From Induced-Fit Assemblies to Ternary Inclusion Complexes with Fullerenes in Corannulene-Based Molecular Tweezers

Abstract

The participation of the tether moiety in fullerene recognition of corannulene-based molecular tweezers is known to be an important factor. In the present work, we describe the synthesis of a set of fullerene receptors bearing two corannulene units located at a suitable distance to effectively interact with C 60 and C 70 . The tether comprises a fluorene-like scaffold where an assortment of different groups with variable electronic properties has been grafted. The photophysical and electrochemical properties of all final compounds have been unveiled and correlated to the donor/acceptor (DA) nature of the tether. Despite these strong variations, their affinity toward fullerenes cannot be correlated in any way to simple DA behavior as the main contribution to the interaction correspond to London dispersion forces. We found, however, that the sulfur-derived subfamily is able to adapt better to the fullerene outer surface slightly increasing the charge transfer and electrostatic attractive interactions being the most outstanding example the case of thiophene 4-S with C 70 as it is capable of forming a ternary 2:1 inclusion complex in solution with an electronic binding energy that offsets entropy and desolvation penalties typically associated with higher-order inclusion complexes.

An Indacenopicene‐based Buckybowl Catcher for Recognition of Fullerenes

“…This resulted in binding constants of K a =(1.08±0.01)×10 3 M −1 for C 70 and K a =(1.50±0.1)×10 2 M −1 for C 60 . The obtained binding values are comparable to similar corannulene‐based receptors [8,10–12] . For ITC measurements, a corannulene receptor has been reported that reaches the same order of magnitude for the binding interactions with C 70 as our buckybowl catcher (literature value: K a = (2.0±0.1)×10 2 M −1 in o ‐DCB) [10] .…”

“…The obtained binding values are comparable to similar corannulene-based receptors. [8,[10][11][12] For ITC measurements, a corannulene receptor has been reported that reaches the same order of magnitude for the binding interactions with C 70 as our buckybowl catcher (literature value: K a = (2.0 � 0.1)×10 2 M À 1 in o-DCB). [10] For NMR titrations, to the best of our knowledge no values are reported that have been measured in o-DCB.…”

“…Such supramolecular complexes possess interesting applications, including the solubilization of pristine fullerenes [5] and the formation of electron transfer complexes using suitable donor molecules [6] . Given the fact that host‐guest interactions strongly profit from a good shape and size complementarity, [7] fullerene receptors employing different types of buckybowls have been demonstrated as a successful approach [8,9,10–12] . Buckybowls are polycyclic aromatic hydrocarbons (PAHs) which are constructed in a similar way as fullerenes, consisting of a combination of five‐ and six‐membered rings, resulting in their curvature.…”

“…[6] Given the fact that host-guest interactions strongly profit from a good shape and size complementarity, [7] fullerene receptors employing different types of buckybowls have been demonstrated as a successful approach. [8,9,[10][11][12] Buckybowls are polycyclic aromatic hydrocarbons (PAHs) which are constructed in a similar way as fullerenes, consisting of a combination of five-and six-membered rings, resulting in their curvature. However, their use in the field of supramolecular chemistry is limited by the availability of these molecules.…”

Intermolecular hydrogen bonding in calix[5]arene derived cavitands regulates the molecular recognition of fullerenes

“…Most remarkably, cavitand 1 provides K a 's in the 10 3 –10 4 M −1 range in a highly competitive solvent ( o -DCB), whereas previously reported hosts based on a single calix[5]arene macrocycle display K a 's in the 10 2 –10 3 range under similar conditions. 18 Constants in the range of those obtained for 1 can be replicated with receptors that feature multiple covalently tethered calix[5]arene 18,19 or corannulene recognition units, 31–33 but such hosts are much more challenging to synthesize and present limited diversification potential. For completeness, we also attempted fitting all our titration data to a 2 : 1 model given existing precedents, 17 resulting in a poor fit in all cases.…”