Rational Design of Noncentrosymmetric Organic–Inorganic Hybrids with a π-Conjugated Pyridium-Type Cation for High Nonlinear-Optical Performance

Organic–inorganic hybrid materials have attracted increasing attention due to their unique superiority by combining the features of organic parts with inorganic parts. Herein, two organic–inorganic hybrid nonlinear-optical crystals, [C 5 H 6 O 2 N 3 ] 2 [IO 3 ] 2 ( I ) and [C 5 H 6 O 2 N 3 ][HSO 4 ]·H 2 O ( II ), were successfully synthesized in aqueous solution by selecting 2-amino-3-nitropyridine as the cation and different anions of [IO 3 ] − and [HSO 4 ] − . The two compounds crystallized in the noncentrosymmetric space groups of P 2 1 and P 2 1 2 1 2 1, respectively. I displays second-harmonic-generation (SHG) effects of 2.4 × KDP (KH 2 PO 4 ) and a large birefringence (Δ n cal ∼ 0.22). Moreover, II exhibits a stronger SHG response of 5.2 × KDP, an enhanced band gap (2.81 eV), as well as a large birefringence (Δ n cal ∼ 0.25). This work points out a new feasible path for the rational design of high-performance organic–inorganic hybrid materials.