Second-harmonic generation , nonlinear optical rotation effects

The nonlinear optical properties of rotaxanes and catenanes were studied mainly by three techniques the optical second and third harmonic generation and the electro-optic Kerr effect. As already mentioned, the harmonic generation techniques give the fast, electronic in origin, molecular and bulk hyperpolarizabili-ties, whereas the electro-optic methods are sensitive to all effects which induce optical birefringence, such as e.g. the rotation of molecules. Therefore the last technique is very useful to study the rotational mobility of molecules and/or their parts. 

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