Organic Materials for Second-Order Non-Linear Optics

Over the past 15–20 years, the non-linear optical (NLO) response of organic molecules has been of wide interest to organic and physical chemists, as well as physicists and chemical engineers. This interest arises from the possible use of such organic materials. In principle, photonics or the hybrid technology optoelectronics, both based on non-linear optical phenomena, can supersede electronics in communication technology. These technologies allow many operations that are currently effected with electron conduction to be replaced by operations based on light conduction. Many problems are encountered when it comes to the translation of a molecular property into a bulk property. It has transpired that some of these problems are not easy to solve with classical NLO-phores that mostly belong chemically to the class of merocyanine dyes. New design strategies for organic molecules and their respective bulk structures, crystals or oriented composite materials like polymers, are needed. Only a more fundamental understanding of these issues will allow rational optimization of molecular and bulk properties. This chapter surveys second-order molecular polarizabilities of organic molecules. Emphasis is given to the underlying of physical principles of non-linear optics (e.g. molecular topology), and to the establishment of structure–property relationships.