Nonlinear Optical Properties of Polyynes: An Experimental Prediction for Carbyne

We present the experimental determination of the vibrational contribution to molecular second hyperpolarizability (γvib) of very long polyynes that have been recently made available thanks to progress in chemical synthesis. Based on a simple theoretical model, the available experimental data allow estimating the asymptotic behavior of the vibrational contribution to molecular hyperpolarizability for increasing chain length.