(C10N2H10)(HI2O6)(HIO3)(IO3): A Birefringent Material Featuring Large π-Conjugated Organic Cation and Two Types of Iodate Anions

Birefringent crystals, which can modulate and polarize light, play a vital role in the development of optical sensors and optoelectronic devices. Herein, we synthesized a new birefringent crystal [(C₁₀N₂H₁₀)(HI₂O₆)(HIO₃)(IO₃)] with large birefringence by integrating the large π-conjugated 4,4′-bipyridine group with two types of iodates anions ([IO₃]⁻ and [HI₂O₆]⁻) characterized by high polarizability anisotropy and strong stereochemically active lone pairs (SCALP). The crystal exhibits a large measured birefringence of 0.171 at 550 nm, surpassing most organic–inorganic hybrid iodate birefringent materials reported in the literature. Theoretical analyses reveal that the optical properties of the crystal arise primarily from the synergistic interactions between the π-conjugated 4,4′-bipyridine group and I–O groups. This research presents an effective method for the strategic integration of large π-conjugated organic cations into iodates, facilitating the design of novel birefringent materials and encouraging further exploration of superior birefringent substances.