The First Photoexcitation Step of Ruthenium-Based Models for Artificial Photosynthesis Highlighted by Resonance Raman Spectroscopy

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• 作者：Carmen Herrmann ; Johannes Neugebauer ; Martin Presselt ; Ute Uhlemann ; Michael Schmitt ; Sven Rau ; Jü ; rgen Popp ; Markus Reiher
• 刊名：Journal of Physical Chemistry B
• 出版年：2007
• 出版时间：May 31, 2007
• 年：2007
• 卷：111
• 期：21
• 页码：6078 - 6087
• 全文大小：493K
• 年卷期：v.111,no.21(May 31, 2007)
• ISSN：1520-5207

文摘

Ruthenium-polypyridine and related complexes play an important role as models for light-harvesting antennasystems to be employed in artificial photosynthesis. In this theoretical and experimental work, the firstphotoexcitation step of a tetranuclear [Ru₂Pd₂] complex composed of two ruthenium-bipyridyl subunits andtwo palladium-based fragments, {[(tbbpy)₂Ru(tmbi)]₂[Pd(allyl)]₂}²⁺ (tbbpy = 4,4'-di-tert-butyl-2,2'-bipyridine,tmbi = 5,6,5',6'-tetramethyl-2,2'-bibenzimidazolate), is investigated by means of experimental and theoreticalresonance Raman spectroscopy. The calculated spectra, which were obtained within the short-timeapproximation combined with time-dependent density functional theory (TDDFT), reproduce the experimentalspectrum with excellent agreement. We also compared calculations on off-resonance Raman spectra, for whicha completely different theoretical approach has to be used, to experimental ones and again found very goodagreement. The [Ru₂Pd₂] complex represents the probably largest system for which a quantum chemicalfrequency analysis and a calculation of conventional Raman as well as resonance Raman spectra with reasonablebasis sets have been performed. A comparison between the resonance Raman spectra of the [Ru₂Pd₂] complexand its mononuclear [Ru] building block [(tbbpy)₂Ru(tmbi)]²⁺ and a normal-mode analysis reveal that the[Ru₂Pd₂] resonance Raman spectrum is composed uniquely from peaks arising from the [Ru] fragment. Thisobservation and an analysis of the Kohn-Sham orbitals mainly involved in the initial electronic excitation inthe TDDFT description of the [Ru₂Pd₂] system support the hypothesis that the initial photoexcitation step of[Ru₂Pd₂] is a charge-transfer excitation from the ruthenium atoms to the adjacent butyl-2,2'-bipyridine ligands.