Solvent-dependent supramolecular assembly behavior of a coumarin-headed amphiphile

To study the effect of solvent on supramolecular self-assembly behaviors, a chiral courmarin-substituted glutamine amphiphile, L/DG-Cm, was synthesized for investigation. It was found that L/DG-Cm self-assembled into short nanotubes in toluene, while it formed longer nanotubes together with an obvious helix nanobelt structure for L/DG-Cm in DMSO, demonstrating that the nanotubes were formed by nanobelt rolling. The CD and CPL spectra revealed the same chiral property of the L/DG-Cm assemblies formed in toluene and DMSO. Theoretical calculations revealed that LG-Cm was prone to forming similar dimer structures in both DMSO and toluene. However, the distinct hierarchical packing ways in toluene and DMSO led to different nanostructures and chiroptical properties. Based on the temperature-dependent UV-visible and CD spectrometric measurements, LG-Cm was observed to aggregate in different supramolecular self-assembly modes, which was the cooperative (nucleation-elongation) mechanism in toluene and the isodesmic model in DMSO. This work proves that the solvent not only affects the self-assembly morphologies and properties but also determines the self-assembly pathways.