**Author details**

#### Søren Hassing

The explaination for this is probably that while the non-adsorbed molecules are randomly ori-

**Figure 9.** DPR values and estimated uncertainty ±0.025 for the DSC samples: *DSC*100,0 (solid, red) and *DSC*0,100 (solid, blue), for the solutions of N719 (dashed, red) and N719-TBP (dashed, blue) for the most prominent Raman bands 1–10,

conditions for the Raman processes in the two situations are very different. From the theoretical section it follows that the polarized Raman signals (and the DPR) obtained from an oriented molecule are determined by the absolute square of those components of the Raman tensor that are selected by the molecular orientation in the coordinate system defined by the laser polarization and the polarization analyzers. For randomly oriented molecules the polarized Raman signals (and the DPR) are determined by the rotational invariants of the Raman tensor. The change in the DPR values between the adsorbed and non-adsorbed molecules that reflects both the molecular orientation and the wavenumber of the absorption spectra are changed. The large average increase of the DPR values, observed e.g. for the *DSC*100/0 relative to the N719 in solution, is probably due to the partial orientation exhibited by the N719 molecules, when they are

shows that these variations are essentially due to the shifts in the absorption spectra combined with the dispersive property of the individual Raman modes. Finally, since we observe very small wavenumber shifts (0–2 cm-1) in the Raman spectra for the resonance-enhanced Raman modes the nature of these modes must be similar for adsorbed and non-adsorbed molecules.

The average orientation of the adsorbed molecules depends on the physical details of the adsorption process and on the spatial structure of the TiO2 substrate. Since for oriented molecules the DPR is determined essentially by the ratio between the absolute square of those components of the Raman tensor, which are selected by the molecular orientation, it seems

. The similarity between the DPR-graphs for the DSCs and the solutions

surface are partially oriented. Thus, the scattering

ented, the molecules adsorbed to the TiO2

adsorbed to the TiO2

see Ref. [32] for details.

158 Raman Spectroscopy and Applications

Address all correspondence to: sh@kbm.sdu.dk

Institute of Chemical Engineering, Biotechnology and Environmental Technology, University of Southern Denmark, Odense M, Denmark
