On the flexibility of 1,4-bis(phenylethynyl)benzene butyl ester organic crystal featuring mobile components

The quest for organic materials with compliant mechanical properties has significantly increased in the past few years in materials science and engineering. Crystalline organic compounds are excellent candidates for exploring and developing those long-lasting properties in the solid state since their fine structural functionalization may provide them with unique flexible behaviors. This study describes the 1,4-bis(phenylethynyl)benzene butyl ester synthesized in four steps and whose crystal can display elastic and elasto-plastic responses upon action with an external stimulus. A detailed characterization by single crystal X-ray diffraction revealed a layered crystal array that results from π-π stacking interactions and C-H···O bonds. Complementarily, variable temperature solid-state 13C and 2H NMR studies were carried out to probe the motion of the different components of the molecule and explore their possible association with the mechanical features. The compiled evidence indicates that the central phenylenes and the butyl groups experience molecular motion at different timescales, which, combined with the crystal array, facilitate the observed elastic and elasto-plastic flexibility. The results presented here not only contribute to advancing our understanding of flexible behavior but also could inspire potential applications such as flexible electronics.