Rotational symmetry dication assembling ferroelectric, thermochromic and circularly polarized luminescent...

Noncentrosymmetric (NCS) structure crystalline materials exhibit a range of high-tech applications; however, the controllable synthesis of NCS materials using achiral molecular building blocks remains a great challenge. Herein, we present a crystal engineering strategy for constructing NCS multifunctional materials. We designed 1,4-diazabicyclo[2.2.2]octane (DABCO) derivative dication, which adopts a chiral conformation, despite lacking chiral carbon atoms. These dications were assembled with tetrahedral [MnX₄]^2- anions to induce asymmetry into the structure. The high directionality H⋯X interactions between the anions and cations induce and stabilize NCS ion-pair structures, leading to NCS crystallization. We successfully obtained an NCS hybrid crystal, [H-Pr-DABCO]MnBr₄ (where H and Pr represent proton and normal-propyl groups, respectively). This compound crystallizes in a polar space group P2₁ at room temperature and undergoes a reversible phase transition between two polar phases. This chiral-polar hybrid crystal integrates multiple functionalities, including switchable dielectric behavior, reversible thermochromism, second-order nonlinear optical activity, ferroelectricity, and circularly polarized luminescence. Moreover, the material exhibits a notable spontaneous polarization of 21.5 µC cm^-2, close to that of the typical inorganic ferroelectric BaTiO₃. This work elucidates a design strategy for constructing multifunctional materials, highlighting their potential for application in advanced devices.