Isolation and Characterization of Persistent Radical Cation and Dication of 2,7-Bis(dianisylamino)pyrene

Abstract

Orbital interaction between 2,7-pyrenylene and two nitrogen redox-active centers effectively reduces the energy difference between HOMO and HOMO-1, both of which were distributed over the two nitrogen centers. In fact, one- and two-electron oxidation of 2,7-bis(dianisylamino)pyrene 3 generated a persistent radical cation and a persistent dication, respectively, and we succeeded in the isolation and single crystal X-ray structural analyses of all three oxidation states. The radical cation was considered as a spin and charge delocalized mixed-valence compound with a semiquinoidal structure. The dication was in an open-shell singlet state with a small singlet-triplet energy gap. The molecular and electronic structures for all three oxidation states of 3 were studied in comparison with the data reported for each oxidation state of closely related bis(triarylamine)s, of which structures were determined by X-ray crystallography.

Pyrene Molecular Orbital Shuffle—Controlling Excited State and Redox Properties by Changing the Nature of the Frontier Orbitals

“…This is in stark contrast to the findings of Zhong et al., who studied the influence of one to four amino substituents in the 1‐, 3‐, 6‐, and 8‐positions of pyrene on the E 1/2 (ox) 1 values . According to their experiments, E 1/2 1 of the 1‐monoamino‐substituted pyrene differs from that of the 1,3‐diamino‐substituted pyrene by only 0.11 V, and from that of the 1,3,6,8‐tetraamino‐substituted pyrene by 0.28 V. In addition, the HOMO energy difference upon going from one to four amino groups in that study is not as large as it is for our compounds 4 and 8 , which underlines the much stronger destabilizing effect on the HOMO of our donor substituents at the 2,7‐positions compared to diarylamino groups at the 1‐, 3‐, 6‐, and 8‐positions.The D‐π‐D compounds 4 and 14 , unlike the mono‐donor substituted compounds, display a second reversible one‐electron oxidation at +0.26 V and +0.11 V, respectively, and a remarkably large potential splitting Δ E (440 mV) for this type of compound (Table ) . In addition, we find that 4 + is very stable with respect to disproportionation to the dication 4 2+ and neutral 4 , as evidenced by a high comproportionation constant K c =2.7×10 7[84] for the reverse process, which is larger than that of our previously reported radical anion of 2,7‐bis(Bmes 2 )pyrene ( D ; K c =5.6×10 4 ) .…”

“…The dihedral angle between the NC 3 and pyrene planes is fairly small and varies between 9.2° and 21.3° in all of our compounds (Table ). For example, the dihedral angle in 2,7‐bis(dianisylamino)pyrene G of 31° is significantly larger …”

“…Very recently, Ito et al. isolated and characterized 2,7‐bis(dianisylamino)pyrene G, (analogue of B ) and its mono‐ and dication, related to our 2,7‐bis(Bmes 2 )pyrene D and its mono‐ and dianion . They analyzed the electronic structures of all three oxidation states and also concluded that the switch in the energetic order of the HOMO−1 and HOMO leads to a large electronic coupling ( V= 2608 cm −1 ) through the pyrene bridge.…”

Studies on Pyrene and Perylene Derivatives upon Oxidation and Application to a Higher Analogue

“…39 Introduction of diphenylamino groups at 2-and 7-positions enable the generation of stable dicationic species but the positive charges are outside of the pyrene core. 40 Its anion version was achieved by the diborylpyrene. 41 A well-known problem of pyrene derivatives is that their emission in the solid state is effectively quenched because Scheme 2.…”

Elaborately Tuning Intramolecular Electron Transfer Through Varying Oligoacene Linkers in the Bis(diarylamino) Systems

“…Moreover, we have noticed that similar in-phase and out-of-phase orbital interactions between the HOMO-1 of the oligoacene linker and the two N 2p orbitals lead to the delocalized distribution of the HOMO across the whole molecule of 1c – 1e (Fig. 8 and S8)59. More importantly, the HOMO level was up-shifted and the LUMO was down-shifted significantly from 1c to 1d and 1e .…”