Guest Encapsulation Alters the Thermodynamic Landscape of a Coordination Host

Abstract

The architecture of self-assembled host molecules can profoundly affect the properties of the encapsulated guests. For example, a rigid cage with small windows can efficiently protect its contents from the environment; in contrast, tube-shaped, flexible hosts with large openings and an easily accessible cavity are ideally suited for catalysis. Here, we report a "Janus" nature of a Pd 6 L 4 coordination host previously reported to exist exclusively as a tube isomer (T). We show that upon encapsulating various tetrahedrally shaped guests, T can reconfigure into a cage-shaped host (C) in quantitative yield. Extracting the guest affords empty C, which is metastable and spontaneously relaxes to T, and the T⇄C interconversion can be repeated for multiple cycles. Reversible toggling between two vastly different isomers paves the way toward controlling functional properties of coordination hosts "on demand".

Guest-Induced Reversible Transformation between an Azulene-Based Pd2L4 Lantern-Shaped Cage and a Pd4L8 Tetrahedron

“…Would an empty [Pd 4 AZU1 8 ] still exist, or would the system revert back to the [Pd 2 AZU1 4 ] cage? In previous examples by Fujita and Klajn, neutral guests were removed from a coordination capsule by washing the cage–guest complex with another solvent. In our case, that technique was not applicable, as both the cage and guest are soluble in the same range of solvents.…”

Photoswitching the fluorescence of nanoparticles for advanced optical applications

“… 102 Moreover, photochromic dyes in coordination cages have also been thoroughly studied by the Klajn group. 105–107 When being encapsulated in Td and D2h-symmetric coordination cages, the photoisomerism of the encapsulated spiropyran can be terminated and maintained, respectively ( Fig. 6B ).…”