Optical and electrochemical properties of novel thermally stable Schiff bases bearing naphthalene unit

A new look at imines and their mixture with PC71BM for organic, flexible photovoltaics

Due to its high electron affinity and electron mobility in a wide absorption range of the visible solar spectrum, [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) is often used as an efficient acceptor in organic photovoltaics. In turn, imines are additives to the active layer of organic solar cells, mainly due to the free electron pair of the imine nitrogen atom and the presence of various chemical groups affecting the polarity and conformations of molecules. However, the attainable efficiency is not as high as expected. Therefore, we have systematically investigated two imines and their mixtures with PC71BM by spectroscopic (the high pressure UV-Vis and frequency domain dielectric), thermoelectric, and mechanical methods for organic, flexible photovoltaics. Both the imines, (N,N'E,N,N'E)-N,N'-([2,2':5',2"-terthiophene]-5,5"-diylbis(methanylylidene))bis(benzo[d]thiazol-2-imine) (SC3) and (6E)-N-((5-(5-(5-((E)-(4-(4-(4-fluorophenyl)thiazol-2-yl)phenylimino)methyl)thiophen-2-yl)thiophen-2-yl)thiophen-2-yl)methylene)-4-(4-(4-fluorophenyl)thiazol-2-yl)benzenamine (SC13), have the same core composed of three thiophene rings but different terminal chains of the molecules. In the imine SC3, the imine bond is followed by benzothiazole rings on both sides of the core, while in SC13, a thiazole ring separates two benzene rings, the terminal one F-substituted. The difference in molecular structure affects the electric properties of the neat imine and its mixed layers. An addition of PC71BM to the imines improves their electric conductivity. The mechanical studies focused on the stress at break and elongation showed superior behaviour compared to fullerene derivative. High pressure systematically reduces the band gap energy, Eg, from 1.68 eV at 0.16 GPa to 1.51 eV at 2.69 GPa for PC71BM, from 1.77 eV at 0.1 MPa to 1.53 eV at 4.15 GPa for SC3, and from 1.99 eV at 0.11 GPa to 1.8 eV at 3.10 GPa for SC13, as determined by the UV-Vis absorbance measurements in a diamond-anvil cell. These Eg reductions reflect the compressed intermolecular interactions that can be used to monitor the structural stability of these compounds. Based on the dielectric studies it was found that the relaxation processes registered for both imines are probably the grain boundary relaxation. Two processes also appear in the systems with PC71BM, but none of them is the one characteristic of imines. The high-frequency process has a dipole character while the low-frequency one is probably the grain boundary relaxation of these systems. The mechanism of quasi-DC conduction in various temperature ranges in the studied systems was also determined.

Preparation of Bis-Thiophene Schiff Alkali-Copper Metal Complex for Metal Corrosion Inhibition

Due to the obvious numerous economic and technical consequences of the corrosion process, its inhibition is one of the most critical aspects of current research. A corrosion inhibitor for the bis-thiophene Schiff base copper-metal complex Cu(II)@Thy-2 was investigated here, which was synthesized via a coordination reaction with a bis-thiophene Schiff base (Thy-2) as a ligand and copper chloride (CuCl₂-2H₂O) as a ligand metal salt. When the corrosion inhibitor concentration was increased to 100 ppm, the self-corrosion current density I_coor reached a minimum of 2.207 × 10^-5 A/cm², the charge transfer resistance reached a maximum of 932.5 Ω·cm², and the corrosion inhibition efficiency reached a maximum of 95.2%, with the corrosion inhibition efficiency showing a trend of increasing first and then decreasing with concentration increase. After adding Cu(II)@Thy-2 corrosion inhibitor, a uniformly distributed dense corrosion inhibitor adsorption film formed on the surface of the Q235 metal substrate, significantly improving the corrosion profile compared to both before and after the addition of the corrosion inhibitor. Before and after the addition of corrosion inhibitor, the metal surface's contact angle CA increased from 54.54° to 68.37°, showing that the adsorbed corrosion inhibitor film decreased the metal surface's hydrophilicity and increased its hydrophobicity.

A comprehensive optical and electrical study of unsymmetrical imine with four thiophene rings and their binary and ternary compositions with PTB7 and PC70BM towards organic photovoltaics

A new unsymmetrical imine with four thiophene rings was synthesized in a one-step reaction, starting from the commercially available and relatively inexpensive reagents. The obtained imine in the form of thin films exhibited photoluminescence properties in the 1.8–2.4 eV energy range and a photoluminescence lifetime of about 0.3 ns. The HOMO and LUMO levels of the imine determined by cyclic voltammetry were at about −5.19 eV and −3.05 eV, respectively. The density functional theory was applied to calculate the geometric and electronic structure of the imine. The UV-Vis spectra showed that the absorption range of the imine overlaps with that of PC₇₀BM, and the absorption peak at the maximum of the imine at 424 nm is located between the two maxima at 404 nm and 461 nm of the fullerene derivative. The electron acceptor and donor activity of the imine was tested in the solar cell architecture: glass/ITO/PEDOT:PSS/active layer/In/Al. The best photovoltaic parameters, with very good reproducibility for each 8 pixels in the cell, were found for the active layer based on ternary mixture PTB7:PC₇₀BM:imine at a weight ratio 8 : 13 : 1, with the power conversion efficiency of about 4%. The external quantum efficiency of devices with the imine was found to be about 40% at 3.3 eV. The thermal imaging together with the recorded current response at increasing potential showed that the presence of imine in the composition has a beneficial impact in terms of current flow stability at temperatures above 200 °C, compared to two component layers with the same imine as an additive.

A new unsymmetrical imine with four thiophene rings was synthesized in a one-step reaction, starting from the commercially available and relatively inexpensive reagents.

End-group functionalization of a conjugated azomethine with ureas for property tailoring

A conjugated azomethine end-capped with phenyl-ureas was prepared by a convergent approach. Hydrogen bonding with the ureas was confirmed and the spectroscopic properties could be enhanced with the supramolecular bonds.

Intramolecular versus intermolecular hydrogen bonds in a novel conjugated dimethylamino-benzylidene-amino-2-naphthoic acid Schiff base

A new compound based on the D-π-A concept, where D = dimethylamino-phenyl and A = naphthoic acid, separated by an imine motif, was designed, synthesized and characterized. The spectral, energetics, and structural characteristics of the compound were studied thoroughly theoretically by density functional theory (DFT) in the gas and aqueous phases and experimentally (steady-state absorption) in aqueous media with various degrees of polarity and hydrogen bonding ability. This compound shows high sensitivity to the polarity, basicity and proton affinity of the environment. Based on DFT, TD-DFT and NBO analysis, the compound exists in the ground-state with both intermolecular and intramolecular hydrogen bond conformations in association with the -COOH, with latter isomer calculated to be more stable. Furthermore, structural changes via intermolecular solute-solvent interactions, dictate electronic modifications and spectral changes. Graphical abstract Acidic and basic sites in DMAMN involved in protonation/deprotonation.

New anthracene-based Schiff bases: Theoretical and experimental investigations of photophysical and electrochemical properties

The new Schiff bases bearing anthracene unit were synthesized from 2-aminoanthracene and various aldehydes such as: benzaldehyde, 4-(diphenylamino)benzaldehyde, 9-phenanthrenecarboxaldehyde, 9-anthracenecarboxaldehyde, and biphenyl-4-carboxaldehyde, 2-naphthaldehyde. Resulted azomethines were characterized by IR, NMR (¹H and ¹³C), elemental analysis and UV-vis spectroscopy. The imine consists of anthracene and biphenyl moieties exhibited liquid crystal properties and their nematic phase showed Schlieren texture. The photoluminescence measurements carried out in solution and in solid state as blend with PMMA revealed the ability of the imines to emission of the blue light with quantum yield efficiency in the range of 2.18-6.03% in blend. Based on the electrochemical experiment they showed value of energy gap (E_g) in the range of 2.5-2.7eV. Additionally, density functional theory (DFT) was applied for calculations of both electronic structure and spectroscopic properties of synthesized Schiff bases. Moreover, the results obtained from preliminary tests of application of the azomethines in organic photovoltaic (OPV) devices confirmed their electron acceptor character.

Ambipolar azomethines as potential cathodic color switching materials

The electrochemical oxidation and reduction reversibility along with the electrochemically mediated color change of triad azomethines were contingent on the central aromatic.