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Dirk M Guldi

Publications and source records attributed to Dirk M Guldi.

At least 55 records · Page 3Linked to original sources
PubMed2005

C(60)-exTTF-C(60) Dumbbells: cooperative effects stemming from two C(60)s on the radical ion pair stabilization.

[structure: see text] The presence of a second C(60) cage in C(60)-exTTF-C(60) triads [exTTF = 9,10-bis(1,3-dithiol-2-ylidene)-9,10-anthraquinone] has beneficial effects on the stabilization of the radical ion pair formed upon irradiation in comparison with the related C(60)-exTTF dyad. Although C(60)-exTTF-C(60) ensembles show no electronic interaction between the electroactive units in the ground state, their irradiation leads to C(60)(*)(-)-exTTF(*)(+)-C(60) species with lifetimes on the order of 600 ns in benzonitrile; these lifetimes are twice those determined for the analogous C(60)-exTTF dyad.

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PubMed2005

Nanoscale organization of a phthalocyanine-fullerene system: remarkable stabilization of charges in photoactive 1-D nanotubules.

Induction of self-organization between zinc phthalocyanine (ZnPc) and C60 moieties in a novel amphiphilic ZnPc-C60 salt results in uniformly nanostructured 1-D nanotubules. Their photoreactivity, in terms of ultrafast charge separation (i.e., approximately 1012 s-1) and ultraslow charge recombination (i.e., approximately 103 s-1), is remarkable. In addition, the observed ZnPc*+-C60*- lifetime of 1.4 ms implies, relative to that of the monomeric ZnPc-C60 ( approximately 3 ns), an impressive stabilization of 6 orders of magnitude.

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PubMed2005

Spectroscopic studies on inclusion properties of fullerenocalix[4]arene conjugates with metal ions.

Metal-chelating properties-in the ground and excited states-of fullerenocalix[4]arenes containing two malonamide substituents at the upper rim and four alkyl ester chains at the lower rim have been studied by means of steady-state absorption, fluorescence spectroscopy, and time-resolved transient absorption spectra. In particular, the influence that Ag+ enforces on the fullerene electronic spectra is due to direct interactions between Ag+ and the surface of C60. The effects stemming from Na+, Mg2+, and Ba2+, on the other hand, are indirect and are introduced through chelating the metal ions to the calix[4]arene moiety. They strongly depend on the molecular structure of the fullerenocalix[4]arenes. No spectroscopic evidence was obtained for any influence caused by Mn2+, although the malonamide groups provide good chelating ability even for this transition metal ion.

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PubMed2005

Electronic communication through pi-conjugated wires in covalently linked porphyrin/C60 ensembles.

Novel photo- and electroactive triads, in which pi-conjugated p-phenylenevinylene oligomers (oPPVs) of different length are connected to a photoexcited-state electron donor (i.e., zinc tetraphenylporphyrin) and an electron acceptor (i.e., C(60)), were designed, synthesized, and tested as electron-transfer model systems. A detailed physicochemical investigation, concentrating mainly on long-range charge separation and charge recombination and kinetics, revealed small attenuation factors beta of 0.03+/-0.005 A(-1). Energy matching between the HOMO levels of C(60) and oPPVs emerged as a key parameter for supporting molecular-wire-like behavior: It favors rapid and efficient electron or hole injection into the oPPV wires. Large electronic coupling values were determined as a result of paraconjugation in the oPPV moieties.

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PubMed2005

Ordering fullerene materials at nanometer dimensions.

The combination of the hydrophobic fullerene core with hydrophilic functional groups of both ionic and nonionic nature produces organized structures with sizes that range from nanometer to micrometer length scales. The driving force toward this spontaneous organization is the amphiphilic character of the fullerene derivatives. To control both shape and size of the supramolecular assemblies and ultimately their function, important parameters that must be tuned are (i) the balance between the hydrophobic and the hydrophilic moieties, (ii) the effect of the environment, typically provided by simple solvents, (iii) the interface on which the aggregation occurs or, more precisely, surface templating effects, and (iv) the solvation process.

Air↗
PubMed2005

Carbon nanotubes in electron donor-acceptor nanocomposites.

This Account presents recent advances in the design, synthesis, characterization, and potential applications of new hybrid materials based on carbon nanotube and electron donors. Fast charge separation and slow charge recombination are consistently observed in a variety of composites that contain porphyrin derivatives. The ultimate goal of using these systems to prepare practical photoelectrochemical devices is discussed, and a cell with a monochromatic efficiency of 8.5% conversion of light into current is illustrated.

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PubMed2004

Materials for organic solar cells: the C60/pi-conjugated oligomer approach.

This tutorial review surveys recent advances in the field of C60/pi-conjugated oligomer donor-acceptor ensembles. In particular, different synthetic strategies are discussed that were developed to link pi-conjugated oligomers, as versatile photoexcited state electron donors, to C60. We highlight relationships between the nature/structural aspects of pi-conjugated donor systems and a variety of physico-chemical features. Modifications of the oligomeric components are discussed under aspects of tailoring (i) the absorption cross-section of the chromophore in the visible region, (ii) the oxidation potential of the oligomeric donor moiety, (iii) the size, shape, or chemical makeup of the oligomer, and (iv) the stabilization of the charge-separated radical ion pairs. In the final section, the applicability of selected materials for the fabrication of photovoltaic devices is analyzed.

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PubMed2004

Langmuir-Shäfer transfer of fullerenes and porphyrins: formation, deposition, and application of versatile films.

Thin films consisting of a fulleropyrrolidine derivative 1 and a novel water-soluble porphyrin 2 were prepared by the Langmuir-Shäfer (LS, horizontal lifting) method. In particular, a solution of 1 in chloroform and dimethyl sulfoxide was spread on the water surface, while porphyrin 2 (bearing peripheral anionic groups) was dissolved into the aqueous subphase. To the best of our knowledge, such a versatile method of film fabrication for fullerene/porphyrin mixed composite films has never been used before. Evidence of the effective interactions between the two moieties at the air-water interface was obtained from the analysis of the floating layers by means of surface pressure versus area per molecule Langmuir curves, Brewster angle microscopy and UV-visible reflection spectroscopy. The characterisation of the LS films by UV-visible spectroscopy reveals that the two constituents behave as discrete and weakly interacting pi systems. The use of polarised light suggests the existence of a preferential direction of the macrocyclic rings with an edge-on arrangement with respect to the substrate surface. Finally, photoaction spectra were recorded from films deposited by only one horizontal lifting onto indium-tin-oxide (ITO) electrodes and the observed photocurrent increased notably with increasing transfer surface pressure.

Fullerenes↗
PubMed2004

Versatile organic (fullerene)-inorganic (CdTe nanoparticle) nanoensembles.

Novel organic (positively charged fullerene)-inorganic (negatively charged CdTe nanoparticle) nanoensembles were devised through electrostatic interactions and probed as versatile donor-acceptor hybrids. Photoirradiation of their homogeneous solutions, containing the electrostatically packed components, let to very long-lived (1.3 ms) charge separated states.

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PubMed2004

Electrostatic interactions by design. Versatile methodology towards multifunctional assemblies/nanostructured electrodes.

This Feature Article describes how multi-site interactions between positively or negatively charged carbon forms, such as fullerenes and single wall carbon nanotubes, and porphyrinic chromophores have been utilized en route towards novel multifunctional and nanostructured materials. Specifically, we discuss (i) the behavior of molecular assemblies in homogeneous solutions and (ii) the controlled self-assembly on surfaces.

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PubMed2004

Unexpected change in charge transfer behavior in a cobalt(II) porphyrin-fullerene conjugate that stabilizes radical ion pair states.

Two cobalt(II) porphyrin-C(60) malonate-linked conjugates, the mono-connected Co1 and the bis-connected trans-2 isomer Co3, have been synthesized for the first time either by direct cyclopropanation with the precursor malonate Co4 or by metalation of the bisadduct H(2)3. For the investigation of the interaction between the porphyrin donor and fullerene acceptor within these dyads, electrochemical and photophysical investigations have been carried out. Compared to Zn3 and trans-2 bisadduct 7, the first reduction of the fullerene moiety within Co3 becomes easier (40 mV in dichloromethane and 20 mV in benzonitrile), indicating significant interactions between the pi-system of the fullerene and the d-orbitals of the central Co atom. Compared to the Co complexes 9, Co4, and Co1, the first oxidation of Co3 is considerably shifted to more positive potentials, if benzonitrile instead of dichloromethane is used as solvent. At the same time, the oxidation is no longer centered on the Co(II) center but on the porphyrin macrocycle, as corroborated by spectroelectrochemistry. A similar solvent dependence was observed in transient absorption spectroscopic measurements. In toluene, benzonitrile and anisole photoinduced electron transfer within Co3 leads to the formation of a charge-separated state Co(II)P.+ -C(60).- with a lifetime of 560 +/- 20 ns in benzonitrile, whereas in other solvents such as THF, nitrobenzene, ortho-diclorobenzene, and tert-butylbenzene the formation of a Co(III)P-C(60).- as transient was detected, which is, however, short-lived (860 +/- 40 ps in THF) and exhibits charge recombination dynamics that are in the Marcus inverted region. Particularly important is the fact that the electronic coupling (V) in Co(III)P-C(60).- is 18 cm(-1) substantially smaller than the V value of 313 cm(-1) in ZnP.+ -C(60).- .

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