Helical foldamers constitute particularly relevant targets in the field of host-guest chemistry, be that as hosts or substrates. In this context, the strategies reported so far to control the dimensions and shape of foldamers mainly involve modifications of the skeleton through covalent synthesis. Herein, we prepared an oligopyridine dicarboxamide foldamer substituted by photo-active tetraphenylethylene units (TPE). We demonstrate that it is possible to toggle the length of a helical foldamer by two means. First, the elongation of foldamers can be tuned by adjusting the concentration, as demonstrated by DOSY NMR spectroscopy and X-ray diffraction analyses on both the single and the double helix structures. Secondly, and in a more original manner, a photo-induced protonation process triggered by TPE units promotes a novel pathway to unfold helical foldamers, leading to dramatic conformational and spectroscopic changes.