Electronic structure of Fe- vs. Ru-based dye molecules

• Published in: The Journal of chemical physics 2013-01, Vol.138 (4), p.044709-044709
• Main Authors: Johnson, Phillip S, Cook, Peter L, Zegkinoglou, Ioannis, García-Lastra, J M, Rubio, Angel, Ruther, Rose E, Hamers, Robert J, Himpsel, F J
• Format: Article
• Language: English
• Subjects: ABSORPTION SPECTROSCOPY; ATOMIC AND MOLECULAR PHYSICS; BINDING ENERGY; BIPYRIDINES; Cage; Charge; Charge transfer; CRYSTAL FIELD; DENSITY FUNCTIONAL METHOD; DYES; ELECTRONIC STRUCTURE; INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; Iron; IRON COMPOUNDS; LIGANDS; METALS; MOLECULES; ORGANOMETALLIC COMPOUNDS; PHENANTHROLINES; PORPHYRINS; RUTHENIUM COMPOUNDS; SOLAR CELLS; X-RAY SPECTRA; X-RAY SPECTROSCOPY
• ISSN: 0021-9606; 1089-7690
• DOI: 10.1063/1.4788617

In order to explore whether Ru can be replaced by inexpensive Fe in dye molecules for solar cells, the differences in the electronic structure of Fe- and Ru-based dyes are investigated by X-ray absorption spectroscopy and first-principles calculations. Molecules with the metal in a sixfold, octahedral N cage, such as tris(bipyridines) and tris(phenanthrolines), exhibit a systematic downward shift of the N 1s-to-π* transition when Ru is replaced by Fe. This shift is explained by an extra transfer of negative charge from the metal to the N ligands in the case of Fe, which reduces the binding energy of the N 1s core level. The C 1s-to-π* transitions show the opposite trend, with an increase in the transition energy when replacing Ru by Fe. Molecules with the metal in a fourfold, planar N cage (porphyrins) exhibit a more complex behavior due to a subtle competition between the crystal field, axial ligands, and the 2+ vs. 3+ oxidation states.