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Herein, we report the synthesis and the study of a novel mixed biradical with BDPA and TEMPO radical units that are covalently bound by an ester group (BDPAesterTEMPO) as a polarizing agent for fast dissolution DNP. The biradical exhibits an extremely high DNP NMR enhancement of >50[thin space (1/6-em)]000 times, which constitutes one of the largest signal enhancements observed so far, to the best of our knowledge.

Herein we report a water-induced single-crystal to single-crystal transformation that involves the formation of hetero-bimetallic paddlewheel clusters in coordination polymers. Through this transformation, which involves the cleavage and formation of different coordination bonds, two different Cu(II)-Zn(II) and Cu(II)-Ni(II) paddle-wheel units exhibiting a 1 : 1 metal ratio were created.

(DT-TTF)[Cu(dcdmp)(2)] (1), (DT-TTF)(2)[Cu(dcdmp)(2)] (2), and (DT-TTF)(3)[Cu(dcdmp)(2)](2) (3) are three new charge transfer salts obtained by electrocrystallization of the donor DT-TTF (dithiophene-tetrathiafulvalene) with the diamagnetic copper complex [Cu(dcdmp)(2)](-) (dcdmp = 2,3-dicyano-5,6-dimercaptopyrazine). Compounds 1 and 3 crystallize in the triclinic system and consist of out-of-registry layers of mixed stacks of donor and acceptor molecules. (DT-TTF)(2)[Cu(dcdmp)(2)] presents a structure similar to the parent spin-ladder systems with donor stacks arranged in pairs; however, a magnetic spin-ladder behavior is not observed probably due to strong interactions between pairs. Compound 3, despite the mixed nature of the stacks, displays relatively high conductivity (7 S/cm) due to a one-dimensional network of interactions between donors.

The synthesis of two novel BDPA-like radicals, a benzyl amino (BAm-BDPA, 7) and a cyano (CN-BDPA, 5) derivative, is reported and their behaviour as polarizing agents for fast dissolution Dynamic Nuclear Polarization (DNP) is evaluated. The radical 7 is a promising candidate for DNP studies since it is soluble in neat [1-13C]pyruvic acid (PA), and therefore the use of an additional glassing agent for sample homogeneity is avoided. In addition, a 60 mM sample of 7 offers optimum 13C NMR signal enhancements using fairly short polarization times (about 1800 s). It is shown that DNP-NMR measurements using 7 can be performed much more efficiently in terms of the signal enhancement per polarization build-up time unit than when using the reference OX63 or BDPA radicals. These enhanced features are translated to a substantial reduction of polarization times that represents an optimum temporary use of the DNP polarizer and allow economized liquid helium consumption.

A study of the magnetic and electrochemical properties of a TEMPO-substituted disulfide diradical in three different environments was carried out: in solution, in the crystal, and as a self-assembled monolayer (SAM) on an Au(111) substrate, and the relationship between them was explored. In solution, this flexible diradical shows a strong spin-exchange interaction between the two nitroxide functions that depends on the temperature and solvent. Structural, dynamic, and thermodynamic information has been extracted from the EPR spectra of this dinitroxide. The magnetic interactions in the crystal include intra- and intermolecular contributions, which have been studied separately and shown to be antiferromagnetic in both cases. Finally, we demonstrate that both the magnetic and electrochemical properties are preserved upon chemisorption of the diradical on a gold surface. The resulting SAM displayed anisotropic magnetic properties, and angle-resolved EPR spectra of the monocrystal allowed a rough determination of the orientation of the molecules in the SAM.

© The Royal Society of Chemistry 2015. The synthesis, structural characterization and the successful application of a carbon centered radical derived from 1,3-bisdiphenylene-2-phenylallyl (BDPA), its benzyl alcohol derivative (BA-BDPA), as a polarizing agent for Dynamic Nuclear Polarization (DNP) are described. The reported BA-BDPA radical meets all the requirements to become a promising candidate for its use in in vivo DNP-NMR experiments: it is soluble in neat [1-13C]pyruvic acid, insoluble in the dissolution transfer solvent and is effective as a polarizing agent in fast dissolution DNP-NMR applications, without the need for using glassing agents. Moreover, it enables a simple but effective in-line radical filtration to obtain hyperpolarized solutions of [1-13C]pyruvic acid free of radicals that offers a better polarization performance. This journal is

© 2014 American Chemical Society. The synthesis and characterization of a novel trityl-TEMPO biradical and the investigation of its properties as Dynamic Nuclear Polarization (DNP) polarizing agent are reported. Comparison with a structurally related monoradical (PTM-TEMPE) or mixtures of the two monoradical components reveals that the biradical has a much higher polarization efficiency and a faster polarization buildup. This o ffers the possibility of faster recycling further contributing to its efficiency as a polarizing agent. (Graph Presented).

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 presents a joint theoretical and experimental characterisation of the structural and electronic properties of two tetrathiafulvalene (TTF)-based acceptor-donor-acceptor triads (BQ-TTF-BQ and BTCNQ-TTF - BTCNQ; BQ is naphthoquinone and BTCNQ is benzotetracyano-p-quinodimethane) in their neutral and reduced states. The study is performed with the use of electrochemical, electron paramagnetic resonance (EPR), and UV/Vis/NIR spectroelectrochemical techniques guided by quantum-chemical calculations. Emphasis is placed on the mixed-valence properties of both triads in their radical anion states. The electrochemical and EPR results reveal that both BQ-TTF-BQ and BTCNQ-TTF-BTCNQ triads in their radical anion states behave as class-II mixed-valence compounds with significant electronic communication between the acceptor moieties. Density functional theory calculations (BLYP35/cc-pVTZ), taking into account the solvent effects, predict charge-localised species (BQ.--TTF-BQ and BTCNQ.--TTF-BTCNQ) as the most stable structures for the radical anion states of both triads. A stronger localisation is found both experimentally and theoretically for the BTCNQ-TTF-BTCNQ anion, in accordance with the more electron-withdrawing character of the BTCNQ acceptor. CASSCF/CASPT2 calculations suggest that the low-energy, broad absorption bands observed experimentally for the BQ-TTF-BQ and BTCNQ-TTF-BTCNQ radical anions are associated with the intervalence charge transfer (IV-CT) electronic transition and two nearby donor-to-acceptor CT excitations. The study highlights the molecular efficiency of the electron-donor TTF unit as a molecular wire connecting two acceptor redox centres. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Consultable des del TDX, Títol obtingut de la portada digitalitzada, Esta Tesis está enmarcada en el emergente campo de investigación denominado electrónica molecular, que se puede definir como el estudio de procesos electrónicos medidos o controlados a escala molecular. La utilización de moléculas en circuitos electrónicos de tamaño nanoscópico representa el mayor grado de miniaturización posible, con las ventajas que ello conlleva como mayor velocidad de operación o bajo coste de fabricación. Actualmente se han realizado grandes avances en la síntesis, caracterización y ensamblaje de moléculas y existen a escala molecular: rectificadores, puertas lógicas electrónicamente configurables, dispositivos NDR (negative differential resistance), transistores de efecto de campo FET, interruptores, memorias, etc. Ahora bien, uno de los requisitos para usar cualquier componente electrónico molecular es la capacidad de unirlo o integrarlo en la estructura de un dispositivo electrónico. Para conectar una molécula a otra, son necesarios los cables o hilos de escala molecular. Es decir, no cualquier molécula con una función útil se puede considerar automáticamente como un dispositivo electrónico, sino que ha de existir una vía para interaccionar con otros componentes; de ahí la importancia de los hilos moleculares. En esta Tesis se han estudiado las propiedades conductoras de diversos compuestos moleculares orgánicos para definir su comportamiento como hilos moleculares. Un método o aproximación para estudiar el transporte de electrones a través de un hilo molecular consiste en utilizar el hilo molecular como puente de unión entre un sistema dador y otro aceptor de electrones, de manera que pueda darse una Transferencia Electrónica Intramolecular (TEI) entre ambos (transferencia de un electrón de un extremo a otro de la misma molécula). Así, se han estudiado diversos compuestos utilizando para ello especies de valencia mixta (sistemas con dos centros redox con valencia formal distinta que se encuentran unidos covalentemente a una estructura puent, The work described in this Thesis is related to the area of molecular electronics, which can be defined as the study of electrical and electronic processes measured or controlled on a molecular scale. Using molecules in nanoscopic electronic circuits means the highest degree of miniaturization is achieved so that a shorter time of data processing can be reached. Nowadays some electronic components exist at the molecular scale such as rectifiers, negative differential resistance (NDR), field effect transistors (FET), switches, memory devices, etc. However, one of the requirements to using any molecular electronic component is the ability to wire it into a device architecture. To connect molecules to one another, molecular-scale wires are necessary. Therefore, describing a molecule doing some useful function does not automatically make it a molecular electronic device-there must be a way to interact with other components. Thus it is important to consider how a molecular electronic device can be wired into a circuit. In this Thesis the conducting properties of different organic molecular compounds have been studied in order to define their behaviour as molecular wires. An approach to study the electron transport through a molecular wire consists of using the molecular wire as a bridging unit between electron donor and acceptor moieties, in order to induce an Intramolecular Electron Transfer between both moieties. Different compounds have been studied using mixed valence species (systems containing two redox centres with different formal valences covalently bridged to a bridge structure or molecular wire). The molecules that have been studied as molecular wires are: tetrathiafulvalene (TTF), 1-5(p-phenylenevinylene) and some aza-derived compounds, as well as these: 1,4-benzoquinone, perchlorotriphenylmethyl radical (PTM) and ferrocene, respectively have been utilised as redox centres. All the formed mixed valence species show an Intramolecular Electron Transfer phenomen