Fig. 2
From: Reversible chromism of spiropyran in the cavity of a flexible coordination cage
Encapsulation of a spiropyrans within a self-assembled cage. a Encapsulation-induced deprotonation of 5. b Changes in the UV/Vis absorption spectra of 4 upon titrating with 5 (all spectra were recorded once equilibrium was reached). c UV/Vis absorption spectra of an aqueous solution containing different molar ratios of 4/5 at the same total concentration of the two species. The resulting Job’s plot reveals that the 4–5 complex has a 1:1 stoichiometry. d Partial 1H NMR spectra (400 MHz, D2O) of 4 in the presence of increasing amounts of 5. The downfield-shifted signals correspond to 4’s imidazole protons. The upfield-shifted signals are due to the methyl groups of encapsulated 5 (eq=equivalent). e Following the binding of guest 5 by cage 4 using UV/Vis absorption spectroscopy and NMR (replotted from b and d). f Two views of the X-ray crystal structure 5⊂4 (the cartoons show the orientation of the cage). The hydrogen atoms were removed for clarity. g The 4-induced ring-opening isomerization of spiropyran 6. h Structural formulas of spiropyrans 7 and 8 investigated as potential guests
