[C(NH2)3]2S2O8: combining delocalized and localized π-conjugate units to achieve strong optical anisotropy

Abstract

A new birefringent crystal [C(NH₂)₃]₂S₂O₈ was obtained by combining the π-conjugated [C(NH₂)₃] cation and the [S₂O₈] groups with localized O–O π-bonds. Optical measurements show that the UV cutoff wavelength of [C(NH₂)₃]₂S₂O₈ is 222 nm, and its birefringence is 0.102 at 546 nm. The calculated results show that its large birefringence is attributed to the synergistic effect of the [C(NH₂)₃] and [S₂O₈] units, which is the first case among known birefringent crystals. These results provide new insights into the design of superior birefringent materials.