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.

Oxidation-Triggered Formation of Diradical Cations from Paramagnetic Molecules and Their Spin Density Evolution

“…The DFT calculations yielded the coupling constant ( J = 1168.6 cm −1 ) for PTD-NN and the coupling constant ( J =340.2 cm −1 ) for POD-NN, with the relevant data provided in Table S2 . The calculated values are within the range of DFT results observed for similar systems [ 1 , 22 , 43 ]. The positive J values indicate that both diradical cations tend to exhibit intramolecular ferromagnetic exchange interactions.…”

“…Indeed, the oxidation potential of phenothiazine is lower than that of the NN and IN groups. This oxidation sequence provides the necessary conditions for the formation of cation diradical [ 1 ]. For PDTN-IN, the positions of the first and third oxidation peaks are nearly identical to those of PDTN-NN, as shown in Figure 3 (orange spectrum).…”

Oxidation-Triggered Formation of Diradical Cations from Paramagnetic Molecules and Their Spin Density Evolution

“…The DFT calculations yielded the coupling constant ( J = 1168.6 cm −1 ) for PTD-NN and the coupling constant ( J =340.2 cm −1 ) for POD-NN, with the relevant data provided in Table S2 . The calculated values are within the range of DFT results observed for similar systems [ 1 , 22 , 43 ]. The positive J values indicate that both diradical cations tend to exhibit intramolecular ferromagnetic exchange interactions.…”

“…Indeed, the oxidation potential of phenothiazine is lower than that of the NN and IN groups. This oxidation sequence provides the necessary conditions for the formation of cation diradical [ 1 ]. For PDTN-IN, the positions of the first and third oxidation peaks are nearly identical to those of PDTN-NN, as shown in Figure 3 (orange spectrum).…”

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 .…”

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 , nitrile 4f and 4i , diyne 1b , 2,2′-dibromo-3,3′-bithiophene, 4,4′-dibromo-3,3′-bithiophene, 3,3′-diiodo-2,2′-bithiophene, and 3,3′-dibromo-2,2′-bibenzo­[ b ]­thiophene were prepared as described in the literature. Nitriles 4a–4e , 4g , and 4h , alkynes 10a - 10c , isocyanate 12 , 1,2-bis­(diphenylphosphino)­ethane (DPPE), 1,2-bis­[bis­(pentafluorophenyl)­phosphino]­ethane (F-DPPE), (±)-2,2′-bis­(diphenylphosphino)-1,1′-binaphthalene ( rac -BINAP), 2,2′-bis­(diphenylphosphino)-1,1′-biphenyl (BIPHEP), 3,3′-dibromo-2,2′-bithiophene were purchased and used as received.…”

“…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.…”

Oxidation-Triggered Formation of Diradical Cations from Paramagnetic Molecules and Their Spin Density Evolution

“…The DFT calculations yielded the coupling constant ( J = 1168.6 cm −1 ) for PTD-NN and the coupling constant ( J =340.2 cm −1 ) for POD-NN, with the relevant data provided in Table S2 . The calculated values are within the range of DFT results observed for similar systems [ 1 , 22 , 43 ]. The positive J values indicate that both diradical cations tend to exhibit intramolecular ferromagnetic exchange interactions.…”

“…Indeed, the oxidation potential of phenothiazine is lower than that of the NN and IN groups. This oxidation sequence provides the necessary conditions for the formation of cation diradical [ 1 ]. For PDTN-IN, the positions of the first and third oxidation peaks are nearly identical to those of PDTN-NN, as shown in Figure 3 (orange spectrum).…”

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 .…”

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 , nitrile 4f and 4i , diyne 1b , 2,2′-dibromo-3,3′-bithiophene, 4,4′-dibromo-3,3′-bithiophene, 3,3′-diiodo-2,2′-bithiophene, and 3,3′-dibromo-2,2′-bibenzo­[ b ]­thiophene were prepared as described in the literature. Nitriles 4a–4e , 4g , and 4h , alkynes 10a - 10c , isocyanate 12 , 1,2-bis­(diphenylphosphino)­ethane (DPPE), 1,2-bis­[bis­(pentafluorophenyl)­phosphino]­ethane (F-DPPE), (±)-2,2′-bis­(diphenylphosphino)-1,1′-binaphthalene ( rac -BINAP), 2,2′-bis­(diphenylphosphino)-1,1′-biphenyl (BIPHEP), 3,3′-dibromo-2,2′-bithiophene were purchased and used as received.…”

“…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.…”

Oxidation-Triggered Formation of Diradical Cations from Paramagnetic Molecules and Their Spin Density Evolution

“…The DFT calculations yielded the coupling constant ( J = 1168.6 cm −1 ) for PTD-NN and the coupling constant ( J =340.2 cm −1 ) for POD-NN, with the relevant data provided in Table S2 . The calculated values are within the range of DFT results observed for similar systems [ 1 , 22 , 43 ]. The positive J values indicate that both diradical cations tend to exhibit intramolecular ferromagnetic exchange interactions.…”

“…Indeed, the oxidation potential of phenothiazine is lower than that of the NN and IN groups. This oxidation sequence provides the necessary conditions for the formation of cation diradical [ 1 ]. For PDTN-IN, the positions of the first and third oxidation peaks are nearly identical to those of PDTN-NN, as shown in Figure 3 (orange spectrum).…”

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 .…”

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 , nitrile 4f and 4i , diyne 1b , 2,2′-dibromo-3,3′-bithiophene, 4,4′-dibromo-3,3′-bithiophene, 3,3′-diiodo-2,2′-bithiophene, and 3,3′-dibromo-2,2′-bibenzo­[ b ]­thiophene were prepared as described in the literature. Nitriles 4a–4e , 4g , and 4h , alkynes 10a - 10c , isocyanate 12 , 1,2-bis­(diphenylphosphino)­ethane (DPPE), 1,2-bis­[bis­(pentafluorophenyl)­phosphino]­ethane (F-DPPE), (±)-2,2′-bis­(diphenylphosphino)-1,1′-binaphthalene ( rac -BINAP), 2,2′-bis­(diphenylphosphino)-1,1′-biphenyl (BIPHEP), 3,3′-dibromo-2,2′-bithiophene were purchased and used as received.…”

“…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.…”