Reaction of C₆₀with Sultines:  Synthesis, Electrochemistry, and Theoretical Calculations of Organofullerene Acceptors

Abstract

The [4 + 2] cycloaddition reaction of o-quinodimethanes, generated in situ from 4,5-benzo-3,6-dihydro-1,2-oxathiin 2-oxides (10a,b, 13, and 19) (sultines), to [60]fullerene is described. Sultines are readily accesible from the commercially available rongalite and smoothly generate o-quinodimethanes, by extrusion of sulfur dioxide, which are efficiently trapped by the active dienophile C60. The cycloadducts formed (21a−d) were further oxidized to the respective p-benzoquinone-containing fullerenes 23a−c. The temperature dependent 1H NMR spectra show a dynamic process of the methylene protons. The activation free energy determined for the boat-to-boat inversion (11.3−11.6 kcal/mol) is remarkably lower than that obtained for other related carbocyclic or heterocyclic analogues. Semiempirical PM3 calculations show that the geometrical features and not the electronic properties of the organic addend in 23 are responsible for the low activation energy barriers. A linear correlation is found between the activation energy barriers and the length of the C62−C63 bond. The electrochemical properties of 23a−c have been rationalized on the basis of DFT-B3P86/3-21G calculations. The attachment of the first electron in the reduction process takes place in either the C60 cage or the organic addend depending upon the nature of the substituents on the p-benzoquinone ring, which controls the relative energy of the LUMO of the p-benzoquinone moiety. A full agreement between the theoretical predictions and the electrochemical measurements is found.

Probing the Orbital Levels of Engineered Fullerenic Molecules from a Nonvolatile Memory Cell

“…The redox capability [2] and electrical conductivity [3] of EFM are notably different from pristine fullerenes and offer more flexibility in tailoring the fabrication process and device characteristics. Most importantly, chemical functionalization in EFM alters the electronic structure of the molecule, creating programmable HOMO-LUMO levels [4] which are crucial for designing resonant tunneling barrier for Flash memory to overcome the scaling bottleneck [5]. This chemical derivation also grants EFM large solubility at room temperature that enables wafer-level fluid-transfer process, which may ease both the process control and manufacture cost in the case of commercialization.…”

Synthesis and Electrochemical Properties of New C60-Acceptor and -Donor Dyads

“…The locations of the first oxidation and reduction events in all type A and B To date, only a few examples of C 60 -acceptor dyads (type B) have been reported. [26] [27] [28] [29] [30] [31] [32] Since C 60 itself systems investigated in this study correspond to the PM3-calculated HOMOs of the neutral species or the SOMOs of is already very electronegative, the choice of suitable electroactive groups is restricted to very strong acceptors such the singly reduced species. as quinone, DCNQI and TCNQ derivatives.…”

“…Cyclic voltammetric investigations of some of these dyads suggest that the first reduction step takes place at the acceptor. [ [32] However, since the difference between the first reduction potential of a quinone-acceptor and that of the fullerene moiety is small, only type B models involving strong acceptors such as TCNQ or DCNQI derivatives represent promising models for effective chargeseparation processes. Better model systems should allow for charge separation in several successive steps, akin to the situation in natural photosynthetic events.…”

“…X-band ESR spectra for the sequential reduction of 6 in toluene/acetonitrile (85:15, v/v): a) after one-electron coulometric tion of 7 in toluene/acetonitrile (85:15, v/v): a) after one-electron coulometric reduction, b) after two-electron reduction, c) after reduction, b) after two electrons, c) after three electrons, d) after four electrons, e) after five electrons; f) ESR spectrum for the mothree-electron reduction, and d) after four-electron reduction noanion radical of 4 generated by electrolytic reduction under identical conditions of 6, 7 and 8. This consideration of the SOMOs of the monoanions provides a more realistic estimation of reduction events than simply considering the LUMOs [32] of the neutral species. The latter qualitatively predicts the cor-anion of 6 are more difficult to perform, since, for example, convergence problems arise.…”

“…Pyrex tubes that were directly glassblown onto the electrochemical cell. After exhaustive electrolysis with the BAS 100W apparatus at the differWhereas benzoquinone-or naphthoquinone-based addends ent potentials corresponding to the various anionic states, the cell are known to be stronger acceptors [32] than the fullerene, was tilted in order to collect a sample in one of the tubes, which the anthraquinone moiety in 6 is a weaker acceptor than the was then flame-sealed. The samples were analysed using the X-C 60 moiety.…”