Quinoid Compounds Research Articles

An n-Doping Cross-Linkable Quinoidal Compound as an Electron Transport Material for Fully Stretchable Inverted Organic Solar Cells.

The photocatalytic activity and inherent brittleness of ZnO, which is commonly used as an electron transport layer (ETL) in inverted organic solar cells (OSCs), have impeded advancements in device stability and the development of fully stretchable OSCs. In this study, an intrinsically stretchable ETL for inverted OSCs through a side-chain cross-linking strategy has been developed. Specifically, cross-linking between bromine atoms on the side chains of a quinoidal compound and the amino groups in polyethylenimine resulted in a film, designated QBr-PEI-50, with high electrical conductivity (0.049 S/m) and excellent stretchability (crack-onset strain>45 %). When used as the ETL in inverted OSCs, QBr-PEI-50 was markedly superior to ZnO in terms of device performance and stability, yielding a power conversion efficiency (PCE) of 18.27 % and a T80 lifetime exceeding 10000 h. Moreover, incorporation of QBr-PEI-50 in fully stretchable inverted OSCs yielded a PCE of 14.01 %, and 80 % of the initial PCE was maintained after 21 % strain, showcasing its potential for wearable electronics.

An n‐Doping Cross‐Linkable Quinoidal Compound as an Electron Transport Material for Fully Stretchable Inverted Organic Solar Cells

AbstractThe photocatalytic activity and inherent brittleness of ZnO, which is commonly used as an electron transport layer (ETL) in inverted organic solar cells (OSCs), have impeded advancements in device stability and the development of fully stretchable OSCs. In this study, an intrinsically stretchable ETL for inverted OSCs through a side‐chain cross‐linking strategy has been developed. Specifically, cross‐linking between bromine atoms on the side chains of a quinoidal compound and the amino groups in polyethylenimine resulted in a film, designated QBr‐PEI‐50, with high electrical conductivity (0.049 S/m) and excellent stretchability (crack‐onset strain>45 %). When used as the ETL in inverted OSCs, QBr‐PEI‐50 was markedly superior to ZnO in terms of device performance and stability, yielding a power conversion efficiency (PCE) of 18.27 % and a T80 lifetime exceeding 10000 h. Moreover, incorporation of QBr‐PEI‐50 in fully stretchable inverted OSCs yielded a PCE of 14.01 %, and 80 % of the initial PCE was maintained after 21 % strain, showcasing its potential for wearable electronics.

Determining Excited-State Absorption Properties of a Quinoid Flavin by Polarization-Resolved Transient Spectroscopy.

As important naturally occurring chromophores, photophysical/chemical properties of quinoid flavins have been extensively studied both experimentally and theoretically. However, little is known about the transition dipole moment (TDM) orientation of excited-state absorption transitions of these important compounds. This aspect is of high interest in the fields of photocatalysis and quantum control studies. In this work, we employ polarization-associated spectra (PAS) to study the excited-state absorption transitions and the underlying TDM directions of a standard quinoid flavin compound. As compared to transient absorption anisotropy (TAA), an analysis based on PAS not only avoids diverging signals but also retrieves the relative angle for ESA transitions with respect to known TDM directions. Quantum chemical calculations of excited-state properties lead to good agreement with TA signals measured in magic angle configuration. Only when comparing experiment and theory for TAA spectra and PAS, do we find deviations when and only when the S0 → S1 of flavin is used as a reference. We attribute this to the vibronic coupling of this transition to a dark state. This effect is only observed in the employed polarization-controlled spectroscopy and would have gone unnoticed in conventional TA.

A para-azaquinodimethane integrated quinoidal conjugated microporous polymer

Quinoidal compounds own unique properties that make them a promising platform for optoelectronic applications.

Quinoid Redox Mediators and Their Involvement in Environmental Pollution Treatment

In recent years, quinoid redox mediators (QRMs) have attracted increasing attention because of their key role in wastewater biotreatment. Previous studies have shown that the anaerobic respiration of many bacteria could be coupled to the reduction and reoxidation of quinone groups. Thus, QRMs are widely involved in the microbial transformation of various organic and inorganic substances. To date, few reviews have focused on the involvement of quinoid compounds in environmental pollution biotreatment processes. In this paper, we review the different types of QRMs that interact closely with microorganisms, the characteristics of those QRMs, the involvement of QRMs during the biotransformation of recalcitrant organic pollutants, heavy metal ions and metallic oxides, and their enhancement on microbial fuel cells. Finally, the future research focus and application prospects with regard to different types of QRMs are proposed. This study can improve our understanding of QRM-mediated environmental pollution biotreatment processes and provide fundamental guidance on what kinds of QRMs are practical for engineering applications.

Electrochemical Sulphenylation/Cyclization of Quinones: A Rapid, Green, and Efficient Access to Cytotoxic Compounds

AbstractUndivided electrochemical cells enable economical preparation of sulphur‐containing naphthoquinones through electrochemical sulphenylation of quinoidal compounds. The environmentally friendly and efficient protocol eliminates the use of chemical oxidants and facilitates the synthesis of the desired molecules. This approach offers an efficient and versatile method to synthesize quinones that exhibit cytotoxicity against cancer cell lines.

Self-Doped n-Type Quinoidal Compounds with Good Air Stability and High Electrical Conductivity for Organic Electronics.

Air stable n-type conductive molecules with high electrical conductivities and excellent device performance have important applications in organic electronics, but their synthesis remains challenging. Herein, we report three self-doped n-type conductive molecules, designated QnNs, with a closed-shell quinoidal backbone and alkyl amino chains of different lengths. The QnNs are self-doped by intermolecular electron transfer from the amino groups to the quinoidal backbone. This process is ascertained unambiguously by experiments and theoretical calculations. The use of a quinoidal structure effectively improves the self-doping level, and thus increases the electrical conductivity of self-doped n-type conductive molecules achieved by a closed-shell structure from<10-4 S cm-1 to>0.03 S cm-1 . Furthermore, the closed-shell quinoidal structure results in good air stability of the QnNs, with half-lives>73 days; and Q4N shows an electrical conductivity of 0.019 S cm-1 even after exposure to air for 120 days. When applying Q6N as the cathode interlayer in organic solar cells (OSCs), an outstanding power conversion efficiency of up to 18.2 % was obtained, which represents one the best results in binary OSCs.

Self‐Doped n‐Type Quinoidal Compounds with Good Air Stability and High Electrical Conductivity for Organic Electronics

AbstractAir stable n‐type conductive molecules with high electrical conductivities and excellent device performance have important applications in organic electronics, but their synthesis remains challenging. Herein, we report three self‐doped n‐type conductive molecules, designated QnNs, with a closed‐shell quinoidal backbone and alkyl amino chains of different lengths. The QnNs are self‐doped by intermolecular electron transfer from the amino groups to the quinoidal backbone. This process is ascertained unambiguously by experiments and theoretical calculations. The use of a quinoidal structure effectively improves the self‐doping level, and thus increases the electrical conductivity of self‐doped n‐type conductive molecules achieved by a closed‐shell structure from&lt;10−4 S cm−1 to&gt;0.03 S cm−1. Furthermore, the closed‐shell quinoidal structure results in good air stability of the QnNs, with half‐lives&gt;73 days; and Q4N shows an electrical conductivity of 0.019 S cm−1 even after exposure to air for 120 days. When applying Q6N as the cathode interlayer in organic solar cells (OSCs), an outstanding power conversion efficiency of up to 18.2 % was obtained, which represents one the best results in binary OSCs.

Convergent Synthesis of the Precursors to Thiophene-Based Quinoids

A convergent (outside-to-center) route was adopted to synthesize the precursors of quinoidal compounds in high yields of 85-93%. With subsequent rearrangement/dehydroxylation and oxidation, a series of thiophene-based quinoids with indandione or oxindole terminal groups were successfully synthesized. This strategy shows good compatibility with versatile central and terminal units, leading to quinoidal compounds with tunable properties.

TFT-CN/P3HT blending active layer based two-component organic field-effect transistor for improved H2S gas detection

To prepare OFET-based sensors by low-cost solution method and improve the sensing ability of polymer OFETs to hydrogen sulfide (H2S), a n-type small molecule dicyanomethylene-terminated quinoid compound (TFT-CN) was blended with P3HT and used as the semiconductor active layer. The introducing of TFT-CN into two-component OFET based sensors greatly improves the sensitivity and selectivity for H2S gas and reduces the limit of detection to 10 ppb level due to the strong binding energy between TFT-CN and H2S. The blending ratio has a great influence on the sensing performance and the sensors show the highest sensitivity for various concentrations of H2S when the ratio of TFT-CN: P3HT is 1: 6 in weight, and the sensitivity can be increased five times than that of the pure P3HT-based sensors. This work proves that it is a simple, effective and low-cost solution method to improve the sensing performance of OFET-based sensors by introducing a functional molecule into conventional polymers which will inspire the performance improvement and application expansion of many traditional materials.

Synthesis and characterization of solution-processed indophenine derivatives for function as a hole transport layer for perovskite solar cells

A series of quinoidal molecules were synthesized via a new variant of the indophenine reaction. The previously reported synthetic route of indophenine dyes involves a one pot procedure starting with isatin and an appropriate 5-membered aromatic heterocycle in the presence of catalytic amount of sulfuric acid. However, the reaction conditions lead to a low yield and a poor selectivity with the formation of several by-products. Herein, we propose a modification of the standard reaction to increase the yield, using tertiary alcohol as a starting material instead of isatin. This modified protocol is highly selective and allows for a very clean reaction, i.e. high yields, isomer-free synthesis and avoids any complex purification issues. Further, this protocol allows access to quinoidal compounds with variable termini and π-conjugated core. The influence of the conjugation length of the π-bridge on the quinoidal electronic structure is investigated by spectroscopic and electrochemical measurements. Meanwhile, the charge carrier mobilities of selected compounds were determined by the space-charge-limited-current method. Their utility as a hole transport material for the perovskite solar cells is demonstrated.

Isomerically Pure Oxindole-Terminated Quinoids for n-Type Organic Thin-Film Transistors Enabled by the Chlorination of Quinoidal Core.

Quinoidal compounds have great potential utility as high-performance organic semiconducting materials because of their rigid planar structures and extended π-conjugation. However, the existence of E and Z isomers adversely affects the charge-transport properties of quinoidal compounds. In this study, three isomerically pure oxindole-terminated quinoids were developed by introducing chlorine atoms in the quinoidal core. The synthesized quinoids were confirmed to have a Z,Z configuration by means of 1 H NMR spectroscopy, density functional theory calculations, and single-crystal X-ray analysis. Importantly, the strategy of chlorination allowed to maintain low-lying frontier molecular orbital energy levels and ensure favorable intermolecular packing. Consequently, all three quinoidal compounds showed n-type transport characteristics in organic thin-film transistors, with electron mobilities up to 0.35 cm2 V-1 s-1 , which is the highest value reported to date for oxindole-terminated quinoids. Our study can provide new guidelines for the design of isomerically pure quinoids with high electron mobilities.

First report of trans-A2B-corrole derived from a lapachone derivative: photophysical, TD-DFT and photobiological assays.

In this work, the synthesis, characterization and photophysical assays of a new trans-A2B-corrole derivative from the naturally occurring quinone are described. β-Lapachone is a naturally occurring quinoidal compound that provides highly fluorescent heterocyclic compounds such as lapimidazoles. The new trans-A2B-corrole compound was obtained from the reaction between 2,3,4,5,6-(pentafluorophenyl)dipyrromethane and the lapimidazole bearing an aldehyde group. The dyad was characterized by high-resolution mass spectrometry (HRMS), NMR spectroscopy (1H, COSY 2D, HMBC, 19F), FT-IR, UV-vis, steady-state and time-resolved fluorescence, electrochemical studies (CV), TD-DFT analysis and photobiological experiments, in which includes aggregation, stability in solution, photostability and partition coefficients assays. Finally, ROS generation assays were performed using 1,3-diphenylisobenzofuran (DPBF) method and the presented compound showed significant photostability and singlet oxygen production.

Furan-Containing Quinoidal Compounds for High-Performance Copper/Silver Electrode-Based n-Channel Organic Transistors

Furan-containing quinoidal compounds FTzTzF-C10 and FTzTzF-C8 were synthesized. These compounds have low lowest unoccupied molecular orbital (LUMO) energy levels and can form a charge transfer complex with Ag and Cu films, proved by cyclic voltammograms and Raman spectra. Single crystal diffraction results reveal that they adopt a lamellar layer structure with strong π–π interactions in crystals. Thin film transistor characterization shows that FTzTzF-C10 and FTzTzF-C8 exhibit n-channel behavior with an electron mobility of 1.18 cm2 V–1 s–1, one of the highest electron mobilities reported for thin film devices based on furan-containing semiconductors. Notably, the performance of FTzTzF-C10 and FTzTzF-C8 devices is nearly independent of the metals (Au, Cu, and Ag) of source–drain electrodes, which is ascribed to the ultrathin charge transfer layer formed by the spontaneous reaction of FTzTzFs and electrodes (Ag, Cu). These results demonstrate that furan is an excellent block for quinoidal semiconductors and promote the development of Cu/Ag electrode-based organic transistors.

Quinoid Pigments of Sea Urchins Scaphechinus mirabilis and Strongylocentrotus intermedius: Biological Activity and Potential Applications.

This review presents literature data: the history of the discovery of quinoid compounds, their biosynthesis and biological activity. Special attention is paid to the description of the quinoid pigments of the sea urchins Scaphechinus mirabilis (from the family Scutellidae) and Strongylocentrotus intermedius (from the family Strongylocentrotidae). The marine environment is considered one of the most important sources of natural bioactive compounds with extremely rich biodiversity. Primary- and some secondary-mouthed animals contain very high concentrations of new biologically active substances, many of which are of significant potential interest for medical purposes. The quinone pigments are products of the secondary metabolism of marine animals, can have complex structures and become the basis for the development of new natural products in echinoids that are modulators of chemical interactions and possible active ingredients in medicinal preparations. More than 5000 chemical compounds with high pharmacological potential have been isolated and described from marine organisms. There are three well known ways of naphthoquinone biosynthesis—polyketide, shikimate and mevalonate. The polyketide pathway is the biosynthesis pathway of various quinones. The shikimate pathway is the main pathway in the biosynthesis of naphthoquinones. It should be noted that all quinoid compounds in plants and animals can be synthesized by various ways of biosynthesis.

On the Reaction of 2-Alkanoylnaphthohydroquinones with Hydroxylamine: Access to Cytotoxic 2-(Hydroxyamino)-1,4-naphthoquinone and Their 3-(Hydroxyimino)alkyl Analogous

Oximes are known for their anti-inflammatory, antimicrobial, antioxidant, and anticancer activities. Frequently, modification of biologically active carbonyl compounds into oximes leads to increased activity. The present study reports the reactivity of 2-alkanoylnaphthohydroquinones against hydroxylamine under aerial conditions. Results show that, depending on the structure of the hydroquinones, the reaction proceeds through two different chemical pathways to produce 2-(hydroxyamino)-1,4-naphthoquinone and their C-3 (hydroxyimino)alkyl derivatives. Both the formation of the quinoid compounds under aerial oxidation and C-C cleavage reactions of hemiaminal intermediates are discussed. In vitro screening of the substituted 1,4-naphthoquinones on a panel of cancer cells reveals moderate cytotoxic activities. Compound 19, 2-(hydroxyamino)-1,4-naphthoquinone, stands out by its anticancer potency against prostate cancer cells as shown by the lowest IC50 value (8.08 μM) and the best selectivity index (3.90).

The Syntheses, Characterization and Field Effect Transistor Performance of Thiazole‐Based Dicyanomethylene‐Endcapped Quinoidal Compounds

AbstractThiazole‐based dicyanomethylene‐endcapped quinoidal compounds, QBTzTT8, QBTzTT16 and QBTzTT24 with different length of alkyl chains, were designed and synthesized. These compounds exhibit a relative low LUMO energy level of −4.55 eV, and can spontaneously react with metals Ag and Cu to form charge transfer complexes which is evidenced by Raman spectra, Infrared spectra and color change. Thin film transistors of QBTzTT16 and QBTzTT24 are fabricated, and metals Ag, Cu and Au are used as source‐drain electrodes. The devices display typical n‐type transistor performance. The mobility of devices shows nearly non‐dependent on source‐drain electrodes, being attributed to the spontaneously formed ultrathin charge‐transfer complex layer at the semiconductor/Cu (Ag) electrode interface. The average electron mobilities of QBTzTT16 and QBTzTT24 are 4.7×10−2 cm2 V−1 s−1 and 6.8×10−2 cm2 V−1 s−1, respectively.

Indandione-Terminated Quinoidal Compounds for Low-Bandgap Small Molecules with Strong Near-Infrared Absorption: Effect of Conjugation Length on the Properties.

Low-bandgap organic semiconductors have attracted much attention for their multiple applications in optoelectronics. However, the realization of narrow bandgap is challenging particularly for small molecules. Herein, we have synthesized four quinoidal compounds, i. e., QSN3, QSN4, QSN5 and QSN6, with electron rich S,N-heteroacene as the quinoidal core and indandione as the end-groups. The optical bandgap of the quinoidal compounds is systematically decreased with the extension of quinoidal skeleton, while maintaining stable closed-shell ground state. QSN6 absorbs an intense absorption in the first and second near-infrared region in the solid state, and has extremely low optical bandgap of 0.74 eV. Cyclic voltammetry analyses reveal that the lowest unoccupied molecular orbital (LUMO) energy levels of the four quinoidal compounds all lie below -4.1 eV, resulting in good electron-transporting characteristics in organic thin-film transistors. These results demonstrated that the combination of π-extended quinoidal core and end-groups in quinoidal compounds is an effective strategy for the synthesis of low-bandgap small molecules with good stability.

Guidelines for Tuning the Excited State Hückel–Baird Hybrid Aromatic Character of Pro‐Aromatic Quinoidal Compounds**

AbstractPro‐aromatic molecules have higher‐energy diradicaloid states that are significantly influenced by resonance structures in which conjugated rings take on Hückel‐aromatic character. Recently, it has been argued that there are also pro‐aromatic molecules that adopt central units with 4nπ‐electron Baird‐aromatic character in the T1 state, although detailed analysis suggests that these compounds are better labelled as T1 Hückel–Baird hybrid molecules where Hückel‐aromaticity dominates. Herein, we consider a series of symmetrically substituted conjugated rings with potential Baird aromaticity in the lowest excited triplet and singlet states. Our computational results allow us to establish general guidelines for the rational design of molecules with excited state Hückel/Baird aromaticity in pro‐aromatic quinoidal compounds. We found two main strategies to promote high Baird aromatic character: 1) anionic and small conjugated rings with electron donating groups as substituents and small exocyclic groups with electron withdrawing substituents, or 2) electron deficient conjugated rings with exocyclic electron–donor substitution.

Guidelines for Tuning the Excited State Hückel–Baird Hybrid Aromatic Character of Pro‐Aromatic Quinoidal Compounds**

Pro-aromatic molecules have higher-energy diradicaloid states that are significantly influenced by resonance structures in which conjugated rings take on Hückel-aromatic character. Recently, it has been argued that there are also pro-aromatic molecules that adopt central units with 4nπ-electron Baird-aromatic character in the T1 state, although detailed analysis suggests that these compounds are better labelled as T1 Hückel-Baird hybrid molecules where Hückel-aromaticity dominates. Herein, we consider a series of symmetrically substituted conjugated rings with potential Baird aromaticity in the lowest excited triplet and singlet states. Our computational results allow us to establish general guidelines for the rational design of molecules with excited state Hückel/Baird aromaticity in pro-aromatic quinoidal compounds. We found two main strategies to promote high Baird aromatic character: 1) anionic and small conjugated rings with electron donating groups as substituents and small exocyclic groups with electron withdrawing substituents, or 2) electron deficient conjugated rings with exocyclic electron-donor substitution.