Pyridine Substitution Enhances Molecular Hyperpolarizability:\nNovel Promising 6MN-Based Chalcone Crystal for Terahertz-Wave Generation

Enhancing\nthe first-order hyperpolarizability of chalcone by including\nfunctional groups with varying electron donating capacities in its\nmolecular structure is an effective strategy for designing organic\nterahertz (THz) crystals. By substitution of a heterocyclic ring (pyridine\nor furan, respectively) for the benzene ring, two chalcone derivatives,\n6MN3PP and 6MN2FP, were designed and synthesized. Solvent evaporation\nwas used to harvest the 5 × 4 × 0.02 mm<sup>3</sup> 6MN3PP\ncrystal, which had second harmonic generation (SHG) efficiency three\ntimes higher than KDP. The differences in macroscopic and microscopic\nnonlinear optical properties between crystals were investigated by\ncombining theoretical calculations with experiments. Additionally,\ncharacterization was done on the optical, dielectric constant, and\nthermal stability. Remarkable, the 6MN3PP crystal has achieved THz\noutput under optical rectification technology, which has great potential\nin nonlinear optical applications.