(CNH)(HIO)(HIO)(IO): 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 [(CNH)(HIO)(HIO)(IO)] with large birefringence by integrating the large π-conjugated 4,4'-bipyridine group with two types of iodates anions ([IO] and [HIO]) 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.