Chemical Tailoring Assisted non-TADF to TADF Switching in Carbazole-Benzophenone Emitter – An In-silico Investigation

Organic light-emitting diodes (OLEDs) have become one of the most popular lighting technologies since they offer several advantages over conventional devices. In carbazole-benzophenone (CzBP) OLED devices, the polymeric form of the compound is previously reported to be Thermally Activated Delayed Fluorescence (TADF)-active (ΔE_ST ≈0.12 eV), while the monomer ( CzBP ) (ΔE_ST≈0.39 eV) does not. The present study examines the effect of chemical tailoring on the optical and photophysical properties of CzBP using DFT and TDDFT methods. The introduction of a single −NO₂ group or di-substitution (−NO₂, −COOH or −CN) in the selected LUMO region of the reference CzBP monomer significantly reduces ΔE_ST≈0.01 eV, projecting these systems as potential TADF-active emitters. Furthermore, the chemical modification of CzBP -LUMO alters the two-step TADF mechanism (T₁→T₂→S₁) in CzBP (E_S₁>E_T2>E_T₁) to the Direct Singlet Harvesting (T₁→S₁) mechanism (E_T2>E_S₁>E_T₁), which has recently been identified in the fourth-generation OLED materials.     

Kinetics and quantification of the electrophilic reactivities of substituted thiophenes and structure‐reactivity relationships

Second‐order rate constants (k₁) have been measured spectrophotometrically for reactions of 2‐methoxy‐3‐X‐5‐nitrothiophene 1a‐c (X = NO₂, CN, and COCH₃) with secondary cyclic amines (pyrrolidine 2a , piperidine 2b , and morpholine 2 c ) in CH₃CN and 91:9 (v/v) CH₃OH/CH₃CN at 20°C. The experimental data show that the rate constants (k₁) values exhibit good correlation with the parameters of nucphilicity (N) of the amines 2a‐c and are consistent with the Mayr's relationship log k (20°C) = s(E + N). We have shown that the electrophilicity parameters E derived for 1a–c and those reported previously for the thiophenes 1d‐g (X = SO₂CH₃, CO₂CH₃, CONH₂, and H) are linearly related to the pK_a values for their gem‐dimethoxy complexes in methanol. Using this correlation, we successfully evaluated the electrophilicity E values of 12 structurally diverse electrophiles in methanol for the first time. In addition, a satisfactory linear correlation (r² = 0.9726) between the experimental (log k_exp) and the calculated (log k_calcd) values for the σ‐complexation reactions of these 12 electrophiles with methoxide ion in methanol has been observed and discussed.     

Synthesis of [?CH2C(CO2Et)2CH2Ar?]n polymers and their unique optical properties by through‐space interactions between Ar and CO groups

Polymers of type [? CH₂C(CO₂Et)₂CH₂Ar? ]_n (Ar = 1,4‐phenylene, 2,6‐naphthylene, 9,10‐anthrylene, or 1,4‐phenylene‐ethynylene‐1,4‐phenylene) were synthesized by alkylation of diethyl malonate with XCH₂ArCH₂X (X = Cl or Br). These polymers exhibited unexpectedly enhanced UV absorption and strong, broad, bathochromically shifted fluorescence spectra compared with the parent Ar compounds. The origin of these photophysical characteristics was postulated to be a configuration interaction between the π→π* excitation of the aromatic moiety and the n→π* excitation of the carbonyl moiety on the trimethylene tether via intramolecular charge transfer. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

New Cu(I) Coordination Complexes Based on Tetrathiafulvalene Substituted Triazol‐pyridine Ligand: Synthesis,Properties and Theoretical Studies

Two Cu(I) complexes based on the thioethyl‐bridged triazol‐pyridine ligand with tetrathiafulvalene unit (TTF‐TzPy, L ), [Cu(I)(Binap)(L)]BF₄ ( 5 , Binap=2,2’‐bis(diphenylphosphino)‐1,1’‐binaphthyl) and [Cu(I)(Xantphos)(L)]BF₄ ( 6 , Xantphos=9,9‐dimethyl‐4,5‐bis(diphenylphosphino)‐xanthene), have been synthesized. All new compounds are characterized by elemental analyses, ¹H NMR and mass spectroscopies. The complex 5 has been determined by X‐ray structure analyses which shows that the central copper (I) ion assumes distorted tetrahedral geometry. The photophysical, computational and electrochemical properties of L and 5 ‐ 6 have been investigated. The most representative molecular orbital energy‐level diagrams and the spin‐allowed singlet? singlet electronic transitions of the three compounds have been calculated with density functional theory (DFT) and time‐dependent DFT (TD‐DFT). The luminescence bands of Cu(I) complexes 5 ‐ 6 have been assigned as mixed intraligand and metal‐to‐ligand charge transfer ³(MLCT+π→π^*) transitions through analysis of the photophysical properties and DFT calculations. The electrochemical studies reveal that 5 ‐ 6 undergo reversible TTF/TTF^+?/TTF²⁺ redox processes and one irreversible Cu⁺→Cu²⁺ oxidation process.     

Different orientations of C=O versus P=O in P(O)NHC(O) skeleton: the first study on an aliphatic diazaphosphorinane with a gauche orientation

Different orientations of P(O) versus C(O) in P(O)NHC(O) skeleton have been discussed in two new phosphorus(V)-nitrogen compounds with formula XP(O)Y and XP(O)Z₂ where X = NHC(O)C₆H₄(4-F) and Y = NHCH₂C(CH₃)₂CH₂NH (1), Z = NHC₆H₄(4-CH₃) (2). Compound 1 is the first example of an aliphatic diazaphosphorinane with a gauche orientation which has been studied by X-ray crystallography; the P=O bond is in the equatorial position of the ring. Both compounds show ⁿ J(F,C) and ^m J(F,H) coupling constants (n = 1, 2, 3 and 4; m = 3 and 4) and ³ J(P,C) > ² J(P,C). Quantum chemical calculations were performed with HF and Density Functional Theory (DFT) methods using 6−31+G(d,p) basis set. A tentative assignment of the observed vibrational bands for these molecules is discussed. Compound 1 shows a deshielded C atom of the carbonyl moiety (in ¹³C NMR spectrum) relative to that of 2, which is supported by IR spectroscopy in which the considerably lower C=O frequency is observed for 1. Comparing the X-ray crystallography and IR spectra of 1 and 2 shows that the acyclic compound 2, containing P=O and C=O bonds in an anti position, are involving in a stronger N–H···O=P hydrogen bond in crystal network. This leads to a weaker P=O and N_C(O)NHP(O)–H bonds and stronger N···O interaction. The N_amide–H is involved in an intramolecular N–H···O hydrogen bond.     

Transition structures and reaction barriers in the styrene–acrylonitrile copolymerization system according to quantum mechanical calculations

The geometries and electronic properties of substrates, transition structures (TS), and product radicals in modeled elementary propagation reactions were studied for the styrene–acrylonitrile monomer system by use of quantum‐mechanical calculations: (DFT/B3‐LYP/6–31G(d), ROMP2/6–311+G(3df,2p)//DFT/B3‐LYP/6–31G(d), and DFT/B3‐LYP/6–311+G(3df,2p)//DFT/B3‐LYP/6–31G(d)) and for some parameters, the high‐level composite method G3 (Gaussian‐3, G3/MP2). Activation enthalpies (ΔH^act) and reaction enthalpies (ΔH_r) for modeled propagation reactions at 298.15 K were evaluated. The enthalpy of activation energy (ΔH^act, kJ/mol) for the investigated elementary reactions rises for the B3‐LYP calculation in the following order: (CH₃A?+S) < (CH₃A?+A) < (CH₃S?+A) < (CH₃S?+S). For three propagation reactions, (CH₃A?+A), (CH₃A?+S), and (CH₃S?+A), correlation between reaction enthalpy and enthalpy of activation suggests weak or negligible polar effects reflecting the Evans–Polanyi relation. However, from the electron affinities and ionization energies values data, it is not excluded that at least for [CH₃A?+S[b]] and [CH₃S?+A[b]] reactions, nucleophilic and electrophilic polar effects, respectively, can also be expected. The dependencies between TS geometries, electronic parameters, and enthalpic effects suggest the presence of a steric factor in all TS, including its exceptionally high contribution to the activation enthalpy for the CH₃S?+S addition. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1827–1844, 2005     

Photophysical and Photoacoustic Properties of π‐Extended Curcumin Dyes. Effects of the Terminal Dimethylamino Electron‐donor and the Bridging Aryl Ring

The synthesis, photophysical and photoacoustic characterization for a series of nine π‐extended quadrupolar curcumin dyes is presented. A systematic evaluation of the π‐bridging unit including the p‐phenyl, naphth‐4‐yl, thien‐2‐yl and hybrid 4‐naphthathien‐2‐yl groups is presented. Furthermore, evaluation of the strongly donating donor‐π‐acceptor‐π‐donor quadrupolar dimethylamino terminated derivatives is also included. Select dyes exhibit excited state absorption at increased laser fluence which translates to the production of a nonlinear enhanced photoacoustic response. In particular, the bis‐4‐dimethylaminonaphtha‐2‐thien‐5‐yl curcuminBF₂ contrast agent DMA‐5 exhibits an excellent molar photoacoustics (PA) emission at both low (9.4 × 10³ V M^?1) and high (1.47 × 10⁵ V M^?1) laser fluence which is confirmed by its strong contrast by photoacoustic tomography (PAT). In summary, the strong absorbance and enhanced photoacoustic properties of naphthyl and thienyl curcuminoids here presented provides great promise for future photoacoustic imaging applications as demonstrated by preliminary PAT studies.     

Synthesis of aryl-functionalized, 1,5-disubstituted 1,2,3-triazoles and derivatives by arylation of zwitterionic ruthenium triazolato complexes

The synthesis of a series of ruthenium 1,5-disubstituted 1,2,3-triazolato complexes, 1,5-disubstituted 1,2,3-triazoles, and a triazolium salt is reported. Treatment of the ruthenium azido complex [Ru]-N₃ ( 1 , [Ru] = (η⁵-C₅H₅)(dppe)Ru, dppe = Ph₂PCH₂CH₂PPh₂) with an excess of ethyl propiolate results in the formation of a mixture of the Z- and E-forms of zwitterionic N(1)-bound N(3)-ethyl acryl-4-carboxylate triazolato complexes [Ru]N₃(CH=CHCO₂Et)C₂H(CO₂) ( Z - 2 ) and ( E - 2 ). The arylation of 2 with aromatic bromides gives a series of cationic N(1)-bound N(3)-ethyl acryl-4-alkoxycarbonyl triazolato complexes {[Ru]N₃(CH=CHCO₂Et)C₂H(CO₂CH₂R)}[Br] ( 3a , R = Ph ; 3b , R = C₆F₅; 3c , R = 4-C₆H₄CN, 3d , R = 2,6-C₆H₃F₂) and the subsequent cleavage of the Ru-N bond of 3a–d gives 1,5-disubstituted 1,2,3-triazoles N₃(CH=CHCO₂Et)C₂H(CO₂CH₂R) ( 4a , R = Ph; 4b , R = C₆F₅; 4c , R = 4-C₆H₄CN; 4d , R = 2,6-C₆H₃F₂) and [Ru]-Br. A 1,2,3-triazolium salt [N₃(CH=CHCO₂Et)(CH₂C₆F₅)C₂H₂][Br] ( 5 ) was formed by transformation of 4b in BrCH₂C₆F₅/chloroform mixture. The structures of Z-3a and Z-5 were confirmed by single-crystal x-ray diffraction analysis and both complexes participate in non-covalent aromatic interactions in the solid-state structures which can be favorable in the binding of DNA/biomolecular targets and have shown great potential in the application of biologically active anticancer drugs.     

Photochemische Reaktionen. 118. Mitteilung [1] Zur vinylogen β-Spaltung von Enonen. UV.-Bestrahlung von 4-(3',7',7'-Trimethyl-2'-oxabicyclo [3.2.0]hept-3'-en-1'-yl)but-3-en-2-on

Vinylogous β-Cleavage of Enones: UV.-irradiation of 4-(3′,7′,7′-trimethyl-2′-oxabicyclo[3.2.0]hept-3′-ene-1′-yl)but-3-ene-2-on On ¹π,π*-excitation (λ = 254 nm) in acetonitrile (E/Z)- 2 is converted into the isomers 4–9 and undergoes fragmentation yielding 10 ; in methanol (E/Z)- 2 gives 7–10 and is transformed into 11 by incorporation of the solvent. On ¹π,π*-excitation (λ λ?347 nm; benzene-d₆) (E)- 2 is isomerized into (Z)- 2 , which is converted into the isomers 3 and 4 by further irradiation. ¹π,π*-Excitation (λ = 254 nm; acetonitrile) of 4 gives 6 and (E)- 9 , whereas UV.-irradiation (λ = 254 nm; acetonitrile-d₃) of 5 yields (E)- 7 and 8 . On ¹π,π*-excitation (λ = 254 nm; acetonitrile) of (E/Z)- 12 the compounds (E)- 14 and (E)- 15 are obtained.     

A Zn(II) luminescent complex with a Schiff base ligand: solution,computational and solid state studies

Abstract

A new mononuclear complex of zinc(II), [Zn(HL)₂]?2DMF (H₂L = (E)-N′-((E)-(hydroxyimino)butan-2-ylidene)salicyloylhydrazide, DMF = N,N-dimethylformamide), was prepared and characterized. Single-crystal X-ray crystallography revealed a six-coordinate zinc(II) surrounded by nitrogen of the oxime function and oxygen and distal nitrogens of the acylhydrazone group. This entity also exists in solution as demonstrated by ¹H-NMR and potentiometric titrations. The computational analysis showed that the molecular orbitals involved in the main electronic transitions of the complex species in solution are centered on the ligand with negligible contribution of the metal ion. The photophysical properties of the complex were evaluated in solution and in the solid state. Luminescence studies showed that the solid has a strong emission at 550 nm with a large Stokes shift with respect to absorption. The solid state fluorescence emission is ascribed to ligand-centered and/or ligand-to-ligand charge transfer transitions, following the DFT results in solution. A comparison with a previously reported mononuclear [Zn(HL)₂] allowed the investigation of the influence of DMF molecules in the structural packing and the luminescence properties.     

Pentiptycene‐Derived Light‐Driven Molecular Brakes: Substituent Effects of the Brake Component

Five pentiptycene‐derived stilbene systems ( 1 R ; R =H, OM, NO, Pr, and Bu) have been prepared and investigated as light‐driven molecular brakes that have different‐sized brake components ( 1 H < 1 OM < 1 NO < 1 Pr < 1 Bu ). At room temperature (298 K), rotation of the pentiptycene rotor is fast (k_rot=10⁸–10⁹ s^?1) with little interaction with the brake component in the trans form ((E)‐ 1 R ), which corresponds to the brake‐off state. When the brake is turned on by photoisomerization to the cis form ((Z)‐ 1 R ), the pentiptycene rotation can be arrested on the NMR spectroscopic timescale at temperatures that depend on the brake component. In the cases of (Z)‐ 1 NO , (Z)‐ 1 Pr , and (Z)‐ 1 Bu , the rotation is nearly blocked (k_rot=2–6 s^?1) at 298 K. It is also demonstrated that the rotation is slower in [D₆]DMSO than in CD₂Cl₂. A linear relationship between the free energies of the rotational barrier and the steric parameter A values is present only for (Z)‐ 1 H , (Z)‐ 1 OM , and (Z)‐ 1 NO , and it levels off on going from (Z)‐ 1 NO to (Z)‐ 1 Pr and (Z)‐ 1 Bu . DFT calculations provide insights into the substituent effects in the rotational ground and transition states. The molar reversibility of the E–Z photoswitching is up to 46 %, and both the E and Z isomers are stable under the irradiation conditions.     

Iron Pentacarbonyl Promoted Addition of CO and MeOH to 1,4-Disubstituted-1,3-butadiyne and Formation of Vinylallyl and Butatriene Ligand Systems

Abstract  Photochemical reaction of methanol solution containing 1,4-diferrocenyl- or 1,4-diphenyl-1,3-butadiynes and iron pentacarbonyl into which CO was constantly bubbled, yielded diiron hexacarbonyl complexes of cumulene ligand systems, [η¹: η³-{RCHC₂CR(COOMe)}Fe₂(CO)₆] (1; E, R = Fc, 2; Z, R = Fc, 5; E, R = Ph, 6; Z, R = Ph) and [η³: η³-{RCHC₂CR(COOMe)}Fe₂(CO)₆] (3; E, R = Fc, 7; E, R = Ph), formed by 1,4-addition of –COOMe and –H to the butadiynes. Additionally, diferrole, [Fe(CO)₄{C(O)CC(Fc)C(O)}₂],4 was obtained in minor quantity. Compounds 1, 2, 5 and 6 contain vinylallyl carbon framework which is stabilized by MeOC=O → Fe bond along with η¹: η³ coordinated Fe₂(CO)₆ unit. Compounds 3 and 7 contain butatriene units which are stabilized by η³: η³ coordinated Fe₂(CO)₆ unit. Characterization of the new compounds was carried out by IR and ¹H and ¹³C NMR spectroscopy and by mass spectrometry. Molecular structures of 2–7 were established by single crystal X-ray diffraction methods. Graphical Abstract  Diiron hexacarbonyl complexes of cumulene ligand systems, [η¹: η³ {RCHC₂CR(COOMe)}] (1; E, R = Fc, 2; Z, R = Fc, 5; E, R = Ph, 6; Z, R = Ph) and [η³: η³-{RCHC₂CR(COOMe)}] (3; E, R = Fc, 7; E, R = Ph) were obtained from photochemical reactions between Fe(CO)₅, CO and methanol. Yield of the minor product, the diferrole, 4, was improved when the photoreaction was carried out in hexane in place of methanol      

Synthesis and reactivity of neodymium(III) amido-tethered N-heterocyclic carbene complexes

The reaction of the heteroleptic Nd(III) iodide, [Nd(L′)(N″)(μ-I)] with the potassium salts of primary aryl amides [KN(H)Ar′] or [KN(H)Ar^*] affords heteroleptic, structurally characterised, low-coordinate neodymium amides [Nd(L′)(N″)(N(H)Ar′)] and [Nd(L′)(N″)(N(H)Ar^*)] cleanly (L′ = t-BuNCH₂CH₂[C{NC(SiMe₃)CHNt-Bu}], N″ = N(SiMe₃)₂, Ar′ = 2,6-Dipp₂C₆H₃, Dipp = 2,6-Prⁱ₂C₆H₃, Ar^* = 2,6-(2,4,6-Prⁱ₃C₆H₂)₂C₆H₃). The potassium terphenyl primary amide [KN(H)Ar^*] is readily prepared and isolated, and structurally characterised. Treatment of these primary amide-containing compounds with alkali metal alkyl salts results in ligand exchange to give alkali metal primary amides and intractable heteroleptic Nd(III) alkyl compounds of the form [Nd(L′)(N″)(R)] (R = CH₂SiMe₃, Me). Attempted deprotonation of the Nd-bound primary amide in [Nd(L′)(N″)(N(H)Ar^*)] with the less nucleophilic phosphazene superbase Bu^tNP{NP(NMe₂)₃}₃ resulted in indiscriminate deprotonations of peripheral ligand CH groups.     

Conformational analysis of N-isopropylbenzohydroxamic acids: crystal structure, DFT, and NMR studies

X-ray crystal structure determinations together with density functional theory (DFT) calculations in vacuo and NMR studies in solution have been carried out for 4-MeOC₆H₄CONPrⁱOH 2a and 3,5-(NO₂)₂C₆H₃CONPrⁱOH 2b. The results were compared with that for the respective N-methyl benzohydroxamic acids. For crystal structures as well as for DFT-optimized geometries of 2 (both isomers) in vacuo, the effect of substituents in aromatic ring manifested by changing of charges is inconspicuous. Studies of potential energy surfaces showed that libration barrier around ω ₁ = 0° is low enough to make electron conjugation feasible, and that for 2b rotation barrier around C(O)N bond is higher by 6 kcal/mol and additionally, that rotation around N–C bond is hindered. A careful analysis of low-temperature ¹H NMR spectra confirmed the greater stability of Z-2a, the greater rigidity of E-2b and the influence of solvent on both isomers population. Despite solvent-dependent conformational alteration, both 2a and 2b crystallize exclusively as E isomers from ethyl acetate solution. Correlations of absolute ¹H, ¹³C, and ¹⁵N shielding calculations with experimental data were also analyzed. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Metal Ions Drive Thermodynamics and Photochemistry of the Bis(styryl) Macrocyclic Tweezer

UV/Vis and NMR spectroscopy were used for the structural elucidation and thermodynamic and photochemical studies of the metal‐coordinated crown‐containing macrocyclic tweezer (E,E)‐ 1 . The bis(styryl) tweezer (E,E)‐ 1 formed two types of complexes with magnesium(II): a 1:1 intramolecular asymmetric sandwich complex [(E,E)‐ 1 ]?Mg²⁺ and a 1:2 complex [(E,E)‐ 1 ]?(Mg²⁺)₂. In the former case, there is direct cation intramolecular exchange (0.299 s^?1, ΔG^≠=69.4 kJ mol^?1) between two parts of the bis(styryl) tweezer (E,E)‐ 1 . Addition of barium(II) to the bis(styryl) tweezer (E,E)‐ 1 led to an intramolecular centrosymmetric sandwich 1:1 complex [(E,E)‐ 1 ]?Ba²⁺. Irradiation of [(E,E)‐ 1 ]?Ba²⁺ afforded reversible intramolecular [2π+2π] photocyclization with excellent stereoselectivity and quantitative yield. In contrast, irradiation of [(E,E)‐ 1 ]?(Mg²⁺)₂ resulted in reversible stepwise E,Z‐isomerization.     

New Insights on the Mechanism of Thermal Cleavage of Unsaturated Bicyclic Diaziridines: A DFT Study

A DFT calculations are carried out at UB3LYP/6‐311++G (3df, 2p) levels of theory to study electrocyclic thermal cleavage of four (R) derivatives of unsaturated bicyclic diaziridines, 1_X‐R , to produce corresponding (Z) and (E) azomethine imides ( 2_X‐Z , 2_X‐E , 3_X‐Z and 3_X‐E ), where X=H, Me, t‐Bu and Ph. Cleavage of 1_X‐R series to form the most stable 3_X‐Z product, (path 2) is found the favored procedure because of delocalized negative charge on five atoms and lower steric effect in related transition state. According to IRC calculations in paths 1 and 2, C⁶ N¹ bond is cleaved before the rate determinating step (transition state). The stability of unsaturated bicyclic diaziridines and their corresponding (Z) and (E) azomethine imides is in the following order in gas phase and chloroform, tetrahydrofuran, and acetone solvents: 3_X‐Z < 3_X‐E < 2_X‐Z < 2_X‐E < 1_X‐R < 1_X‐S .     

Copper(II) complexes of acylhydrazones: synthesis,characterization and DNA interaction

Two new acylhydrazone copper(II) complexes of 4‐hydroxy‐N′‐[(1E)‐1‐(4‐methylphenyl)ethylidene]benzohydrazide (HL¹) and 4 ethyl [4‐({(2E)‐2‐[1‐(4‐methylphenyl)ethylidene]hydrazinyl}carbonyl)phenoxy]acetate (HL²) have been synthesized and characterized. The structures of both acylhydrazone and copper(II) complexes were identified by elemental analysis, infrared spectra, UV–visible electronic absorption spectra, magnetic susceptibility measurements, TGA and powder X‐ray diffraction. DNA binding and DNA cleavage activities of the synthesized copper complexes were examined by using UV‐visible titration and agarose gel electrophoresis, respectively. The effect of complex concentration on the DNA cleavage reactions in the absence and presence of H₂O₂ was also investigated. The results indicate that all the complexes bind slightly to calf thymus DNA and cleavage pBR322 DNA. The mechanistic studies demonstrate that a hydrogen peroxide‐derived species and singlet oxygen (¹O₂) are the active oxidative species for DNA cleavage. Copyright © 2013 John Wiley & Sons, Ltd.     

Oxidation Chemistry of Inorganic Benzene Complexes

The oxidation of the 28 VE cyclo‐E₆ triple‐decker complexes [(Cp^RMo)₂(μ,η⁶:η⁶‐E₆)] (E=P, Cp^R=Cp( 2 a ), Cp*( 2 b ), Cp^Bn( 2 c )=C₅(CH₂Ph)₅; E=As, Cp^R=Cp*( 3 )) by Cu⁺ or Ag⁺ leads to cationic 27 VE complexes that retain their general triple‐decker geometry in the solid state. The obtained products have been characterized by cyclic voltammetry (CV), EPR, Evans NMR, multinuclear NMR spectroscopy, MS, and structural analysis by single‐crystal X‐ray diffraction. The cyclo‐E₆ middle decks of the oxidized complexes are distorted to a quinoid ( 2 a ) or bisallylic ( 2 b , 2 c , 3 ) geometry. DFT calculations of 2 a , 2 b , and 3 persistently result in the bisallylic distortion as the minimum geometry and show that the oxidation leads to a depopulation of the σ‐system of the cyclo‐E₆ ligands in 2 a – 3 . Among the starting complexes, 2 c is reported for the first time including its preparation and full characterization.