A Pyrazinamide–Iodic Acid Cocrystal Exhibiting Strong Second Harmonic Generation for Nonlinear Optics

The development of high‐performance second‐order nonlinear optical (NLO) crystals with novel structural architectures remains a significant challenge. In this study, we present a new cocrystal, PZA‐IA (C 5 H 5 N 3 O∙HIO 3 ), which was synthesized by combining pyrazinamide (PZA) and iodic acid (IA). The cocrystal crystallizes in the polar space group Pca 2 1 . Its asymmetric unit comprises one C 5 H 5 N 3 O molecule and one HIO 3 molecule, which are linked by a strong hydrogen bond between the HIO 3 molecule's O─H group and the aromatic nitrogen atom of the C 5 H 5 N 3 O molecule. PZA‐IA exhibits exceptional comprehensive NLO properties: a strong second harmonic generation (SHG) response of 6.0 × KH 2 PO 4 , a wide band gap of 3.55 eV, a suitable birefringence of 0.143 at 1064 nm enabling phase matching, and a high laser‐induced damage threshold of 380.1 MW cm −2 . First‐principles calculations reveal that both molecular components contribute synergistically to the SHG effect. PZA and IA account for 59.96% and 39.51% of the total response, respectively. This work provides a new strategy for designing NLO materials in the future.