The fluorescence enhancement (“turn‐on”) response of the amyloid‐sensing dye thioflavin T (ThT) is examined in vacuo, where solvent interactions are absent. Upon the complexation of ThT with a derivatized β‐cyclodextrin, heptakis‐[6‐deoxy‐6‐(3‐sulfanylpropanoic acid)]‐β‐cyclodextrin, turn‐on responses in both the gas phase and solution phase were observed. In contrast, turn‐on response was not detected when ThT was bound to gaseous cucurbit[7]uril or human telomeric DNA 22AG, whereas clear turn‐on response occurs in solution. The observed difference in turn‐on response in the gas phase emphasizes the key interplay between chromophore, host and solvent and demonstrates the utility of gas‐phase spectroscopy to tease out the balance among intermolecular forces driving the behavior of important chromophores in solution.

A new form of DNA-binder Hoechst 33258 is stabilised upon desolvation. Altered optical properties include a distinct green fluorescence.