Tailored protective groups for surface immobilization of ruthenium dyes
McKenna reaction conditions are applied to [Ru(4,4’-(CH2PO3Et2)2(bpy)](PF6)2 model chromophore in order to yield [Ru(4,4’-(CH2PO3TMS2)2(bpy)](Br2-x)(PF6)x (x = 0 – 2) (2) by replacing the alkyl moieties of the phosphonates by TMS groups (TMS = trimethylsilyl). The model complex is immobilized onto both NiO powder and NiO electrodes on FTO (fluorine doped tin oxide) using organic solvents. The stability of surface binding in aqueous media as well as the DSC performance of 2 are tested and compared to a conventional dye of the structure [Ru(4,4’-(CH2PO3TBA2)2(bpy)](PF6)2 (1) (TBA = tetrabutyl ammonium). This is the first example of a ruthenium based chromophore with a phosphonic acid silyl-ester being directly immobilized onto a NiO surface. Additionally, complex 2 exhibits superior stability towards desorption in aqueous media, at the same time showing improved DSC performance and stability in acetonitrile and, a slightly higher dye loading on the electrode surface compared to 1.