Third-order nonlinear optical properties of in-backbone substituted oligo(triacetylene) chromophores

A new approach to tuning the nonlinear optical properties of hybrid oligo(triacetylene) compounds is studied. The method is based on the insertion of a central heterospacer group between two (E)-hex-3-ene-1,5-diyne moieties. A significant increase in the second hyperpolarizability γ is expected if the central spacer fragment is an extended conjugated chromophore. We present a series of molecules with enhanced second hyperpolarizability caused by the presence of highly conjugated spacer groups, which increase the overall π-electron delocalization. Some metal complexes obtained from the coordination of these hybrid oligomers to transition-metal centers have also been investigated and revealed substantial differences in the capacities of the metal centers to act as electronic bridges. Finally, we show that theoretical predictions of the relative differences in the second hyperpolarizabilities of the new spacer compounds are in good agreement with the experimental results.