RESUMO
For a molecular system, size and shape are of elementary importance for its function and properties. Therefore, the determination of distances within a molecule is essential. However, the commonly used methods are only suitable for distances smaller than 4â Å or larger than 15â Å. Here, we show that by incorporating a molecular spring, we can measure distances in macrocycles in the range of 10â Å using 13 C NMR spectroscopy. The accuracy of the method also allows to determine the temperature dependence of the distances. In one case, we find a contraction of the length by almost 10 % upon heating. This shrinking due to heating can be considered as inverse thermoelasticity at the molecular level and is a previously completely overlooked phenomenon that can be used in the future as a tool to change the length and, thus, the function of a system.
