Cations and Anions of Dibenzo[a,e]pentalene and Reduction of a Dibenzo[a,e]pentalenophane

Abstract

Dibenzo[a,e]pentalene (DBP) is a non‐alternant conjugated hydrocarbon with antiaromatic character and ambipolar electrochemical behavior. Upon both reduction and oxidation, it becomes aromatic. We herein study the chemical oxidation and reduction of a planar DBP derivative and a bent DBP‐phane. The molecular structures of its planar dication, cation radical and anion radical in the solid state demonstrate the gained aromaticity through bond length equalization, which is supported by nucleus independent chemical shift‐calculations. EPR spectra on the cation radical confirm the spin delocalization over the DBP framework. A similar delocalization was not possible in the reduced bent DBP‐phane, which stabilized itself by proton abstraction from a solvent molecule upon reduction. This is the first report on structures of a DBP cation radical and dication in the solid state and of a reduced bent DBP derivative. Our study provides valuable insight into the charged species of DBP for its application as semiconductor.

Enantiopure nanohoops through racemic resolution of diketo[n]CPPs by chiral derivatization as precursors to DBP[n]CPPs

“…Open Each DBP unit can reversibly accept up to two electrons, upon which it assumes aromatic character with 18 π-electrons. 47 In positive scan direction, both 1 and 2 displayed four reversible oxidations each at half-wave potentials of E1/2 = 0.42, 0.64, 0.83 and 1.01 V for 1 and at E1/2 = 0.60, 0.81, 0.94 and 1.10 V for 2 (all vs. Fc/Fc + ). The first oxidations likely stem from the DBP units based on the HOMO distribution (Figure 4B) and since…”

“…The further oxidation processes could either be based on the PP linkers or the DBP units, which can undergo two oxidations to furnish an aromatic 14π-electron system. 47 In summary, the optical properties of diketo[n]CPPs 3 and 4 are dominated by the PP linkers with high fluorescent quantum yields. In DBP[n]CPPs 1 and 2, the DBP units lead to ambipolar electrochemical character with both reversible oxidations and reductions.…”

“…DBP is a non-alternant, 16 π-electron system with antiaromatic character, 45,46 which bestows ambipolar electrochemical character 47 to DBP[n]CPPs 1 and 2. 48 Its small bandgap is due to an increased HOMO and decreased LUMO energy in comparison to an alternant hydrocarbon of similar size.…”

Chiral Dibenzopentalene‐Based Conjugated Nanohoops through Stereoselective Synthesis

“…The cyclic voltammogram of (+)‐1 demonstrates its ambipolar electrochemical character due to the DBP units [20] (Figure 6 B). A reversible reduction occurred at a half‐wave potential of E 1/2 =−1.71 V, and two quasi‐reversible oxidations appeared at E 1/2 =0.63 and 0.80 V (all vs. Fc/Fc + ).…”

“…We herein present the dibenzo[ a , e ]pentalene (DBP)‐based chiral nanohoops (+)‐1 and (−)‐1 consisting of six DBP units and four phenylene rings (Figure 1 A), accessed in a stereoselective synthesis. The DBP units endow ambipolar electrochemical behavior to the hoop, [20] they possess antiaromatic character, [21, 22] and their lack of a dividing mirror plane when bent makes nanohoop 1 chiral. After rubicene‐containing hoops reported by the Isobe group [23] and [2]DBP[12]CPP nanohoops synthesized by us, [24] this is the third synthetic report incorporating a non‐alternant hydrocarbon into a nanohoop and the second using an antiaromatic unit [25] .…”