Photophysics and photochemistry of azole fungicides: triadimefon and triadimenol

Photophysics and photochemistry of pesticides triadimefon {1-(4-chlorophenoxy)-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 studied in the solution. The excited singlet states were identified by comparison with the absorption spectra of adequate model compounds, in several solvents. The first excited singlet state of triadimefon is an n, pi* state localized on the carbonyl group, while higher excited states are localized on the chlorophenoxy group and have a pi, pi* character. The lowest singlet state of triadimenol is pi, pi* state, since a methoxyl group replaces the carbonyl 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 photodegradation quantum yield of triadimefon in cyclohexane at 313 run is 0.022. Triadimenol is photostable, under the same conditions. Two major photodegradation products of triadimefon and triadimenol were identified: 4-chlorophenol and 1,2,4-triazole. 4-Chlorophenoxyl radicals were detected by flash photolysis, suggesting a homolytic cleavage of the C-O bond of the asymmetric carbon. (C) 2001 Elsevier Science B.V. All rights reserved.