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

Enhancing the first-order hyperpolarizability of chalcone by including functional groups with varying electron donating capacities in its molecular structure is an effective strategy for designing organic terahertz (THz) crystals. By substitution of a heterocyclic ring (pyridine or furan, respectively) for the benzene ring, two chalcone derivatives, 6MN3PP and 6MN2FP, were designed and synthesized. Solvent evaporation was used to harvest the 5 × 4 × 0.02 mm3 6MN3PP crystal, which had second harmonic generation (SHG) efficiency three times higher than KDP. The differences in macroscopic and microscopic nonlinear optical properties between crystals were investigated by combining theoretical calculations with experiments. Additionally, characterization was done on the optical, dielectric constant, and thermal stability. Remarkable, the 6MN3PP crystal has achieved THz output under optical rectification technology, which has great potential in nonlinear optical applications.