Singlet Oxygen Quantum Yields of Different Photosensitizers in Polar Solvents and Micellar Solutions

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Abstract
The singlet oxygen luminescence method and the photochemical methods using 1,3-diphenylisobenzofuran ( DPBF ) or bilirubin ditaurate ( BDT ) as chemical quenchers were employed to determine the single oxygen quantum yields (ΦΔ) of different phthalocyanines and tris(2,2″-bipyridyl)ruthenium(II) dichloride in dimethylformamide ( DMF ) or aqueous micellar solution of 0.1 M CTAC (cetyltrimethylammonium chloride). Additionally, a perylenetetracarboxylic acid diimide derivative was examined in DMF . In a series of tetrasulfonated phthalocyanines ( PTS ) the following order was found: ZnPTS > GaPTS > AlPTS ≈ H2PTS > CoPTS . In general, the singlet oxygen quantum yields are higher in DMF than in 0.1 M CTAC/H2O . The results obtained with the photochemical systems are comparable with those obtained by the photophysical method.The photochemical DPBF method results in absolute values of ΦΔ. However, in micellar solution, chain reactions occur when DPBF is used as chemical quencher in the photo-oxidative process. This problem can be overcome by adding sodium thiosulphate which is able to destroy the endoperoxide initially formed. BDT can be used as quencher in different solvents to determine ΦΔrelative to a photosensitizer with known singlet oxygen quantum yield in the respective solvent.In comparison to the chemical methods the luminescence method exhibits the advantage that side reactions of the quencher are excluded. But normally the ΦΔvalues obtained are relative to a reference, since absolute determinations need much larger efforts.

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