Helical Molecular Springs under High Pressure

Although the unique structure of helicenes resembles molecular springs, the effects of pressure on their extension–contraction cycles have rarely been explored. Herein, we investigated the fluorescence of two π-extended [n]helicenes with different helical lengths n, here named [7] and [9], under high pressure in a diamond anvil cell. Based on experimental results and theoretical calculations, the mechanical and fluorescent properties of the molecular springs were found to be influenced not only by the intermolecular packing, but also by the intramolecular π-π interactions between their overlapping helixes. As a more rigid molecular spring, [9] exhibited a more sensitive response of its fluorescence to hydrostatic pressure than [7]. Our results provide new insights into structure-property relationships under high-pressure conditions and verify the potential of helicenes as molecular springs for future applications in molecular machines.