DITHIOPHENES AS SINGLET OXYGEN SENSITIZERS

Abstract— The nematicidal compounds, 5‐methyl‐2,2′dithienyl, 5‐phenyl‐2,2′‐dithienyl and 5,5′‐dichloro‐2,2′‐dithienyl, generate singlet oxygen upon photoactivation with near‐UV light. Two chloro‐substituted dithienylethenes have similar properties that are farless efficient. The nematode Aphelenchus avenae was rapidly killed by the photoactivated dithienyls under aerobic but not under anaerobic conditions,indicating that nematicidal activity of these compounds is related to their sensitizing properties. Furthermore,these nematodes did not expire in the presence of these compounds maintained in the dark. Sensitizing properties were studied by following the inhibition ofglucose–6‐phosphate dehydrogenase by the photoactivated compounds and protection of enzyme activity by various additions. Only singlet oxygen quenchers were effective. The enzyme was inactivated 3 to 4 times faster in D20 compared to H20.Bleaching of p‐nitrosodimethylaniline in the presence of imidazole and the dithiophenes and a specific reaction with the olefin adamantylideneadamantane were additional evidence of generation of singlet oxygen by the photoactivated compounds.