(3‐C₆H₁₀N₂)ZnX₄ (X = Cl and Br): Two Excellent UV Nonlinear Optical Crystals Designed by Combination of π‐conjugated and [ZnX₄]²⁻ Tetrahedral Units

To design excellent UV nonlinear optical crystals, via a combination of the two excellent genes, planar π-conjugated 3-(aminomethyl)pyridinium ((3-AMP)²⁺, (C₆H₁₀N₂)²⁺) and d¹⁰ metallic tetrahedral anion, two novel organic-inorganic hybrid (3-C₆H₁₀N₂)ZnX₄ (X = Cl and Br) bulk crystals are synthesized using a simple solution method. Remarkably, they exhibit excellent UV nonlinear optical performances, including in short UV absorption edge (229 and 235 nm), robust second harmonic generation (SHG) intensity (2.05 and 4.36 × KDP), suitable large birefringence (0.129-0.144@546 nm) and short phase-matching wavelength (238 and 262 nm). First-principles calculations elucidate that the excellent SHG performances of (3-AMP)ZnCl₄ and (3-AMP)ZnBr₄ are dominated by the synergetic contributions of planar π-conjugated (C₆H₁₀N₂)²⁺ and distorted [ZnX₄]^2- tetrahedral groups. This research not only provides two NLO-active genes but also paves the way for efficient exploration and rational design of organic-inorganic hybrid new NLO materials with optimal balanced optical performances.