Supramolecular chemistry chiral systems

Abstract The preparation of chiral functional materials with new, improved, and interesting properties is aided tremendously by control of the spatial arrangement of the functional units within them. The use of non-covalent interactions is absolutely critical in this regard, and the molecular-supramolecular balance has to be strictly controlled. The conducting, magnetic and optical properties of chiral materials whose function is profoundly influenced by supramolecular chemistry will be reviewed. Special emphasis is placed on the control of helical arrangements in liquid crystalline systems, in which both chiral induction and spontaneous resolution are important phenomena which can be controlled. 

If we mutually compare chiroptical methods, we find a remarkable complementarity that can be used as advantage when a particular system is investigated by the selection of chiroptical procedures. ECD [1, 24], which is a far reaching technique, tends to see a molecule as a whole and provides chiral information via chromophores and their properties [25-27]. This far-reaching nature of ECD can be utilized, for example, in supramolecular chemistry, where chirality is introduced into the system by a chiral, but spectroscopically neutral matrix. However, it is observed on an inherently nonchiral chromophore, like, for example, porphyrine [28-36]... 

Most applications of ECD spectroscopy in supramolecular chemistry, which can be counted to hundreds, involve proofs of existence and determination of properties (chirality) of potentially chiral supramolecular structures. The convergence of the ECD amplitude is taken as a criterion of pure enantiomers. The loss of structure upon the change of physico-chemical properties can be followed by the decrease of CD signal. Another concept uses chromophores [24] for testing the three dimensional structure of supramolecular systems. If the isolated chromophore is not chiral and induced circular dichroism (ICD) is observed in the system, we can sometimes deduce the structure of the chromophoric environment (see section 8.4.2). Ab initio calculations open another possibility to employ ECD into supramolecular chemistry (Section 8.1.3). 

G. Seeber, B.E.F. Tiedemann and K.N. Raymond (2006) Top. Curr. Chem., vol. 265, p. 147 - Supramolecular chirality in coordination chemistry takes chiral systems beyond mononuclear complexes to supramolecular assemblies. 

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