1,720,997 research outputs found
Fullerene pyrazine dyads: Intramolecular energy transfer route to the fullerene moiety
No full textTorres-Garcia G, Guldi DM, Mattay J. Fullerene pyrazine dyads: Intramolecular energy transfer route to the fullerene moiety. JOURNAL OF INFORMATION RECORDING. 2000;25(3-4):273-279.A synthetic route to 1,4-diazine-fused [60]fullerenes has been developed based on the Diels-Alder reaction of 2,3-bis(trimethylsiloxy)butadiene and [60]fullerene followed by oxidation to the corresponding 1,2-diketone and condensation with 1,2-diamines. These bichromophoric compounds promote the UV/Vis absorption and act as light-harvesting systems involving energy transfer from the pyrazine chromophor to the fullerene unit. A detailed investigation of the photophysical steps will be presented which finally lead to fullerene triplet states
Organic functionalization and optical properties of carbon onions
No full textHere we report, for the first time, a method for chemically
functionalizing onions from arc discharge soots. The new methodology not only allows the isolation of giant fullerenes, but especially renders them soluble in organic solvents, such that their solution properties can be studied for the first time
Molecular wires – long-range electron tunneling and hopping in novel donor-acceptor ensambles
No full textA Three-Level Luminescent Response in a Pyrene/Ferrocene Rotaxane
No full textA solvent switchable rotaxane equipped with a pyrene stopper and with two ferrocenyl units on the macrocycle is reported, in which three different states, two nondegenerate and one degenerate, can be obtained in different solvents at room temperature. This is accompanied by high contrast changes in fluorescence intensity of the pyrene stopper by the presence of the ferrocenyl moieties on the macrocycle, which quench the emission of pyrene more efficiently with proximity
Synthesis and photophysical investigation of new porphyrin derivatives with beta-pyrrole ethynyl linkage and corresponding dyad with [60] fullerene
Full text linkTwo new beta-substituted arylethynyl meso-tetraphenylporphyrins, 2-[(4'-formyl) phenyl] ethynyl-5,10,15,20-tetraphenylporphyrin ( system A) and 2-[(4'-methyl) phenyl] ethynyl-5,10,15,20-tetraphenylporphyrin ( system B) and their zinc derivatives were synthesized by palladium catalysis, using a synthetic approach that affords high yields of the target systems. Comparative ultraviolet-visible (UV-vis), NMR, and cyclic voltammetry studies of such macrocycles reveal the presence of an extensive conjugation between the tetrapyrrolic ring and the linker, through pi-pi orbital interaction. This interaction was observed in the form of a "push-pull" effect that moves the electronic charge between the porphyrin and the aldehyde group of system A. System B, bearing a methyl group instead of the formyl group, was synthesized in order to evaluate the effect of the substitution on the charge delocalization, which is necessary to corroborate the push-pull mechanism hypothesis. The new porphyrin, system A, was also used as a starting material for the synthesis of new porphyrin-fullerene dyads in which the [60] fullerene is directly linked to the tetrapyrrolic rings by ethynylenephenylene subunits. Fluorescence and transient absorption measurements of the new dyads reveal that ultrafast energy and electron transfer occur, respectively, in nonpolar and polar solvents, with high values of the rate constant. The UV-vis, NMR, and cyclic voltammetry results show that it is possible for both energy and electron transfer between porphyrin and fullerene to take place through the pi-bond interaction. Such results evidence that the coupling between the donor and acceptor moieties is strong enough for possible photovoltaic applications
Mimicking Photosynthesis: Covalent And Supramolecular [60]Fullerene Based Donor-Acceptor Ensembles
No full textIntramolecular energy transfer in fullerene pyrazine dyads
No full textGuldi DM, Torres-Garcia G, Mattay J. Intramolecular energy transfer in fullerene pyrazine dyads. The Journal of Physical Chemistry A. 1998;102(48):9679-9685.Excited-state properties of three different pyrazine derivatives 4-6 were probed by emission and transient absorption spectroscopy. They display emission maxima at 464 (4), 417 (5), and 515 nm (6) that are redshifted with respect to their strong UV ground-state absorption and formed with overall quantum yields (Phi) of 0.156, 0.22, and 0.13, respectively. Once photoexcited, these triplet excited pyrazines undergo rapid intermolecular energy transfer to a monofunctionalized fullerene derivative (7) with bimolecular rate constants ranging from 3.64 x 10(9) M-1 s(-1) (6) to 1.1 x 10(10) M-1 s(-1) (4). The product of these bimolecular energy-transfer reactions is in all cases the fullerene triplet excited state. Functionalization of pristine C-60 With the investigated pyrazine derivatives promotes the UV-vis absorption characteristics and, in turn, improves the light-harvesting efficiency of the resulting dyads 1-3 relative to pristine C-60. Photoexcitation of the pyrazine moieties in dyads 1-3 leads to the formation of their singlet excited states. In contrast to the pyrazine models, photoexcitation of dyad 1-3 is followed by rapid intramolecular deactivation processes of the latter via energy transfer to the fullerene ground state with half-lives between 37 and 100 ps. In turn, energy transfer transforms the short-lived and moderately redox-active singlet excited states of pyrazine into the highly reactive fullerene triplet excited state. The latter is found to produce effectively singlet oxygen (O-1(2)) with quenching rate constants for 1-3 of (1-1.5) x 10(9) M-1 s(-1). Similarly, reductive quenching of the triplet excited states in dyads 1-3 via electron transfer with diazabicyclooctane (DABCO) occurs with rate constants of (5.2-9.4) x 10(7) M-1 s(-1)
Supramolecular hybrids of [60]fullerene and single-wall carbon nanotubes
No full textNoncovalent interactions between purified HiPCO single-wall carbon nanotubes (SWNT) and a [60]fullerene–pyrene dyad, synthesized through a regioselective double-cyclopropanation process, produce stable suspensions in which the tubes are very well dispersed, as evidenced by microscopy characterization. Cyclic voltammetry experiments and photophysical characterization of the suspensions in organic solvents are all indicative of sizeable interactions of the pyrene moiety with the SWNT and, therefore, of the prevalence in solution of [60]fullerene–pyrene⋅SWNT hybrids
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