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Published on: August 23, 2012
Solar cell sensitizer models [Ru(bpy-R)2(NCS)2] probed by spectroelectrochemistry
Sara Kämper1, Alexa Paretzki, Jan Fiedler
1Institut für Anorganische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70550 Stuttgart, Germany.
Inorganic Chemistry
|February 11, 2012
Summary
Ruthenium complexes with bpy-R ligands undergo metal-centered oxidation and ligand-centered reductions. Spectroelectrochemistry and DFT calculations reveal electronic changes impacting IR spectra and spin density distribution.
Area of Science:
- Coordination Chemistry
- Materials Science
- Physical Chemistry
Background:
- Ruthenium complexes with bipyridine (bpy) ligands are crucial in various applications, including solar cells.
- Understanding their electronic structure and redox properties is key to optimizing their performance.
- Spectroelectrochemistry and computational methods provide insights into frontier orbitals and charge transfer.
Purpose of the Study:
- To investigate the spectroelectrochemical and electron paramagnetic resonance (EPR) properties of novel ruthenium complexes.
- To elucidate the electronic structure and redox behavior of [Ru(bpy-R)(2)(NCS)(2)] complexes.
- To correlate experimental findings with density functional theory (DFT) calculations for excited state and oxidized forms.
Main Methods:
- Synthesis and characterization of four ruthenium complexes: [Ru(bpy-R)(2)(NCS)(2)] with R = H (1), 4,4'-(CO(2)Et)(2) (2), 4,4'-(OMe)(2) (3), and 4,4'-Me(2) (4).
- Spectroelectrochemistry in the UV-vis and IR regions.
- In situ electron paramagnetic resonance (EPR) spectroscopy.
- Density functional theory (DFT) calculations.
Main Results:
- Experimental and DFT data confirm metal-to-ligand (Ru → bpy) charge-transfer characteristics.
- Compounds exhibit one metal-centered oxidation and multiple ligand-centered reductions.
- One-electron reduction induces significant IR absorption and ligand-to-ligand intervalence charge-transfer transitions.
- Oxidation of Ru(II) to Ru(III) causes splitting and red-shifting of the N-C stretching band, with DFT suggesting spin density on sulfur.
Conclusions:
- The studied ruthenium complexes display predictable redox behavior, with distinct electronic transitions upon reduction and oxidation.
- Spectroelectrochemical and EPR studies, supported by DFT, provide a comprehensive understanding of their electronic structure.
- The findings are relevant for designing ruthenium complexes for applications such as TiO(2)-based solar cells.
