Effect of poly-HEMA hydrophilic gel environment on the photo-physical behavior of rhodamine dyes

The absorption spectra of rhodamine B (RB) chloride, rhodamine 6G (R6G) tetrafluoroborate and rhodamine 6G chloride in poly-2-hydoxyethyl methacrylate hydrogel (PHEMA) matrix were studied using absorption spectroscopy in the visible region. The transport and aggregative properties of these ionic dyes in aqueous solution across the hydrophilic gel were also investigated. The similarities of absorption spectra of RB in aqueous solutions and in hydrogel host suggest that the hydrogel framework has a minor effect in their absorption spectra. In contrast, there is a relatively strong interaction or electrostatic forces between R6G dyes and the hydrogel matrix. The permeability of R6G chloride through hydrogel host is seen to be markedly higher than RB chloride and R6G tetrafluoroborate.