Deprotonation-Regulated Conformational Switching in Malonates Enables High-Performance Ultraviolet Polar Crystals

Polar crystal materials hold significant potential for advanced scientific and technological applications; however, their synthesis remains challenging due to stringent symmetry requirements. In this work, flexible π-conjugated malonate groups with high polarity and diverse conformations were employed as polar functional basic modules (FBMs) to overcome this challenge. Three new crystals, RbLi(C3H2O4)·H2O, Rb2Li(C3H3O4)3·H2O, and C(NH2)3(C3H3O4), were successfully synthesized via a deprotonation-regulated conformational switching strategy. Remarkably, all three compounds crystallize in polar space groups and simultaneously exhibit strong second-harmonic generation responses (1.5–3.0 × KH2PO4 (KDP)), large birefringence (0.043–0.163@546 nm), and short UV cutoff edges (230–244 nm). This study not only discovers three promising UV polar crystals but also elucidates the conformational evolution of malonate-based FBMs, offering valuable guidance for the rational design of new polar crystal materials.