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Two generations of polyphosphorhydrazone (PPH) dendrimers were synthesized and fully functionalized with TEMPO radicals via acrylamido or imino group linkers to evaluate the impact of the linker substitution on the radical-radical interactions. A drastic change in the way that the radicals interacted among them was observed by EPR and CV studies: while radicals in Gn -imino-TEMPO dendrimers presented a strong spin-spin interaction, in the Gn -acrylamido-TEMPO ones they acted mainly as independent radicals. This shows that these interactions could be tuned by the solely substitution of the radical linker, opening the perspective of controlling and modulating the extension of these interactions depending on each application. The chemical properties of the linker strongly influence the spin-spin exchange between pendant radicals.

This study analyses some hydrological driving forces and their interrelation with surface-flow initiation in a semiarid Caatinga basin (12 km2), Northeastern Brazil. During the analysis period (2005 – 2014), 118 events with precipitation higher than 10 mm were monitored, providing 45 events with runoff, 25 with negligible runoff and 49 without runoff. To verify the dominant processes, 179 on-site measurements of saturated hydraulic conductivity (Ksat) were conducted. The results showed that annual runoff coefficient lay below 0.5% and discharge at the outlet has only occurred four days per annum on average, providing an insight to the surface-water scarcity of the Caatinga biome. The most relevant variables to explain runoff initiation were total precipitation and maximum 60-min rainfall intensity (I60). Runoff always occurred when rainfall surpassed 31 mm, but it never occurred for rainfall below 14 mm or for I60 below 12 mm h−1. The fact that the duration of the critical intensity is similar to the basin concentration time (65 min) and that the infiltration threshold value approaches the river-bank saturated hydraulic conductivity support the assumption that Hortonian runoff prevails. However, none of the analysed variables (total or precedent precipitation, soil moisture content, rainfall intensities or rainfall duration) has been able to explain the runoff initiation in all monitored events: the best criteria, e.g. failed to explain 27% of the events. It is possible that surface-flow initiation in the Caatinga biome is strongly influenced by the root-system dynamics, which changes macro-porosity status and, therefore, initial abstraction. Copyright © 2016 John Wiley & Sons, Ltd.

6 pages, 5 figures, 1 scheme, We show that electron transfer from the perchlorotriphenylmethide anion (PTM−) to Y@C82(C2v) is an instantaneous process, suggesting potential applications for using PTM− to perform redox titrations of numerous endohedral metallofullerenes. The first representative of a Y@C82-based salt containing the complex cation was prepared by treating Y@C82(C2v) with the [K+([18]crown-6)]PTM− salt. The synthesis developed involves the use of the [K+([18]crown-6)]PTM− salt as a provider of both a complex cation and an electron-donating anion that is able to reduce Y@C82(C2v). For the first time, the molar absorption coefficients for neutral and anionic forms of the pure isomer of Y@C82(C2v) were determined in organic solvents with significantly different polarities., This work was supported in part by the Spanish Direcci ón General de Investigació n (DGI; project POMAs, CTQ2010-19501/BQU), the Generalitat de Catalunya (2009SGR00516), the bilateral CSICNFBR project 2008RU0073, the RFBR (09-03-91291-INIS-a and 13- 03-01291-a), the Presidium of the RAS (program no. 8), and the European project ERC StG 2012-306826 e-GAMES. E.L. thanks CIBER-BBN, an initiative funded by the VI National R&D&i Plan 2008-2011, Iniciativa Ingenio 2010, Consolider Program, CIBER Actions and financed by the Instituto de Salud Carlos III with assistance from the European Regional Development Fund.

A new family of hydrated molecular metals based on the bis(ethylenethio- tetrathiafulvalene) (BET-TTF) donor was developed. A metal stable down to 0.5 K was obtained for the first time from this donor, perhaps due to the absence of disorder in the peripheral sulfur atoms. A hint of superconducting transition in some crystals of the BET-TTF2Br·3H2O salt was observed.

Macrocyclic C60-(π-conjugated oligomer) dyads have been prepared from the corresponding bis-malonates by a macrocyclization reaction on the C60 sphere. In both multicomponent systems, the fullerene moiety and the π-conjugated oligomer subunit are at the van der Waals contact due to the cyclic structure. Interestingly, the characteristic π-π* electronic transition band of the conjugated system is significantly red-shifted in both dyads with respect to the corresponding model compounds lacking the fullerene unit (Δλmax = 24 to 34 nm). Whereas the absorption properties are dramatically affected by the intramolecular electronic interactions between the conjugated bridging system and the accepting C60 spheroid, cyclic voltammetry revealed only small changes in their redox potentials. However, these intramolecular interactions have a significant influence on the electronic coupling of the two terminal aniline redox units of the conjugated system in the dyads. Actually, when compared to the corresponding model compound 14·+, delocalization of the positive charge in the mixed-valence species derived from the dyad 1 is more difficult due to the π-π interactions of the conjugated system with the electron-withdrawing fullerene group. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Organic conducting fiber-like materials hold great promise for the development of nanowires that can act as connections in miniature electronic devices, as an alternative to inorganic nanometer scale structures. This article presents a conducting organic tetrathiafulvalene-based supramolecular material which possesses a rich phase behavior with different packing of the molecules in the different forms, evidenced by electron spin resonance (ESR) spectroscopy. The distinct phases of conducting nanofibers can be easily fabricated through the temperature control of their preparation process from a xerogel by doping with iodine vapors. A total of four conducting phases have been identified conclusively using ESR spectroscopy as the key analytical tool. Three of the phases show a good long-term stability and areas in which the I-V curves have ohmic behavior when studied by current sensing (conducting) AFM. They offer promise for applications where electrical nanometer scale connections are required.

Functionalized gold nanoparticles with complementary H-bonding groups can control the secondary structure of xerogel fibers formed by a molecular conductor thanks to their incorporation into the nanowires, which show metal-like conductivity once doped without the need for annealing. The picture shows a photograph of the xerogel, TEM images of Au particles in the gel and a single fiber, and an AFM image revealing the texture of the gel.

The gold and nickel bisdithiolene complexes based on new highly extended ligands incorporating fused tetrathiafulvalene and thiophene moieties (alpha-tdt=thiophenetetrathiafulvalenedithiolate and dtdt=dihydro- thiophenetetrathiafulvalenedithiolate), were prepared and characterised by using cyclic voltammetry, single crystal X-ray diffraction, EPR, magnetic susceptibility and electrical transport measurements. These complexes, initially obtained under anaerobic conditions as diamagnetic gold monoanic [nBu(4)N][Au(alpha-tdt)(2)] (4), [nBu(4)N][Au(dtdt)(2)] (3) and nickel dianionic species [(nBu(4)N)(2)][Ni(alpha-tdt)(2)] (8), [(nBu(4)N)(2)][Ni(dtdt)(2)] (7), can be easily oxidised to the stable neutral state just by air or iodine exposure. The monoanionic complexes crystallise in at least two polymorphs, all of which have good cation and anion segregation in alternated layers, the anion layers making a dense 2D network of short SS contacts. All of the neutral complexes, obtained as microcrystalline or quasi amorphous fine powder, present relatively large magnetic susceptibilities that correspond to effective magnetic moments in the range 1-3 mu(B) indicative of high spin states and very high electrical conductivity that in case of the Ni compound can reach sigma(RT) approximately 250 S cm(-1) with a clear metallic behaviour. These compounds are new examples of the still rare single-component molecular metals.

Derivatives of 9-[2-(1,3-dithiol-2-ylidene)ethylidene]thioxanthene have been synthesized using Horner-Wadsworth-Emmons reactions of (1,3-dithiol-2-yl)phosphonate reagents with thioxanthen-9-ylidene-acetaldehyde (5). Further reactions lead to the sterically crowded cross-conjugated "vinylogous tetrathiafulvalene" derivative 9-[2,3-bis-(4,5-dimethyl-1,3-dithiol-2-ylidene)-propylidene]thioxanthene (10). X-ray crystallography, solution electrochemistry, optical spectroscopy, spectroelectrochemistry, and simultaneous electrochemistry and electron paramagnetic resonance spectroscopy, combined with theoretical calculations performed at the B3LYP/6-31G(d) level, elucidate the interplay of the electronic and structural properties in these molecules. For compound 10, multistage redox behavior is observed: the overall electrochemical process can be represented by 10-->10(.+)-->10(2+)-->10(4+) with good reversibility for the 10-->10(.+)-->10(2+) transformations. At the tetracation stage there is the maximum gain in aromaticity at the dithiolium and thioxanthenium rings. Theory predicts that for 10, 10(.+), and 10(2+) the trans isomers are more stable than the cis isomers (by ca. 2-18 kJ mol(-1)), whereas for 10(4+) the cis isomer becomes more stable than the trans isomer (by ca. 25 kJ mol(-1)) [trans and cis refer to the arrangement of the two dithiole moieties with respect to the central ==C(R)--C(H)== fragment]. These data explain the detection in cyclic voltammograms of both trans and cis isomers of 10 and 10(.+) during the reduction of 10(4+) at fast scan rates (>100 mV s(-1)) when the cis-trans isomerization is not completed within the timescale of the experiment. The X-ray structure of the charge-transfer complex (CTC) of 10 with 2,4,5,7-tetranitrofluorene-9-dicyanomethylenefluorene (DTeF) [stoichiometry: 10(.+)(DTeF)(2) (.-)2 PhCl] reveals a twisted conformation of 10(.+) (driven by the bulky thioxanthene moiety) and provides a very rare example of segregated stacking of a fluorene acceptor in a CTC.

Derivatives of 9-(1,3-dithiol-2-ylidene)fluorene (9) and 9-(1,3-dithiol-2-ylidene)thioxanthene (10) have been synthesised using Horner-Wadsworth-Emmons reactions of (1,3-dithiol-2-yl)phosphonate reagents with fluorenone and thioxanthen-9-one. X-ray crystallography, solution electrochemistry, optical spectroscopy, spectroelectrochemistry and simultaneous electrochemistry and electron paramagnetic resonance (SEEPR), combined with theoretical calculations performed at the B3P86/6-31G** level, elucidate the interplay of the electronic and structural properties in these molecules. These compounds are strong two-electron donors, and the oxidation potentials depend on the electronic structure of the oxidised state. Two, single-electron oxidations (E(1)oxE(1)ox) were observed for 9-(1,3-dithiol-2-ylidene)fluorene systems (9). In contrast, derivatives of 9-(1,3-dithiol-2-ylidene)thioxanthene (10) display the unusual phenomenon of inverted potentials (E(1)oxE(1)ox) resulting in a single, two-electron oxidation process. The latter is due to the aromatic structure of the thioxanthenium cation (formed on the loss of a second electron), which stabilises the dication state (10(2+)) compared with the radical cation. This contrasts with the nonaromatic structure of the fluorenium cation of system 9. The two-electron oxidation wave in the thioxanthene derivatives is split into two separate one-electron waves in the corresponding sulfoxide and sulfone derivatives 27-29 owing to destabilisation of the dication state.

The synthesis and study of structural and electronic properties of mono-ferrocenyl π-conjugated complexes 5a–d, whose electronic characteristics have been systematically varied by introducing an electron-donating or electron-withdrawing substituent either at the 1-position or at the 4-position of the 2-aza-1,3-butadiene moiety linked to the ferrocenyl unit, are presented. The structural and electronic properties of the homobimetallic complex 5f, with two ferrocene units linked through the asymmetric and oxidizable 2-aza-1,3-butadiene bridge, is also reported. The crystal structures of complexes 5b, 5d, and 5f show a large degree of conjugation in this family of compounds. Complexes 5 show a rich electrochemical behavior due both to the oxidation of ferrocenyl units and the 2-aza-1,3-butadiene bridge, as revealed by cyclic voltammetry. Radical cations 5+· were prepared from 5 by coulometric oxidations following their generation by absorption spectroscopy. The electronic properties of all reported neutral and oxidized π-conjugated complexes have been investigated by means of UV/Vis–near-IR, EPR and 57Fe Mossbauer spectroscopy. The detailed study of mono-oxidized species 5a+·–5f+· has permitted the determination of the influence of an asymmetric bridge with an electroactive character on the intramolecular electron transfer (IET) phenomenon, thus demonstrating that the 2-aza-1,3-butadiene bridge promotes the IET between the two metallic units of 5f+· through two different pathways. The experimental data and conclusions are supported by DFT computations (B3LYP/3-21G*) and time-dependent DFT methods. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

The synthesis, characterisation, and X-ray structure of a new strained asymmetric diferrocene derivative (2) is reported. Compound 2 acts as a highly specific electrochemical and optical Mg(2+) ion sensor, as revealed by spectroscopic and electrochemical techniques. Thus, in the presence of Mg(2+), a new redox peak appears in the cyclic voltammogram (CV) that is anodically shifted compared to the E(1/2) of the free receptor (DeltaE(1/2)=340 mV). Diferrocene derivative 2 also gives a highly visual response upon addition of Mg(2+), namely a change of colour from orange to deep purple. In addition, compound 2 does not show any significant sensing activity in the presence of Ca(2+) or alkaline ions. On protonation, it is converted into the stable diferrocenylcarbenium salt 4, in which two different modes of stabilisation of the alpha-carbocationic centre are clearly demonstrated by a combination of (1)H NMR and (57)Fe Mössbauer spectroscopic measurements. Finally, by a partial (chemical or electrochemical) oxidation, compound 2 forms the asymmetric mixed-valence species 2(+), which can be isolated as the solid salt 6 by using CF(3)SO(3) (-) as a counterion. This mixed-valence species shows a fast intramolecular electron-transfer process, as ascertained by several spectroscopic techniques.

Three new charge-transfer salts of tetrathiafulvalene (TTF)-based donors with thiocyanato- or selenocyanato-metal complex anions have been synthesised. The salts isolated were [BMDT-TTF][Cr(NCS)] (1), [TM-TTF][Cr(NCS)]·2CHCN (2) and [TM-TTF][Cr(NCSe)]·2CHCN (3) [BMDT-TTF = bis-(methylenedithio)tetrathiafulvalene and TM-TTF = tetramethyltetrathiafulvalene]. Single crystals of compound 1 crystallise in the monoclinic C2/c space group with a = 37.286(3), b= 10.0539(6), c= 21.069(2) A, β = 124.348(4)°, V = 6520.9(9) A and Z = 4. Compound 3 was also suitable for an X-ray diffraction study, however the anionic part, [Cr(NCSe)] was highly disordered and the best solution gave a final R factor of 16.4%. A solution was found for the monoclinic space groupo C2/m with a = 113.787(3), b= 19.507(3), c = 14.735(5) A, β = 102.90(3)°, V = 3862.9(17) A and Z = 2. For compound 1 there are several S ⋯ S close atomic contacts between the donors and acceptors, but there is no discernible magnetic exchange between ions. Such an interaction was previously observed in related salts such as [TTF][Cr(NCS)(phenanthroline)] and [donor] [M(NCS)(isoquinoline)] [M = Cr, Fe and donor = TTF, BEDT-TTF or TM-TTF (tetramethyltetrathiafulvalene)]. Compounds 1 to 3 are all paramagnetic semiconductors in which the magnetic susceptibility is dominated by the Cr-containing anions. The structure-function relationship, along with a comparison with related compounds, indicates that there is no long-range magnetic order because there are no π-stacking interactions between donor and acceptor; these types of interactions are seen in all of the bulk magnets of this type in which the donor spin is magnetically coupled to the anion. © Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003.

decrease of transmission (absorption increase) appears. This decrease cannot be explained by the photodegradation effect and can be accounted for by the photoinduced reorientation of azo groups. The increase of the transmission from D (a minimum point in curve a) to E indicates that azo chromophores with their long axis oriented in the direction perpendicular to the pump polarization also become photodegraded. In curve b, a decrease of transmission after the initial fast jump is observed (see the inset of Fig. 4), which is attributed predominantly to the photoinduced orientation effects. After this decrease, photodegradation in the direction perpendicular to the pump polarization dominates and therefore the transmission increases. Compared to curve b, the fast decrease of the transmission from C to D in curve a is due to the fact that the concentration of the azo dye trans isomers with their orientation parallel to the p? pump polarization is higher due to the prior pk pump excitation. We have reported on the experimental investigation of PIB in thin films fabricated by electrostatic sequential adsorption of CRP films. The formation of this large birefringence is attributed to the polarization-selective photodegradation of the azo dyes within the matrix of the polyelectrolyte. The investigations on photoinduced absorption change, dichroism, Raman and infrared spectra support the conclusion. Photoinduced alignment of azobenzene chromophores results in only a small contribution to the birefringence. The molecular structural details of the polarization-dependent PDAC matrix controlled photodegradation of CR are not completely clear at the present time. Further investigation of the photochemical reaction is necessary in order to thoroughly understand the mechanism involved in the polarization-selective photodegradation process. Nevertheless, we have successfully recorded holographic gratings based on this unusual PIB effect. A diffraction efficiency of 9 % in the first order was obtained with just a 1.3 mm thick film. The recorded birefringent gratings were stable and did not exhibit any long-term decay. We also observed that heating does not remarkably change the diffraction of the recorded grating on the film up to ~290.0 C. Above this temperature, discoloration and loss of materials from the film surface is observed. With azo dye‐containing polymers where photoinduced pure orientation effects play a major role similar or even better refractive index modulations in special cases and stability while maintaining reversibility have been achieved. Given the stable (including thermal stability) PIB exhibited by the electrostatic self-assembly CRP films, the assembled dye‐molecular composite films are especially suited to irreversible applications, such as long-term optical data storage, light-weight diffractive optical elements, and low-cost phase retarders at red or near infrared wavelength.

This research was supported by the Universita di Padova, Italy(grant numbers PRAT-CPDA123307 and CPDA153122, Attrezza-ture Scientifiche Finalizzate Alla Ricerca 2014) and the ItalianMinistero dell'Universita e della Ricerca (MIUR) (PRIN-2010-112010CX2TLM_002, E. B. fellowship). This work was carried outwithib the framework of the COST Action CM1205, CatalyticRoutines for Small Molecules Activation (CARISMA). The SpanishDireccion General de Investigacion (BeWell Grant numberCTQ2013-40480-R) and L'Agencia de G estio d'Ajuts Universitarisi de Recerca (AGAUR) (grant number 2014-SGR-17) are also ac-knowledged. CIBER-BBN is an initiative funded by the VI Na-tional R&D&i Plan 2008–2011, Iniciativa Ingenio 2010, Consol-ider Program, CIBER Actions and financed by the Instituto deSalud Carlos III with assistance from the European Regional De-velopment Fund.

A domino process is described combining an ene reaction between two alkynes and a Diels—Alder cycloaddition of the vinylallene formed.