C3N6H7SO3NH2: non-π-conjugated tetrahedra decoupling π-conjugated groups achieving large optical anisotropy and wide band gap

Abstract

The exploration of birefringent crystals with large optical anisotropy and wide band gaps is a hot and challenging research topic. In this work, a new organic–inorganic hybrid crystal C₃N₆H₇SO₃NH₂ was successfully designed and synthesized by the aqueous solution method. The UV-vis diffuse spectrum shows that it exhibits a large experimental band gap of 5.53 eV. The decoupling of the non-π-conjugated [NH₂SO₃] groups to the melamine π-conjugated system results in a short cutoff edge of 206 nm, and the planar structure of the π-conjugated groups makes the compound maintain a higher birefringence (0.340@546 nm). The calculation results of the density of states (DOS) and electron density difference (EDD) show that the optical properties are derived from the synergistic interaction of [NH₂SO₃] and [C₃N₆H₇] groups. The introduction of non-π-conjugated groups can effectively decouple π-conjugated interactions between π-conjugated groups, which is an effective way to design large birefringent and wide band gap birefringent crystals.