| 1. |
- Gauden, Magdalena, et al.
(författare)
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Role of Solvent, pH, and Molecular Size in Excited-State Deactivation of Key Eumelanin Building Blocks: Implications for Melanin Pigment Photostability.
- 2008
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 130:50, s. 17038-17043
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Tidskriftsartikel (refereegranskat)abstract
- Ultrafast time-resolved fluorescence spectroscopy has been used to investigate the excited-state dynamics of the basic eumelanin building block 5,6-dihydroxyindole-2-carboxylic acid (DHICA), its acetylated, methylated, and carboxylic ester derivatives, and two oligomers, a dimer and a trimer in the O-acetylated forms. The results show that (1) excited-state decays are faster for the trimer relative to the monomer; (2) for parent DHICA, excited-state lifetimes are much shorter in aqueous acidic medium (380 ps) as compared to organic solvent (acetonitrile, 2.6 ns); and (3) variation of fluorescence spectra and excited-state dynamics can be understood as a result of excited-state intramolecular proton transfer (ESIPT). The dependence on the DHICA oligomer size of the excited-state deactivation and its ESIPT mechanism provides important insight into the photostability and the photoprotective function of eumelanin. Mechanistic analogies with the corresponding processes in DNA and other biomolecules are recognized.
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| 2. |
- Palermo, V., et al.
(författare)
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Influence of molecular order on the local work function of nanographene architectures : A Kelvin-probe force microscopy study
- 2005
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Ingår i: ChemPhysChem. - : Wiley. - 1439-4235 .- 1439-7641. ; 6:11, s. 2371-2375
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Tidskriftsartikel (refereegranskat)abstract
- We report a Kelvin-probe force microscopy (KPFM) investigation on the structural and electronic properties of different submicronscale supramolecular architectures of a synthetic nanographene, including extended layers, percolated networks and broken patterm grown from solutions at surfaces. This study made it possible to determine the local work function (WF) of the different p-conjugated nanostructures adsorbed on mica with a resolution below 10 nm and 0.05 eV. It revealed that the WF strongly depends on the local molecular order at the surface, in particular on the delocalization of electrons in the p-states, on the molecular orientation at surfaces, on the molecular packing density, on the presence of defects in the film and on the different conformations of the aliphatic peripheral chains that might cover the conjugated core. These results were confirmed by comparing the KPFM-estimated local WF of layers supported on mica, where the molecules are preferentially packed edge-on on the substrate, with the ultraviolet photoelectron spectroscopy microscopically measured WF of layers adsorbed on graphite, where the molecules should tend to assemble face-on at the surface. It appears that local WF studies are of paramount importance for understanding the electronic properties of active organic nanostructures, being therefore fundamental for the building of high-performance organic electronic devices, including field-effect transistors, light-emitting diodes and solar cells. © 2005 Wiley-VCH Verlag GmbH & Co. KGaA.
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| 3. |
- Tsao, H.N., et al.
(författare)
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From ambi- To unipolar behavior in discotic dye field-effect transistors
- 2008
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Ingår i: Advanced Materials. - : Wiley. - 0935-9648 .- 1521-4095. ; 20:14, s. 2715-2719
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Tidskriftsartikel (refereegranskat)abstract
- A study was conducted to demonstrate solution-processable ambipolar organic field-effect transistors based on a discotic dye. Such single component devices allow the study of the influence of supramolecular ordering on FET charge transport properties. These transistors exhibited ambipolarity even without any structural order. The absence of p-type behavior could not be explained by the increase of hole injection barrier or by interface trapping. It was rather observed that the change in morphology most probably lead to such a phenomenon. These findings further suggest that besides charge injection barriers and interface trapping, structural composition, that is, microscopic domain boundaries together with local defects in one-dimensional columnar systems, also trigger the loss of ambipolarity owing to lowering of the minority charge carrier mobility.
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| 4. |
- Zhi, L., et al.
(författare)
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Solid-state pyrolyses of metal phthalocyanines : A simple approach towards nitrogen-doped CNTs and metal/carbon nanocables
- 2005
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Ingår i: Small. - : Wiley. - 1613-6810 .- 1613-6829. ; 1:8-9, s. 798-801
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Tidskriftsartikel (refereegranskat)abstract
- Solid-state pyrolysis of organometallic precursors has emerged as an alternative method for preparing carbon nanostructures such as carbon nanotubes (CNT) and carbon anions. The morphology of the tubes can be controlled by the nature of the precursors and the pyrolysis procedures, and micrometer long nanotubes, composed of metal carbide wires encased in a graphitic sheath. Cobalt phthalocyanine (CoPc) as well as iron phthalocyanine were pyrolyzed at different temperatures to obtain CNTs. HRTEM and energy-dispersion X-Ray analysis disclosed that the core consisted of long, iron-containing single crystals and that the core was fully surrounded by crystallized graphic carbon. Iron-filled carbon nanotubes were also obtained from the pyrolysis of ferrocene by CVD method. Encapsulated iron carbide were also observed inside the carbon nanotubes formed after pyrolysis of FePc. These nanotubes and nanocables were considered useful for assembling miniaturized electronic device and sensors.
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