Porphyrins and Related Compounds as Photoactivatable Insecticides. 2. Phototoxic Activity of Meso‐Substituted Porphyrins

We have recently proposed the use of porphyrin sensitizers as photoinsecticidal agents. Our present findings show that the phototoxic efficiency of porphyrins toward the Mediterranean fruit fly Ceratitis capitata is strongly dependent on their chemical structure. Thus, two highly hydrophilic porphyrins, such as a tetraanionic and a te‐tracationic meso‐substituted derivative, show a very low photoactivity even upon prolonged irradiation with full‐spectrum visible light. The phototoxicity increases upon increasing the hydrophobicity of the porphyrin molecule; out of the compounds examined by us, the highest pho‐tocidal activity is exhibited by a dicationic amphophilic porphyrin, namely cis‐(JV‐methyl‐piridyl), c/s‐diphenyl‐porphine, which causes 100% mortality upon 1 h irradiation with a fluence rate of 1220 μ.E s‐lm‐2even at a concentration as low as 0.85 mM. The differences in photoactivity are not related to differences in the photo‐physical and photobiological properties or to differences in the rate of porphyrin uptake and clearance by the flies.