Chirality expression from hierarchical foldamer-mesoscopic helical silica frameworks†

Abstract

The interaction between racemic quinoline-derived helical oligoamide foldamers and mesoscopic silica-based helical frameworks was investigated. These foldamers displayed distinct chiroptical properties such as electronic and vibrational circular dichroism (ECD and VCD, respectively) and circularly polarized luminescence (CPL) when interacting with silica nanohelices (INHs) deposited as thin films. Dissymmetry factors (g_abs and g_lum) were influenced by drying kinetics, silica surface functional groups, and foldamer concentration and length. Washing co-assembled films of quinoline octamers and INHs in order to separate the two, revealed that ECD signals originated from molecular solution of foldamers which decreased over 7 minutes, indicating enantiomeric enrichment even though modest (∼4%) induced by INHs. The induced foldamer handedness matched with the helicity of the INHs. Enantiopure foldamers (helically locked M or P oligomers) exhibited enhanced or reduced ECD signals depending on their helicity alignment with INHs. This study highlights the interplay between molecular chirality and supramolecular organization of foldamers directed by silica nanohelices.