Evaluation of a broad variety of coumarins,chromones, their furohomologues and thione analogues as phototoxins activated by UVA and visible light

The potential of a new kind of light-induced pesticide action was evaluated for a broad variety (32) of natural photosensitizers and their thione derivatives. The latter were synthesized to shift the absorption spectra towards the visible region and to increase the triplet and singlet oxygen quantum yields. Qualitative and quantitative evaluation of growth inhibition of Fusarium culmorum (F. G. Smith) Sacc. produced by these photosensitizers under UVA and visible light was performed on silica gel plates and in liquid medium. The results show that the phototoxicity per excited molecule of the thione derivatives using UVA light was similar to that of their parent natural compounds. On the other hand, only the thione derivatives were photoactive under visible light irradiation. These compounds show encouraging levels of phototoxicity against F. culmorum, both in liquid culture and on silica plates, and may have potential for use as photoactive pesticides.