Dithienopyrrole Derivatives with Nitronyl Nitroxide Radicals and Their Oxidation to Cationic High‐Spin Molecules

Abstract

Three 1 N‐phenyl nitronyl nitroxide (NN) 4‐substituted dithieno[3,2‐b:2′,3′‐d]pyrrole (DTP) derivatives with R1=4‐phenyl‐, 4H‐, and 4‐methylthiothiophenyl‐ (R12DTP‐Ph‐NN, R1=H, Ph and MeSTh) were designed, synthesized and characterized. The electrochemical properties were studied by cyclic voltammetry (CV). All the molecules exhibited two main oxidation peaks, first for radical cation and next for dication formation. The cation and dication formation were also confirmed by UV/Vis absorption spectroscopy for Ph2DTP‐Ph‐NN and MeSTh2DTP‐Ph‐NN titrated with tris(4‐bromophenyl)aminiumhexachloroantimonate (magic blue). In addition, the cation and dication formation were verified by EPR spectroscopy. Finally, the exchange interactions (J/kB) of NN and radical cation were calculated by DFT studies.

Nitronyl Nitroxide Bifunctionalized Electron-Poor Chromophores: Synthesis of Stable Dye Biradicals by Lewis Acid Promoted Desilylation

“…Notably, the UV/vis absorption maxima of the nitronyl nitroxides are almost unchanged with respect to the diamagnetic precursors (Δ ṽ abs ≤ 488 cm –1 , Figure and Table ) and are slightly bathochromically shifted compared to the unsubstituted parent compounds, − which can be explained by the extension of the conjugated π-system by the additional phenylene groups. Larger deviations between the biradical and silylated precursors can be detected between 250 and 450 nm, due to the absorption of the nitronyl nitroxide radical unit in the shorter wavelength region. ,, Furane and thiophene bridged DPP derivatives feature sharp absorption bands with pronounced vibronic progression (Figure , magenta and green lines), whereas the phenylene derivatives (Figure , blue lines) are characterized by broad, featureless absorption bands. This different behavior is well-known among heteroaromatic diketopyrrolopyrroles and can be explained by the higher degree of planarity due to the sterically less demanding heterocyclic substituents .…”

“…As oxidation potentials between 330 and 520 mV are typically observed for NNs in literature, the first oxidation process can be ascribed to the formation of an oxammonium cation from the respective (bi)radical. 13,18,19,27,34,48,53 This is further corroborated by analogous CV and DPV studies of the silylated precursors (Figures S29 and S30 and Table S1), which reveal a similar redox behavior as observed for the respective nitronyl nitroxides, but the pronounced oxidation event at 366− 422 mV (all potentials vs Fc 0/+ ), being observed for all NN, is absent in PBI−Si, IIn−Si, and PhDPP−Si. Electron-rich ThDPP−Si and FuDPP−Si exhibit an additional oxidation process between 300 and 400 mV (Figure S30), which can be ascribed to the DPP chromophore oxidation, although these processes occur at slightly higher potentials (500 mV) in the unsubstituted parent chromophore 54 due to the smaller πsystem.…”

“…Larger deviations between the biradical and silylated precursors can be detected between 250 and 450 nm, due to the absorption of the nitronyl nitroxide radical unit in the shorter wavelength region. 12,25,48 Furane and thiophene bridged DPP derivatives feature sharp absorption bands with pronounced vibronic progression (Figure 1, magenta and green lines), whereas the phenylene derivatives (Figure 1, blue lines) are characterized by broad, featureless absorption bands. This different behavior is well-known among heteroaromatic diketopyrrolopyrroles and can be explained by the higher degree of planarity due to the sterically less demanding heterocyclic substituents.…”

Iridium-Catalyzed [2 + 2 + 2] Cycloaddition of Bithiophen-Linked Diynes with Nitriles: Scope and Mechanistic Study with Quantum Chemical Calculation

“…All solvents were dried and distilled before use by the usual procedures. [Ir(cod)Cl] 2 , 14 nitrile 4f 15 and 4i, 16 diyne 1b, 8a 2,2′-dibromo-3,3′-bithiophene, 17 4,4′dibromo-3,3′-bithiophene, 18 3,3′-diiodo-2,2′-bithiophene, 19 Procedure for the Preparation of 1a. To a solution of CuI (38.0 mg, 0.200 mmol), PdCl 2 (PPh 3 ) 2 (140 mg, 0.200 mmol), and 2,2′-dibromo-3,3′-bithiophene (650 mg, 2.01 mmol) in DIPA (20 mL) was added propyne (12.0 mL, 12.0 mmol; 1.0 M solution in THF) at room temperature.…”

Oxidative Desulfurization Activity of NIT Nitroxide Radical Modified Metallophthalocyanine

“…Compared with TEMPO, the unpaired electrons in NIT radicals are delocalized on two equal N-O groups, resulting in a wider electron distribution and higher activity [31]. The randomness of the substituents for aldehyde group used in raw materials makes the NIT radicals a good modifying group [32,33]. In order to solve the problems that metallophthalocyanines has low catalytic acti at room temperature, the NIT nitroxide radical was bonded to the support metallopht ocyanine (MPc(COOH)4Cl8) through chemical bonds to prepare the metallophthaloc nine (MPc(COOH)4Cl8) -NIT catalysts in the present study.…”