Design Novel Chalcone Crystals for Enhancement of Nonlinear Optical Activity and Higher Molecular Structural Stability

In the design of molecular organic nonlinear optical (NLO) chalcone crystals, how to balance the stability of the crystal structure and the π-conjugation length while enhancing the NLO activity of the chromophore remains a challenge. In this study, we have synthesized a series of crystals 6MNPP (C₂₀H₁₆O₂, Pca2₁), 6MN4TP (C₂₁H₁₈O₂, Pca2₁), 6MN4EP (C₂₂H₂₀O₂, Pca2₁), and 6MN3TP (C₂₁H₁₈O₂, P2₁) by adding a benzene ring in D−π–A−π–D structure design and introducing new functional groups with large differences in electron-donating ability at both ends of the molecule. All four crystals are non-centrosymmetric structures, and the identification of NLO activity has been well demonstrated by analysis and characterization. Remarkably, 6MNPP crystals are competitive with similar NLO chalcone crystals, mainly including a higher second harmonic generation efficiency (9 × KDP) and higher melting point (T_m = 151.6 °C). Furthermore, first-principles calculations show that the second-order NLO coefficient d₁₅ = 7.843 pm/V, at1064 nm. All the results suggest that 6MNPP crystals have significance potential in the NLO applications.