Porphyrinoids supramolecular

Borovkov VV, Inoue Y (2006) Supramolecular Chirogenesis in Host-Guest Systems Containing Porphyrinoids. 265 89-146... 

Supramolecular Chirogenesis in Host-Guest Systems Containing Porphyrinoids... 

Keywords Supramolecular chemistry Chirality Porphyrinoids Host-guest Aggregation... 

So far, several reviews have been published, some of which refer to supramolecular chirogenic porphyrinoid-containing systems to a greater or lesser extent. Therefore, before moving to specific examples of this area, we shall give an overview of some of these articles. 

The third type of review primarily focused on the different aspects of chirality and contained some porphyrin-based supramolecular chirogenic systems as examples. For example, Finn, Wenzel, and Wilcox discussed various methods and reagents for the determination of ee and absolute configuration using different spectroscopic approaches [35,36] whilst Allenmark, Pasternack, Kobayashi, Formaggio et al. addressed the induced and electronic CD upon the intra- and intermolecular interactions considering several porphyrinoid chromophores [37-40]. 

As the simplest, and thus most easily understandable and widely applicable structural type, supramolecular chirogenic systems based on monomeric achiral and racemic porphyrinoids will be discussed first. 

The representative examples of chirogenic assemblies on the basis of achiral monomeric porphyrinoids exposed to a chiral influence clearly show their great importance and wide applicability in various fields. The major chiroptical properties of these relatively simple supramolecular systems include transferring the chiral information and controlling the induced asymmetry by different factors. However, another type of chirogenic process— modulation of inherent chirality is going to be illustrated for chiral porphyrins in the next sections. 

The aforementioned representative examples of chirogenic supramolecular systems based on monomeric porphyrinoids clearly demonstrate their vital importance and wide applicability in various fields, while many aspects of the operating mechanisms and especially chiroptical properties have yet to be comprehensively investigated and well understood. However, in many cases just a monomeric porphyrin cannot function properly without the synergetic assistance of another porphyrin unit (or several porphyrins) that give rise to chirogenic supramolecular assemblies built upon the dimeric/oligomeric porphyrinoids, which will be discussed in subsequent sections. 

Chirogenic supramolecular systems based on dimeric/oligomeric porphyrinoids can also be classified according to their complexity and structural features. First, the assemblies consisting of two or more monomeric porphyrins fixed in an asymmetrical fashion by chiral bridges via supramolecular binding will be examined. 

Supramolecular systems on the basis of dimeric and oligomeric porphyrinoids are varied depending upon the chirality of the supramolecular counterparts, type of the covalent linkage, and number of the porphyrin subunits. Firstly, we shall examine examples of the assemblies consisting of achiral and racemic bis-porphyrinoid hosts and chiral guests. 

In contrast, the last type of chirogenic supramolecular systems consisting of aggregated porphyrinoids to be considered in the next section brings wider structural variability at a sacrifice in the geometrical certainty. 

The supramolecular assemblies involving aggregated porphyrinoids similarly to other types of previously discussed systems could be reasonably divided into different categories on the basis of achiral, chiral monomeric, and dimeric porphyrinoids. Again, the simplest monomeric achiral porphyrinoids will be presented first. 

Besides the relatively weak asymmetry fields discussed above, chirogenic processes in various aggregated and self-assembled systems on the basis of achiral porphyrinoids can be driven by more conventional (and more powerful) chiroptical influences upon interacting with a supramolecular counterpart possessing optical activity. 

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