Substituents Effects on Two Related Families of Dyes for Dye Sensitized Solar Cells: [Ru(4,4′-R,R-2,2′-bpy)3]2+ and [Ru(4,4′-COOH-2,2′-bpy)(4,4′-R,R-2,2′-bpy)2]2+

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Abstract
We studied the influence of the substituents over the composition of the molecular orbitals, electronic transitions, and reactivity of several ruthenium derivatives. We found a good agreement with the previously reported experimental data. In these theoretical calculations including spin–orbit coupling, we study several ruthenium-tris-(2,2′-bipyridine) substituted dyes, which do or do not have an anchoring group to get attached to the semiconductor surface. It was observed that the complexes that have electron-donor substituents might be more efficient to donate electrons if they are anchored to a semiconductor than those complexes that have electron-acceptor substituents. Therefore, the results suggest that these dyes with electron-donor substituents will give better yields in photocurrent generation. Also, the localization of the lowest unoccupied molecular orbital over the ligand that has the anchoring will help to improve electron injections into the TiO2 nanoparticles. We propose here several not yet synthetized dyes, which could be used in this kind of device, due to their interesting molecular properties.