Pyridinium-Functionalized Pyromellitic Diimides with Stabilized Radical Anion States

Optical and Electrochemical Properties of a Photosensitive Pyromellitic Diimide Derivative of Cymantrene

Photochemical properties of symmetrical pyromellitic diimide containing two cymantrenyl fragments at two nitrogen atoms were studied with IR, NMR, UV-vis, ESI-MS, and cyclic voltammetry. It was found that new unstable chelates are formed during photolysis. At the same time, the CO ligand dissociates from two Mn(CO)3 fragments during photoexcitation, which dramatically changes the electronic and redox properties of the molecule compared to the cymantrene derivative containing one imide fragment. Photolysis leads to a color change from light yellow to green. DFT calculations confirmed the possibility of the formation of complexes due to the loss of one or two CO ligands from manganese atoms. The results obtained with variation of photolysis conditions demonstrated the hemilabile character of the Mn-O=C(imide) bond. On addition of external ligands, the color and electrochemical properties changed, which is promising for the use of this complex as a sensor for small molecules.

ESIPT-based benzazole-pyromellitic diimide derivatives. A thermal, electrochemical, and photochemical investigation

This study describes the synthesis of new pyromellitic diimide (PMDI) derivatives obtained in good yields from the reaction between pyromellitic dianhydride and aminobenzazoles reactive to proton-transfer in the excited state (ESIPT). In this investigation, a non-ESIPT PMDI was also prepared for comparison. These compounds presented absorption maxima in the ultraviolet region attributed to the allowed ¹π-π* electronic transitions. Redshifted absorptions were observed for the ESIPT compounds (3b-3c) due to their π-extended conjugation if compared to the non-ESIPT dye (3a). The compounds presented fluorescence emissions between 300 and 600 nm, dependent on the solvent polarity and their chemical structures. While compound 3a presents a single emission, a dual fluorescence could be observed for compounds 3b-3c. As expected for ESIPT compounds, the emission at higher energies could be related to the excited enol conformer (E*), and the emission with a large Stokes shift was attributed to the keto tautomer (K*). All compounds presented fluorescence emission in the solid state, whereas the ESIPT derivatives presented redshifted emissions with a large Stokes shift, as expected. Cyclic voltammetry was employed to investigate the electrochemical properties of these compounds. The HOMO and LUMO energy levels were estimated at -5.40 to -5.00 eV and -2.84 to -2.62 eV, and good thermal stability (T_d > 150 °C) was observed. Quantum chemical calculationsusingTD-DFT and DFT were performed to investigate the electronic and photophysical features of the molecules.

Synthesis and Properties of Electron-Deficient and Electron-Rich Redox-Active Ionic π-Systems

There is growing interest towards the design and synthesis of organic redox-active systems, which exist in ionic form. Multi- redox systems entail life-sustaining processes like photosynthesis and cellular respiration. The significant challenge for material scientists is to rationally design complex molecular materials that can store and transfer multiple electrons at low operational potentials and are stable under ambient conditions. Also, important are the designed ionic π-systems that combine efficient electron and ion transport. Here, we discuss the synthesis of ionic π-systems which exist in the closed-shell form. Firstly, different classes of ionic arylenediimides and viologens with different π-linkers are discussed from the synthetic, structural and redox perspective. These ionic π-systems are based on the electron deficient π-scaffolds, and are shown to accumulate upto six electrons. We then discuss electron-rich ionic arylenediimides which can exist in anionic form or zwitterionic form. The anionic electron donors have absorption extending to the near Infrared (NIR) region and can be stabilized in aqueous solution. We also discuss the effect of the electron accumulation on the aromaticity and non-aromaticity of the naphthalene and the imide rings of the naphthalenediimides. We finally discuss in brief, the applications related to the organic mixed ionic-electronic conductors.

Functional Pyromellitic Diimide as a Corrosion Inhibitor for Galvanized Steel: An Atomic-Scale Engineering

Corrosion of metal/steel is a major concern in terms of safety, durability, cost, and environment. We have studied a cost-effective, nontoxic, and environmentally friendly pyromellitic diimide (PMDI) compound as a corrosion inhibitor for galvanized steel through density functional theory. An atomic-scale engineering through the functionalization of PMDI is performed to showcase the enhancement in corrosion inhibition and strengthen the interaction between functionalized PMDI (F-PMDI) and zinc oxide (naturally existing on galvanized steel). PMDI is functionalized with methyl/diamine groups (inh1 (R = -CH₃, R' = -CH₃), inh2 (R = -CH₃, R' = -CH₂CH₂NH₂), and inh3 (R = -C₆H₃(NH₂)₂, R' = -CH₂CH₂NH₂). The corrosion inhibition parameters (e.g., orbital energies, electronegativity, dipole moment, global hardness, and electron transfer) indicate the superior corrosion inhibition performance of inh3 (inh3 > inh2 > inh1). Inh3 (∼182.38 kJ/mol) strongly interacts with ZnO(101̅0) compared to inh2 (∼122.56 kJ/mol) and inh1 (∼119.66 kJ/mol). The superior performance of inh3 has been probed through charge density and density of states. Larger available states of N and H (of inh3) interact strongly with Zn and O_surf (of the surface), respectively, creating N-Zn and H-O_surf bonds. Interestingly, these bonds only appear in inh3. The charge accumulation on O_surf, and depletion on H(s), further strengthens the bonding between inh3 and ZnO(101̅0). The microscopic understanding obtained in this study will be useful to develop low-cost and efficient corrosion inhibitors for galvanized steel.

Azine Steric Hindrances Switch Halogen Bonding to N-Arylation upon Interplay with σ-Hole Donating Haloarenenitriles

An interplay between 4-bromo- and 4-iodo-5-nitrophthalonitriles (XNPN, X=Br or I) and any one of the azines (pyridine 1, 4-dimethylaminopyridine 2, isoquinoline 3, 4-cyanopyridine 4, 2-methylpyridine 5, 2-aminopyridine 6, quinoline 7, 1-methylisoquinoline 8, and 2,2'-bipyridine 9) proceeds differently depending on steric and electronic effects of the heterocycles. Sterically unhindered azines 1-3 underwent N-arylation to give the corresponding azinium salts (characterized by ¹ H and ¹³ C{H} NMR and high-resolution ESI-MS). In contrast, azines 4-9 with sterically hindered N atoms or bearing an electron-withdrawing substituent, form stable co-crystals with XNPN, where two interacting molecules are bound by halogen bonding. In all obtained co-crystals, X⋅⋅⋅N structure-directed halogen bonds were recognized and theoretically evaluated including DFT calculations (PBE0-D3/def2-TZVP level of theory), QTAIM analysis, molecular electrostatic potential surfaces, and noncovalent interaction plot index. Estimated energies of halogen bonding vary from -7.6 kcal/mol (for 6 ⋅ INPN) to -11.4 kcal/mol (5 ⋅ INPN).

Gas-Induced Ion-Free Stable Radical Anion Formation of Organic Semiconducting Solids as Highly Gas-Selective Probes

The formation of stabilized radical anions on organic materials in the solid state is an important issue in radical-based fundamental research and various applications. Herein, for the first time, we report on gas-induced ion-free stable radical anion formation (SRAF) of organic semiconducting solids with high gas selectivities through the use of organic field-effect transistor (OFET) gas sensors and electron spin resonance spectroscopy. In contrast to the previously reported SRAF, which requires either anionic analytes in solution and/or cationic substituents on π-electron-deficient aromatic cores, NDI-EWGs consist of an n-type semiconducting naphthalene diimide (NDI) and various electron-withdrawing groups (EWGs) that exhibit non-ion-involved, gas-selective SRAF in the solid state. In the presence of hard Lewis base gases, NDI-EWG-based OFETs exhibit enhanced conductivity (Current-ON mode) through the formation of an SRAF NDI/gas complex, while in the presence of borderline and soft Lewis base gases, NDI-EWG-based OFETs show decreased conductivity (Current-OFF mode) by the formation of a resistive NDI/gas complex. Organic semiconducting solids with EWGs exhibiting highly gas-selective solid-SRAF constitute a very promising platform for radical-based chemistry and can be used in various applications, such as highly gas-selective probes.

Anion–π and anion–π-radical interactions in bis(triphenylphosphonium)-naphthalene diimide salts

Anion–π-radical interaction plays a key role in photophysical and magnetic properties.

Anion–π interactions of highly π-acidic dipyridinium-naphthalene diimide salts

A highly π-acidic dipyridinium-naphthalene diimide acceptor shows anion–π interactions with halides and PF₆⁻.