Structure and photochemical properties of 2-(N-benzoyl-N-phenylaminomethylene)- and 2-(N-p-nitrobenzoyl-N-phenylaminomethylene)-3(2H)-benzo[b]thiophenones

Conclusions It was established by x-ray crystallographic investigation that the inhibition of the photochromism of the nitro derivative (IIb) compared with compounds (I) and (IIa) is due to the difference in the structure of the molecules and to the realization of the low-lying triplet n^* state, due to the presence of the p-nitro group. The flattening of the p-nitrobenzoyl fragment and its rotation from the plane of the molecule evidently promote localization of the photoexcitation energy in this conjugated fragment of the molecule and lead to nonradiative deactivation of the excited S^1* state by intercombination conversion through the n triplet state and, finally, to a marked decrease in the yields of the fluorescence and the phototransformations.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1544–1548, July, 1989.The authors are grateful to M. I. Knyazhanskii for assistance in the discussion of the results.