Photoinduced electron transfer in rhodamine B-containing amorphous titania gels

Abstract

Amorphous titania gel films containing the dye rhodamine B (RhB) were prepared by a sol–gel method, without heating. The RhB existed in the films as the RhB cation, which was transformed into the rhodamine 110 (Rh110) cation; its xanthene skeleton then decomposed during irradiation with visible light. This process was induced by electron transfer from the RhB cation to the titania gel matrix, because formation of the RhB radical on loss of an electron caused sequential dissociation of the N-ethyl groups. During irradiation with visible light a photocurrent was observed in electrodes coated with the RhB-containing titania gel and immersed in an I2–LiI electrolyte. This photocurrent resulted from electron injection from the LUMO level of the dye into conduction band-like states of the titania gel. Because of its effective electron supply the electrolyte inhibited dissociation of the N-ethyl groups of RhB.