Construction of photoswitchable rotaxanes and catenanes containing dithienylethene fragments.

Mechanically interlocked structures such as rotaxanes and catenanes provide a novel backbone for constructing functional materials with unique structural characteristics. In this study, we have designed and synthesized a series of photoswitchable rotaxanes and catenanes containing photochromic dithienylethene fragments using a template-directed clipping approach based on dynamic imine chemistry. Their structures have been confirmed using NMR, mass spectrometry and elemental analysis. Investigations into their photoisomerization properties indicated that these dithienylethene-based mechanically interlocked molecules have good reversibility and excellent fatigue resistance upon irradiation with UV or visible light. Interestingly, the mechanically interlocked molecules containing two dithienylethene backbones display around a 2-fold increase in the molar absorption coefficient compared with that of the mono dithienylethene derivative. Furthermore, the introduction of the fluorophore pyrene in the dithienylethene component facilitates these molecules to serve as fluorescent switches.