Photocatalytic transformation of Rhodamine B to Rhodamine-110 – The mechanism revisited

Understanding of the TiO2-assisted phototransformations observed for fundamentally important derivatives of Rhodamine B is expected to bring consistent and eventually comprehensive knowledge on behavior of this dye. The photocatalytic transformations of Rhodamine B in solution irradiated with visible light embrace an N-deethylation process eventually forming Rhodamine-110 rather than degradation of the chromophore. The N-deethylation of Rhodamine B was studied in solution and for the first time in the solid state. In this work, the influence of the wavelength of incident light on the photocatalytic processes involving Rhodamine dyes, is presented. The results indicate that the selection of wavelength is crucial to govern the pathway of RhB degradation. The N-deethylation process does not require reactive oxygen species, as assumed in literature, but the photoinduced electron transfer between the adsorbed RhB molecule and the TiO2 support, followed by radical transformations of the dye, plays a key role.