The chiral α-trifluoromethylalanine is shown to induce and control the screw-sense preference of short Aib oligomers. Due to the electronic properties of the CF3 group, the screw-sense is inversed compared to that induced by its non-fluorinated isosteric l-α-MeVal analogue. It also plays the role of 19F NMR reporter allowing the easy determination of both the magnitude of the screw-sense preference