An organic-inorganic hybrid birefringent material with diverse functional groups

Birefringent materials are vital materials to modulate the polarization of light, and play a key role in plorization devices such as linear optical devices, optical communication devices, and fiber optic sensors. It is still a challenge to design excellent birefringent materials. Herein, we report an organic-inorganic hybrid oxalate birefringent material, (CN4H7)SbC2O4F2(H2O)(0.5), by introducing organic delocalized pi-conjugated [CN4H7](+) and [C2O4](2-) groups, and stereochemical active inorganic SbO4F2 polyhedra. (CN4H7)SbC2O4F2(H2O)(0.5) exhibits a large birefringence (Delta n = 0.126@546 nm) that is almost equal to that of the well-known birefringent material alpha-BaB2O4. Theoretical calculations reveal that the distinguished birefringence should stem from the synergistic arrangement of pi-conjugated [CN4H7](+) and [C2O4](2-) planar groups, and highly distorted SbO4F2 polyhedra with a stereochemically active lone pair. The synergistic effect of pi-conjugated systems and the lone pair electrons greatly boosts the birefringence, which is helpful for the development of high-performance birefringent materials.