Third-order microscopic nonlinearities of very long chain polyenes: saturation phenomena and conformational effects Original Research Article

Using the living cyclopolymerization of diethyldipropargylmalonate, very long polyenes (up to 1100 carbon–carbon double bonds) are now available. Molecular masses of these polyenes are determined using the MALDI-TOF technique. Third-order polarizabilities γ of polyene-like molecules with very long conjugation length (N up to 1100 carbon–carbon double bonds) are measured using third-harmonic generation at 1.9 μm in THF solutions. γ values saturate around N=60 double bonds. Modelization of the dependence of γ with respect to N is based on a representation of a conjugated chain as a collection of planar segments separated by large angular breaks. A very good quantitive agreement between calculated and experimental data, both in terms of saturation length and γ/N values is clearly demonstrated.