A Tunable Cyclic Container: Guest‐Induced Conformational Switching, Efficient Guest Exchange, and Selective Isolation of C₇₀ from a Fullerene Mixture

Abstract

An adaptable cyclic porphyrin dimer with highly flexible linkers has been used as an artificial molecular container that can efficiently encapsulate various aromatic guests (TCNQ/C /C ) through strong π-π interactions by adjusting its cavity size and conformation. The planar aromatic guest (TCNQ) can be easily and selectively exchanged with larger aromatic guests (C /C ). During the guest-exchange process, the two porphyrin rings switch their relative orientation according to the size and shape of the guests. This behavior of the cyclic container has been thoroughly investigated by using UV/Vis spectroscopy, NMR spectroscopy, and X-ray crystal structure determination of the host-guest assemblies. The electrochemical and photophysical studies demonstrated the occurrence of photoinduced electron transfer from bisporphyrin to TCNQ/C /C in the respective host-guest assemblies. The cyclic host can form complexes with C and C with association constants of (2.8±0.2)×10 and (1.9±0.3)×10 m , respectively; the latter value represents the highest binding affinity for C reported so far for zinc(II) bisporphyrinic receptors. This high selectivity for the binding of C versus C allows the easy extraction and efficient isolation of C from a C /C fullerene mixture. Experimental evidence was substantiated by DFT calculations.

Double-Circularly Connected Saloph-Belt Macrocycles Generated from a Bis-Armed Bifunctional Monomer

“…To the best of our knowledge, the best reported selectivity for C 70 over C 60 is K a (C 70 )/ K a (C 60 ) ≈ 1000 (in toluene) achieved by the quadruply bridged porphyrin dimer with three-dimensional shape-persistent framework synthesized via alkyne metathesis . As for the macrocycles, many fullerene receptors display moderate selectivity (up to 1 order of magnitude), ,,− , and limited examples with rigid frameworks exhibit the selectivity of K a (C 70 )/ K a (C 60 ) > 100. ,− Thus, the rigid belt-shaped scaffold of [ S4 Zn 4 X 4 ] is considered to be a key factor to realize the strong binding and selectivity toward C 70 . The cavity size of [ S4 Zn 4 X 4 ] probably matched better with C 70 , as can be inferred from the compressive deformation of [ S4 Zn 4 X 4 ] into a parallelogram when including C 60 (Figure c).…”

“…The fullerenes were then investigated as the guest for the macrocycle. ,,,− Studies of preferential binding of fullerenes by designed receptors have been reported, ,− which can lead to its efficient separation method. However, the selective binding of a specific fullerene over the others by 2 orders of magnitude is challenging. − The formation of a new species was indicated by 1 H NMR upon the addition of 1 equiv of C 60 to [ S4 Zn 4 X 4 ] (Figure b, Figure S41). ESI TOF-MS measurement of the sample gave the signals assigned to [C 60 · S4 Zn 4 ·H n ] n + ( n = 2, 3), a 1:1 host–guest complex (Figure c).…”

Fully Conjugated Pyrene–BODIPY and Pyrene–BODIPY–Ferrocene Dyads and Triads: Synthesis, Characterization, and Selective Noncovalent Interactions with Nanocarbon Materials

“…Design of new chromophores that are capable of harvesting sunlight in the low-energy visible and near-infrared (NIR) spectral envelopes attracted a lot of attention in recent decades because of the potential use of such systems in organic- and dye-sensitized solar cells. − In addition, the ability to facilitate relatively strong noncovalent interactions between such chromophores and nanocarbon-based electron-accepting materials (fullerenes, nanotubes, and graphene) is thought to be advantageous in the processing of high-efficiency organic bulk heterojunction solar cells. − To achieve this goal, many porphyrins, − subphthalocyanines, − and boron-dipyrromethenes (BODIPYs) were functionalized with a variety of electron-donating groups that improve donor–acceptor (D–A) interactions between extended π-systems. Alternatively, the introduction of the polyaromatic fragments that are either conjugated or not conjugated into chromophores’ π-system can also improve noncovalent interactions in these D–A assemblies. − Covalently bound pyrene was shown to facilitate noncovalent interactions with carbon nanotubes and graphene. − It has also been shown that when pyrene fragments are decoupled from the chromophores’ π-system, this extended aromatic group can facilitate an unwanted pyrene-to-chromophore electron-transfer process as well as the formation of a chromophore-centered triplet state. − We have recently demonstrat...…”

Playing with the cavity size of exTTF-based self-assembled cages

“…[27][28][29][30][31][32][33][34][35][36] This is one of the reasons why many strategies have been developed to reach tridimensional polyhedral cavities of various geometries, nuclearities and sizes. [37][38][39][40] Tuning the cavity volume of the latter constitutes an important parameter when addressing binding selectivity issues, notably for application in the separation of gases, 41 small hydrocarbons, 42 PAHs 43,44 or fullerenes, [45][46][47][48][49][50][51] as well as for selective catalysis. [52][53][54][55][56][57] Such a control over the cavity volume can notably be attained by adjusting the size of the starting polypyridyl ligand.…”