Application of benzoyl-substituted hemithioindigo as a molecular switch in porphyrin-quinone recognition

The benzoyl-substituted hemithioindigo 1 with Z-configuration was obtained as the sole product from the reaction of 7-ethylbenzo[b]thiophen-3(2H)-one with phenylglyoxal. Irradiation of 1 produced the [2+4] cycloadduct 2, instead of the usual Z-E isomerization product. The cycloadduct 2 is completely dissociated back to 1 on heating; the interconversion between 1 and 2 shows good repeatability. This reversible property is applied to the molecular switch in the hydrogen-bonded quinone recognition of the 5,15-cis-bis(ureidophenyl)porphyrin 3.