Deciphering the structure-property relationship in coumarin-based supramolecular organogel materials

Understanding the influence of the molecular architecture on the self-assembly and properties of supramolecular organogel materials is necessary for elucidating the structure-property relationship. Although conventional gelation motifs (e.g., amides, long alkyl side chains, and steroidal groups) have been considered essential for the effective gel process, the lack of gelation motifs hinders the development and self-assembly of non-conventional gelators. Herein, coumarin-based derivatives (1–12) without a conventional gelation motif were designed and synthesised by inducing a one-step reaction that entails fine-tuning the molecular architecture, particularly the position of the nitrogen atom in pyridine, the substitution position of pyridine, and the placement of methyl in coumarin. A previous gelation study revealed that 7-substituted coumarin-based derivatives with methyl (1–4) are highly efficient gelators that can self-assemble to form different nanostructures, and gelate various polar protic solvents. After small-scale modification of the molecular structures, Derivatives 5–6 self-assembled and only formed gels in the alcohol phase, whereas gels were not formed by Derivatives 7–12 in various solvents. Interestingly, the fluorescence property of these gels was significantly influenced by the dielectric constant and viscosity of the solvent. Furthermore, differences in the self-assembly and fluorescence of gelators were numerically investigated by performing density functional theory calculations and all-atom molecular dynamics simulations. This study provides a foundation for the development of a low-cost, non-conventional supramolecular organogel system with minimal building blocks, a modifiable self-assembly pathway, and alterable properties.