Abstract
By combining extended π-conjugated structures and halogen substituents, two novel chalcone-based optical THz crystals were designed: CBC (C22H17ClO2, Pc) and TFBC (C23H17F3O2, P21). These crystals were synthesized and successfully grown using the solution evaporation method. The effects of different types and quantities of halogen substituents on hydrogen bonding interactions, molecular alignment, and nonlinear strength were analyzed. The second harmonic generation (SHG) efficiency, thermal stability, transmission spectra, dielectric constant, and THz generation of the crystals were characterized. Theoretical calculations were conducted to determine the hyperpolarizability, band gap, density of states, and nonlinear optical coefficients of the crystals. The results showed that the synthesized crystals exhibited higher transparency (≥85%) and SHG efficiencies of 9.5 times and 6.2 times that of standard potassium dihydrogen phosphate (KDP), respectively, compared to previously reported chalcone NLO crystals. For the first time, the THz generation efficiency of the two crystals was confirmed through the optical rectification method, with TFBC demonstrating a wider THz spectrum range compared to CBC.
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