Photophysical and photochemical properties of a water-soluble perylene diimide derivative

Abstract

The absorbance maximum of synthesized water soluble perylene 4-carboxylphenyl-bis-diimide (PECA) is found to be about 50nm lower in water, as compared to absorbance in organic solvents, and the singlet energy is 61.4kcalmol−1 in aqueous solutions, compared to 54.4kcalmol−1 in organic solvents. The fluorescence quantum yields were similar in both media but radiative and fluorescence lifetimes are found to be enhanced about twice (τf from 8 to 15ns), and the rate of fluorescence is decreased twofold in aqueous solution, as compared to organic solutions. PECA is proven to produce reactive superoxide anion and/or hydroperoxy radical in aqueous solutions, in the pH range of 6–12 (φPECAO2−=0.062 at pH=9). The superoxide/hydroperoxy formation is found to be enhanced in the presence of ferric ions (φPECAO2−=0.10 at pH=9). The quantum yield of fluorescence emission, Qf, was measured to be 1.00 at pH 11.85, and 0.87 at pH 6.60. The difference is attributed to an aggregation effect due to low solubility in neutral aqueous solution. Fluorescence quenching by Co+2 ions has yielded a quenching rate of 2.3×1012M−1s−1 for perylene diimide. The degradation of bromacil and 2,4-dichlorophenoxyacetic acid (2,4-D) pesticides in neutral aqueous solutions has proven that PECA/Fe+3 solar photocatalyst is as reactive as singlet oxygen in photo oxidations for organic pollutants. High thermal and photo stabilities and the regain of catalysts on precipitation, are the advantages with respect to classical triplet organic photosensitizers (methylene blue, rose bengal, etc.) employed for singlet oxygen photodegradations.