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 nπ^* 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 nπ triplet state and, finally, to a marked decrease in the yields of the fluorescence and the phototransformations.