Origin of the saturation of the third-order optical nonlinear response of one-dimensional conjugated systems

The coupled quantum oscillator model is applied to the evaluation of conformational effects in thiophene and polyene oligomers. Thermochromism measurements on heptathiophene are presented and modeled. The effect of conformation is also studied in recently published nonlinear optical experiments on polyene oligomers. It is shown that the model accounts for a masterplot which summarizes the length dependence of the optical properties of conjugated molecules.