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The photochemistry and photophysics of papaverine N‐oxide in polar aprotic and protic solvents has been studied in detail. Complex energy and charge‐transfer phenomena between chromophores occur in papaverine. New photochemistry for the papaverine N‐oxide system is reported. Irradiation in protic media results in the formation of an emissive charge‐transfer state with ensuing intramolecular hydroxylation in high isolated yields (75–80%).

Two reasons for the poor performance of the iron-thionine photogalvanic cell are first the low solubility of thionine, which means that the incident solar radiation is absorbed too far from the illuminated electrode, and secondly the formation of dimers which do not undergo the desired photoredox reaction. The synthesis and photoelectrochemical characterization of several isomeric disulphonated thionines are reported. All the isomers examined are sufficiently soluble to absorb solar radiation close to the illuminated electrode of a photogalvanic cell and show no evidence of dimerization via stacking interactions a t concentrations up to 1 O-3M. Using the following techniques, the transparent disc electrode, flash photoelectrolysis, and stopped flow, the kinetic parameters have been determined to see how well the conditions needed for an efficient photogalvanic system are met. The 4,6-isomer of disulphonated thionine is the only isomer that fulfills the required kinetic constraints.