Anchor‐Functionalized Push‐Pull‐Substituted Bis(tridentate) Ruthenium(II) Polypyridine Chromophores: Photostability and Evaluation as Photosensitizers

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Abstract
Stable push‐pull substituted heteroleptic bis(tridentate) ruthenium(II) polypyridine complexes with COOH or 2,2′‐bipyridine anchor groups have been prepared and characterized by 1H, 13C and 15N NMR 1D and 2D spectroscopy, infrared spectroscopy, elemental analysis, high‐resolution ESI mass spectrometry, electrochemistry, UV/Vis absorption spectroscopy, luminescence spectroscopy, and density functional calculations. The complexes feature a pronounced electronic directionality and high absorption wavelengths up to λmax = 544 nm extending to 720 nm as a result of favorable push‐pull substitutions. A remarkable photostability in the presence of water and coordinating ions (I–) was discovered for the tridentate complexes when compared with the standard ruthenium sensitizer N719 and tris(bidentate) [Ru(bpy)3](PF6)2, which are highly photolabile under the same conditions (photodissociation/photosubstitution). The complexes were studied as photosensitizers in dye‐sensitized solar cells. The incident photon‐to‐current conversion efficiency follows the absorption spectra into the NIR region. However, the high positive charge of the complexes (2+) favors the recombination of the injected electrons with I3– of the redox electrolyte, which is evidenced by high dark currents and short electron recombination lifetimes, leading to low cell performances compared with cells with the negatively charged N719 dye.

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