Porphyrinoids monomeric

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. 

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. 

While self-assembled and aggregated chirogenic systems are mainly based on monomeric porphyrinoids, a further increase of the pigment multiplicity, despite raising the overall complexity of supramolecular structures, may lead to novel functional properties and new applications. Therefore, in the last section we shall show a few examples of self-assembled and aggregated systems constructed from dimeric and oligomeric porphyrins. 

Many successM methods have been reported for the synthesis of porphyrinoids. Symmetric porphyrin synthesis is achieved by cyclic tetramerizalion using a-free pyrroles and aldehyde [6]. a-Hydroxymethylpyrroles are also employed suc-cessfiiUy in the cyclic tetramerization method [7]. For the synthesis of unsymmetric porphyrinoids, oligomeric pyrroUc units are condensed under acidic conditions. These mediods are categorized by the number of pyrroles (or five-membered heterocycles) in the units. The [2 + 2] and [3 -h 1 ] methods are common in the synthesis of porphyrins [8] the [3 - - 2] and [3+1 + 1] methods are employed for the synthesis of sap-phyrins [9] and the [2 + 2] method provided porphyrins and corroles [10]. For the preparation of 7t-expanded porphyrinoid precursors by using these methods, monomeric or oligomeric equivalents of isoindoles are required and these preparations are first introduced. 

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