per-Alkoxy-pillar[5]arenes as Electron Donors: Electrochemical Properties of Dimethoxy-Pillar[5]arene and Its Corresponding Rotaxane

Abstract

1,4-dimethoxypillar[5]arene undergoes reversible multielectron oxidations forming stable radical cations, a property retained when incorporated in [2]rotaxanes, suggesting that pillar[5]arenes can be employed as viable, yet unreported, electron donors.

Spectroelectrochemical Behaviour of 1,4‐Dimethoxypillar[5]arene (P5A) and its Monomer in Different Organic Solvents

“…Contrary to our results, no quinone formation was observed by Pearce et al. [13] Control experiments in a glove box under dry conditions showed the same initial three peaks, but the fourth, irreversible, peak disappeared (Figure S1.10). This shows that even the minute amount of water absorbed during preparation of the electrolyte can change the oxidation of P5A.…”

“…The main differences between the CVs recorded here, and those described by Champness' group [13] are the interpretation of the electron numbers for the three oxidation steps and the shape of the third reduction peak (Figure 1B; SI 1.1B) marked as III'. The sharpness of this peak could be attributed to an adsorption process on the electrode surface.…”

“…Increasing the applied potential from 0.4 V to 1.6 V results in new absorption bands with maxima at 443 nm/464 nm and 260 nm and a slight decrease of the intensity band at 295 nm. As reported by Champness, [13] the new absorption band, in the region 400-500 nm, corresponds to various oxidised states of P5A. The band at 260 nm, generated from n-π* transition, is assigned to the corresponding 1,4-dimethoxypillar[n]arene [5-n]quinones.…”

“…[8,9] The latest research on the redox properties of the fully alkylated pillar [5]arene: 1,4-dimethoxypillar [5]arene (P5A) and its analogues with one (P4AQ1) or two quinone units (P3AQ2) were conducted by Champness et al, in dichloromethane containing 0.4 M tetrabutylammonium tetrafluoroborate as a supporting electrolyte. [13] Cyclic voltammograms of P5A, recorded in the negative potential range, did not show any redox processes. However, in the positive range of potentials, three consecutive oxidation peaks and corresponding reduction peaks were observed.…”

“…Based on spectroelectrochemical experiments, all these processes were described as chemically reversible. [13] According to the authors of this work, the use of a dry aprotic solvent such as dichloromethane prevented oxidation of dimethoxybenzene units to their corresponding quinones. Various studies can be found in the literature relating to the solvent's influence on the obtained electrochemical response of dimethoxybenzene.…”