Synthesis and crystal structures of cofacial bischlorin. Octaethylchlorin-based structural models for the special pair in photosynthesis

yields the first cofacial bischlorin with structural characteristics mimicking those of the special pair in photosynthesis. Owing to their structural similarity to the 'special pair ' in the photosynthetic reaction centre, cofacial chlorin dimers serve as biomimetic models to investigate the primary steps of photo-synthesis, charge separation and electron transfer. In order to fully understand the photophysical behaviour of such com-pounds, detailed information on their conformation and the relative spatial arrangement of the subunits is necessary; ideally the geometry of such dimers should be as close as possible to the situation in vivo, i.e. cofacial structure with parallel ring orientation and partial overlap of the n systems. Several bistetrapyrrole systems showing such features have been described,24 however, detailed information is available onl