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4. Quantitative resonant soft x-ray reflectivity from an organic semiconductor single crystal.

Author

Capelli, R., Da Como, E., Kociok-Köhn, G., Fontanesi, C., Verna, A., and Pasquali, L.

Subjects
SINGLE crystals, SOFT X rays, ORGANIC semiconductors
Abstract

Resonant soft X-ray reflectivity at the carbon K-edge was applied to a trigonal tetracene single crystal. The angular resolved reflectivity was quantitatively simulated describing the tetracene crystal in terms of its dielectric tensor, which was derived from the anisotropic absorption cross section of the single molecule, as calculated by density functional theory. A good agreement was found between the experimental and theoretically predicted reflectivity. This allows us to assess the anisotropic optical constants of the organic material, probed at the carbon K-edge, in relation to the bulk/surface structural and electronic properties of the crystal, through empty energy levels. [ABSTRACT FROM AUTHOR]

Published
2019
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13. Displacement of polarons by vibrational modes in doped conjugated polymers

Author

Anderson, M., primary, Ramanan, C., additional, Fontanesi, C., additional, Frick, A., additional, Surana, S., additional, Cheyns, D., additional, Furno, M., additional, Keller, T., additional, Allard, S., additional, Scherf, U., additional, Beljonne, D., additional, D’Avino, G., additional, von Hauff, E., additional, and Da Como, E., additional

Published
2017
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14. Control of electrons' spin eliminates hydrogen peroxide formation during water splitting

Author

Mtangi, W., Tassinari, F., Vankayala, K., Vargas Jentzsch, A., Adelizzi, B., Palmans, A.R.A., Fontanesi, C., Meijer, E.W., Naaman, R., Mtangi, W., Tassinari, F., Vankayala, K., Vargas Jentzsch, A., Adelizzi, B., Palmans, A.R.A., Fontanesi, C., Meijer, E.W., and Naaman, R.

Abstract

The production of hydrogen through water splitting in a photoelectrochemical cell suffers from an overpotential that limits the efficiencies. In addition, hydrogen-peroxide formation is identified as a competing process affecting the oxidative stability of photoelectrodes. We impose spin-selectivity by coating the anode with chiral organic semiconductors from helically aggregated dyes as sensitizers; Zn-porphyrins and triarylamines. Hydrogen peroxide formation is dramatically suppressed, while the overall current through the cell, correlating with the water splitting process, is enhanced. Evidence for a strong spin-selection in the chiral semiconductors is presented by magnetic conducting (mc-)AFM measurements, in which chiral and achiral Zn-porphyrins are compared. These findings contribute to our understanding of the underlying mechanism of spin selectivity in multiple electron-transfer reactions and pave the way toward better chiral dye-sensitized photoelectrochemical cells.

Published
2017

15. Displacement of polarons by vibrational modes in doped conjugated polymers

Author

Anderson, M., Ramanan, C., Fontanesi, C., Frick, A., Surana, S., Cheyns, D., Furno, M., Keller, T., Allard, S., Scherf, U., Beljonne, D., D'Avino, G., von Hauff, E., Da Como, E., Anderson, M., Ramanan, C., Fontanesi, C., Frick, A., Surana, S., Cheyns, D., Furno, M., Keller, T., Allard, S., Scherf, U., Beljonne, D., D'Avino, G., von Hauff, E., and Da Como, E.

Abstract

Organic pi-conjugated polymers are deemed to be soft materials with strong electron-phonon coupling, which results in the formation of polarons, i.e., charge carriers dressed by self-localized distortion of the nuclei. Universal signatures for polarons are optical resonances below the band gap and intense vibrational modes (IVMs), both found in the infrared (IR) spectral region. Here, we study p-doped conjugated homo-and copolymers by combining first-principles modelling and optical spectroscopy from the far-IR to the visible. Polaronic IVMs are found to feature absorption intensities comparable to purely electronic transitions and, most remarkably, show only loose resemblance to the Raman or IR-active modes of the neutral polymer. The IVM frequency is dramatically scaled down (up to 50%) compared to the backbone carbon-stretching modes in the pristine polymers. The very large intensity of IVMs is associated with displacement of the excess positive charge along the backbone driven by specific vibrational modes. We propose a quantitative picture for the identification of these polaron shifting modes that solely based on structural information, directly correlates with their IR intensity. This finding finally discloses the elusive microscopic mechanism behind the huge IR intensity of IVMs in doped polymeric semiconductors.

Published
2017
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16. An unforeseen polymorph of coronene by the application of magnetic fields during crystal growth

Author

Potticary, J., Terry, L.R., Bell, C., Papanikolopoulos, A.N., Christianen, P.C.M., Engelkamp, H., Collins, A.M., Fontanesi, C., Kociok-Kohn, G., Crampin, S., Da Como, E., Hall, S.R., Potticary, J., Terry, L.R., Bell, C., Papanikolopoulos, A.N., Christianen, P.C.M., Engelkamp, H., Collins, A.M., Fontanesi, C., Kociok-Kohn, G., Crampin, S., Da Como, E., and Hall, S.R.

Abstract

Contains fulltext : 158779.pdf (publisher's version ) (Open Access)

Published
2016

17. Spin Filtering in Electron Transport Through Chiral Oligopeptides

Author

Kettner, M., primary, Göhler, B., additional, Zacharias, H., additional, Mishra, D., additional, Kiran, V., additional, Naaman, R., additional, Fontanesi, C., additional, Waldeck, David H., additional, Sęk, Sławomir, additional, Pawłowski, Jan, additional, and Juhaniewicz, Joanna, additional

Published
2015
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18. HREELS study of the adsorption mechanism and orientational order of thione molecules on Cu(100)

Author

Allegretti F., De Renzi V., Biagi R., del Pennino U., Contini G., Di Castro V., Mariani C., Betti M.G., and Fontanesi C.

Abstract

Organic molecules with sulfur-containing headgroups interacting with noble metal surfaces represent a fruitful class of systems with potential relevance in new device technology. Within this context, the room temperature adsorption of 2-mercaptobenzoxazole (MBO) on the Cu(100) surface has been studied by high-resolution electron energy-loss spectroscopy (HREELS) as a function of molecular exposure. At low coverage, the HREEL spectra present only one mode at 93 meV (750 cm-1), which is attributed to the out-of-plane C–H bending gCH. Its off-specular angular dependence indicates that the molecules lie almost flat on the surface. At higher coverage, the MBO layer orders in a p(2¥2) superstructure, and energy loss peaks at higher energies appear. These features can be assigned to in-plane vibrations indicating that the molecular axis tilts toward a more vertical position, thus allowing a closer molecular packing. Assignment of the HREELS peaks is confirmed by estimation of the gas phase normal modes of the free molecule, evaluated by ab initio methods. The absence of the N–H stretching mode in the HREEL spectra indicates that the H atom bonded to nitrogen in the gas-phase molecule is lost upon adsorption, suggesting that MBO molecule adsorbs on the Cu surface as a thiolate.

Published
2003

37. Decrease in Toxic Potential of Mixed Tensides Maintained below the Critical Micelle Concentration: An in vitro Study.

Author

Benassi, L., Bertazzoni, G., Magnoni, C., Rinaldi, M., Fontanesi, C., and Seidenari, S.

Subjects
KERATINOCYTES, SKIN diseases, SERUM, CONDUCTOMETRIC analysis, ELECTROCHEMICAL analysis
Abstract

Sodium lauryl sulphate (SLS) is an anionic tenside widely utilized in commercial topical preparations that may cause skin irritation. It has been shown that the barrier damage caused by SLS in vivo is lower when SLS is used in combination with other tensides which are able to reduce the critical micelle concentration (CMC). The aim of our study was to evaluate if the cytotoxic effect of SLS is reduced by the association with different tensides also at concentrations well below the CMC. Normal human keratinocytes from plastic surgery were grown in serum-free medium. At subconfluency, the cells were treated with SLS at a dose of 0.0025% in combination with cocamidopropyl betaine, Tween 20 and Tween 80 at the minimum toxic dose. Following tenside treatment, the culture medium was changed, and after 24 h the cells were collected for 3H-thymidine incorporation, the MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide) assay and neutral red (NR) uptake. The cytotoxic effect on normal human keratinocytes, as evaluated by 3H-thymidine incorporation, MTT assay and NR uptake, was significantly decreased by the combination with all the tested tensides. The correlation between cytotoxicity and physical properties was also studied by a conductimetric assay to investigate the mechanism involved in this toxicity reduction. [ABSTRACT FROM AUTHOR]

Published
2003
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