Photo-responsive [2]catenanes: synthesis and properties.

A series of novel dithienylethene-based macrocycles containing ammonium moieties has been synthesized. They have been employed as templates to construct [2]catenanes showing their photoisomerization properties by means of a dynamic covalent chemistry approach. Their structures have been reliably confirmed by NMR, ESI-MS or MALDI-QTOF-MS, and elemental analysis, and their energy-minimized structures of open- and closed-ring isomers were investigated by the theoretical calculation. Investigation of the photochromic properties of these dithienylethene-based [2]catenanes has revealed good reversibility and excellent fatigue resistance upon irradiation with UV or visible light. Notably, formation of the [2]catenanes enhanced the photochromic properties compared with those of the corresponding macrocyclic ammonium salt, implying that the non-covalently interacting components of the [2]catenanes could affect the photoswitchable properties.