Understanding Color Tuning and Reversible Oxidation of Conjugated Azomethines

Abstract

With the aim of achieving reversible oxidation and color tuning, the effect of the central aromatic on the spectroscopic, electrochemical, and spectrochemical properties of a series of electrochromic azomethine triads was investigated. The absorption of the alkylated thiophene derivatives was blue-shifted relative to their unalkylated counterparts when the central aromatic was either a bi-or terthiophene. It was further found that the alkylated thiophene derivatives had larger Stokes shifts than their unsubstituted counterparts. Theoretical calculations demonstrated that the torsion angles of these alkylated cores with respect to the flanking azomethines were responsible for the spectroscopic effects. While the electrochemical oxidation potential of the triads varied by only 100 mV, the reversibility of their anodic process was contingent on the central aromatic. The absorption of the electrochemically produced state red-shifted between 165 and 280 nm from its corresponding neutral state, leading to perceived color changes between orange and blue. Reversible color changes were chemically mediated with ferric chloride/hydrazine. The absorption of the chemically oxidized state shifted between 155 and 220 nm from the corresponding neutral state, contingent on the central aromatic. The palette of perceived colors that was possible with oxidation included orange, yellow, blue, and gray.

New Thiophene Imines Acting as Hole Transporting Materials in Photovoltaic Devices

“…Therefore, new stable, processable organic compounds that are able to meet the continually increasing demands are being sought. − Among the various π-conjugated compounds, azomethines have attracted broad research interest as components in optoelectronic devices. − Imines are synthesized under mild reaction conditions, where only water is formed as a byproduct (the reaction is not harmful to the environment), and do not require a complicated purification process and metal catalysts. − , The possibility of modification of the azomethine structure through the appropriate selection of amines and carbonyl compounds allows for the preparation of new compounds with the desired properties. Considering the chemical structure of the investigated imines for organic electronics, special attention is paid to heterocyclic azomethines with a thiophene unit. − Compounds with a thiophene structure exhibit many desirable properties in optoelectronics, such as low oxidation potentials, low band-gap energy, good electrical conductivity, and chemical and thermal stability. ,− ,, Apart from the various fields of imine applications, they are also investigated as materials for photovoltaic (PV) cells. − Nowadays, they are examined in bulk heterojunctions (BHJs), − dye-sensitized solar cells (DSSCs), and perovskite solar cells (PSCs). − Bogdanow...…”

Spacer Conjugation and Surface Support Effects in Monolayer Electrochromic Materials

“…Traditional EC materials are based on relatively thick layers of organic, − organometallic, , or inorganic − compounds or composites that change their absorbance or reflectance through an electrochemical redox process . Among others, terpyridine (tpy)-based ligands have been shown to form stable complexes with a wide range of metal ions in different oxidation states. ,,, Since the seminal works by Constable, , the synthetic methodology of tpy derivatives has been significantly improved. − In contrast to bpy-based asymmetric ligands that often form a mixture of facial and meridional isomers, tpy-containing ligands are structurally more appealing, because they form well-defined six-coordinate cationic Fe­(II), Co­(II), Ru­(II), and Os­(II) complexes where two ligating moieties are situated in an orthogonal fashion.…”

Engaging the Reversible Bonds of an Immobilized Styreno-Thiophene Film

“…Conjugated azomethines such as 2B and 2C can be electrochemically oxidized. , Their oxidation results in significant color changes with new absorptions that are bathochromically shifted from the neutral form . The electroactivity of the immobilized film of poly-2A on glass slides coated with indium–tin oxide (ITO) was evaluated.…”