Perylene Bisimide Radicals and Biradicals: Synthesis and Molecular Properties

Abstract

Unprecedented neutral perylene-3,4:9,10-tetracarboxylic acid bisimide (PBI) radicals and biradicals were synthesized by facile chemical oxidation of 4-hydroxyaryl-substituted PBIs. Subsequent characterization by optical and magnetic spectroscopic techniques, as well as quantum chemical calculations, revealed an open-shell singlet biradical ground state for the PBI biradical OS-2(..) (〈s(2)〉=1.2191) with a relatively small singlet-triplet energy gap of 0.041 eV and a large singlet biradical character of y=0.72.

Radical and Diradical Formation in Naphthalene Diimides through Simple Chemical Oxidation

“…and singlet diradical NDI‐2 .. are generated by simple chemical oxidation using PbO 2 . These results are different from our previous study on the formation of PBI (di)radical by chemical oxidation . For the formation of radical and diradical in PBI derivatives, anionic species should be primarily generated.…”

“…In the case of NDI‐2 , we predicted two resonance forms of closed‐shell Kekulé and open‐shell diradical structures by chemical oxidation (Scheme ). According to Clar's aromatic sextet rule, the number of aromatic sextet rings determines which resonance structure is more stable . Therefore, diradical structure might be more stable than closed‐shell Kekulé structure because only the diradical structure has Clar's aromatic sextet rings.…”

Intersystem Crossing in Naphthalenediimide–Oxoverdazyl Dyads: Synthesis and Study of the Photophysical Properties

“…The observed lifetime of the triplet state of the NDI unit in the current dyads is much shorter than the intrinsic triplet state lifetime of the NDI chromophore (ca. 32–276 μs), which is reasonable because the triplet state localized on the NDI can be quenched by the stable radical . This is also proved by measuring the ns TA spectra of NDI‐Ph with increasing concentrations of Ph‐Vz (Supporting Information, Figure S31).…”

“…Based on the energy levels of the D 1 and the Q 1 states of NDI‐Ph‐Vz, we propose that the interaction between the radical (in the doublet state) and the NDI chromophore (in the triplet state) is ferromagnetic, that is, J >0 and the D 1 state has higher energy than the Q 1 state (Table , Supporting Information, Figure S37). Direct determination of the magnitude of the spin exchange coupling of the radical with the chromophore at the excited state is impossible, although the relative energies of the D 1 and Q 1 states can be derived from electron spin polarization dynamics . The occurrence of π‐conjugation between the radical and the chromophore may increase the exchange magnitude, thus our calculated J= 0.07 eV (564 cm −1 ) is reasonable.…”

Stable Organic (Bi)Radicals by Delocalization of Spin Density into the Electron‐Poor Chromophore Core of Isoindigo

“…Molecules with a large biradical character and a small singlet–triplet energy gap like OS‐2 .. are usually characterized by comparatively short lifetimes. Thus super‐heptazethrenes and phenoxyl substituted rylene bisimides and corannulenes with similar molecular properties (Δ E ST =0.041–0.082 eV, y= 0.64–0.83) readily decompose within hours under ambient conditions in solution and/or weeks in the solid state. Conversely, so far available materials with comparable stabilities like OS‐2 .. ( τ 1/2 =several weeks in solution and infinite in the solid state) exhibit considerably larger singlet–triplet energy gaps, smaller biradical characters or require substantial spin delocalization .…”