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Three small molecules consisting of thieno‐fused naphthalimide units connected via aromatic linkers were synthesized to study the effect of fused thiophene rings on the properties of naphthalimide‐based molecules. A protocol for the synthesis of thienonaphthalimide‐based molecules without prior preparation and use of thienonaphthalimide precursors and organoelement compounds (organolithium, organotin, or organoboron compounds) was developed. The protocol is based on double thienannulation of bis‐alkyne substrates with sodium sulfide. The thin‐film morphology, photophysical and electrochemical properties of the obtained small molecules were studied. Single‐layer non‐doped organic light‐emitting diodes based on fluorene‐bridged thienonaphthalimide dimer showed yellow emission with luminance of 2200 cd/m2, and current efficiency of 0.35 cd/A. Combination of transient electroluminescence and photo‐CELIV methods allowed to estimate electron and hole mobility in the synthesized compounds; both are in order of 10−6 cm2V−1 s−1. [ABSTRACT FROM AUTHOR]

Continuous-wave X-band electron paramagnetic resonance (EPR) of fullerene C70 molecules excited to a triplet state by continuous light illumination was studied in molecular glasses of o-terphenyl and cis/trans-decaline and in the glassy polymers polymethylmethacrylate (PMMA) and polystyrene (PS). Above ∼100 K, a distinct narrowing of EPR lineshape of the triplet was observed, which was very similar for all systems studied. EPR lineshape was simulated reasonably well within a framework of a simple model of random jumps, which implies that the C70 molecule performs isotropic orientational motion by sudden jumps of arbitrary angles. In simulations, a single correlation time τc was used, varying in the range of 10-7-10-8 s. Near and below 100 K electron spin echo (ESE) signals were also obtained which were found to decay exponentially. Correlation times τc obtained from simulation of the EPR spectra in the slow-motion limit (τc close to 10-7 s) turned out to be in good agreement with the phase memory times TM of the ESE decay, which additionally supports the employed simple model. The observed motional effects provide evidence that the nanostructure of the solid glassy media of different origins is soft enough to allow a large asymmetric C70 molecule to reorient rapidly. Except for the EPR spectra of the triplet, in the center of the spectra, a small admixture of a narrow line was also observed; its possible nature is briefly discussed. [ABSTRACT FROM AUTHOR]

Electron spin echo (ESE) was applied to study transversal spin relaxation of photoexcited triplet state of fullerene C70 molecules in glassy o-terphenyl and cis-/trans-decalin matrices (glass transition temperatures of 243 and 137 K, respectively). The relaxation rate T2-1 was found to increase sharply above 110 K in o-terphenyl and above 100 K in decalin. It is suggested that this increase arises from interaction of 3C70 pseudorotation with fast molecular librations in the matrix. Both these types of motion involve atomic vibrations and are uniaxial in their nature, the known literature data on Raman light scattering and others indicate that molecular librations may be thermally activated in glasses just near 100 K. The increase in T2-1 near 100 K is not observed for photoexcited triplet state of fullerene C60, for which pseudorotation is not uniaxial. As the fullerene molecule has a size much larger than that for glass solvent molecules, it is likely that molecular librations in the matrix are of collective nature. [ABSTRACT FROM AUTHOR]

A paramagnetic Cys 4 [Fe] center was detected by pulse EPR in Na + -translocating NADH:quinone-oxidoreductase (Na + -NQR) by influence of this center on transverse and longitudinal spin relaxation of Na + -NQR flavin radicals. The oxidation state of the Cys 4 [Fe] center was Fe 3+ in the oxidized and Fe 2+ in the reduced Na + -NQR, as deduced from the temperature dependence of spin relaxation rates of different flavin radicals. A high-spin state of iron in the Cys 4 [Fe] center was assigned to both forms of Na + -NQR. [ABSTRACT FROM AUTHOR]

Abstract: X-band echo-detected electron paramagnetic resonance (ED EPR) spectra of triplet state of fullerene C70 generated by continuous light illumination were found to correspond below 30K to a non-equilibrium electron spin polarization. Above 30K spectra are characteristic of Boltzmann equilibrium. Spectra were simulated fairly well with zero-field splitting parameters D =153MHz and E and distributed within the range of 6–42MHz. The origin of E distribution is attributed to the Jahn–Teller effect, which in glassy matrix is expected to depend on the local surrounding of a fullerene molecule (a so-called E-strain). In the center of ED EPR spectra a narrow hole was observed. With increase of the microwave pulse turning angle this hole transforms into a single narrow absorptive line. Numerical simulations by density matrix formalism confirm that central hole originates from a simultaneous excitation of both allowed electron spin transitions of the triplet (T 0 ↔ T + and T 0 ↔ T −), because of their degeneracy at this spectral position. Also explanations are given why this hole has not been observed in the previously reported experiments on continuous wave EPR and on ED EPR under laser pulse excitation. [Copyright &y& Elsevier]

Redox properties of all EPR-detectable prosthetic groups of Na+-translocating NADH:quinone oxidoreductase (Na+-NQR) from Vibrio harveyi were studied at pH 7.5 using cryo-EPR spectroelectrochemistry. Titration shows five redox transitions. One with Em = -275 mV belongs to the reduction of the [2Fe-2S] cluster, and the four others reflect redox transitions of flavin cofactors. Two transitions (Em¹ = -190 mV and Em² = -275 my) originate from the formation of FMN anion radical, covalently bound to the NqrC subunit, and its subsequent reduction. The remaining two transitions arise from the two other flavin cofactors. A high potential (Em = -10 mV) transition corresponds to the reduction of riboflavin neutral radical, which is stable at rather high redox potentials. An Em = -130 mV transition reflects the formation bf FMN anion radical from a flavin covalently bound to the NqrB subunit, which stays as a radical down to very low potentials. Taking into account the EPR-silent, two-electron transition of noncovalently bound FAD located in the NqrF subunit, there are four flavins in Na+-NQR all together. Defined by dipole-dipole magnetic interaction measurements, the interspin distance between the [2Fe-2S]+ cluster and the NqrB subunit-bound FMN anion radical is found to be 22.5 ± 1.5 A, which means that for the functional electron transfer between these two centers another cofactor, most likely FMN bound to the NqrC subunit, should be located. [ABSTRACT FROM AUTHOR]

The heart of the oxygen-evolving complex (OEC) of photosystem II is a Mn4OxCa cluster that cycles through five different oxidation states (S0 to S4) during the light-driven water-splitting reaction cycle. In this study we interpret the recently obtained 55Mn hyperfine coupling constants of the S0 and S2 states of the OEC [Kulik et al. J. Am. Chem. Soc. 2005, 127, 2392-2393] on the basis of Y-shaped spin-coupling schemes with up to four nonzero exchange coupling constants, J. This analysis rules out the presence of one or more Mn(IIions in So in methanol (3%) containing samples and thereby establishes that the oxidation states of the manganese ions in S0 and S2 are, at 4 K1 Mn4(III, III, III, IV) and Mn4(III, IV, IV, IV), respectively. By applying a ‘structure filter’ that is based on the recently reported single-crystal EXAFS data on the Mn4OxCa cluster [Yano et al. Science 2006, 314, 821-825] we (i) show that this new structural model is fully consistent with EPR and 55Mn-ENDOR data, (ii) assign the Mn oxidation states to the individual Mn ions, and (iii) propose that the known shortening of one 2.85 Å Mn-Mn distance in S0 to 2.75 Å in S1 [Robblee et al. J. Am. Chem. Soc. 2002, 124, 7459-7471] corresponds to a deprotonation of aμ-hydroxo bridge between MnA and MnB, i.e., between the outer Mn and its neighboring Mn of the μ3-oxo bridged moiety of the cluster. We summarize our results in a molecular model for the S0 → S1 and S1 → S2 transitions. [ABSTRACT FROM AUTHOR]

[Display omitted] Two new compounds BT-PDI and BT2-PDI2 were synthesized by the Sonogashira reaction between 4,7-diethynyl-2,1,3- benzothiadiazole and bromoperylene diimide derivatives. The HOMO and LUMO energy levels estimated by UV-VIS spectroscopy and cyclic voltammetry were –5.66/–3.75 and –5.33/–3.41 eV for the BT-PDI and BT2-PDI2, respectively; both compounds form high-quality and smooth coatings on the perovskite surface with the root mean square roughness values 5.95 and 7.80 nm for the BT-PDI and BT2-PDI2 films, respectively; the electron mobilities in the solid films estimated by photo-CELIV method are equal to 5.0 × 10–5 and 3.0 × 10–5 cm2 V–1 s–1, respectively. Both compounds being tested as electron transport layers in perovskite solar cells showed efficiency values of 14.44 and 13.01% for BT-PDI and BT2-PDI2, respectively. [ABSTRACT FROM AUTHOR]

Spin-lattice relaxation times T1 of photoexcited triplets ³C70 in glassy decalin were obtained from electron spin echo inversion recovery dependences. In the range 30-100 K, the temperature dependence of T1 was fitted by the Arrhenius law with an activation energy of 172 cm-1. This indicates that the dominant relaxation process of ³C70 is described by an Orbach-Aminov mechanism involving the higher triplet state t2 which lies 172 cm-1 above the lowest triplet state T1. Chemical modification of C70 fullerene not only decreases the intrinsic triplet lifetime by about ten times but also increases T1 by several orders of magnitude. The reason for this is the presence of a low-lying excited triplet state in ³C70 and its absence in triplet C70 derivatives. The presence of the higher triplet state in C70 is in good agreement with the previous results from phosphorescence spectroscopy. [ABSTRACT FROM AUTHOR]

The article states that powered by light-induced charge separations that generate oxidizing equivalents of about +1.3 Volt, photosystem II (PSII) has the unique capability to oxidize water to molecular oxygen. A manganese complex housed in a special protein environment that also controls proton movements and the access of water catalyzes water splitting. This functional unit of PSII is referred to as the oxygen-evolving complex. PSII created the aerobic atmosphere on earth and may serve as a model for technical approaches to split water by sunlight, which is a prerequisite for a sustainable hydrogen economy. In this article, the authors report manganese pulse ENDOR spectra for the oxidation states at Q-band frequency.

[Display omitted] New small molecule photovoltaic materials containing benzimidazole fragment were prepared by cross-coupling of the corresponding 1-bromo-4-(imidazol-2-yl)benzenes with multiborylated/stannylated polycyclic (het)arenes. Energies of HOMO/LUMO levels were calculated from cyclic voltammetry and UV/VIS spectroscopy data and are within the ranges –5.27... –5.73 and –2.33...–2.89 eV, respectively. Solar cells based on three different perovskites as light absorbing layers and compound SM7 as electron transporting material demonstrated power conversion efficiency values up to 10.78% without doping additives or perovskite engineering. [ABSTRACT FROM AUTHOR]

Although the photovoltaic performance of the composite of poly-3-hexylthiophene (P3HT) with semiconducting single-walled carbon nanotubes (s-SWCNT) is promising, the short-circuit current density jSC is much lower than that for typical polymer/fullerene composites. Out-of-phase electron spin echo (ESE) technique with laser excitation of the P3HT/s-SWCNT composite was used to clarify the origin of the poor photogeneration of free charges. The appearance of out-of-phase ESE signal is a solid proof that the charge-transfer state of P3HT+/s-SWCNT− is formed upon photoexcitation and the electron spins of P3HT+ and s-SWCNT− are correlated. No out-of-phase ESE signal was detected in the same experiment with pristine P3HT film. The out-of-phase ESE envelope modulation trace for P3HT/s-SWCNT composite was close to that for the polymer/fullerene photovoltaic composite PCDTBT/PC70BM, which implies a similar distance of initial charge separation in the range 2–4 nm. However, out-of-phase ESE signal decay with delay after laser flash increase for P3HT/s-SWCNT composite was much faster, with a characteristic time of 10 µs at 30 K. This points to the higher geminate recombination rate for the P3HT/s-SWCNT composite, which may be one of the reasons for the relatively poor photovoltaic performance of this system. [ABSTRACT FROM AUTHOR]

A series of four new oligomeric derivatives of NFA , NFA(S) , NFA(Se) and NFA(N) with terminal perylene diimide groups modified with heteroatoms of S, Se, and N, were successfully synthesized and fully characterized by a variety of physicochemical methods. Due to deep LUMO levels, all compounds have an electron-acceptor character, which allows them to perform as electron transport compounds in perovskite solar cells of p-i-n architecture. The highest efficiency of 17.23 % was delivered by the solar cells with NFA(Se) electron transporting layer. [Display omitted] • A series of new oligomers with terminal perylene diimide groups modified with heteroatoms of S, Se, and N, were synthesized. • Optical and electronic properties of the new compounds were studied. • All the compounds were studied as new type materials for electron transport layer for perovskite solar cells. • The highest efficiency of 17.23 % was delivered by the solar cells with NFA(Se) electron transporting layer. [ABSTRACT FROM AUTHOR]

Two acceptor small molecules consisting of 2‐(11‐oxoanthra[2,1‐b]thiophen‐6‐ylidene)dipropanedinitrile frameworks connected by a bis(thiophen‐2‐ylethynyl)arene bridge were synthesized by the two‐step sequence of Sonogashira cross‐coupling and Knoevenagel condensation in order to investigate their performance as non‐fullerene acceptors in organic solar cells. Optical, electrochemical and photovoltaic properties of new 2,2′‐[2,2′‐(5,5′‐(arenediyl)bis(ethyne‐2,1‐diyl)bis(thien‐5,2‐diyl))bis(11‐oxoanthra[2,1‐b]thiophen‐6‐ylidene)]dipropanedinitriles and previously studied analogs of 2,2′‐[2,2′‐arenediylbis(11‐oxoanthra[1,2‐b]thiophene‐6‐ylidene)]dipropanedinitriles were compared to assess the effect of introducing ethynylthiophene units between the arene linker and the 2‐(11‐oxoanthrathiophen‐6‐ylidene)propanedinitrile units. Despite the proper energy level alignment and morphology, composites of the newly synthesized compounds with the PBDB‐T donor polymer demonstrate a moderate PCE of 0.54 %. The small value of the short circuit current as compared to composites with fullerene acceptors is probably due to the low electron mobility in the newly synthesized compounds. The low electron mobility, in turn, is probably cause by the LUMO localization at the edge units of the acceptor‐type molecules, in contrast to the almost uniform LUMO delocalization over the whole π‐conjugated system for high‐performing non‐fullerene acceptors such as ITIC. [ABSTRACT FROM AUTHOR]

Spectroscopic and photovoltaic properties of composites of purified and subsequently fluorinated single‐walled carbon nanotubes (F‐SWCNTs) with conjugated polymer poly(3‐hexylthiophene) (P3HT) are tested. Adding cyclohexanone into o‐dichlorobenzene solution of P3HT and F‐SWCNTs significantly affects the composite morphology and promotes P3HT/F‐SWCNT nanofilament formation, as evidenced from atomic force microscopy (AFM) images of spin‐coated composite films. Also, nanofilament formation enhances quenching of P3HT photoluminescence by F‐SWCNTs. The performance of P3HT‐based organic photovoltaics (OPV) devices with separated semiconducting SWCNTs and F‐SWCNTs as the acceptor component of the active layer is comparable. Light‐induced electron paramagnetic resonance (EPR) signal intensity in P3HT/F‐SWCNT composite films and frozen solutions grows with increase in F‐SWCNT content, which is a signature of photoinduced electron transfer. Dramatic change in SWCNT electronic structure upon fluorination is also evidenced by UV–vis– near infra red optical absorption spectra, from which the bandgap of about 1.0 eV is derived for F‐SWCNTs. Overall, the experimental results confirm that fluorination efficiently converts metallic SWCNTs into semiconducting ones, and F‐SWCNTs can be used for as an electron acceptor component in OPV devices, in combination with polymer donors. Presently, the performance of P3HT/F‐SWCNT devices is limited by F‐SWCNT aggregation into bundles, which decreases P3HT/F‐SWCNT interface area. [ABSTRACT FROM AUTHOR]

The low accessibility of natural gas fields and transporting pipelines requires portable online analyzers of the composition of natural gas, ensuring nearly chromatographic precision and capable of in situ analysis of a wide range of gases, including infrared-inactive ones (hydrogen, oxygen, nitrogen, chlorine). We have developed an express method of gas analysis meeting all the requirements for analysis of natural gas and its derivative mixtures using a portable 532 nm Raman spectrometer rigidly connected to a hollow-core crystal photonic fiber. [ABSTRACT FROM AUTHOR]

The syntheses of 2,7-diamino-1,3,6,8-tetraazabenzopyrene framework was achieved through CuI-catalyzed double annulation of 1,4-diiodoanthraquinone with guanidine. In addition, the preparation of series of 2,7-disubstituted 1,3,6,8-tetraazabenzopyrenes functionalized by NR 2 , C O, Cl, alkoxy and phenoxy groups with good yields was achieved through the simple transformations such as diazotization, alkylation and nucleophilic aromatic substitution. The properties of 1,3,6,8-tetraazabenzopyrenes synthesized were studied by DFT-calculations, optical and photoluminescence spectroscopy, cyclic voltammetry and light-induced EPR spectroscopy. The luminescence of amino derivatives is quenched in acidic solutions depending on the degree of protonation. Image 1 • Reaction of guanidine with 1,4-diiodoanthraquinone leads to 2,7-diamino-1,3,6,8-tetraazabenzopyrene. • 2,7-Diamino-1,3,6,8-tetraazabenzopyrene is promising precursors for further functionalization. • Chlorine atoms in 1,3,6,8-tetraazabenzopyrenes are good leaving groups for reactions with nucleophiles. [ABSTRACT FROM AUTHOR]

A concise organolithium‐free route to build electron‐accepting molecules consisting of two 2‐(11‐oxoanthra[1,2‐b]thiophen‐6‐ylidene)propanedinitrile units connected by functionalized π‐conjugated linkers was developed. Annulation of two thiophene rings in one step was achieved through chemoselective cyclocondensation of a bis(ethynylanthraquinone) substrate with sodium sulfide. Finally, electron‐accepting dicyanomethylene moieties were introduced by Knoevenagel condensation with malodinitrile. The synthesized 2,2′‐[2,2′‐arenediylbis(11‐oxoanthra[1,2‐b]thiophene‐6‐ylidene)]dipropanedinitriles were studied by UV/Vis and fluorescence spectroscopy, cyclic voltammetry, and DFT calculations. The acceptor properties of these compounds were confirmed by efficient light‐induced electron transfer in their blend with a donor polymer, poly(3‐hexylthiophene‐2,5‐diyl), detected by electron paramagnetic resonance spectroscopy. [ABSTRACT FROM AUTHOR]

Annulation of the two pyrimidine rings with anthraquinone through the simple condensation of the 1,5-diiodoanthraquinone with guanidine was employed to build 1,3,7,9-tetraazaperylene framework functionalized by NH 2 , C=O, aliphatic and alkoxy-groups. The properties of the synthesized 1,3,7,9-tetraazaperylenes were studied by cyclic voltammetry, optical and luminescence spectroscopy and DFT-calculations. Remarkably, the vacuum-deposited thin film of 1,3,7,9-tetraazaperylene functionalized by 2-ethylhexyloxy groups demonstrated photoluminescence quantum yield as high as 55%, which is even higher than that for toluene solution (33%). [ABSTRACT FROM AUTHOR]

Temporal shape of electron spin echo (ESE) signal of photoinduced spin-correlated radical pairs (SCRP) in composite of conductive polymer P3HT and substituted fullerene PCBM is studied in details. ESE signals of radical pairs (RP) P3HT + /PCBM − are calculated in realistic model, taking into account finite microwave pulse length. Inhomogeneous broadening of resonant lines and interradical distance distribution are included. Experimentally observed ESE time-domain shape was found to contradict predictions of conventional SCRP theory, which would be valid in the case of very fast electron transfer. Thus, instantaneous formation of singlet SCRP is not the case for P3HT + /PCBM − pair, and spin system has enough time to evolve coherently during sequential electron transfer. While it is impossible to reproduce experimental data within simple singlet SCRP model, assumption of presence of additional – with respect to what is predicted by singlet SCRP theory – AE (absorption/emission) spin polarization gives convincing accordance with the experiment. Density matrix of RP P3HT + /PCBM − is a superposition of two contributions, namely the parts reflecting (i) antiphase polarization of original singlet-born SCRP and (ii) additional AE-polarization which is generated during initial stage of charge separation. AE-polarization affects experimental ESEEM (electron spin echo envelope modulation) traces, as well as ESE shape, making impossible their interpretation via simple singlet SCRP model. However, this effect can be eliminated by averaging of ESEEM traces over EPR spectral positions. Finally, choosing the optimal gate for ESE time-domain integration and proper microwave detection phase tuning are considered. [ABSTRACT FROM AUTHOR]

Series of 1,8-diazabenzopyrenes and 1,7-diazaperylenes with thienyl or 4-(phenylamino)phenyl groups were designed and synthesized by a one-pot process from the functionalized terminal alkynes and either 1,4- or 1,5-diiodoanthraquinones in order to investigate the effect of extending π-conjugation at the 2,7- and 2,8-positions on the optical and electrochemical properties. The substances synthesized were characterized by X-ray analysis, cyclic voltammetry, UV–vis and luminescence spectroscopy. Energies and spin-densities of frontier molecular orbitals were calculated by DFT. Practically planar crystal structures of 1,8-diazabenzopyrene and 1,7-diazaperylene with thienyl groups were confirmed by X-ray diffraction data. Solid-state luminescence was obtained for the synthesized substances in drop-casted films and in 1,4-dioxane/water mixtures. [ABSTRACT FROM AUTHOR]

Photochemical properties of regioregular poly(3-hexylthiophene) (P3HT), fullerene derivative [6,6]-phenyl C61-butyric acid methyl ester (PC 60 BM) and their 1:1 mixture in argon-saturated toluene solution were studied by optical spectroscopy and nanosecond laser flash photolysis ( λ ex = 532 nm). Separate excitation of components leads to formation of corresponding triplet state of fullerene ( 3 PC 60 BM*, λ max = 710 nm, ϵ max = 22400 M −1 cm −1 , φ T = 0.29) and polymer ( 3 P3HT*, λ max = 850 nm, ϵ 750 nm ≤ 10 5 M −1 cm −1 , φ T ≥ 0.19). Excitation of P3HT/PC 60 BM mixture leads to effective energy transfer from 3 P3HT* to the ground state of fullerene with a formation of 3 PC 60 BM*. No evidence of ion-radical P3HT + and PC 60 BM − formation was obtained though electron transfer between 3 P3HT* and 1 PC 60 BM is energetically favorable in studied system. Presumably ultrafast back electron transfer takes place in geminate P3HT + /PC 60 BM − pair with regeneration of the ground states of P3HT and PC 60 BM. [ABSTRACT FROM AUTHOR]

Novel naphtho[4,3,2,1- lmn ][2,9]phenanthrolines were synthesized via reaction between 1,5-diethynyl-9,10-anthraquinones and urea in DMF. Their HOMO and LUMO levels determined from optical spectroscopy and cyclic voltammetry are in good agreement with those determined from quantum chemical calculation. Light-induced electron transfer from the semiconducting polymer MEH-PPV to the synthesized molecules was detected by EPR-spectroscopy, showing their possible applicability as electron acceptors in bulk heterojunction organic solar cells. The synthesized naphtho[4,3,2,1- lmn ][2,9]phenanthrolines can be used as building blocks for larger molecules with an extended π-conjugated system, which can be used as acceptors in organic photovoltaics. [ABSTRACT FROM AUTHOR]

Na+-translocating NADH:quinone oxidoreductase (Na+-NQR) is a component of respiratory electron-transport chain of various bacteria generating redox-driven transmembrane electrochemical Na+ potential. We found that the change in Na+ concentration in the reaction - medium has no effect on the thermodynamic properties of prosthetic groups of Na+-NQR from Vibrio harveyi, as was revealed by the anaerobic equilibrium redox titration of the enzymes EPR spectra. On the other hand, the change in Na+ concentration strongly alters the EPR spectral properties of the radical pair formed by the two anionic semiquinones of FMN residues bound to the NqrB and NqrC subunits (FMNNqrB and FMNNqrC). Using data obtained by pulse X- and Q-band EPR as well as by pulse ENDOR and ELDOR spectroscopy, the interspin distance between FMNNqrB and FMNNqrC was found to be 15.3 Å in the absence and 20.4 Å in the presence of Na+, respectively. Thus, the distance between the covalently bound FMN residues can vary by about S Å upon changes in Na+ concentration. Using these results, we propose a scheme of the sodium potential generation by Na+-NQR based on the redox- and sodium-dependent conformational changes in the enzyme. [ABSTRACT FROM AUTHOR]

An analysis of the electronic structure of the [MnIIMnIII(μ-OH)-(μ-piv)2(Me3tacn)2](ClO4)2 (PivOH) complex is reported. It displays features that include: (i) a ground 1/2 spin state; (ii) a small exchange (J) coupling between the two Mn ions; (iii) a mono-μ-hydroxo bridge, bis-μ-carboxylato motif; and (iv) a strongly coupled, terminally bound N ligand to the MnIII. All of these features are observed in structural models of the oxygen evolving complex (OEC). Multifrequency electron paramagnetic resonance (EPR) and electron nuclear double resonance (ENDOR) measurements were performed on this complex, and the resultant spectra simulated using the Spin Hamiltonian formalism. The strong field dependence of the 55Mn-ENDOR constrains the 55Mn hyperfine tensors such that a unique solution for the electronic structure can be deduced. Large hyperfine anisotropy is required to reproduce the EPR/ENDOR spectra for both the MnII and MnIII ions. The large effective hyperfine tensor anisotropy of the MnII, a d5 ion which usually exhibits small anisotropy, is interpreted within a formalism in which the fine structure tensor of the MnIII ion strongly perturbs the zero-field energy levels of the MnIIMnIII complex. An estimate of the fine structure parameter (d) for the MnIII of -4 cm-1 was made, by assuming the intrinsic anisotropy of the MnII ion is small. The magnitude of the fine structure and intrinsic (onsite) hyperfine tensor of the MnIII is consistent with the known coordination environment of the MnIII ion as seen from its crystal structure. Broken symmetry density functional theory (DFT) calculations were performed on the crystal structure geometry. DFT values for both the isotropic and the anisotropic components of the onsite (intrinsic) hyperfine tensors match those inferred from the EPR/ENDOR simulations described above, to within 5%. This study demonstrates that DFT calculations provide reliable estimates for spectroscopic observables of mixed valence Mn complexes, even in the limit where the description of a well isolated S = 1/2 ground state begins to break down. [ABSTRACT FROM AUTHOR]

Abstract: The electronic properties of the Mn4O x Ca cluster in the S 2 state of the oxygen-evolving complex (OEC) were studied using X- and Q-band EPR and Q-band 55Mn-ENDOR using photosystem II preparations isolated from the thermophilic cyanobacterium T. elongatus and higher plants (spinach). The data presented here show that there is very little difference between the two species. Specifically it is shown that: (i) only small changes are seen in the fitted isotropic hyperfine values, suggesting that there is no significant difference in the overall spin distribution (electronic coupling scheme) between the two species; (ii) the inferred fine-structure tensor of the only MnIII ion in the cluster is of the same magnitude and geometry for both species types, suggesting that the MnIII ion has the same coordination sphere in both sample preparations; and (iii) the data from both species are consistent with only one structural model available in the literature, namely the Siegbahn structure [Siegbahn, P. E. M. Accounts Chem. Res. 2009, 42, 1871–1880, Pantazis, D. A. et al., Phys. Chem. Chem. Phys. 2009, 11, 6788–6798]. These measurements were made in the presence of methanol because it confers favorable magnetic relaxation properties to the cluster that facilitate pulse-EPR techniques. In the absence of methanol the separation of the ground state and the first excited state of the spin system is smaller. For cyanobacteria this effect is minor but in plant PS II it leads to a break-down of the S T =½ spin model of the S 2 state. This suggests that the methanol–OEC interaction is species dependent. It is proposed that the effect of small organic solvents on the electronic structure of the cluster is to change the coupling between the outer Mn (MnA) and the other three Mn ions that form the trimeric part of the cluster (MnB, MnC, MnD), by perturbing the linking bis-μ-oxo bridge. The flexibility of this bridging unit is discussed with regard to the mechanism of O-O bond formation. [Copyright &y& Elsevier]

Robust electrode materials without the addition of binders allow increasing efficiency of electrical storage devices. We demonstrate the fabrication of binder-free electrodes from modified single-walled carbon nanotubes (SWCNTs) for electrochemical double-layer capacitors (EDLCs). Modification of SWCNTs included a sonication in 1,2-dichlorobenzene and/or fluorination with gaseous BrF3 at room temperature. The sonication caused the shortening of SWCNTs and the splitting of their bundles. As a result, the film prepared from such SWCNTs had a higher density and attached a larger amount of fluorine as compared to the film from non-sonicated SWCNTs. In EDLCs with 1M H2SO4 electrolyte, the fluorinated films were gradually defluorinated, which lead to an increase of the specific capacitance by 2.5–4 times in comparison with the initial values. Although the highest gravimetric capacitance (29 F g−1 at 100 mV s−1) was observed for the binder-free film from non-modified SWCNT, the fluorinated film from the sonicated SWCNTs had an enhanced volumetric capacitance (44 F cm−3 at 100 mV s−1). Initial SWCNT films and defluorinated films showed stable work in EDLCs during several thousand cycles. [ABSTRACT FROM AUTHOR]

• Thin films P3HT, PCDTBT, DRCN5T and BTR are photooxidized in air under visible light. • X- and Q-band EPR spectra of photodegraded films were obtained. • Concentration of the long-living radicals higher than hole trap density. Photodegradation of thin films of organic semiconducting electron-donor materials P3HT, PCDTBT, DRCN5T and BTR upon illumination with visible light in air was studied. The changes of UV–vis absorption, photoluminescence and EPR spectra were monitored as functions of illumination time. Stable radicals were generated at concentrations that exceed the values of charge carrier density of organic solar cells in the operating conditions. Increase of the radical concentration was observed for P3HT, PCDTBT, DRCN5T. On the contrary, for BTR the radical concentration drops to zero after initial increase. This indicates different photodegradation processes in studied materials. [ABSTRACT FROM AUTHOR]

• New materials are synthetized introducing an TCNQ moiety to anthra[2,3- b ]thiophene core. • Fused aromatic TCNQs are potential non-fullerene acceptors for organic photovoltaics. • Vacuum-free fabricated OPV devices based on thiophene-fused TCNQs shows PCE of 0.71%. Three novel molecules based on thiophene-fused 11,11,12,12-tetracyano-9,10-anthraquinodimethane (TCAQ) units linked through functionalized π-conjugated arene bridges are synthesized by three-step sequence of Sonagashira coupling, double thioannulation and Knoevenagel condensation. The energy of their frontier orbitals shows that these molecules are suitable for replacing fullerenes as electron acceptors in composites with conjugated donor polymers used in organic photovoltaics (OPV). The composite of polymer donor PCDTBT with fluorene-linked thiophene-fused TCAQs demonstrates good solubility in organic solvents and bulk heterojunction morphology with characteristic donor and acceptor domain size of several tens of nanometers, favourable for photoelectric conversion. This composite also exhibits prominent light-induced EPR signal indicating efficient photoinduced free charge generation. OPV devices based on this composite were fabricated by vacuum-free method. They show photoelectric conversion with maximum PCE of 0.71%. [ABSTRACT FROM AUTHOR]

Experimental results on the properties of a recently discovered new collective state, the magnetofermionic condensate, are summarized herein. Condensation occurs in a fermionic system, a quantum Hall insulator (filling factor ν = 2), as a result of the formation of a dense ensemble of long‐lived spin cyclotron magnetoexcitons, composite bosons. At temperatures below 1 K, the exciton ensemble exhibits a sharp enhancement in its response to an external electromagnetic field due to the formation of a super‐absorbing state that interacts coherently with the electromagnetic field. Simultaneously, the electrons below the Fermi level rearrange to form a new non‐equilibrium radiative recombination channel. The condensate shows a sharp decrease in viscosity and the ability to spread over macroscopically large distances, on the order of a millimeter, at a speed of ≈103cms−1. Due to this rapid long‐distance spin transfer, new opportunities in the field of spintronics have been opened up. [ABSTRACT FROM AUTHOR]

Light-induced electron transfer from the regioregular poly(3-hexylthiophene) to the synthesized molecules is detected by an EPR spectroscopy technique. [ABSTRACT FROM AUTHOR]