Molecular motion–structure–property correlation in a polymorphic AIEgen with mechanochromic and piezoelectric functions

Establishing direct correlations between molecular motion, crystal structure, and macroscopic properties is essential for designing responsive functional materials. Here, we report a malononitrile-based aggregation-induced emission luminogen (AIEgen), TPA-CN , that crystallizes into multiple polymorphs exhibiting distinct optoelectronic behaviors. In dilute solution, TPA-CN exhibits excitation-dependent emission spanning from sky blue to red under irradiation from 375 to 425 nm, arising from conformational flexibility and multiple excited-state transitions. In the solid state, subtle differences in crystal packing—governed by torsional angles and intermolecular interactions that modulate dipole moments—lead to pronounced variations in luminescence color and piezoelectric response. Mechanical grinding induces mechanochromic emission shifts without phase transitions, as confirmed by PXRD. Comparative analysis of crystallographic data, Hirshfeld surface mapping, and non-covalent interaction (NCI) calculations reveals that weak intermolecular interactions critically regulate crystal packing, ultimately producing distinct emission colors and behaviors. Notably, the non-centrosymmetric polymorph ( Pca 2₁) exhibits strain-sensitive piezoelectric currents up to 562 pA under 0.51 % strain, with a piezoelectric coefficient ( d ₃₃) of 1.77 pm·V −1 and a low Young's modulus of 6.75 GPa. Parallel device configurations further enhance mechanical sensitivity, enabling detection of microvibrations. This study reveals how minor conformational changes, and polymorphic packing can orchestrate dual photonic and piezoelectric functions, establishing a unified motion–structure–property paradigm. These insights advance the rational design of multifunctional organic materials for flexible sensing, soft electronics, and energy-harvesting applications. • Molecular Adaptability to Polymorphism : The malononitrile-based AIEgen TPA-CN exhibits excitation-dependent emission in solution due to conformational flexibility. Its solid-state polymorphs, governed by subtle packing and conformational variations, display significantly distinct luminescence colors. • Piezoelectric Sensitivity & Amplification : The non-centrosymmetric TPA-CN polymorph demonstrates remarkable strain-sensitive piezoelectricity, generating currents up to 562 pA under minimal strain (0.51%). Parallel device configurations further amplify sensitivity, enabling microvibration detection. • Mechanism-Driven Material Design : This work establishes a unified motion-structure-property relationship, providing a foundational framework for designing multifunctional organic materials tailored for sensing and energy applications.