Construction of Mechanically Interlocked Fluorescence Photoswitchable [2]Rotaxane with Aggregation-Induced Emission and Molecular Shuttling Behaviors.

Here, we report the design, synthesis, and optical behaviors of a multistimuli responsive [2]rotaxane system constructed from noncovalent interactions between diarylethene (DAE)-based axle and a tetraphenylethene (TPE)-based macrocycle using a snapping supramolecular assembly approach. The shuttling behavior of the macrocycle (Ring-TPE) between dialkylammonium and urea stations could be realized by the influence of acid-base stimuli using 1H NMR spectroscopy. Switching between the open-form (OF) [2]rotaxanes (DAE-R1-OF and DAE-R2-OF) is highly reversible using external chemical stimuli. These rotaxane systems exhibit enhanced blue fluorescence in their aggregation states despite being weak or nonemissive in solution. A significant increase in fluorescence emission intensity of typical TPE in DAE-R1-OF and DAE-R2-OF at ca. 467 nm was observed as the water content was increased to ≥70% in CH3CN/H2O solvent mixtures. However, the fluorescence emission of TPE at its maximum aggregation state (95% fw) could be rapidly quenched upon UV light irradiation due to a very efficient energy transfer from the excited TPE (donor) to the closed form of DAE (acceptor). In contrast, OF DAE does not affect the fluorescence of the TPE unit, which remains at high level. Furthermore, the [2]rotaxanes showed excellent photochromic and fluorescent properties in solution, making them suitable for information storage and reversible photo-patterning applications.

Stiff-Stilbene-Bridged Biscalix[4]arene as a Highly Light-Responsive Supramolecular Gelator.

A newly designed stiff-stilbene functionalized biscalix[4]arene in its cis form Z-1 could be near-quantitatively photoswitched to the trans-isomer E-1 under irradiation of 385 nm UV light. The trans-biscalix[4]arene E-1 was found to be a supergelator in nonpolar organic solvents, e.g., cyclohexane, hexane, pentane, and ether, with critical gelation concentrations as low as 0.2, 0.5, 0.5, and 0.4% w/v, respectively. The cis-trans configurational isomerism of biscalix[4]arene 1 resulted in distinct self-assembly modes, leading to interesting microscopic morphological changes from honeycomb and ringlike structures to rodlike dense fibrous networks.