Resonance micro-Raman spectrophotoelectrochemistry on nanocrystalline TiO2 thin film electrodes sensitized by Ru(II) complexes

Resonance micro-Raman spectrophotoelectrochemistry combines spatial resolution, offering the ability to detect the vibration properties of separate components in the dye nanocrystalline cell, with a dynamic, control of the electrochemical interface via the applied potential. This enables us to obtain new insights in the mechanism of photosensitization of large band-gap semiconductors, elucidate the interactions between the semiconductor, dye and redox couple, detect the creation of new species and/or the existence of parasite reactions and finally permit the optimization of the cell's performance. Our group was the first to study the dye chemisorption on nanocrystalline titanium dioxide thin films using resonance micro-Raman spectroscopy. The investigation was extended to polarized dye-sensitized working photoelectrodes aiming at elucidating the vibrational properties of the dye, especially in the aromatic region as well as those of the iodides in the range of the oxide vibration bands. Recent investigations revealed the presence of new vibration bands in the low wave number region, mainly at 112 and 167 cm(-1) and the dependence of their intensity on the applied potential. In the present work, we confirm the general character of the phenomenon by using a number of dyes with a variety of ligands. The vibrational properties of sensitized electrodes and corresponding cells realized with dyes recently synthesized (containing PPh3, bdmpp, dc-bpy, iph-terpy, phpa-terpy, Cl-, and NCS- ligands) are compared with photoelectrodes and cells using commercial dyes (N3 and black-dye). We examine the influence of the dye, the redox couple, the electrolyte, the titania preparation technique and the laser excitation line on the presence of these bands as well as on their behavior under anodic and cathodic bias. The nature of these bands is discussed on the basis of the sensitization mechanism and this allows their attribution to new species formed during the cell's operation. (C) 2004 Elsevier B.V. All rights reserved.