Filling Helical Nanotubes with C₆₀

Abstract

We report herein the complexation of a string of buckminsterfullerenes in chloroform by our recently discovered selfassembled, helical nanotubes.[1] The poorly soluble C 60 molecules are solubilized by the nanotubes and they also experience the helicity of the environment, as demonstrated by induced circular dichroism (ICD). Previously reported C 60 receptors-mostly aza-crown ethers, calixarenes, and porphyrins [2] -require lengthy syntheses and only bind isolated fullerenes. Our polymeric, dynamic receptor is prepared in one step and represents an entirely new class of C 60 -complexing structures; it also allows the hitherto unknown formation of a one-dimensional C 60 array.We recently reported the synthesis [3] of a-amino acid functionalized naphthalenediimides (Scheme 1) and their self-assembly into hydrogen-bonded nanotubes.[1] The crystal structure of these helical superstructures shows the presence of tubular cavities with a mean diameter of 12.4 , which is well-suited to accommodate C 60 molecules with a van der Waals (vdW) radius of about 10.3 . [4] Colorimetric studies were carried out to test the C 60 complexation ability of the helical nanotubes. Solutions of l-and d-1-3 as well as 5 in chloroform were left to stand over solid C 60 . A drastic color change from pale yellow to dark orange or brown was seen within a few minutes. This color change is quite different from that observed upon mere addition of a saturated solution of C 60 in chloroform (pale purple) to the initial solution (Figure 1, inset). The visible region of the absorption spectrum (Figure 1, inset) is marked by the appearance of the absorbance bands characteristic of C 60 , as well as an additional, broad band centered around 452 nm (identified with * ). This band, best visualized by subtracting the naphthalenediimide (NDI) spectrum from the spectrum of the complex (Figure 1, blue trace), is very similar to an absorbance normally only seen in C 60 films [6] and aggregates; [7] it has been attributed to interactions between fullerenes.[8] This proximity effect, which has not previously been reported [4] for C 60 constrained within channels, indicates that the fullerenes are tightly packed within our system, although we cannot rule out a contribution from NDI-C 60 interactions.The uptake of C 60 corresponds to the appearance of the bands at 258 and 328 nm in the UV region of the absorption spectrum of 1 + C 60 . Comparison of a solution of 1 + C 60 in chloroform with known NDI concentration and a saturated solution of C 60 in chloroform allows calculation of the C 60 uptake. We found that depending on NDI concentration, and, to a lesser degree, on the amino acid side chain, the C 60 concentration increased up to 16-fold in the presence of NDI nanotubes relative to the solubility of C 60 in chloroform.The amount of C 60 taken up into the nanotubes is in good agreement with C 60 being contained inside the nanotubular core rather than interacting with the outside of the tubes. To quantify the ratio of NDI to C 60 molecules, we recorded the a...

Thermally Reduced Graphene Oxide Nanohybrids of Chiral Functional Naphthalenediimides for Prostate Cancer Cells Bioimaging

“…The formation of a supramolecular self-assembly of NDIs, different from that observed in solid state, can be studied by circular dichroism (CD) measurements in solution. [ 36 ] Previous studies [ 52 ] have shown that NDIs containing aromatic side groups can lead to the formation of nanotubular structures. [ 53 ] However, the choice of solvent can play a signifi cant role in the structural arrangement of supramolecular building blocks.…”

“…[ 30,31,33 ] The assembly process between NDIs and nanomaterials such as C 60 , C 70 , and SWNTs has been explored, by us and others. [ 33,[35][36][37] Recently, an interest in understanding their interactions with planar carbon system (denoted here PCS) has emerged and these are believed to be based on noncovalent contacts such as π-stacking coupled with hydrophobic interactions and Coulombic attractions of the electron deficient NDI core to the electron rich surface of graphene and its derivatives. [ 38 ] Zhang et al [ 39 ] demonstrated the ability of NDIs to interact with allotropes of carbon on a supramolecular level by showing the improved dispersion stability of graphene in water when complexed with N , N ′-bis-[2-(ethanoic acid sodium)]-NDI after exfoliation of sheets of graphene by sonication.…”

Solubilization of C60 by micellization with a thermoresponsive block copolymer in water: Characterization, singlet oxygen generation, and DNA photocleavage

“…The spectra show absorption bands at 261 and 340 nm. The significant tailing of the absorption band up to around 700 nm was observed, which may be attributed to interactions between fullerenes 34. It is known that the electron deficient double bonds of C 60 interact with the pendent amide groups in PNVP due to charge transfer interaction 35.…”

“…up to around 700 nm was observed, which may be attributed to interactions between fullerenes. 34 It is known that the electron deficient double bonds of C 60 interact with the pendent amide groups in PNVP due to charge transfer interaction. 35 The charge transfer and hydrophobic interactions induce the C 60 /PNIPAM m -b-PNVP n micelle formation comprising a C 60 /PNVP core.…”

Synthesis and properties of star polymers with a C5‐symmetric bowl‐shaped aromatic core

“…Preliminary studies were then performed to investigate the interaction between the aromatic core of the star polymers and fullerene, C 60 . For this, 13 C NMR spectroscopy, as demonstrated by Sanders41 and others,42, 43 was chosen as an analytical tool. To aid the measurements and the analysis, 13 C‐rich C 60 was used.…”