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M Angeles Herranz

Publications and source records attributed to M Angeles Herranz.

11 recordsLinked to original sources
PubMed2006

Self-assembly of C(60) pi-extended tetrathiafulvalene (exTTF) dyads on gold surfaces.

The first self-assembly of a C60 pi-extended tetrathiafulvalene (exTTF) dyad on a gold surface is reported. Four fullerene derivatives, two of them containing p-quinonoid pi-extended tetrathiafulvalenes (exTTFs), have been synthesized, and their solution electrochemistry has been investigated by means of cyclic voltammetry. Fullerene-containing SAMs of thioctic acid derivatives 3 and 6 have also been investigated by cyclic voltammetry. The cyclic voltammograms of both compounds exhibit three reversible reduction waves, and for compound 6, one irreversible oxidation process corresponding to the oxidation of the exTTF subunit is observed. Stable self-assembled monolayers (SAMs) of fullerene derivative 3 were formed on gold surfaces, whereas dyad 6 does not present a very clear electrochemical response, most probably as a result of structural rearrangements on the monolayer or charge transfer between the C60 and exTTF moieties.

Electrochemistry↗
PubMed2005

The first fulleropyrrolidine derivative of Sc3N@C80: pronounced chemical shift differences of the geminal protons on the pyrrolidine ring.

The first pyrrolidine adduct on Sc(3)N@C(80) was synthesized and fully characterized. Addition of the N-ethylazomethine ylide occurs regioselectively on a [5,6] double bond on the surface of the icosahedral symmetry Sc(3)N@C(80), exactly in the same position as that described previously for a Diels-Alder adduct of the same compound.(11a,b) This addition pattern results in symmetric pyrrolidine carbons and unsymmetric geminal hydrogens on the pyrrolidine ring, as confirmed by (1)H and (13)C NMR spectroscopy, especially by HMQC. The shielding environment experienced by these geminal hydrogens differs by 1.26 ppm, indicative of pronounced ring current effects on the surface of this endohedral fullerene. This represents the first fully characterized pyrrolidine adduct on an endohedral metallofullerene.

Journal Article↗
PubMed2004

[60]fullerene-stoppered porphyrinorotaxanes: pronounced elongation of charge-separated-state lifetimes.

A series of Sauvage-type porphyrinorotaxanes containing [60]fullerene stoppers have been synthesized by a convergent route. Photoinduced energy transfer and electron-transfer reactions in these rotaxanes yield long-distance charge-separated radical-pair states, whose lifetimes in solution at ambient temperatures are as high as 32 mus, depending on the distance between the fullerene and zinc porphyrin chromophores.

Journal Article↗
PubMed2004

Convergent synthesis and photophysics of [60]fullerene/porphyrin-based rotaxanes.

A series of Sauvage-type rotaxanes containing [60]fullerene and tetraarylporphyrin moieties has been synthesized by a convergent route. Photoinduced energy-transfer and electron-transfer reactions in these rotaxanes yield long-lived change-separated states, in agreement with the large distance between the fullerene and porphyrin chromophores.

Journal Article↗
PubMed2004

The first fullerene-heterofullerene dyad.

The highly regioselective attack of a C(60) malonate containing a terminal acetyl function to the heterofullerene cage C(59)N leads to the formation of the first fullerene-heterofullerene dyad, representing a new scaffold for directional energy transduction.

Journal Article↗
PubMed2003

Synthesis, electrochemistry and self-assembled monolayers of novel tetrathiafulvalene (TTF) and pi-extended TTF (exTTF) disulfides.

The synthesis of a new series of tetrathiafulvalene (TTF) and pi-extended TTF (exTTF) disulfides and the electrochemical properties of self-assembled monolayers derived from these compounds are described. When the intermediate bromides 3 and 7 were reacted with thiourea, followed by basic hydrolysis, the expected thiol formation was not observed and only disulfides were obtained. A mechanism is proposed to explain the self-oxidation process of these compounds. For the first time SAMs of exTTF derivatives were prepared. Electrochemical data for SAMs of 6 and 8 reveal a single two-electron chemically reversible oxidation process to form a dicationic state, typical of the exTTF system. The SAMs are stable over extended periods of time and show electrochemical stability upon repeated potential scans.

Journal Article↗
PubMed2003

Evidence for the formation of singly bonded dimers during the reductive electrochemistry of methanofullerenes.

Four methanofullerene derivatives, with phosphonate or sulfone groups attached to a C(60) core through a Bingel procedure, were synthesized to probe their stability upon electrolytic reduction. Derivatives 1 and 2 are the most stable upon electroreduction and do not exhibit retro-cyclopropanation reactions until more than three electrons per C(60) derivative are transferred. The cyclopropane ring is then removed and C(60)(>CH(2))(n) (n=1-3) products result from reactions of the trianion of C(60) with the solvent, CH(2)Cl(2). The situation with diphosphonate 3 or phosphonatecarboxylate 4 is dramatically different. For 3, quantitative retro-cyclopropanation occurs when 2.8 e(-) per molecule are transferred. In the case of 4, when more than two electrons per molecule are transferred, there is evidence of the reversible formation of a very stable intermediate, which is oxidized at a potential 500 mV more positive than the first fullerene-based reduction of the parent compound. Electrolysis of a simple C(70)-Bingel monoadduct (5) also exhibits the formation of a similar intermediate. On the basis of cyclic voltammetry, ESR spectroscopy, and MALDI analysis of products, the intermediate observed during the electrolysis of compounds 4 and 5 is assigned to a dimeric structure.

Journal Article↗
PubMed2003

Probing charge separation in structurally different C60/exTTF ensembles.

The scope of the present work is to highlight the effects stemming from different C60/exTTF linkages (exTTF = 9,10-bis(1,3-dithiol-2-ylidene)-9,10-dihydroanthracene)-either via an anthracene unit or a dithiole ring. Particular emphasis is placed on photoinduced electron-transfer features. Therefore, we devised a new series of C60-exTTF ensembles, synthesized via 1,3-dipolar cycloaddition and Diels-Alder cycloaddition reactions, in which exTTF units are separated from C60 by two single bonds (3a-c, 4), one vinylene unit (5a), or two vinylene units (5b). The cyclic voltammetry reveals an amphoteric redox behavior with remarkably strong electron-donor ability of the trimethyl-substituted exTTF moiety in 4 and 5a,b. Steady-state and time-resolved photolytic techniques show that the fullerene singlet excited state in (3a-c, 4, and 5a,b) is subject to a rapid electron-transfer quenching. The resulting charge-separated states, that is C60*(-)-exTTF*+, were identified by transient absorption spectroscopy. We determined radical pair lifetimes of the order of 200 ns in benzonitrile. This suggests (i) that the positive charge of the exTTF*+ is delocalized over the entire donor rather than localized on one of the 1,3-dithiole rings and (ii) that linking exTTF via the anthracene or 1,3-dithiole ring has no appreciable influence. Increasing the donor-acceptor separation via implementing one or two vinylene units as spacers led to improved radical pair lifetimes (5a: tau = 725 ns; 5b: tau = 1465 ns).

Journal Article↗
PubMed2003

Retrocyclopropanation reactions of fullerenes: complete product analyses.

Mono- and bis-pyrene malonates 1 and 2 were synthesized and reacted with C(60) to prepare the corresponding Bingel adducts 3 and 4. These compounds were characterized electrochemically and exhibited the well-established retrocyclopropanation reaction when subjected to bulk electrolytic reductions. For the first time, it was possible to perform detailed product analyses after the retrocyclopropanation reactions, and these showed the presence of the original malonates 1 and 2 along with C(60), in reasonable yields, around 50%.

Journal Article↗