Toward On-Demand Polymorphic Transitions of Organic Crystals via Side Chain and Lattice Dynamics Engineering

Controlling polymorphism,
namely, the occurrence of multiple crystal
forms for a given compound, is still an open technological challenge
that needs to be addressed for the reliable manufacturing of crystalline
functional materials. Here, we devised a series of 13 organic crystals
engineered to embody molecular fragments undergoing specific nanoscale
motion anticipated to drive cooperative order–disorder phase
transitions. By combining polarized optical microscopy coupled with
a heating/cooling stage, differential scanning calorimetry, X-ray
diffraction, low-frequency Raman spectroscopy, and calculations (density
functional theory and molecular dynamics), we proved the occurrence
of cooperative transitions in all the crystalline systems, and we
demonstrated how both the molecular structure and lattice dynamics
play crucial roles in these peculiar solid-to-solid transformations.
These results introduce an efficient strategy to design polymorphic
molecular crystalline materials endowed with specific molecular-scale
lattice and macroscopic dynamics.

调控多晶型（polymorphism）——即特定化合物可呈现多种晶体晶型的现象——仍是一项亟待解决的技术难题，对于功能性晶体材料的可靠制备而言亟需攻克。本研究设计了共计13种有机晶体，通过工程化手段使其包含可发生特定纳米级运动的分子片段，该运动有望驱动协同有序-无序相变（cooperative order–disorder phase transitions）。研究团队结合偏振光学显微镜（polarized optical microscopy）与冷热台（heating/cooling stage）联用技术、差示扫描量热法（differential scanning calorimetry）、X射线衍射（X-ray diffraction）、低频拉曼光谱（low-frequency Raman spectroscopy），以及密度泛函理论（density functional theory）与分子动力学（molecular dynamics）计算，证实了所有晶体体系中均存在协同相变，并阐明了分子结构与晶格动力学（lattice dynamics）在这类特殊固-固转变（solid-to-solid transformations）中的关键作用。本研究结果为设计具备特定分子尺度晶格与宏观动力学特性的多晶型分子晶体材料提供了一种高效策略。