Characterization of the adsorption of ru-bpy dyes on mesoporous TiO2 films with UV-Vis, Raman, and FTIR spectroscopies

In the present work the adsorption of a new dye, [Ru(dcbpyH(2))(2)(bpy-TPA(2))](PF6)(2), and the well-known (Bu4N)(2)-[Ru(dcbpyH)(2)(NCS)(2)] complex on mesoporous anatase films were investigated to clarify the role of the carboxylate groups in the anchoring process of the dyes on the semiconductor surface. For this purpose UV-vis, Raman, resonance Raman, and ATR-FTIR spectroscopies have been used. The results of the Raman experiments at different excitation wavelengths demonstrate that photoinduced charge-transfer processes take place efficiently between the adsorbate and the substrate. Moreover, this is the first time that the Raman spectrum of a Ru-bpy dye (in this case, the dye N719) adsorbed on TiO2 has been obtained without the resonance condition, only by means of SERS enhancement. The coordination of both complexes on the TiO2 paste films is proposed to occur via bidentate or bridging linkage.