Ferrocenes as Materials Displaying Non-Linear Optical Properties

2 Ferrocenes as Materials Displaying Non-linear Optical Properties. One of the most recent applications of ferrocene molecules exploits their non-linear optical properties. Firstly, however, we must describe the concept of ffffnon-linear optical properties.67,68 

The study of the changes of phase, frequency and intensity that the incident radiation undergoes on passing through the material constitutes the field of non-linear optics (NLO). It, in fact, focuses on the description of deviations from the linear behaviour predicted by the laws of classical optics. 

An electric field induces a polarization of the charge within a single molecule by the instantaneous displacement of the electrons with respect to the nucleus. In this manner an induced dipole and, hence, a dipolar moment, p, are generated. When the applied field is weak, the induced charge displacement is proportional to the strength of the field  

When the material is composed of an aggregation of molecules, one speaks of macroscopic polarization P, and for weak applied fields this is linearly dependent on the susceptibility % of the material in question, according to the relationship P = x E- 

It is evident that in centrosymmetric non-linear media the induced polarization in the +E direction is equal (in absolute value) to the induced polarization in the opposite direction -E. However, in 

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