Organic radical batteries (ORBs) are a promising class of electrochemical power sources employing organic radicals as redox-active groups. This article reports on the development of a versatile ...on-substrate electrode setup for spectroelectrochemical Electron Paramagnetic Resonance (EPR) measurements on redox conductive polymers for ORBs. Quantitative
in operando
EPR experiments performed on electrochemical cells with a di-TEMPO Ni-Salen polymer as active electrode material demonstrate a strong decrease in the number of paramagnetic centers upon oxidizing the film. The distinct EPR signatures of the TEMPO-containing polymer and its fragments in different molecular environments are used to study its degradation upon repeated cycling. A comparison between the number of EPR-active sites and the number of electrochemically active charges, as measured by cyclic voltammetry, provides information on the nature of the degradation process. Low-temperature
ex situ
pulse EPR measurements on the oxidized polymer film reveal the spectrum of dilute nitroxide species, which may be associated with electrochemically inactive islands. These experiments pave the way for advanced EPR techniques for accurately determining distances between adjacent paramagnetic centers and thus for identifying performance-limiting loss mechanisms, which can eventually help develop strategies for making ORBs powerful contenders on the path towards sustainable electrochemical power sources.
A versatile on-substrate electrode setup was developed and used to perform quantitative
in operando
EPR as well as low-temperature pulse EPR experiments on electrochemical cells containing a redox conductive polymer as energy-storage material.
The half-lantern PdII 2 complexes trans-(O,C)-Pd(ppz)(μ-O∩N)2 (1) and trans-(E,N)-Pd(ppz)(μ-E∩N)2 (E∩N is a deprotonated 2-substituted pyridine; E = S (2), Se (3); Hppz = 1-phenylpyrazole) were ...cocrystallized with 1,4-diiodotetrafluorobenzene (FIB) to give cocrystals 1·(FIB) and (2−3)·2(FIB); the parent complexes and the cocrystals were studied by X-ray crystallography. The crystal structure of trans-(O,C)-1·FIB is assembled mainly by the I···O halogen bonding (XB) to give the @PdII 2O···I(areneF)I···O@PdII 2 linkage, while trans-(E,N)-(2–3)·2(FIB) are built by the joint action of I···Pd and I···E XBs, thus furnishing the PdII 2···I(areneF)I···E@PdII 2 (E = S, Se) cluster. Detailed theoretical (DFT) studies with the application of the QTAIM, ELF, NBO, IGM, SAPT, and HSAB methods revealed several types of attractive noncovalent interactions in the cocrystals, namely, the I···Pd, I···E (E = O, S, Se), I···C, π–π-stacking, and π···F interactions. I···Pd is a rare type of XB involving the metal center as an XB acceptor, the Pd···Pd communication facilitating the I···Pd bonding. The I···Pd and I···E bonds are comparable in strength (the bond interaction energies being between −7 and −13 kcal/mol), but the former is controlled by dispersion forces, while the latter is mostly governed by an electrostatic term.
This work is devoted to a multiscale computational study of metal complexes with SalEn-type Schiff bases aggregation phenomena, which play an important role in the synthesis of polymeric conductive ...films on electrode surfaces and strongly affect the structure of the resulting polymers. The choice of six relatively simple Ni(Schiff) complexes considered in this study was based on the expected steric and electronic effects of substituents and was intended to reflect the variety of molecular-level properties. Molecular dynamics simulations were used to study the adsorption layers formation. A link between the possible dimer structures and the properties of films adsorbed at inert surfaces was established, and the primary types of possible structures for noncovalently bound dimeric complexes were identified. Quantum chemical DFT calculations were employed to investigate bimolecular aggregates. The existence of stable bimolecular units of Ni(Schiff) complexes is mainly determined by dispersion interactions, while their structure is predominantly governed by electrostatic interactions. The existence of the most favorable plane-parallel structure type was confirmed for all the complexes considered in this study. Along with the formation of hydrogen bonds, d–d and π–d orbital interactions are possible for some of the complexes, though these types of bonding appear to have a relatively small effect on the orientation of molecules in dimeric units.
Metal-
polymers are electrochemically active metallopolymers functionalized with multiple redox centers, with a potential for high performance in various fields such as heterogeneous catalysis, ...chemical sensors, energy conversion, saving, and storage. In light of the growing world demand for the development of superior energy storage systems, the prospects of employing these polymers for advancing the performance of supercapacitors and lithium-ion batteries are particularly interesting. This article provides a general overview of the results of investigating key structure-property relationships of metal-
polymers and using them to design polymer-modified electrodes with improved energy storage characteristics. The results of independent and collaborative studies conducted by the members of two research groups currently affiliated to the Saint–Petersburg State University and the Ioffe Institute, respectively, along with the related data from other studies are presented in this review.
Porphyrin–fullerene dyads were intensively studied as molecular donor–acceptor systems providing efficient photoinduced charge separation (CS). A practical advantage of the dyads is the possibility ...to tune its CS process by the porphyrin periphery modification, which allows one to optimize the dyad for particular applications. However, this tuning process is typically composed of a series of trial stages involving the development of complex synthetic schemes. To address the issue, we synthesized a series of dyads with properties switching between electron and energy transfer in both polar (benzonitrile) and nonpolar (toluene) media and developed a computation procedure with sufficient reliability by which we can predict the CS properties of the dyad in different media and design new dyads. The dyads photochemistry was established by conducting ultrafast transient absorption studies in toluene, anisole, and benzonitrile. The most crucial step in computational modeling was to establish a procedure for correction of the electronic-state energies obtained by DFT so that the effects of the electron correlation and the long-range interactions are properly incorporated. We also carried out standard electrochemical measurements and show that our computation approach predicts better thermodynamics of the dyads in different solvents.
The theoretical data for the half‐lantern complexes {Pt(CN^
)(μ‐SN^
)}2 1–3; CN^
is cyclometalated 2‐Ph‐benzothiazole; SN^
is 2‐SH‐pyridine (1), 2‐SH‐benzoxazole (2), 2‐SH‐tetrafluorobenzothiazole ...(3) indicate that the Pt⋅⋅⋅Pt orbital interaction increases the nucleophilicity of the outer dz2
orbitals to provide assembly with electrophilic species. Complexes 1–3 were co‐crystallized with bifunctional halogen bonding (XB) donors to give adducts (1–3)2⋅(1,4‐diiodotetrafluorobenzene) and infinite polymeric 1⋅1,1′‐diiodoperfluorodiphenyln. X‐ray crystallography revealed that the supramolecular assembly is achieved through (Aryl)I⋅⋅⋅dz2
PtII XBs between iodine σ‐holes and lone pairs of the positively charged (PtII)2 centers acting as nucleophilic sites. The polymer includes a curved linear chain ⋅⋅⋅Pt2⋅⋅⋅I(areneF)I⋅⋅⋅Pt2⋅⋅⋅ involving XB between iodine atoms of the perfluoroarene linkers and (PtII)2 moieties. The 195Pt NMR, UV/Vis, and CV studies indicate that XB is preserved in CH(D)2Cl2 solutions.
Shedding light: Half‐lantern dz2PtII2 complexes in which the PtII2 center exhibits increased nucleophilicity of the outer orbitals were assembled with symmetric diiodoperfluoroarene halogen bonding (XB) donors to give extended supramolecular arrays formed through (Aryl)I⋅⋅⋅dz2PtII XB, which were studied by XRD and by extensive theoretical calculations. Cyclic voltammetric, 195Pt NMR, and UV/Vis studies provided evidence that the XB is preserved in solution.
Electroactive redox materials, encompassing redox polymers, metal–organic frameworks, and intercalation materials, play an important role in a wide range of emerging applications. However, many ...theoretical issues concerning quantitative thermodynamic description of such materials remain unclear so far. Existing variants of electrochemical intercalation isotherms (namely, the Langmuir–Frumkin isotherm, which often applies to redox polymers and electroactive solid materials, and the reformulated isotherm, accounting for the phase character of the potential distribution within the material) do not explain the dependence of redox materials’ voltammetric responses on the electrolyte concentration. In addition to that, studies show that the reformulated isotherm has a higher value of the so-called short-range interaction parameter at which phase separation starts and asymmetric single-phase regions in comparison to the Langmuir–Frumkin isotherm. A simple modification, accounting for the possibility of both positive and negative ions of the electrolyte solution to intercalate the electroactive redox material, leads to a new variant of electrochemical intercalation isotherm, which includes Langmuir–Frumkin and reformulated isotherms as limiting cases. The new model explains the dependence of redox materials’ voltammetric responses on the electrolyte concentration. Theory predicts the dependence of short-range interaction parameters at which phase separation starts on the electrolyte composition. Thus, the new electrochemical intercalation isotherm shows the dependence of its unstable, metastable, and stable regions on the electrolyte concentration and ion distribution coefficients. It opens up a possibility to tune material characteristics such as sizes of single-phase/two-phase regions. In some particular cases, it is possible to induce or eliminate the phase transition by changing the concentration of the electrolyte. We believe that studying such properties may help in future realization of new smart materials with superior characteristics for electrochemical energy storage, use in chemical sensors, medical applications, and so forth.
The need for environmentally benign portable energy storage drives research on organic batteries and catalytic systems. These systems are a promising replacement for commonly used energy storage ...devices that rely on limited resources such as lithium and rare earth metals. The redox-active TEMPO (2,2,6,6-tetramethylpiperidin-1-oxyl-4-yl) fragment is a popular component of organic systems, as its benefits include remarkable electrochemical performance and decent physical properties. TEMPO is also known to be an efficient catalyst for alcohol oxidation, oxygen reduction, and various complex organic reactions. It can be attached to various aliphatic and conductive polymers to form high-loading catalysis systems. The performance and efficiency of TEMPO-containing materials strongly depend on the molecular structure, and thus rational design of such compounds is vital for successful implementation. We discuss synthetic approaches for producing electroactive polymers based on conductive and non-conductive backbones with organic radical substituents, fundamental aspects of electrochemistry of such materials, and their application in energy storage devices, such as batteries, redox-flow cells, and electrocatalytic systems. We compare the performance of the materials with different architectures, providing an overview of diverse charge interactions for hybrid materials, and presenting promising research opportunities for the future of this area.
Imidoylamidinate-based heteroleptic bis(2-phenylbenzothiazole)iridium(III) and -rhodium(III) complexes (bt)2M(N∩N) (bt = 2-phenylbenzothiazole, N∩N = N′-(benzodthiazol-2-yl)acetimidamidyl ...(Ir1 and Rh1), N′-(6-fluorobenzodthiazol-2-yl)acetimidamidyl (Ir2), N′-(benzodoxazol-2-yl)acetimidamidyl (Ir3), N′-(1-methyl-1H-benzodimidazol-2-yl)acetimidamidyl (Ir4); yields 70–84%) were obtained by the reaction of the in situ-generated solvento-complex (bt)2M(NCMe)2NO3 and benzodthia/oxa/N-methylimidozol-2-amines in the presence of NaOMe. Complexes Ir1–4 exhibited intense orange photoluminescence, reaching 37% at room temperature quantum yields, being immobilized in a poly(methyl methacrylate) matrix. A photophysical study of these species in a CH2Cl2 solution, neat powder, and frozen (77 K) MeOC2H4OH–EtOH glass matrixalong with density-functional theory (DFT), ab initio methods, and spin–orbit coupling time-dependent DFT calculationsverified the effects of substitution in the imidoylamidinate ligands on the excited-state properties. Electrochemical (cyclic voltammetry and differential pulse voltammetry) and theoretical DFT studies demonstrated noninnocent behavior of the imidoylamidinate ligands in Ir1–4 and Rh1 complexes due to the significant contribution coming from these ligands in the HOMO of the complexes. The iridium(III) species exhibit a ligand (L, 2-phenylbenzothiazole)-centered (3LC), metal-to-ligand (L′, imidoylamidinate) charge-transfer (3ML′CT,3MLCT) character of their emission. The imidoylamidinate-based iridium(III) species were proved to be effective as the emissive dopant in an organic light-emitting diode device, fabricated in the framework of this study.
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