Edifices Built via H Bonds and Other Host-Guest Interactions

To mimic energy transfer processes in light-harvesting antenna complexes, Sessler and coworkers developed in 1991 the idea of assembling by noncovalent bonds a zinc porphyrin acting as an energy donor and a free-base 

The aim of these multiporphyrin systems was to study the energy transfer reaction from the singlet excited state of the zinc(II) porphyrin to the free-base porphyrin within a hydrogen-bond assembly. Nevertheless, it was difficult to explain unambiguously the luminescence quenching of the zinc porphyrin. Due to the flexibility around the amino group, intracomplex diffusional quenching of the zinc porphyrin excited state by the free-base porphyrin could not be ruled out. 

In biological photosystems, electron transfer proceeds through non-covalently linked protein pathways. In order to understand the electronic coupling provided by a hydrogen-bond interface, a noncovalent bis-chromophoric system 5 

The cage structure 6 is composed of two face-to-face porphyrins linked at both sides via six hydrogen bonds to two triaminopyridine entities. The distance between the cofacial porphyrins is estimated to be 10 A. The initial nieso 5,15-diuracil-substituted porphyrin has two rotameric forms, a syn and an anti, due to the relative orientations of the two uracil groups with respect to the porphyrin plane. In the self-assembling process, the syn rotamer yielded the major component, the cage structure, whereas the anti conformer yielded a zig-zag strand structure. As for the properties expected by such systems, metalation of one of the porphyrins allows for the creation of a self-assembled donor-acceptor system while complexation of the porphyrins with zinc(Il) allows for the cage cavity to be used as a 

A particular way of assembling two water-soluble porphyrins within a common system is to use the highly 

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Multiporphyrin Edifices Built via H Bonds and Other Host-Guest Interactions. 4... 

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