Switching Properties of a Spiropyran–Cucurbit[7]uril Supramolecular Assembly: Usefulness of the Anchor Approach

Abstract

A nitrospiropyran, which was modified with a cadaverine-derived anchor, was investigated with respect to its thermally-induced isomerizations, hydrolytic stability of the merocyanine form, and the photochromic ring closure. The host-guest complexation of the anchor by the cucurbit [7]uril macrocycle, evidenced by absorption titration, NMR spectroscopy, and electrospray ionization mass spectrometry, produced significant improvements of the switching properties of the photochrome: a) a ca. 70 times faster appearance of the merocyanine form, b) a practically unlimited hydrolytic stability of the merocyanine (two and a half days without any measureable decay), and c) a fast, clean, and fatigueresistant photoinduced ring-closure back to the spiro form. The importance of an adequate molecular design of the anchor was demonstrated by including control experiments with spiropyrans with a shorter linker or without such structural asset.

Characterization of the Thermal and Photoinduced Reactions of Photochromic Spiropyrans in Aqueous Solution

“…The synthesis of 1 , 5 2 , 9 4 , 44 and 6 (7) have been described earlier, whereas the synthesis of 3 and 5 are outlined in the Supporting Information. The ring-opened forms (MC and MCH + ) were prepared by heating the SP isomer in an aqueous solution at pH 1 until the sample was fully converted to the MCH + form (ca.…”

“…These compounds have been studied in the contexts of photo- and pH controlled DNA-binding, 5,7 photoinduced cytotoxicity, 9 membrane interactions, 8 and supramolecular complex formation. 44 Owing to the potential applicability in diverse fields, the ring-opening mechanism, 46−48 conformational distribution, 48,49 and photochemical properties 50,51 of various derivatives have also been addressed by theoretical investigations. Although the spiropyrans represent a very versatile class of photochromic compounds with several promising candidates for future use in biological applications, the behavior in aqueous media is relatively unexplored.…”

Visible Light–Induced Supra‐Amphiphilic Switch Leads to Transition from Supramolecular Nanosphere to Nanovesicle Activated by Pillar[5]arene‐Based Host–Guest Interaction

“…Therefore, the UV–vis spectroscopy was conducted to characterize the photoresponsiveness of the guest G and host–guest complex WP5⊃G ( Figure a,b). In UV–vis spectra of G in aqueous solution, two absorption peaks at 268 and 515 nm were observed, which are the characteristic peaks of G S and G M, respectively (Figure a, red line) . The peak at 515 nm indicates the spontaneous isomerization of G S to G M because water stabilizes G M due to hydrogen‐bonding interaction.…”

Drug Delivery by Controlling a Supramolecular Host–Guest Assembly with a Reversible Photoswitch

“…As an example, the mole fraction of the flavylium cation at the equilibrium is estimated to be 14 % for a 1.9×10 −5 m solution of 1 a in the presence of 5.0×10 −4 m of CB7 at pH 3.9 (see the Supporting Information). It is worth noting that the design of reversibly addressable multicomponent systems consisting of CB host–guest complexes and photoresponsive switches is not a trivial task, because the presence of the host macrocycle often leads to a stabilization of the photoproduct . However, it is also important to note that, for drug delivery applications, reversibility is not a pre‐requirement at all.…”