Photoinduced electron transfer in porphyrin−quinone cyclophanes, 6. Porphyrin−quinone cyclophanes with gradually varied acceptor strength: Syntheses and characterizations

For studying intramolecular electron−transfer reactions, three groups of double− and single−bridged porphyrin−quinone cyclophanes 1−4, 5−9, and 11−14, resp., with gradual variation of quinone acceptor strengths were synthesized. As key intermediates for building up the porphyrin−cyclophane skeleton the correspondingly 3,6−substituted 1,4−bis[4−(2−formylphenyl)−butyl]−2,5−dimethoxybenzenes 15−20 were synthesized. Condensation with pyrrole yielded the doubly bridged porphyrin cyclophanes 42−45; via the bis(dipyrrolylmethyl) derivatives 46−51 and 64−67 the single−bridged porphyrin cyclophanes 58−63 and 72−75 were obtained by acidic condensation with triethyl formate. Cleavage of the methoxy groups and oxidation yielded the corresponding porphyrin−quinone systems. Some magnesium and zinc complexes of these cyclophanes are described. Spectroscopic data (MS, 1H NMR) are reported in support of the proposed structure