Editorial [Hot Topic:Polyphenols(Guest Editor: Poul Erik Hansen)]

Polyphenols are a very diverse class of compounds. In the present volume the emphasis is on Schiff bases and azo compounds containing one or more hydroxy group. Such polyphenols have many interesting properties and uses. Photochromism is an extremely important feature to be used in many context in society. o-Hydroxy Schiff bases show this feature in a number of cases. A model for the process is now suggested. X-ray crystallography is providing unique information about tautomeric equilibria in the solid state, when experiments are done at variable temperatures. The detailed informations allow a characterization of the features favouring one form over the other. Infra Red spectroscopy is a very important tool in the study of tautomeric systems with intramolecular hydrogen bonds. Anharmonicity is central to this class of compounds and related to that bandwidths. Polarization of bonds is another central feature. Schiff bases are very important in a number of biological reactions, not the least in vision. For such complex systems, the use of chemometric methods is invaluable.