From centrosymmetric (C 4 H 8 N 5 )(SbF 4 ) to polar (C 4 H 7 N 4 O)(SbF 4 ): a new UV nonlinear optical material achieved by functional group modulation

The design and synthesis of new ultraviolet nonlinear optical (NLO) materials is challenging due to the constraint relationship between their NLO efficiency and optical bandgap. Using a functional group modulation strategy, the π-conjugated organic cations and the distorted [SbF₄]^- anions are assembled in both antiparallel and parallel arrangement modes, resulting in two new organic-inorganic hybrid fluoroantimonites, namely, centrosymmetric (C₄H₈N₅)(SbF₄) and polar (C₄H₇N₄O)(SbF₄). The polar (C₄H₇N₄O)(SbF₄) demonstrates excellent comprehensive properties, including a strong SHG effect (4.2 × KDP), a wide bandgap (4.40 eV) and a short phase matchable wavelength (263 nm). This SHG intensity is the largest among the organic-inorganic hybrid perfluoroantimonites with an optical bandgap >4.20 eV. The SHG density calculation indicates that the NLO performance of (C₄H₇N₄O)(SbF₄) mainly comes from the parallel-arranged organic groups, with their contribution accounting for 89.49%. This work proves that the arrangement of π-conjugated organic ligands can be modulated to a parallel mode by adjusting the number of hydrogen bond donors. Combined with a wide HOMO-LUMO gap, the functional group modulation method is an effective strategy for designing and synthesizing ultraviolet NLO materials.