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Functional K-doping of eumelanin thin films: Density functional theory theory and soft x-ray spectroscopy experiments in the frame of the macrocyclic protomolecule model (Articolo in rivista)

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Functional K-doping of eumelanin thin films: Density functional theory theory and soft x-ray spectroscopy experiments in the frame of the macrocyclic protomolecule model (Articolo in rivista) (literal)

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P. Borghetti1, P. Ghosh2, C. Castellarin-Cudia3, A. Goldoni3, L. Floreano4, A. Cossaro4, A. Verdini4, R. Gebauer5, G. Drera1, and L. Sangaletti1 (2012)
Functional K-doping of eumelanin thin films: Density functional theory theory and soft x-ray spectroscopy experiments in the frame of the macrocyclic protomolecule model
in The Journal of chemical physics; American Institute Of Physics (AIP), Melville (Stati Uniti d'America)
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P. Borghetti1, P. Ghosh2, C. Castellarin-Cudia3, A. Goldoni3, L. Floreano4, A. Cossaro4, A. Verdini4, R. Gebauer5, G. Drera1, and L. Sangaletti1 (literal)

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1I-LAMP and Dipartimento di Matematica e Fisica, Università Cattolica, via dei Musei 41, 25121 Brescia, Italy 2Department of Chemistry and Physics, Indian Institute of Science Education and Research (IISER), 900, NCL Innovation Park, Dr. Homi Bhabha Road, Pune 411008, Maharashtra, India 3Sincrotrone Trieste S.C.p.A., Basovizza S.S.14 Km. 163.5, 34149 Trieste, Italy 4IOM-CNR, Laboratorio TASC, S.S.14 Km. 163.5, I-34149 Basovizza, Italy 5The Abdus Salam International Centre for Theoretical Physics (ICTP), Strada Costiera 11, 34151 Trieste, Italy (literal)

Titolo

Functional K-doping of eumelanin thin films: Density functional theory theory and soft x-ray spectroscopy experiments in the frame of the macrocyclic protomolecule model (literal)

Abstract

We demonstrate the possibility to achieve the doping of eumelanin thin films through K+ incorporation during the electrodeposition of the film. K-doping changes the optical properties of the eumelanin thin films, reducing the energy gap from 1.0 to 0.6 eV, with possible implications for the photophysical properties. We have identified the doping-related occupied and unoccupied electronic states and their spectral weight using resonant photoemission spectroscopy (ResPES) and x-ray absorption at the C and N K-edges (near edge x-ray absorption fine spectroscopy, NEXAFS). All data are consistently interpreted by ab initio calculations of the electronic structure within the frame of the macrocycle model developed for the eumelanin protomolecule. Our analysis puts in evidence the intercalation of K with one specific oligomer (a tetramer composed of one indolequinone and 3 hydroquinone monomers) in correspondence of the nitrogen macrocycle. The predicted variation of the tetramer spacing is also in agreement with the recent x-ray diffraction experiments. The charge donation from K to N and C atoms gives rise to new electronic states at the top of the valence band and in NEXAFS resonances of the unoccupied orbitals. The saturation of the tetramer macrocycles leaves an excess of K that bind to N and C atoms in alternative configurations, as witnessed by the occurrence of additional spectral features in the carbon-related ResPES measurements. (literal)

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