(C<sub>10</sub>N<sub>2</sub>H<sub>10</sub>)(HI<sub>2</sub>O<sub>6</sub>)(HIO<sub>3</sub>)(IO<sub>3</sub>): A Birefringent\nMaterial Featuring Large π‑Conjugated Organ

Birefringent crystals, which can modulate and polarize\nlight, play\na vital role in the development of optical sensors and optoelectronic\ndevices. Herein, we synthesized a new birefringent crystal [(C<sub>10</sub>N<sub>2</sub>H<sub>10</sub>)(HI<sub>2</sub>O<sub>6</sub>)(HIO<sub>3</sub>)(IO<sub>3</sub>)] with large birefringence by integrating\nthe large π-conjugated 4,4′-bipyridine group with two\ntypes of iodates anions ([IO<sub>3</sub>]<sup>−</sup> and [HI<sub>2</sub>O<sub>6</sub>]<sup>−</sup>) characterized by high polarizability\nanisotropy and strong stereochemically active lone pairs (SCALP).\nThe crystal exhibits a large measured birefringence of 0.171 at 550\nnm, surpassing most organic–inorganic hybrid iodate birefringent\nmaterials reported in the literature. Theoretical analyses reveal\nthat the optical properties of the crystal arise primarily from the\nsynergistic interactions between the π-conjugated 4,4′-bipyridine\ngroup and I–O groups. This research presents an effective method\nfor the strategic integration of large π-conjugated organic\ncations into iodates, facilitating the design of novel birefringent\nmaterials and encouraging further exploration of superior birefringent\nsubstances.