Photophysics and photochemistry of azole fungicides: triadimefon and triadimenol

Photophysics and photochemistry of pesticides triadimefon {1-(4-chloropheno xy)-3,3-dimethyl-1-(1H-1,2,4-triazol-1-yl) butanone} and triadimenol {1-(4- chlorophenoxy)-3,3-dimethyl-1-(1H-1,2,4-triazol-1-yl) butan-2-ol} were stud ied in the solution. The excited singlet states were identified by comparis on with the absorption spectra of adequate model compounds, in several solv ents. The first excited singlet state of triadimefon is an n, pi* state loc alized on the carbonyl group, while higher excited states are localized on the chlorophenoxy group and have a pi, pi* character. The lowest singlet st ate of triadimenol is pi, pi* state, since a methoxyl group replaces the ca rbonyl group of triadimefon. Triadimefon shows a weak fluorescence from the n, pi* state, upon excitation at both 310 and 250 nm. This suggests a fast intramolecular energy transfer process from the localized pi, pi* state of the chlorophenoxy group to the n, pi* state of the carbonyl group. The pho todegradation quantum yield of triadimefon in cyclohexane at 313 run is 0.0 22. Triadimenol is photostable, under the same conditions. Two major photod egradation products of triadimefon and triadimenol were identified: 4-chlor ophenol and 1,2,4-triazole. 4-Chlorophenoxyl radicals were detected by flas h photolysis, suggesting a homolytic cleavage of the C-O bond of the asymme tric carbon. (C) 2001 Elsevier Science B.V. All rights reserved.