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.