Predicting and Rationalizing Piezoelectricity in Racemic Bioorganic Molecular Crystals

Racemic crystals, often presumed to favour centrosymmetric packing and lack polar functionality, conceal an unlikely and underexplored capacity for longitudinal piezoelectricity. Here, we report a broad computational exploration demonstrating that certain bioorganic racemic systems exhibit pronounced piezoelectric responses, comparable to leading single-crystal materials. Despite their inherent mirror symmetry at the molecular level, the modelled crystal structures lack inversion symmetry, giving rise to significant electrical polarisation under mechanical stress, as predicted by our density functional theory (DFT) calculations. Our top-performing stable racemic crystals exhibit effective longitudinal piezoelectric strain response of up to 28 pC/N, more than twice that of benchmark DL-alanine (12.5 pC/N), combined with low dielectric constants (<5) and high mechanical flexibility. These results position our modelled racemic molecular systems as a promising, bio-friendly platform for soft, sustainable and lead-free piezoelectric devices. Our findings overturn conventional assumptions about the structural and functional limitations of racemic crystals as a material class, revealing their suitability for next-generation piezoelectric applications. Six of the racemic organic systems studied exhibit piezoelectric strain coefficients exceeding 10 pC/N, highlighting their viability as efficient and environmentally friendly alternatives to conventional inorganic materials.