Hydrogen‐Bond‐Modulated Alignment of Iminodiacetic Acid Cations for Achieving Ultraviolet Second Harmonic Generation

Abstract With the advancement of laser technology, there is an urgent need to develop ultraviolet (UV) nonlinear optical (NLO) crystals with balanced performance. To simultaneously achieve a large bandgap, an appropriate birefringence, and a strong second harmonic generation (SHG) response, the [NH ₂ (CH ₂ COOH) ₂ ] ⁺ cation is selected as the functional building unit (FBU), leveraging its hybrid structure composed of both π‐conjugated and non‐π‐conjugated moieties. The (H ₂ PO ₃ ) ⁻ and (H ₂ PO ₂ ) ⁻ , featuring different numbers of hydrogen‐bond donors and acceptors, are selected as the direction‐guiding components to modulate the arrangement of the organic cations, promoting a preferential alignment. Accordingly, two novel organic‐inorganic hybrid compounds—[NH ₂ (CH ₂ COOH) ₂ ]H ₂ PO ₂ (IDAHPO) and [NH ₂ (CH ₂ COOH) ₂ ]H ₂ PO ₃ (IDAPO) are successfully synthesized. Among them, IDAHPO demonstrates a well‐balanced NLO property, including enhanced SHG response (1.2 × KDP and 0.13 × β ‐BBO), appropriate birefringence (Δ n = 0.118 @ 546 nm), and a short UV cut‐off edge (208 nm). This combination of properties enables the material to achieve phase‐matched SHG output of 266 nm, a critical and highly sought‐after laser wavelength. This strategy establishes a novel approach for the rational design and synthesis of UV NLO materials.