International audienceThe synthesis of the 3Gc0T zero generation dendrimer with a cyclotriphosphazene core functionalized with nitroxyl radicals in its six branches has been performed. The radical units have been used as probes to... more
International audienceThe synthesis of the 3Gc0T zero generation dendrimer with a cyclotriphosphazene core functionalized with nitroxyl radicals in its six branches has been performed. The radical units have been used as probes to determine the orientation of the six branches in solution experimentally by Electron Paramagnetic Resonance (EPR) spectroscopy compared with the structure obtained in the solid state by X-ray diffraction. The orientation of the dendrimer branches is the same in solution as in the solid state
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An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely... more
An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely... more
An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
The search for new biomedical applications of dendrimers has promoted the synthesis of new radical-based molecules. Specifically, obtaining radical dendrimers has opened the door to their use in various fields such as magnetic resonance... more
The search for new biomedical applications of dendrimers has promoted the synthesis of new radical-based molecules. Specifically, obtaining radical dendrimers has opened the door to their use in various fields such as magnetic resonance imaging, as anti-tumor or antioxidant agents, or the possibility of developing new types of devices based on the paramagnetic properties of organic radicals. Herein, we present a mini review of radical dendrimers based on polyphosphorhydrazone, a new type of macromolecule with which, thanks to their versatility, new metal-free contrast agents are being obtained, among other possible applications.
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Two generations of phosphorous 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... more
Two generations of phosphorous 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.
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A novel mixed biradical polarizing agent (BDPAesterTEMPO) showing one of the largest NMR signal enhancements to be observed so far in fast dissolution Dynamic Nuclear Polarization (dDNP).
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Charge transfer/transport in molecular wires over varying distances is a subject of great interest. The feasible transport mechanisms have been generally accounted for on the basis of tunneling or superexchange charge transfer operating... more
Charge transfer/transport in molecular wires over varying distances is a subject of great interest. The feasible transport mechanisms have been generally accounted for on the basis of tunneling or superexchange charge transfer operating over small distances which progressively gives way to hopping transport over larger distances. The underlying molecular sequential steps that likely take place during hopping and the operative mechanism occurring at intermediate distances have received much less attention given the difficulty in assessing detailed molecular-level information. We describe here the operating mechanisms for unimolecular electron transfer/transport in the ground state of radical-anion mixed-valence derivatives occurring between their terminal perchlorotriphenylmethyl/ide groups through thiophene-vinylene oligomers that act as conjugated wires of increasing length up to 53 Å. The unique finding here is that the net transport of the electron in the larger molecular wires i...
Research Interests: Biochemistry, Evolutionary Biology, Genetics, Biophysics, Chemistry, and 15 moreQuantum Chemistry, Molecular Biology, Computational Biology, Biotechnology, Raman Spectroscopy, UV, Chemical Physics, Medicine, Chemical Kinetics, Electron, Electron Transport, CHEMICAL SCIENCES, Quantum Tunnelling, Charge transfer, and Superexchange
Invited for the cover of this issue is the group of Giulia Licini at Università di Padova, Italy, in collaboration with the NANOMOL research group at the Institute of Materials Science of Barcelona, Spain. The cover image shows the change... more
Invited for the cover of this issue is the group of Giulia Licini at Università di Padova, Italy, in collaboration with the NANOMOL research group at the Institute of Materials Science of Barcelona, Spain. The cover image shows the change in geometry of an amino triphenolate vanadium(V) complex, which is detected by EPR spectroscopy.
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Hetero-bimetallic paddlewheel clusters in coordination polymers are formed through a water-induced single-crystal to single-crystal transformation.
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Research Interests: Engineering, Biochemistry, Biophysics, Chemistry, Inorganic Chemistry, and 15 moreBiotechnology, Nanoparticle, Ecology, Cell Biology, Medicine, Gold Nanoparticles, Electron, CHEMICAL SCIENCES, Ferromagnetism, American Chemical Society, Antiferromagnetic Interactions, EdX, Antiferromagnetism, Electron Paramagnetic Resonance, and Magnetic interactions
The diradical acceptor-donor-acceptor triad 1(••), based on two polychlorotriphenylmethyl (PTM) radicals connected through a tetrathiafulvalene(TTF)-vinylene bridge, has been synthesized. The generation of the mixed-valence radical anion,... more
The diradical acceptor-donor-acceptor triad 1(••), based on two polychlorotriphenylmethyl (PTM) radicals connected through a tetrathiafulvalene(TTF)-vinylene bridge, has been synthesized. The generation of the mixed-valence radical anion, 1(•-), and triradical cation species, 1(•••+), obtained upon electrochemical reduction and oxidation, respectively, was monitored by optical and ESR spectroscopy. Interestingly, the modification of electron delocalization and magnetic coupling was observed when the charged species were generated and the changes have been rationalized by theoretical calculations.
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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)... more
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 allow...
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A novel triradical compound with a P=S core and three branches functionalized with 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO) radicals is synthesized and characterized by IR, 1H NMR, 31P NMR, and EPR spectroscopy and MALDI‐TOF mass... more
A novel triradical compound with a P=S core and three branches functionalized with 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO) radicals is synthesized and characterized by IR, 1H NMR, 31P NMR, and EPR spectroscopy and MALDI‐TOF mass spectrometry, and its chemical structure is confirmed by X‐ray diffraction analysis. The triradical shows neither spin exchange interactions between its radical units nor detectable dipolar interactions. This is consistent with the separation between the radical units found in its X‐ray diffraction structure, and discounts the existence of intramolecular interactions. This conclusion is confirmed by an EPR concentration study. The concentration at which intermolecular interactions start to appear is determined (5×10−3 m) and this concentration should be taken into account as a higher concentration limit when studies on intramolecular radical–radical interactions in polyradicals with similar structure are required. SQUID magnetometry analysis of the comp...
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... Corresponding authors: e-mail aida@fa.upc.edu, nuria@fa.upc.edu, Phone: 0034 93 401 68 80, Fax: 0034 93 401 60 90 Studies of electron spin resonance (ESR) are reported on several types of single-walled carbon nanotubes (SWCNTs)... more
... Corresponding authors: e-mail aida@fa.upc.edu, nuria@fa.upc.edu, Phone: 0034 93 401 68 80, Fax: 0034 93 401 60 90 Studies of electron spin resonance (ESR) are reported on several types of single-walled carbon nanotubes (SWCNTs) synthe-sized by different methods. ...
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Bistable molecules that behave as switches in solution have long been known. Systems that can be reversibly converted between two stable states that differ in their physical properties are particularly attractive in the development of... more
Bistable molecules that behave as switches in solution have long been known. Systems that can be reversibly converted between two stable states that differ in their physical properties are particularly attractive in the development of memory devices when immobilized in substrates. Here, we report a highly robust surface-confined switch based on an electroactive, persistent organic radical immobilized on indium tin oxide substrates that can be electrochemically and reversibly converted to the anion form. This molecular bistable system behaves as an extremely robust redox switch in which an electrical input is transduced into optical as well as magnetic outputs under ambient conditions. The fact that this molecular surface switch, operating at very low voltages, can be patterned and addressed locally, and also has exceptionally high long-term stability and excellent reversibility and reproducibility, makes it a very promising platform for non-volatile memory devices.
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Research Interests: Biochemistry, Physiology, Biophysics, Chemistry, Free Radicals, and 15 morePhotochemistry, Biotechnology, Medicine, Electron Transfer, Ct, CHEMICAL SCIENCES, Solutions, Solution, Charge transfer, Dimer, Heterocyclic compounds, Electron Paramagnetic Resonance, Molecular Structure, ESR, and Aggregation Phenomena
Radical anions 1(-•)-5(-•), showing different lengths and incorporating up to five p-phenylenevinylene (PPV) bridges between two polychlorinated triphenylmethyl units, have been prepared by chemical or electrochemical reductions from the... more
Radical anions 1(-•)-5(-•), showing different lengths and incorporating up to five p-phenylenevinylene (PPV) bridges between two polychlorinated triphenylmethyl units, have been prepared by chemical or electrochemical reductions from the corresponding diradicals 1-5 which were prepared using Wittig-Horner-type chemistry. Such radical anions enabled us to study, by means of UV-vis-NIR and variable-temperature electron spin resonance spectroscopies, the long-range intramolecular electron transfer (IET) phenomena in their ground states, probing the influence of increasing the lengths of the bridges without the need of using an external bias to promote IET. The temperature dependence of the IET rate constants of mixed-valence species 1(-•)-5(-•) revealed the presence of two different regimes at low and high temperatures in which the mechanisms of electron tunneling via superexchange and thermally activated hopping are competing. Both mechanisms occur to different extents, depending on t...
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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... more
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 th...
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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... more
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...
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A new compound (1) formed by two antiparallelly disposed tetracyano thienoquinoidal units has been synthesized and studied by electrochemistry, UV/Vis‐NIR, IR, EPR, and transient spectroscopy. Self‐assembly of1on a Au(111) surface has... more
A new compound (1) formed by two antiparallelly disposed tetracyano thienoquinoidal units has been synthesized and studied by electrochemistry, UV/Vis‐NIR, IR, EPR, and transient spectroscopy. Self‐assembly of1on a Au(111) surface has been investigated by scanning tunneling microscopy. Experiments have been rationalized by quantum chemical calculations.1exhibits a unique charge distribution in its anionic form, with a gradient of charge yielding a neat molecular in‐plane electric dipole momentum, which transforms out‐of‐plane after surface deposition due to twisted→folded conformational change and to partial charge transfer from Au(111). Intermolecular van der Waals interactions and antiparallel trapezoidal shape fitting lead to the formation of an optimal dense on Au(111) two‐dimensional assembly of1.
