio calculations, and physical characterization support that the tz2- ligand is a closed-shell planar dianion with unique structural features vastly different from those of the tz, tz˙- and H2tz species.

The Reduction of Metallabenzenes: Different Scenarios Highly Dependent on the Central Group 14 Elements, Si vs. Ge.

In order to synthesize a silabenzenyl anion, in which the anionic carbon atom of a phenyl anion was replaced with a silicon atom, the reductive dearylation reaction of 1-Tbt-2-tert-butyl-silabenzene (Tbt=2,4,6-tris[bis(trimethylsilyl)methyl]phenyl) with KC8 was attempted. Unexpectedly, this reaction resulted in the formation of a dianion species without the elimination of the Tbt group. This is totally different from the reactions of Tbt-substituted germa- or stannabenzene with KC8 , which resulted in the formation of the corresponding heavy analogues of phenyl anion, together with the elimination of Tbt group. Experimental and theoretical investigation revealed that one of the protons of the o-benzyl positions of the Tbt group was abstracted by the negatively charged silicon atom of an in-situ generated intermediate. Compared with the previously reported germanium system, the contrasting results indicate that the central heavy group 14 element has a great influence on the elimination step of the Tbt group.

Improved Bipolar Properties of Ester-Functionalized Discotic Diimine-Dithiolene Complexes.

A series of platinum diimine-dithiolene complexes with a 5,6-dihydro-1,4-dithiin-2,3-dithiolato (dddt2- ) dithiolene ligand and a bipyridine carrying tris-alkoxyphenyl fragments connected through an ester linker (bpyCn, n=8, 12, 16, 10(s), 20) (Scheme 1) has been developed. The mesomorphic properties of the ligands and of the platinum complexes have been investigated by a combination of DSC, POM and SAXS analyses. The platinum complexes were found to self-organize into columnar mesophases of hexagonal symmetry over large temperature range including room temperature. Their electronic properties were also characterized by a combination of electrochemistry, absorption and emission spectroscopy measurements and TD-DFT calculations. Besides being liquid crystalline, these compounds can undergo two oxidation processes and two reduction processes in a fully reversible manner, allowing the isolation of stable dicationic and dianionic species. Such a behavior is highly promising for the development of ambipolar semiconducting soft materials.

Synthesis, Spectral Investigation and Biological Studies of New Transition Metal Complexes with Flouren Drived Schiff-base ligand

The new Schiff-base ligand [H2L] 1-(9H-flouren-9-ylidene)-4-phenylthiosemicarbazide and its metal complexes with Mn(II),Co(II),Zn(II)andCd(II) are reported. The ligand derived from the condensation reaction of (4a,9a-Dihydro-flouren-9-one) with (4-phenylthiosemicarbazide) in mole ratio of 1:1. Upon complex formation, the ligand behaves as a dianionic bidentate species forming monomeric complexes of general formula [M(L)2] and [M(L)2(H2O)2] , (M=Mn(II), Co(II), Zn(II) and Cd(II). The modes of bonding and overall geometry of the complexes were determined through (FTIR, UV-Vis, 1H.NMR) along with elemental analysis, metal content, and conductance. These studies revealed octahedral geometry for the Mn(II) complex and tetrahedral for the Co(II), Zn(II) and Cd(II) complexes. Biological activity of the ligand and its metal complexes against gram positive bacterial strain Bacillus (G+) and gram negative bacteria Pseudomonase (G-) revealed that the metal complexes become less resistive to the microbial activities as compared to the free ligand.

Analysis of the role of the pH in the anchoring of alkylphosphonic acid on a TiO2 surface: A DFTB study

The reactivity of a (110) rutile titanium dioxide surface functionalized with neutral, anionic and di-anionic forms of dodecyl-phosphonic acid was studied by Density Functional based Tight Binding theory to simulate different pH conditions. Functionalization of this surface is relevant for at least two reasons: a) to protect the surface against external agents (e.g., by preventing the proliferation of bacteria in medical implants) and b) to use these organic–inorganic hybrid materials to facilitate the anchoring of other molecules. Comparing the results obtained in the gas phase and in water, experimental findings are better modelled by considering the hydration energy of the acids and the solvation-desolvation process involving the acids and the surface. In water, in all protonation states, acid molecules interact with the hydrated surface as a mono-negative charged species due to proton transfer before the grafting process. The formation of bi-dentate, di-anionic acid species, due to a proton transfer process or a change of pH, is favoured by anchoring alkylphosphonic acid to the rutile.

Controlled introduction of functional groups at one P atom in [Cp*Fe(η5-P5)] and release of functionalised phosphines.

By salt metathesis reactions of the anionic complexes of the type [Cp*Fe(η4-P5R)]- (R = tBu (1a), Me (1b), -C[triple bond, length as m-dash]CPh (1c); Cp* = 1,2,3,4,5-pentamethylcyclopentadienyl) with organic electrophiles (XRFG; X = halogen; RFG = (CH2)3Br, (CH2)4Br, Me) a variety of organo-substituted polyphosphorus ligand complexes of the type [Cp*Fe(η4-P5RRFG)] (2) are obtained. Thereby, organic substituents with different functional groups (FG), such as halogens or nitriles, are introduced. In [Cp*Fe(η4-P5RR')] (2a: R = tBu, R' = (CH2)3Br), the bromine substituent can be easily substituted, leading to functionalized complexes [{Cp*Fe(η4-P5tBu)}(CH2)3{Cp*Fe(η4-P5Me)}] (4) and [Cp*Fe(η4-P5RR')] (5) (R = tBu, R' = (CH2)3PPh2) or by abstraction of a phosphine to the asymmetric substituted phosphine tBu(Bn)P(CH2)3Bn (6). The reaction of the dianionic species [K(dme)2]2[Cp*Fe(η4-P5)] (I') with bromo-nitriles leads to [Cp*Fe{η4-P5((CH2)3CN)2}] (7), allowing the introduction of two functional groups attached to one phosphorus atom. 7 reacts with ZnBr2 in a self-assembly reaction to form the supramolecular compound [Cp*Fe{η4-P5((CH2)3CN)2}ZnBr2]n (8).

Intersystem Crossing Rates in Photoexcited Rose Bengal: Solvation versus Isolation.

We compare the intersystem crossing rate, kISC, of Rose Bengal (RB) in an aqueous pH 12 solution with the corresponding relaxation rates of four different RB-derived anion and dianion species isolated in the gas phase: the doubly deprotonated dianion ([RB-2H]2-), the singly deprotonated monoanion ([RB-H]-), and the corresponding singly negatively charged sodium and cesium adducts ([RB-2H + Na]- and [RB-2H + Cs]-, respectively). Each of them was probed following photoexcitation of their first singlet excited states (S1) at or near room temperature. The solution was studied by transient absorption spectroscopy, whereas the mass-selected anions were characterized by time-resolved photoelectron spectroscopy─all with ca. 50 femtosecond temporal resolution. [RB-H]- shows an S1 lifetime of ca. 80 ps; the solution ensemble, thought to consist primarily of solvated dianion chromophores, shows a similar lifetime of ca. 70 ps. By contrast, the isolated dianion, [RB-2H]2-, has a much longer lifetime. Superimposed on S1 decay attributable mainly to intersystem crossing, all four isolated anions also show some rapid oscillatory features of the transient photoelectron signal on a 4-5 ps timescale after excitation. Interestingly, an analogous phenomenon is also seen in the transient absorption measurements. We attribute it to a librational oscillation as the S1 state, initially populated in the S0 geometry, relaxes into its excited state equilibrium structure. Some implications of these observations for RB photophysics and interpretation of solution measurements are discussed─also in terms of density functional theory and time-dependent density functional theory calculations of ground and excited states.

Electrochemical behaviour of 2,2′-bibenzimidazoles: Voltammetric, in situ UV–vis- and EPR-spectroelectrochemical and computational studies

• The electrochemical properties of 2,2′-bibenzimidazole and its substituted analogues have been investigated by cyclic voltammetry, square-wave voltammetry and in situ UV–vis- and EPR-spectroelectrochemistry. • The nature of the formed in the electrochemical process radicals has been elucidated. • The formation of 2,2′- bibenzoimidazolylidene species and the mechanism of the electrochemical reduction process have been postulated. The electrochemical properties of 2,2′-bibenzimidazole and its substituted analogues 5,6-dimethyl-2,2′-bibenzimidazole, 5,5′,6,6′-tetramethyl-2,2′-bibenzimidazole as well as 1,1′-dimethyl-2,2′-bibenzimidazole were investigated by cyclic voltammetry (CV) and square-wave voltammetry (SWV) combined with mechanistic studies by means of in situ UV–vis- and EPR-spectroelectrochemistry. The data obtained for N H derivatives suggest the formation of 2,2′-bibenzoimidazolylidene species via ECEC reaction mechanism consisting of two successive one-electron transfers accompanied by proton migration. The resulting species undergo further one-electron reduction with the formation of stable anion-radicals, whose structures have been identified by in situ UV–vis- and EPR-spectroelectrochemical measurements and supported by the computational study using density functional theory (DFT) calculations. In contrast to N H derivatives, the electrochemical reduction of N,N -dimethyl substituted derivative leads to radical anion and dianion species.

Electrochemically Promoted Benzylation of [60]Fullerooxazolidinone.

Benzylation of the electrochemically generated dianion from N-p-tolyl-[60]fullerooxazolidinone with benzyl bromide provides three products with different addition patterns. The product distribution can be dramatically altered by varying the reaction conditions. Based on spectral characterizations, these products have been assigned as mono-benzylated 1,4-adduct and bis-benzylated 1,2,3,16- and 1,4,9,25-adducts, respectively. The assigned 1,2,3,16-adduct has been further established by X-ray diffraction analysis. It is believed that the 1,4-adduct is obtained by decarboxylative benzylation of the dianionic species, while bis-benzylated 1,2,3,16- and 1,4,9,25-adducts are achieved via a rearrangement process. In addition, the electrochemical properties of these products have been studied.

A C 54 B 2 Polycyclic π-System with Bilayer Assembly and Multi-Redox Activity

A C ₅₄ B ₂ Polycyclic π-System with Bilayer Assembly and Multi-Redox Activity

Room-Temperature Ferromagnetism in Perylene Diimide Organic Semiconductor.

The development of pure organic magnets with high Curie temperatures remains a challenging task in material science. Introducing high-density free radicals to strongly interacting organic molecules may be an effective method to this end. In this study, a solvothermal approach with excess hydrazine hydrate is used to concurrently reduce and dissolve rigid-backbone perylene diimide (PDI) crystallites into the soluble dianion species with a remarkably high reduction potential. The as-prepared PDI powders comprising radical anion aggregates are fabricated by a subsequent self-assembly and spontaneous oxidation process. The results of magnetic measurements show that the PDI powders exhibit room-temperature ferromagnetism and a Curie temperature higher than 400 K, with a vast saturation magnetization that reaches ≈1.2 emu g-1 . Elemental analysis along with the diamagnetic signal of the ablated residue are used to rule out the possibility that the magnetism is due to metal contamination. The findings suggest that the long-range ferromagnetic ordering can survive at room-temperature in organic semiconductors, and offers a new optional way to create room-temperature magnetic semiconductors.

Radical Anions and Dianions of Naphthalenediimides Generated within Layer-by-Layer Zirconium Phosphonate Thin Films.

Chemical reduction of N,N'-bis(2-phosphonoethyl)-1,4,5,8-naphthalenediimide (PNDI) with the reducing agent sodium dithionite gave stable colored reduced species, both in homogeneous solutions and in self-assembled thin films. When colorless PNDI aqueous solutions were titrated with the reducing agent, stepwise reduction was observed, giving first the radical anion (PNDI-•) and then the dianion (PNDI2-) species, which were detected by UV-visible-NIR spectroscopy, allowing the unambiguous determination of absorption maxima and molar absorptivities for each species. The radical anion PNDI-• was found to form π-dimers in water, but monomeric PNDI-• was formed in the presence of the cationic surfactant cetyltrimethylammonium bromide, indicating association with the micelles. Thin films of PNDI with 25 layers were grown by the zirconium phosphonate method on quartz substrates. Reduction of the films with sodium dithionite also produced radical anions and dianions of PNDI. However, reduction in the films was much slower than in solution, evidencing the compactness of the films. Moreover, reduction in the films did not proceed to completion, even with excess of the reducing agent, which can be attributed to the repulsion of negative charges within the film.

Design and Synthesis of a C3 Symmetrical Phenalenyl Derivative with Three Oxo Groups by Regioselective Deoxygenation/Oxygenation.

Tri-tert-butylated 4,7-dihydroxyphenalenone was designed and synthesized from a corresponding 4,9-dimethoxyphenalenone derivative by regioselective deoxygenation/oxygenation. The 4,7-dihydroxyphenalenone derivative showed a chromic behavior accompanied by protonation and deprotonation, giving monocation and dianion species, respectively, and their C3 symmetric electronic structures were elucidated by experimental and theoretical methods.