Dimeric Capsules with a Nanoscale Cavity for [60]Fullerene Encapsulation

Abstract

The acid-assisted and guest-induced formation of superstructures was achieved by the addition of haloacetic acids to a toluene solution of the resorcin[4]arene derivatives 1 and [60]fullerenes. The formation of dimeric superstructures that encapsulated a nanosized guest molecule was observed when appropriate acids, such as haloacetic acids, and suitable guest molecules, such as [60]fullerenes, were co-added to a toluene solution of cavitand 1 that has four pyridine units, whereas a complicated equilibrium between several species was detected without [60]fullerenes, and the formation of discrete superstructures was not monitored in the absence of haloacetic acids. The spectroscopic data indicate that the formed [60]fullerene-encapsulated complexes have the structure of 2. These complexes are self-assembled through pyridinium-anion-pyridinium interactions and by pi-pi and van der Waals interactions. The rate of decomplexation of 2 is estimated to be 3.1 s(-1) from a 2D exchange NMR spectrum. The [60]fullerene encapsulation process can be controlled by modifying the amounts of acids used, changing the temperature of the system, altering the ratio of acid/base, and even through varying the solvent polarity. Moreover, the fluorescence spectra show band-narrowing spectral changes and a retardation of the relaxation characteristics of isolated and isotropic [60]fullerenes, which indicates that the environmental change around [60]fullerene is induced upon its encapsulation.