Deethylation and Degradation of Dry Rhodamine B Films Under Visible Light Irradiation

Abstract

Rhodamine B is a commonly used fluorescent dye in many different fields of research. It is a dye that can change colour by losing ethyl groups, deethylation. It is also possible for rhodamine B to degrade under irradiation, making it unable to emit light. Previously it was seen that rhodamine B in solution only undergoes reactions, that lead to the loss of ethyl groups, when a photocatalyst is present under visible light irradiating. However recently it has been seen that these reactions can occur without the presence of a photocatalyst for dry films of rhodamine B. To further understand the reactions that take place, we have studied and modeled the photo induced degradation and deethylation rhodamine B under various conditions. This was done by illuminating dry films of rhodamine B in contact with glass and or air and recording the spectrum the dye emits at several points in time during irradiation. With these spectra we modeled the dynamics of deethylation and degradation using a simple rate-equation model. The dye in contact with glass degrades faster than when not in contact with glass, and changes colour when in contact with both glass and air. This means dry rhodamine B can react without the presence of a photocatalyst under visible light irradiation.