Unveiling KuQuinone Redox Species: An Electrochemical and Computational Cross Study

Abstract

The study of the electrochemical properties of variegated quinones is a fascinating topic in chemistry. In fact, redox reactions occurring with quinoid scaffolds are essential for most of their applications in biological systems, in photoelectrochemical devices, and in many other fields. In this paper, a detailed investigation of KuQuinones’ redox behavior is presented. The distinctiveness of such molecules is the presence in the structure of two condensed naphthoquinone units, which implies the possibility to undergo multiple one-electron reduction processes. Solvent, supporting electrolyte, and hydrogen bond donor species effects have been elucidated. Changing the experimental parameters provoked significant shift of the redox potential for each reduction process. In particular, additions of 2,2,2-trifluoroethanol as a hydrogen bond donor in solution as well as Lewis acid coordination were crucial to obtain important shifts of the redox potentials toward more favorable values. UV–vis–NIR spectroelectrochemical experiments and DFT calculations are also presented to clarify the nature of the reduced species in solution.

A Sustainable Improvement of ω-Bromoalkylphosphonates Synthesis to Access Novel KuQuinones

“…Conversely, KuQuinones characteristic peaks were clearly observed in the aromatic region of the spectra. On the other hand, 31 P NMR analysis unambiguously confirmed the effectiveness of the hydrolysis [62]. In fact, by comparing the 31 P NMR spectra in DMSO-d 6 of the phosphonate esters with the corresponding phosphonic acids (Figure 1), a shift of about 5 ppm fields was observed, according to literature data [62].…”

“…With respect to photoelectrochemical applications, we have been recently involved in the use of metal-free quinoid compounds, i.e., KuQuinones (KuQs), as photosentisiz-ers on indium-tin oxide (ITO) [28], NiO [29] and on SnO 2 [30], due to their favorable electrochemical and photophysical properties [31]. In this respect, terminal hydroxy or carboxylic acid functionalities were introduced in KuQuinone structure to ensure a stable and effective metal oxide binding.…”

“…The following are available online at https://www.mdpi.com/article/10 .3390/org2020010/s1, FigureS1:1 H NMR spectrum of 1 in CDCl 3 ; FigureS2:31 P NMR spectrum of 1 in CDCl 3 ; Figure S3: Mass spectrum of 1; Figure S4: 1 H NMR spectrum of 2 in CDCl 3 ; Figure S5: 31 P NMR spectrum of 2 in CDCl 3 ; Figure S6: Mass spectrum of 2; Figure S7: 1 H NMR spectrum of 3 in CDCl 3 ; Figure S8: 31 P NMR spectrum of 3 in CDCl 3 ; Figure S9: Mass spectrum of 3; Figure S10: 1 H NMR spectrum of 4 in CDCl 3 ; Figure S11: 13 C NMR spectrum of 4 in CDCl 3 ; Figure S12: 31 P NMR spectrum of 4 in CDCl 3 ; Figure S13: HRMS spectrum of 4; Figure S14: UV-vis spectrum of 4; Figure S15: ATR-IR spectrum of 4; Figure S16: 1 H NMR spectrum of 7 in DMSO-d 6 ; Figure S17: 31 P NMR spectrum of 7 in DMSO-d 6 ; Figure S18: HRMS of 7; Figure S19: ATR-IR spectrum of 7; Figure S20: 1 H NMR spectrum of 5 in CDCl 3 ; Figure S21: 13 C NMR spectrum of 5 in CDCl 3 ; Figure S22: 31 P NMR spectrum of 5 in CDCl 3 ; Figure S23: HRMS spectrum of 5; Figure S24: UV-vis spectrum of 5 in CHCl 3 ; Figure S25: ATR-IR spectrum of 5; Figure S26: 1 H NMR spectrum of 8 in DMSO-d 6 ; Figure S27: 31 P NMR spectrum of 8 in DMSO-d 6 ; Figure S28: HRMS spectrum of 8; Figure S29: ATR-IR spectrum of 8; Figure S30: 1 H NMR spectrum of 6 in CDCl 3 ; Figure S31: 13 C NMR spectrum of 6 in CDCl 3 ; Figure S32: 31 P NMR spectrum of 6 in CDCl 3 ; Figure S33: HRMS spectrum of 6; Figure S34: UV-vis spectrum of 6 in CHCl 3 ; Figure S35: ATR-IR spectrum of 6; Figure S36: 1 H NMR spectrum of 9 in DMSO-d 6 ; Figure S37: 31 P NMR spectrum of 9 in DMSO-d 6 ; Figure S38: HRMS spectrum of 9; Figure S39: ATR-IR spectrum of 9.…”

KuQuinone as a Highly Stable and Reusable Organic Photocatalyst in Selective Oxidation of Thioethers to Sulfoxides

“…KuQ belongs to a family of quinoid compounds, characterized by a pentacyclic skeleton . The extended conjugation confers a broad and intense absorption spectrum in the visible range and a low reduction potential: , both resulted in crucial features for KuQ photoelectrocatalytic applications. − Considering the growing interest in organic photocatalysts, KuQ is here explored for the first time as a homogeneous metal-free photocatalyst for the selective oxidation of interesting organic substrates, such as thioethers.…”

A Neutral‐pH Aqueous Redox Flow Battery Based on Sustainable Organic Electrolytes

“…[43][44][45][46][47][48][49] Z. Zhao et al [50] used 1,1'bis(sulfonate)-ferrocene dianion disodium salt pared with the anthraquinone-2,7-disulfonic acid disodium salt; on the other hand, ferrocene decomposed under the acidic conditions used to stabilize the anthraquinone. [42] Considering our expertise in synthesis and applications of electro-active molecules, in particular metallocenes, [51][52][53][54] we synthesized in this work the 1,1'-bis(sulfonate)-ferrocene dianion disodium salt (DSÀ Fc) and two viologen-derivatives, as catholyte and anolyte, respectively, to produce a sustainable neutral-pH AORFB. The performances of the synthesized electrolytes were evaluated in terms of solubility, degradation capacity, retention, and electrical power generation.…”