Construction and optical properties of dithienylethene-based photoswitchable [n]rotaxane (n = 2, 3)

- Photoswitchable [n]rotaxanes based on dithienylethene unit were synthesized.
- The photochromic properties and fluorescence behaviors were also investigated.
- Non-covalent components could influence the photoswitching properties.
- Photochromic signal (such as molar absorption coefficient) t can be integrated.

Mechanically interlocked structures such as rotaxanes and catenanes provide a novel backbone for constructing functional materials with unique structural characteristics. In this study, the novel photoswitchable [n]rotaxanes 11 and 12 based on dithienylethene unit were efficiently synthesized by the classical template-directed clipping approach. And their structures were well-confirmed by NMR, MS and elemental analysis. Investigation on photochromic properties indicated that dithienylethene-based [n]rotaxanes had good reversibility and excellent fatigue resistance upon irradiation with UV or visible light. And they displayed also excellent fluorescence switchable behavior. Interestingly, It was found that [2]rotaxane 11 had better photoisomerization properties in comparison to its corresponding macrocycle 4, which indicated that the non-covalent components on the [2]rotaxane 11 could influence the photoswitching properties. Furthermore, the mechanically interlocked molecules containing two dithienylethene backbones displayed around a 2-fold increase in the molar absorption coefficient compared with that of the mono dithienylethene derivative, which was consistent with the reported [n]rotaxane 9 and 10.

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