Unraveling temperature-dependent supramolecular polymorphism of naphthalimide-substituted benzene-1,3,5-tricarboxamide derivatives

Abstract

Temperature plays a crucial role in regulating polymorphism in supramolecular polymers. Understanding the mechanism behind temperature-dependent supramolecular polymorphism is crucial as it provides an opportunity to tailor polymorphs for specific properties and applications. In this study, we present our findings on a naphthalimide-substituted benzene-1,3,5-tricarboxamide derivative, R-Nap-1, which exhibits two distinct polymerization pathways at varying temperatures. At 313 K, polymerization results in the formation of an M-chiral polymorph, whereas at 253 K, a P-chiral polymorph is formed. Both polymorphs are notably stable, remaining unchanged for over six months under ambient conditions. Theoretical calculations and experimental investigations allowed us to elucidate the mechanisms underlying these polymorphic transformations. The formation of the M-chiral polymorph at 313 K is attributed to the nucleation and growth of R-Nap-1 monomers once their concentration surpasses a critical threshold. Conversely, at lower temperatures (e.g., 253 K), the monomers undergo facile transformation into dimers due to a lower energy barrier and reduced Gibbs energy compared to the monomeric state. Subsequently, these dimers undergo nucleation-elongation to form the P-chiral polymorph when their concentration exceeds the critical polymerization concentration. The stability and lack of interconversion between the two polymorphs can be attributed to their close thermodynamic stabilities, as evidenced by variable-temperature CD spectra and DFT calculations. These findings highlight the importance of accurate temperature control in supramolecular polymerization processes, making a significant contribution to the understanding of supramolecular polymorphism, thus advancing the field of supramolecular chemistry.