Photoelectrochemistry for Measuring the Photocatalytic Activity of Soluble Photosensitizers

We introduce a rapid method to test the photocatalytic activity of singlet-oxygen-producing photosensitizers using a batch cell, a LED laser and a conventional potentiostat. The strategy is based on coupling of photo-oxidation of hydroquinone and simultaneous electrochemical reduction of its oxidized form at a carbon electrode in an organic solvent (methanol). This scheme gives an immediate response and avoids complications related to long-term experiments such as oxidative photo-degradation of photosensitizers and singlet oxygen traps by reactive oxygen species (ROS). Among the tested compounds, a fluoro-substituted subphthalocyanine showed the highest photocurrent and singlet oxygen quantum yield (phi(Delta)) in comparison to phenoxy- and tert-butyl-substituted analogues, whereas the lowest photocurrents and yields were observed for aggregated and dimeric phthalocyanine complexes. The method is useful for fast screening of the photosensitizing activity and represents the first example of one-pot coupling of electrochemical and photocatalytic reactions in organic media.