[C(NH2)3]2PO3(OH): A Deep-Ultraviolet Birefringent Crystal Enabled by Synergy of π-Conjugated Cations and Heteroleptic Tetrahedra

Birefringent materials are crucial optical materials that enable the control of polarized light in optical technologies, yet achieving high birefringence in systems dominated by non-π-conjugated units in the deep-ultraviolet (UV) region remains a significant challenge. Herein, a birefringent material, [C(NH2)3]2PO3(OH), was successfully synthesized by integrating π-conjugated [C(NH2)3] units and heteroleptic tetrahedra [PO3(OH)]. The short UV cutoff edge (<200 nm) and large birefringence (0.086 @ 546 nm) make [C(NH2)3]2PO3(OH) a potential deep-UV birefringent crystal. This study provides the experience for the design of deep-UV optical crystals.