Conjugation length, nonlinear optics, molecular

The nonlinear optical properties of polydiacetylenes are subject of an increasing interest in last years (1-4). This is due to the fact that polydiacetylenes are a one-dimensionnal system of higly polarizable conjugated tt elections The polarization depends strongly on electron delocalization length Moreover, the electronic origin of hyperpolarizability implies short response times On the other hand, the wave dispersed measurements of molecular hyperpolarizabilities yield information about forbidden electronic transitions In fact the bulk polarization can be developped in external electric field power series ... 

Kanbara, H., Kobayashi, H., Kaino, T, Ooba, N., and Kurihara, T., Molecular-length dependence of third-order nonlinear optical properties in conjugated organic materials, J. Phys. 

The molecular hyperpolarizability of charged ionic compounds was not directly accessible for measurement until the HRS method was reestablished [36]. Therefore only recently research has been focused on the effect of donor or acceptor substitution and elongation of the conjugation path length to demonstrate the engineering guidelines for enhancing molecular optical nonlinearities. 

---