Phototransformation of Stilbene in van der Waals Nanocapsules

Abstract

We have utilized para-hexanoylcalix[4]arene nanocapsules as hosts to carry out phototransformations of cis- and trans-stilbene. Single-crystal X-ray diffraction studies were performed to define precisely the location of encapsulated stilbenes inside the capsule and to analyze possible pathways of phototransformation. cis-Stilbene stacks as a pi-pi dimer located at the center of the capsule, whereas trans-stilbene does not form such a dimer. Irradiation of the crystalline inclusion complexes of each isomer of stilbene in the solid state leads to the appearance of the second isomer, and after prolonged photolysis, photodimerization also occurs. syn-Tetraphenylcyclobutane is formed as the major product of dimerization and its yield depends on the time and intensity of irradiation. In most cases, the single crystals of the complexes remain intact during irradiation; hence, the nanocapsules have the potential to serve as robust nanoreactors in the solid state. The confinement in the nanocapsules is sufficient to keep the reacting molecules together, although this is less restrictive than for trans-stilbene crystals, in which the molecules cannot achieve a favorable orientation for dimerization.

Metallo-supramolecular capsules

“…Recent work by Ananchenko et al has described a series of van der Waals capsular assemblies formed by a series of p-alkanoylcalix [4]arenes [57][58][59]. The particular novelty associated with these assemblies is the ability to exchange the encapsulated guest species within a single crystal.…”

Mixed metal-organic nanocapsules

“…Encapsulated space is represented by a spheroid. (B) van der Waals capsule formed by two p-acylcalix [4]arenes, showing interdigitation of the hydrophobic alkyl chains [19,20]. bonded donors on the terminal portion, two such subunits can self-assemble into 'tennis ball' or 'softball'-shaped pseudospherical capsules, stabilized by hydrogen bonds (Fig.…”

Supramolecular Solids as a Medium for Single‐Crystal‐to‐Single‐Crystal E/Z Photoisomerization: Kinetic Study of the Photoreactions of Two Zn‐Coordinated Tiglic Acid Molecules

“…[25] This is often not the case for supramolecular solids. [18,19,26,27] In addition, isolation of a molecule in a supramolecular complex prevents the [2 + 2] dimerization or polymerization which frequently occur when C=C bonds are stacked in a parallel (or anti-parallel) fashion in crystals. [28] In preceding work we reported the SCSC E/Z isomerization of the E modification of (E)-2-methylbut-2-enoic acid, tiglic acid (HTA, see below) and chloroacrylic acid embedded in a CECR framework (CECR = C-ethylcalix [4]resorcinarene), [18,19] the latter reaction starting from both the pure Z and the pure E isomers.…”