The meso–β-linkage as structural motif in porphyrin-based donor–acceptor compounds

Synthetic strategies for using the meso–β-linkage as a structural motif in electron transfer mimics have been tested. Exploratory syntheses of directly meso–β-linked bis- and trisporphyrins and the first representative X-ray structure of a meso–β-linked bisporphyrins are reported. The structure reveals a unique form of intramolecular π–π stabilization between one porphyrin and a meso-aryl substituent in a second porphyrin unit that accounts for the stability of different atropisomers in trimers. Using β-formyl porphyrins, dipyrromethanes, and suitable quinone precursor aldehydes, mixed condensations gave convenient access to porphyrin–porphyrin–quinone (P–P–Q) donor–acceptor systems consisting of a meso–β-linked bisporphyrin, a spacer, and a quinone acceptor.