Discrete Supramolecular Donor–Acceptor Complexes

Gayathri, S. Shankara; Wielopolski, Mateusz; Pérez, Emilio M.; Fernández, Gustavo; Sánchez, Luis; Viruela, Rafael; Ortı́, Enrique; Guldi, Dirk M.; Martín, Nazario

doi:10.1002/anie.200803984

Cited by 110 publications

(56 citation statements)

References 42 publications

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“…The stoichiometry of 42 to C 60 varies a 1 : 1 complex to a 2 : 2 complex, depending upon the solvents [70]. Upon photoexcitation at the corresponding CT band of the complexes, photoinduced electron transfer (PET) from the receptors to fullerene readily took place in benzonitrile to form a fully charge-separated C 60 Á À exTTF þ À state [71]. They investigated the relative contributions of the concave-convex p-p interaction to bind C 60 using the host 41 and the other tweezers-shaped hosts 43-45 with various curvatures (Figure 3.18).…”

Section: Receptors Based On Bowl-shaped Conjugated Systemsmentioning

confidence: 99%

Receptors for Pristine Fullerenes Based on Concave–Convex π–πInteractions

Kawase

2012

Supramolecular Chemistry of Fullerenes and Carbon Nanotubes

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In 1990, Kr€ atchmer and coworkers reported the extraction of fullerenes (C 60 and C 70 ) from carbon soot using aromatic solvents (Figure 3.1) [1]. After this discovery, receptor molecules for fullerenes have been extensively studied for separation and purification of fullerenes. Supramlecular chemists have found that traditional host molecules composed of electron-rich aromatic rings such as calix[n]arenes 1-4, oxacalix[3]arenes 5, and cyclotriveratrylenes (CTV) 6 ( Figure 3.2) can be employed for the purpose. The crystallographic analyses of these complexes with C 60 clearly indicated the importance of the p-p interactions between the convex p surface of C 60 and the concave p surface of the traditional host molecules. On the other hand, except a few examples, the traditional hosts bound fullerenes only in solid state. In order to bind with fullerenes more tightly, two strategies have been presented to construct the well preorganized p cavity so far. First, electron-rich aromatic units are introduced to the host molecule as appendants (Figure 3.2a). Second, two host molecules are linked by appropriate tether(s) to form a dimeric structure with a creft-, ring-, or ball-shaped cavity (Figure 3.2b). The binding abilities of the modified receptors fairly increased in comparison with those of simple traditional hosts. On the other hand, new receptors based on curved conjugated systems such as corannulene 7, extended TTF (exTTF) 8, and carbon nanorings (Figure 3.3) have been developed recently. These compounds possess a concave p surface matching to the convex surface of C 60 . Cyclic [6]paraphenyleneacetylene ([6]CPPA) 9 and the related compounds have smooth belt-shaped structure similar to a cut piece of carbon nanotube, and thus may be termed carbon nanorings. These receptors form stable inclusion complexes with fullerenes both in solution and in the solid state, and are good model compounds to explore the nature of the concave-convex p-p interactions. This chapter discusses the fullerene receptors bearing a cavity surrounded by p-orbitals, the so-called p cavity, the concept of molecular designs, and the nature of p-p interactions. The survey of the fullerene receptors should provide an insight into the supramolecular properties of curved conjugated systems. Although the receptor Supramolecular Chemistry of Fullerenes and Carbon Nanotubes, First Edition. Edited by Nazario Martin and Jean-Francois Nierengarten.

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Section: Receptors Based On Bowl-shaped Conjugated Systemsmentioning

confidence: 99%

Receptors for Pristine Fullerenes Based on Concave–Convex π–πInteractions

Kawase

2012

Supramolecular Chemistry of Fullerenes and Carbon Nanotubes

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“…The short lifetime values are indeed an indirect proof of the orbital overlapping between both electroactive species that experience a fast recombination in solution [55]. Time-dependent DFT theoretical calculations (B3LYP/6−31 G * * ) predict that the lower energetic transitions (∼480 nm) occur between the HOMO and HOMO+1 levels, located on the exTTF receptor, and the LUMO+4 which spreads on the whole C 60 molecule.…”

Section: Concave Electroactive Receptors For Fullerenesmentioning

confidence: 96%

Supramolecular Receptors for Fullerenes

Fernández

Sánchez

Martán

2010

Ideas in Chemistry and Molecular Sciences

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Since the extraction of fullerenes from the carbon soot using aromatic solvents [1], the interaction between the convex surface of fullerenes and the flat π surface of aromatic moieties has received increasing attention [2]. Fullerene [3] is a polyenic structure constituted by 12 pentagonal and 20 hexagonal rings, in which each carbon atom possess sp 2,3 hybridization [4]. The existence of pentagonal rings provokes a curvature and, therefore, a weak polarization on its surface between the 5 : 6 ring junctions, which represent centers of positive charge, and the negatively charged 6 : 6 fusions [5, 6]. This anisotropic distribution of the electronic charge is the basis to determine the interactions with other substrates.There are two main driving forces to design supramolecular receptors for fullerenes: on one hand, it would be feasible for an effective purification from their natural extraction sources, mainly carbon soot and fullerite. On the other hand, in combination with electron donor receptors, we could design highly organized architectures that can find application in optoelectronics, where the organization of the active materials plays a crucial role in the improvement and precise operation of the devices.In the design of supramolecular receptors for fullerenes we have to consider the neutral features of fullerenes. Therefore, there are some energetic factors to take into account that will determine the final properties and the nature of the interactions involved in the supramolecular complexes: (i) van der Waals forces, (ii) electrostatic interactions, (iii) induction energy, (iv) charge-transfer, and (v) desolvation [7, 8].Considering the nature of all of these noncovalent forces and the geometry and electronic features of C 60 and its higher congeners, van der Waals and solvophobic interactions should be decisive in the stability of the C 60 -receptor complexes [9]. The large global area of fullerenes, consequence of their spherical geometry, and their nonpolar character make these noncovalent effects key factors to attain highly stabilized complexes. Thus, the direct strategy consists in increasing the aromatic

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“…Cyclic voltammetry showed that both TTFs have similar oxidation potential values as shown by a broad four-electron wave centered at 0.42 V. This might be the reason for the equilibrium between the two different charge-separated excited states (exTTF 1 )-(exTTF 2 ) •+ -C 60 •− and (exTTF 1 ) •+ -(exTTF 2 )-C 60 •− that show two different lifetimes of 664 ns and a remarkable 111 μs, respectively, in dimethylformamide (DMF). Gayathri et al [21] have taken advantage of the curved geometry of exTTF for the molecular recognition of the convex exterior surface of C 60 by the concave surface of π-exTTF derivatives to synthesize a variety of supramolecular donor-acceptor structures. Two different molecular tweezers (7, 8) based on exTTF bearing either an isophthalic or terephthalic diester spacer were designed to be used as host for C 60 ( Fig.…”

Section: Covalent and Supramolecular Ttf-fullerene Systemsmentioning

confidence: 99%