Strong Second Harmonic Generation and Nonlinear Optical Activity in Chiral Supramolecular Polymers.

The growing demand for advanced optical materials has made nonlinear photonics a key area of research, particularly for developing new technologies. Therefore, this study focuses on chiral supramolecular structures, which are highly promising due to their exceptional second-order optical susceptibility (χ(2)) values. In particular, we investigated the origin and optical activity of second harmonic generation (SHG) in chiral polybinaphthalenes using femtosecond laser pulses. Our outcomes reveal a high χ(2) value, up to 7 pm/V, influenced by the attached chromophores at the polymer backbone. Structural analysis showed rodlike/helical structures that promote directional preference for the SHG signal. Simulations unveil that the SHG process is connected to the quasi-phase matching process, and the material's robust chiral structure leads to high optical activity observed via lock-in amplifier detection. In conclusion, the conjunction of high SHG values and optical activity of these supramolecular structures makes them excellent candidates for chiral photonics applications.