Special Issue "Electrochemical Behavior of the Nonbenzenoid Aromatic Hydrocarbon Azulene and Its Derivatives 2022"

A special issue of Symmetry (ISSN 2073-8994). This special issue belongs to the section "Chemistry: Symmetry/Asymmetry".

Deadline for manuscript submissions: 30 November 2023 | Viewed by 4126

Special Issue Editors

Faculty of Applied Chemistry and Materials Science, University Politehnica of Bucharest, 1-7 Polizu Street, 011061 Bucharest, Romania
Interests: physical chemistry; organic electrochemistry
Special Issues, Collections and Topics in MDPI journals
Center of Organic Chemistry of the Romanian Academy, 202B Spl. Independentei, 060023 Bucharest, Romania
Interests: organic chemistry; syntheses, properties and reaction mechanisms; azulenes; diazenes; heteroaromatics
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear colleagues,

The blue nonbenzenoid aromatic hydrocarbon azulene is a naphthalene isomer. However, these two hydrocarbons are essentially different. While naphthalene enjoys biaxial symmetry, azulene has only one x-axis symmetry. This peculiarity gives to azulene system an asymmetrical charge distribution with important consequences. From these consequences the presence of significant dipole moment and remarkable chemical, electronic, or optical behavior can be noticed. Therefore, for this system many technical applications have been found. The capture or release of an electron ensures the generation of anion or cation radicals stabilized by cyclopentadienyl or tropylium structures, and they can thus serve as raw materials in electrochemical reactions. The following areas of research are expected to be addressed:

  1. Electrochemically studied azulene compounds with technical applications: synthesis and chemical behavior;
  2. Electrochemical behavior of azulene compounds of interest;
  3. In silico approaches for prediction of the electrochemical properties of azulene derivatives;
  4. Modified electrodes based on azulene compounds of interest;
  5. Homogeneous and heterogeneous recognition based on azulene derivatives.

Dr. Eleonora Mihaela Ungureanu
Dr. Alexandru C. Razus
Guest Editors

Manuscript Submission Information

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Keywords

  • azulene derivatives
  • synthesis
  • chemical behavior
  • electrochemical properties
  • DFT calculations
  • modified electrodes based on azulene derivatives
  • molecular recognition

Published Papers (4 papers)

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Research

17 pages, 7780 KiB  
Article
Electrochemistry of Rhodanine Derivatives as Model for New Colorimetric and Electrochemical Azulene Sensors for the Detection of Heavy Metal Ions
Symmetry 2023, 15(3), 752; https://doi.org/10.3390/sym15030752 - 18 Mar 2023
Cited by 2 | Viewed by 830
Abstract
Rhodanine (R) is a heterocycle having complexing properties for heavy metal (HM) ions. Considering the similar electron-donating character of diethylaminobenzene and azulene, electrochemical characterization of (Z)-5-(azulen-1-ylmethylene)-2-thioxo-thiazolidin-4-one (R1) and 5-(4 diethylamino-benzylidene)-2-thioxo-thiazolidin-4-one (R2) was performed to establish [...] Read more.
Rhodanine (R) is a heterocycle having complexing properties for heavy metal (HM) ions. Considering the similar electron-donating character of diethylaminobenzene and azulene, electrochemical characterization of (Z)-5-(azulen-1-ylmethylene)-2-thioxo-thiazolidin-4-one (R1) and 5-(4 diethylamino-benzylidene)-2-thioxo-thiazolidin-4-one (R2) was performed to establish their common features. Chemically modified electrodes based on R1 and R2 were compared for HM recognition. Evidence for the formation of films was provided by scanning and controlled potential electrolysis, and HM recognition experiments were performed using their films. Parallel studies for analysis of HMs by complexation in solution were performed by UV-Vis. The analogy between R1 and R2 created the premise for easier selection of compounds for certain applications. The performance of the chemically modified electrodes was evaluated as detection limits for HMs. The azulene monomer (R1) proved to be the best candidate for Pb(II) detection, being about eight times more sensitive than R2. However, in solution, R2 proved to be a good choice for optical measurements, having a higher absorption coefficient. These results support the two ligands having different behaviors in homogeneous and heterogeneous systems. Full article
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21 pages, 8691 KiB  
Article
Advanced Materials Based on Azulenyl-Phenyloxazolone
Symmetry 2023, 15(2), 540; https://doi.org/10.3390/sym15020540 - 17 Feb 2023
Viewed by 766
Abstract
Chemically modified electrodes (CMEs) based on 2-phenyl-4-((4,6,8-trimethylazulen-1-yl)methylene)oxazol-5(4H)-one (M) were obtained by irreversible electrooxidation of M in millimolar solutions in 0.1 M tetrabutylammonium perchlorate (TBAP) in acetonitrile. These CMEs were characterized by a ferrocene redox probe, electrochemical impedance spectroscopy (EIS), X-ray photon [...] Read more.
Chemically modified electrodes (CMEs) based on 2-phenyl-4-((4,6,8-trimethylazulen-1-yl)methylene)oxazol-5(4H)-one (M) were obtained by irreversible electrooxidation of M in millimolar solutions in 0.1 M tetrabutylammonium perchlorate (TBAP) in acetonitrile. These CMEs were characterized by a ferrocene redox probe, electrochemical impedance spectroscopy (EIS), X-ray photon spectroscopy (XPS), and scanning electron microscopy (SEM). The influence of the preparation conditions (charge and potential) was examined. The CMEs were finally used for the analysis of synthetic samples of heavy metal (HM) ions. The paper highlights the importance of potential and electropolymerization charge on the film properties, with accent on recognition of HMs, in order to identify the best conditions for their detection in water. The observed findings are relevant for further design and development of advanced materials based on azulenyl-phenyloxazolone for the analysis of HMs in water. Full article
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13 pages, 6325 KiB  
Article
Electrochemical Studies of Azulene Modified Electrodes
Symmetry 2023, 15(2), 514; https://doi.org/10.3390/sym15020514 - 15 Feb 2023
Cited by 1 | Viewed by 1038
Abstract
Previous studies performed on 2-(azulen-1-yldiazenyl)-5-phenyl-1,3,4-thiadiazole (T) showed that T is a ligand with complexing properties towards heavy metals (HMs) in solution and can be attached to electrode surfaces. Films of T were deposited on glassy carbon to obtain chemically modified electrodes [...] Read more.
Previous studies performed on 2-(azulen-1-yldiazenyl)-5-phenyl-1,3,4-thiadiazole (T) showed that T is a ligand with complexing properties towards heavy metals (HMs) in solution and can be attached to electrode surfaces. Films of T were deposited on glassy carbon to obtain chemically modified electrodes (T-CMEs), either through scanning or using controlled potential electrolysis in tetrabutylammonium perchlorate in acetonitrile. They were investigated using cyclic voltammetry (CV), differential pulse voltammetry (DPV), electrochemical impedance spectroscopy (EIS), and spectroelectrochemistry. All methods provided evidence for showing the formation of insulating films, with properties depending on their electropolymerization potential. CV and EIS studies of T-CMEs in tetrabutylammonium perchlorate in acetonitrile as supporting electrolyte, and in the presence of a ferrocene redox probe resulted in a thickness of ~10 µm, an active surface area about 6 times higher than the geometrical one, and conductivity of about 10−6 S/cm. This characterization performed using voltammetric techniques reveals the symmetry of the reversible anodic and cathodic redox CV peaks for the polymer, while spectroelectrochemistry shows the intensification of the charge transport process through polarons, due to the anodic polarization of the film. Full article
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11 pages, 3373 KiB  
Article
Solvent Effects and Metal Ion Recognition in Several Azulenyl-Vinyl-Oxazolones
Symmetry 2023, 15(2), 327; https://doi.org/10.3390/sym15020327 - 24 Jan 2023
Viewed by 898
Abstract
The spectral properties of several azulene-oxazolone derivatives containing a phenyloxazolone moiety linked to a substituted azulene ring via a C=C double bond were studied in different solvents of varying polarity. The solvatochromism and the ability of azulene-oxazolone derivatives to recognize heavy metal ions [...] Read more.
The spectral properties of several azulene-oxazolone derivatives containing a phenyloxazolone moiety linked to a substituted azulene ring via a C=C double bond were studied in different solvents of varying polarity. The solvatochromism and the ability of azulene-oxazolone derivatives to recognize heavy metal ions were investigated. In order to estimate the contribution of the non-specific and specific solute–solvent interactions, multiple linear regression analysis using Kamlet–Taft, Catalan and Laurence parameters was applied. These azulene derivatives demonstrate positive solvatochromism. The methyl and isopropyl substituents at the seven-membered azulene ring determine the highest red shifts of the absorption maxima of these azulenyl-vinyl-oxazolones. According to Catalan and Laurence models, the solvent polarizability is a more significant parameter in describing the solvatochromic properties of the azulene-oxazolone derivatives. The azulene-oxazolone compounds under study showed a good response to heavy metal cations (Cd2+, Hg2+, Cu2+ and Pb2+). Full article
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Planned Papers

The below list represents only planned manuscripts. Some of these manuscripts have not been received by the Editorial Office yet. Papers submitted to MDPI journals are subject to peer-review.

The blue nonbenzenoid aromatic hydrocarbon azulene is a naphthalene isomer. However, these two hydrocarbons are essentially different. While naphthalene enjoys biaxial symmetry, azulene has only one x-axis symmetry. This peculiarity gives to azulene system an asymmetrical charge distribution with important consequences. From these consequences the presence of significant dipole moment and remarkable chemical, electronic, or optical behavior can be noticed. The following areas of research are expected to be addressed:

  1. Electrochemically studied azulene compounds with technical applications: synthesis and chemical behavior;
  2. Electrochemical behavior of azulene compounds of interest;
  3. In silico approaches for prediction of the electrochemical properties of azulene derivatives;
  4. Modified electrodes based on azulene compounds of interest;
  5. Homogeneous and heterogeneous recognition based on azulene derivatives.

Dr. Eleonora Mihaela Ungureanu
Dr. Alexandru C. Razus
Guest Editors

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