1. Introduction

The search for organic materials for non-linear optics (NLO) has revealed quite many compounds with high efficiency for frequency doubling of laser light, but they suffer from a lack of transparency. This is due to the generally accepted design of a NLO material which consists in connecting a donor and an acceptor group by a conjugated bridge which leads to highly coloured materials. To avoid the problems with this approach, we started to develop compounds whose hyperpolarizability relies on the existence of weak bonds. Here, the silatranes represent a well-studied class of stable molecules with a weak Si-N bond. Silatranes (2,8,9-trioxa-5-aza-1-silabicyclo[3.3.3]undecanes) are a special case of pentacoordinate silicon with unusal properties which have gained considerable interest over the last decades [1,2,3,4]. Interestingly, the silicon-nitrogen bond is ignored in the name used by Chemical Abstracts (it should rather be a tricyclic system).

We introduced chirality as only compounds which crystallize in non-centrosymmetric space groups give non-vanishing hyperpolarizabilities as bulk materials, e.g. in crystalline form, which is important for applications in devices. Only very few silatranes with a chiral backbone are known up to now [5,6]. Starting with (1S)-$\beta$-pinene as the source of chirality, we have prepared such a chiral silatrane and characterized it by X-ray structure analysis [7].

  

Figure 1: X-Ray structure of our chiral silatrane

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