Rose Bengal (RB) is a halogenated fluorescein dye that is a highly efficient photosensitizer that has been used in a variety of environmental and biomedical applications. It has also been the focus of extensive research to work out the kinetic and mechanistic details of the underlying reactions that occur during applications such as photodynamic therapy [PDT]. Since RB is an efficient absorber and has a high intersystem crossing quantum yield, it is readily excited to the triplet state which forms singlet oxygen [1O2] by energy transfer to ground state molecular oxygen. While O2 photosensitization by RB has been widely studied in many solvents, it has not been studied systematically in octanol. Octanol is a biorelevant, microheterogeneous that is commonly used to model the hydrophobicity of biological systems in experimental and computational studies.
In this investigation, the photooxidation of RB in octanol will be compared to the reaction in isotropic solvents, including phosphate buffer and butanol to investigate the impact of solvent microheterogeneity on the reaction. The light-induced degradation of RB in the selected solvents is monitored using wavelength- and frequency-resolved fluorescence spectroscopy. Fluorescence emission-decay (time- or frequency domain) measurements can be arranged in matrix format, making them amenable to numerical analysis and enabling computational isolation of the spectra and decay profiles of the components of the photoirradiated samples. The kinetics and mechanism(s) of the photooxidation reaction will be studied using the spectra and kinetics of the sample components.
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