Coordination Nanocage Research Articles

Host to Guest Energy Transfer in a Self-assembled Supramolecular Nanocage Observed by Picosecond Fluorescence Quenching

Abstract The host–guest energy transfer process in a self-assembled system was investigated by picosecond time-resolved fluorescence spectroscopy. A self-assembled coordination nanocage (Pd6L4) was photoexcited and the appearance of the fluorescence from an encapsulated guest acridine dye molecule was observed. The time constant (1.3 ns) as well as the efficiency (9%) of the energy transfer from the nanocage to the guest molecule was determined.

Cavity-directed synthesis within a self-assembled coordination cage: highly selective [2 + 2] cross-photodimerization of olefins.

Herein reported is the highly selective [2 + 2] cross-photodimerization of olefins within a self-assembled coordination cage that acts as a molecular flask in an aqueous medium. An M(6)L(4) coordination nanocage that self-assembles from six Pd(II) complexes and four tridentate ligands accommodates two different kinds of large olefin molecules such as acenaphthylene and 5-ethoxynaphthoquinone in a pairwise selective fashion. This prerequisite recognition mode makes possible the selective [2 + 2] cross-photodimerization of the olefins within the cavity. The reaction is extremely efficient in terms of reaction rate, stereoselectivity, and, most importantly, pairwise selectivity. Maleimide derivatives, which themselves are photochemically inactive under ordinary conditions, are also cross-dimerized with acenaphthylene or dibenzosuberenon quite efficiently. These results are in sharp contrast to those of common photodimerization in organic media, where the yields and selectivities are generally poor to moderate. The key step of the exclusive formation of the cross-dimers stems from the selective formation of ternary complexes before irradiation, which is governed by the size compatibility of the guests with the confined space of the cavity.

Self-assembled M(6)L(4)-type coordination nanocage with 2,2'-bipyridine ancillary ligands. Facile crystallization and X-ray analysis of shape-selective enclathration of neutral guests in the cage.

Hollow and roughly spherical cage 1 (ca. 2 nm in diameter) is self-assembled from 2,4,6-tri(4-pyridyl)-1,3,5-triazine (2) and Pd(diamine)(ONO(2))(2) (3). This cage compound enclathrates a variety of neutral organic molecules in an aqueous phase. Unlike cage 1a, which possesses ancillary ethylenediamine ligands on the metal centers, 2,2'-bipyridine(bipy)-protected cage 1b is easily crystallized, making possible the detailed analysis of the enclathration geometry of guests by X-ray crystallographic study. It is found that guests are enclathrated in three different manners, depending upon the shape and the size of the guests: tetrahedral 1:4 complexation, orthogonal 1:2 complexation, and a simple 1:1 complexation. The solution structures elucidated by NMR are in good accordance with the solid structure, showing that the enclathration geometries in the solid state are kept even in solution.

“Ship-in-a-Bottle” Formation of Stable Hydrophobic Dimers of cis-Azobenzene and -Stilbene Derivatives in a Self-Assembled Coordination Nanocage

“Ship-in-a-Bottle” Formation of Stable Hydrophobic Dimers of <i>cis-</i>Azobenzene and -Stilbene Derivatives in a Self-Assembled Coordination Nanocage