Radical and Diradical Formation in Naphthalene Diimides through Simple Chemical Oxidation

Abstract

We successfully synthesized, for the first time, a naphthalene diimide (NDI) radical and diradical by simple chemical oxidation using lead(IV) dioxide. The formation of the (di)radical is confirmed by UV/Vis/NIR absorption, H NMR, and electron paramagnetic resonance (EPR) measurements. In particular, temperature-dependent EPR, SQUID (superconducting quantum interference device) measurements, and quantum calculations demonstrated that the generated NDI diradical has a singlet diradical character of y=0.69 in the ground state. Subsequent characterization of this (di)radical revealed its stabilities, large two-photon absorption cross-section, and short excited-state lifetime.

Carbene derived diradicaloids – building blocks for singlet fission?

“…zethrenes, 58 – 60 phenalenyles, 61 , 62 quinodimethanes, 63 – 67 or diindeno fused π-systems. 68 , 69 The bisnitroxide ( 5 ), 70 – 74 bisoxoverdazyl ( 6 ), 75 and bisquinone ( 7 ) 76 – 79 were chosen as examples for heteroatom incorporation and supposedly very high diradical character.…”

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 .…”

Magnetoelectric Radical Hydrocarbons

“…Recently, there has been a growing interest in the study of organic radical materials with unpaired electrons of open‐shell electronic structures that exhibit electronic cooperative interactions . Molecular radicals are an especially interesting condensed matter associated with the atomic center in a molecule, where the weak unpaired electron interactions can lead to a macroscopically characteristic state in bulk assemblies (high‐temperature molecular magnet, superconductor, etc.).…”

“…The coupling between the magnetic and the electric orders generates novel functionalities, which do not exist in either single state . In recent years, there has been an enormous effort to discover new classes of polycyclic aromatic hydrocarbons (PAHs) with two or more functionalities, for example, magnetism and conductivity, ferroelectricity and optoelectronics, which is partially associated with complex charge transfer and radical interactions. The relationship between magnetic order characteristics and charge order has rarely been studied in PAHs, which is distinctly different from the typical ME effect in inorganic materials, especially the inorganic single solid phase with magnetoelectric effect .…”