Supramolecular Dynamics of Cyclic [6]Paraphenyleneacetylene Complexes with [60]‐ and [70]Fullerene Derivatives: Electronic and Structural Effects on Complexation

Abstract

Although a variety of host molecules have been studied extensively to elucidate the inclusion phenomena of buckminsterfullerene C 60 , the supramolecular properties of other fullerenes, including fullerene derivatives, are not yet well understood. [1][2][3] In contrast to I h -symmetrical C 60 , these other fullerenes are perturbed structurally and electronically. It has been known that the electronic properties of [60]fullerene derivatives correlate well with the electronegativity of the attached atoms.[4] For example, the attachment of electronpositive silicon atoms considerably increase the electron density of the p systems of [60]fullerene derivatives. [4,5] Recently we found that the carbon nanoring 1 (cyclic [6]paraphenyleneacetylene) forms stable inclusion complexes with the fullerenes C 60 , C 70 , and C 61 (COOEt) 2 2 in solution as well as in the solid state. [2b, 6] Dynamic 1 H NMR spectra have revealed the interesting features of these complexes: 1) the Gibbs activation energies for dissociation (DG°d is ) provide a reliable measure for evaluating the stability of the fullerene complexes and 2) the center of each fullerene is not aligned with the center of 1, and the activation energy for vibration of a C 70 molecule around the center of the cavity is higher than the value for dissociation of the complex, while that of C 60 is lower. These results can be attributed to the structural difference between C 60 and C 70 . The inclusion phenomena of C 70 have been studied from the viewpoint of purification of fullerenes; [2] however, the difference in the supramolecular properties of C 60 and C 70 has not been studied in detail so far. To explore the nature of the curved conjugated systems, and to construct new supramolecular structures based on fullerene derivatives, [7] we have studied the dynamic behavior of the complexes of 1 with several fullerene derivatives (3-10) including the silylated fullerenes 6 and 7.[5]New methanofullerene derivatives 3-5, 9, and 10[8] were prepared in moderate yields by treating the corresponding malonic esters with fullerenes under the conditions used by Camps and Hirsch.[9] The formation and regiochemistry of these new compounds were confirmed by transesterification into the known derivatives 2 and 8. [10][11][12] Fullerene derivatives 3-10 form stable inclusion complexes with 1 in CD 2 Cl 2 solutions.[13] Figure 1 shows the spectral changes of 1·7 and 1·9 as typical examples. Similar to the 1 H NMR spectra of 1·2, [6b] the spectrum of 1 shows two singlets of equal intensity at À100 8C in the presence of an equal amount of 3-7, but only one singlet at 30 8C. However, one of the aromatic signals of 1 that appears as a singlet in the presence of an equal amount of 8-10 at 30 8C begins to broaden at about À20 8C, and two relatively small singlets of equal intensity first appear at about À50 8C. The major signal finally splits into two singlets of equal intensity at À80 8C (Figure 1 b). The spectral changes indicate that the methano[70]fullerene complexes should exist in an e...

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

“…The DG z dis values are on the order of 65 (8.5 AE 0.2 kcal/mol) < 64 (8.8 AE 0.2 kcal/mol) < 63 (9.4 AE 0.2 kcal/mol) < C 60 (9.9 AE 0.3 kcal/mol). Therefore, an increase in electron density weakens the binding between the host and the guest [90]. When the van der Waals distance (0.34 nm) is taken into account, [8]-and [9] CPPAs, 58 and 59, have almost perfect complementarity to [5]-and [6]CPPA, 55 and 58, respectively.…”

Size‐Selective Encapsulation of C60 by [10]Cycloparaphenylene: Formation of the Shortest Fullerene‐Peapod

“…14–16 Although Kawase et al. have reported the complexation of cycloparaphenyleneacetylenes with fullerenes,17–21 there have been no reports of the formation of host–guest complexes with CPPs so far. During studies on the synthesis of CPPs22–24 by our own approach25 and elucidation of their properties,26, 27 we found the first example of a host–guest complex of CPP and C 60 28.…”

Transcriptome profiling reveals histone deacetylase 1 gene overexpression improves flavonoid, isoflavonoid, and phenylpropanoid metabolism in Arachis hypogaea hairy roots

“…075-05111, C 28 H 22 N 4 O 6 , Wako, Osaka, Japan) and a highly selective fluorescent BES-H 2 O 2 -Ac H 2 O 2 probe (Cat No. 028-17811, C 28 H 11 F 7 O 8 S, Wako) to measure superoxide anion content and H 2 O 2 content, respectively, in addition to intracellular ROS levels ( Kawase et al, 2004 ; Teranishi, 2007 ). After washing with phosphate-buffered saline (PBS) solution, we soaked the hairy roots in the PBS solution with the BES-H 2 O 2 -Ac fluorescence probe and the superoxide anion chemiluminescent probe for 20 min.…”