Investigation of the intensity dependent transition from saturable absorption to reverse saturable absorption and ultrafast negative refraction in terthiophene-based chalcone derivatives

Two novel chalcone derivatives C12 & C13 are designed and synthesized. Terthiophene group is employed to provide the planar π-conjugated system in these molecules while the molecular planarity is tuned by the different substitutions at the terminal group. The ultrafast optical nonlinearities are investigated via transient absorption spectrum and Z-scan. It is generally assumed that a large planar π-system and strong intramolecular charge transfer can enhance the optical nonlinearities in organic nonlinear optical materials. However, the molecule with larger planar molecular structure displayed weaker nonlinear absorption due to the competition between saturable absorption and reverse saturable absorption. With DFT calculation, the structure-property relation and the enhancement of π-conjugated system on nonlinear absorption and refraction are discussed. The investigations and discussions may provide a different perspective of the nonlinear absorption and refraction in these organic molecules and the results also suggest that these chalcone derivatives are potential nonlinear refraction materials for all-optical applications.