Fullerene-Assisted Photoinduced Charge Transfer of Single-Walled Carbon Nanotubes through a Flavin Helix

Abstract

One of the greatest challenges with single-walled carbon nanotube (SWNT) photovoltaics and nanostructured devices is maintaining the nanotubes in their pristine state (i.e., devoid of aggregation and inhomogeneous doping) so that their unique spectroscopic and transport characteristics are preserved. To this effect, we report on the synthesis and self-assembly of a C60-functionalized flavin (FC60), composed of PCBM and isoalloxazine moieties attached on either ends of a linear, C-12 aliphatic spacer. Small amounts of FC60 (up to 3 molar %) were shown to coassembly with an organic soluble derivative of flavin (FC12) around SWNTs and impart effective dispersion and individualization. A key annealing step was necessary to perfect the isoalloxazine helix and expel the C60 moiety away from the nanotubes. Steady-state and transient absorption spectroscopy illustrate that 1% or higher incorporation of FC60 allows for an effective photoinduced charge transfer quenching of the encased SWNTs through the seamless helical encase. This is enabled via the direct π-π overlap between the graphene sidewalls, isoalloxazine helix, and the C60 cage that facilitates SWNT exciton dissociation and electron transfer to the PCBM moiety. Atomistic molecular simulations indicate that the stability of the complex originates from enhanced van der Waals interactions of the flexible spacer wrapped around the fullerene that brings the C60 in π-π overlap with the isoalloxazine helix. The remarkable spectral purity (in terms of narrow E(S)ii line widths) for the resulting ground-state complex signals a new class of highly organized supramolecular nanotube architecture with profound importance for advanced nanostructured devices.

Halogen Bonding: A Halogen-Centered Noncovalent Interaction Yet to Be Understood

“…Similarly, Varadwaj et al showed that charge transfer is a factor controlling the equilibrium constants of late first-row transition metal complexes (the so-called Irving-Williams series) [96], and have suggested it to be a major driving force to provide geometrical stability to organic-inorganic perovskites in gas-phase adducts [97][98][99]. Given the conflicting views on charge transfer emerging from various groups, and given that the concepts of charge transfer, charge separation, as well as charge recombination, have been widely utilized to develop a variety of donor-acceptor functional materials (e.g., organic photovoltaics) [71,[100][101][102][103][104], it seems to us from the various conflicting arguments summarized above that the concept of charge transfer is yet to be fully understood. There is clearly a pressing need for rigorous methodical developments to resolve the issue.…”

“…(a) Unit cell and 2 × 2 supercell and (b) [002] slicing pattern. (c)[101] Slicing pattern. Type-II and -I bonding patterns between interacting monomers in the crystal are shown in (d,e), respectively, with the IGM isosurfaces corresponding to these interactions in green volumes.…”

Bimodal supramolecular functionalization of carbon nanotubes triggered by covalent bond formation

“…16–18 On the other hand, noncovalent chemistry occurs under equilibrium, and offers the possibility of switching the interactions on and off in response to stimuli. 19–21 …”

Chiral and random arrangements of flavin chromophores along cyclic peptide nanotubes on gold influencing differently on surface potential and piezoelectricity

“…Flavin is a naturally occurring electron mediator, and has been used in several articial molecular assembling systems, for example, by incorporating it into self-assembled monolayers [19][20][21] and combination with single-walled carbon nanotubes. 22 In the present paper, avin is therefore introduced into peptide nanotubes to study the way how the 3-dimensional arrangement of the avin groups in the peptide nanotube bundles inuences the electric outputs of the molecular assemblies on a gold substrate. Two kinds of cyclic tri-b-peptides of cyclo(b-Asp(avin)-b-Ala-b-Ala) (C3FAA) and cyclo(b-Asp(avin)-ethylenediamine-succinic acid) (C3FES) are designed ( Fig.…”