Phenothiazine derivatives have found many applications in todays chemical industry; they have been and are used primarily as dye--stuffs, antioxidants and in pharmaceutical preparations. This application is due to the discovery of their neuroleptic activity (1) (e.g. Chlorpromazine), but allergic skin reactions and ocular opacity are known to occur during therapy.Assuming that these side effects might be primarily initiated by light induced electron or energy transfers, investigations on the conditions where such transfers take place with high efficiency and with some specificity are of fundamental interest. Phenothiazine and its N-alkylated derivatives have also been of interest as electron donating substrates in early investigations of photochemically induced charge separation (2-5), necessary for a successfull photochemical energy conversion. Besides phototoxicity, which might involve oxygen, and energy conversion, just two examples of model investigations, phenothiazine derivatives are convenient probes in micelles and mixed aggregates, model systems themselves for preparative applications (6) as well as biomimetic environments (7). PhenothiazinePhenothiazine is readily oxidized when irradiated in solution with chlorinated hydrocarbones 08). The reaction has been shown to be an electron transfer generating the phenothiazine (PTH) radical cation (ΡΤΗ + ') and the halogen anion as shown in equation 1. hv , PTH + RC1• PTH + R* + Cl (1) Photooxidation may lead to a similar electron transfer yielding PTH + * and superoxide, hv . PTH + 0 2 • PTH + ' + 0"' (2) 7