Fullerene recognition with molecular tweezers made up of efficient buckybowls: a dispersion-corrected DFT study

Abstract

In 2007, Sygula and co-workers introduced a novel type of molecular tweezers with buckybowl pincers that have attracted the substantial interest of researchers due to their ideal architecture for recognizing fullerenes by concave-convex π∙∙∙π interactions (A. Sygula et al., J. Am. Chem. Soc., 2007, 129, 3842). Although in recent years some modifications have been performed on these original molecular tweezers to improve their ability for catching fullerenes, very few improvements were achieved to date. For that reason, in the present work a series of molecular tweezers have been devised and their supramolecular complexes with C60 studied at the B97-D2/TZVP//SCC-DFTB-D and B97-D2/TZVP levels. Three different strategies have been tested: (1) changing the corannulene pincers to other buckybowls, (2) replacing the tetrabenzocyclooctatetraene tether by a buckybowl, and (3) adding methyl groups on the molecular tweezers. According to the results, all the three approaches are effective, in such a way that a combination of the three strategies results in buckycatchers with complexation energies (with C60) up to 2.6 times larger than that of the original buckycatcher, reaching almost -100 kcal mol(-1). The B97-D2/TZVP//SCC-DFTB-D approach can be a rapid screening tool for testing new molecular tweezers. However, since this approach does not reproduce correctly the deformation energy and this energy represents an important contribution to the total complexation energy of complexes, subsequent higher-level re-optimization is compulsory to achieve reliable results (the full B97-D2/TZVP level is used herein). This re-optimization could be superfluous when quite rigid buckycatchers are studied.

Dissecting the concave–convex π‐π interaction in corannulene and sumanene dimers: SAPT(DFT) analysis and performance of DFT dispersion‐corrected methods

“…S5). This behavior is similar to that previously described as “flaps” stabilizing this kind of complexes . In both cases, the equilibrium distances are larger than in cora and sumaS homodimers, reflecting the larger depth of suma and sumaCO.…”

“…For suma‐suma and sumaCO‐sumaCO, the overall picture is similar, but now there is a clear increase in the electrostatic and dispersion contributions, partially compensated by an analogous increment in repulsion. This can be qualitatively related to favorable CH‐π interactions in the case of the sumanene dimer, as already shown in previous work by our group; in the case of sumaCO dimer, the carbonyl oxygen can also interact with the hydrogen atoms on the CH groups on the rim of the other bowl, (the most stable structure is staggered, See NCI plots in Supporting Information Fig. S5).…”

“…Besides corannulene and sumanene, other larger buckybowls have been studied over the last years . Theoretical studies of different buckybowl‐fullerene dimers have allowed to get insight into the factors favoring the interaction with fullerenes . In previous work of our research group, it has been shown that extending the π surface of the bowl leads to enhanced interactions, although the bowl must keep some flexibility to adapt to the fullerene shape .…”

“…Theoretical studies of different buckybowl‐fullerene dimers have allowed to get insight into the factors favoring the interaction with fullerenes . In previous work of our research group, it has been shown that extending the π surface of the bowl leads to enhanced interactions, although the bowl must keep some flexibility to adapt to the fullerene shape . Also, the presence of other stabilizing contacts such as CH‐π interactions (as in sumanene, for instance) resulted in larger stabilities …”

On the estimation of the strength of supramolecular complexes of fullerenes

“…In particular, buckycatcher I has become a popular benchmark to develop new density functionals . Theoretical calculations have made important contributions to the design of new fullerene receptors, and to shed light into the properties of multishell fullerenes, where a fullerene hosts a smaller cage . In particular our research group has been interested in the study of new fullerene receptors .…”