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Introduction of diarylethene based MOFs

https://doi.org/10.1016/j.mtsust.2022.100149

Although the azobenzene class of photochromes is known to experience drastic structural alteration, only modest light absorption changes are exhibited and the photo-induced isomerization process is imperceptible to human eyes. Different from azobenzene photochromes, diarylethene derivatives undergo photo-triggered isomerization involving ring-opening and ring-closing transformations induced via UV and visible light irradiation, respectively. Moreover, such transformation is often accomplished by color changes as two isomers suggest different light absorption performance; for example, strong UV light results in the absorption in ring-opening isomers while strong visible light causes the absorption in ring-closing isomers [32]. The primary features of diarylethene derivatives are impressive fatigue-resistance and thermally irreversible properties. Apart from that, they also possess high photostability enabling these derivatives to undergo more than 104 phototriggered coloration/decoloration cycles with a lifetime longer than a thousand years under 30 °C [33].

Diarylethene based MOFs are also equipped with superior photo-induced color switching properties and photostability. Jason and their co-workers reported the first MOFs containing dithienylethene (DET), named DMOF-1@DTE [34]. When irradiated under UV light (365 nm), the DMOF-1@DTE-o crystals immediately turned to dark red, and then switched back to their pristine colorless state via replacement of UV irradiation with visible light. Besides, the photo-induced generation of red species in crystals occurred faster than the latter switching back to the colorless state. Furthermore, such coloration/decoloration cycles can be repeated numerous times [15]. In addition, Michael et al. [34] reported bistable diarylethene-based MOFs. The yellow crystals of ring-opening PSZ-1 could be converted to violette crystals of ring-closing PSZ-1 upon exposure to UV-light (λ < 254 nm), and then returned to yellow crystals of PSZ-1-open with subsequently exposed visible light (λ > 515 nm). Furthermore, such reversible color changing photoisomerization can be maintained for 5 cycles under irradiation of 5 UV/Visible light circulations.

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