Synthesis, EPR and ENDOR of [60]Fulleropyrrolidine Bisadducts with Nitroxide Addends: Magnitude and Sign of the Exchange Interaction

Abstract

The magnitude and sign of the electron exchange interaction J between two nitroxide radicals in a series of [60]fullerene bisadducts (trans‐4 bisadduct shown) have been measured. The J value correlates with the distance between and the relative orientation of the unpaired electron molecular orbitals.

Synthesis and characterization of bispyrrolidine derivatives of H2@C60: differentiation of isomers using 1H NMR spectroscopy of endohedral H2

“…As reported, 8,12 comparison of the UV-Vis spectra between 400 and 700 nm region allowed the correlative assignment of structures of the five isomers of 1 (see Fig. S2-Fig.…”

“…Transient EPR spectroscopy of C 60 triplet excited state was also used to differentiate the C 60 bisadduct isomers. 7 Recently, Mazzoni and coworkers 8 reported synthesis and EPR study of C 60 pyrrolidine bisadducts with nitroxide addends. Due to line broadening caused by nitroxide radicals, structure assignment of these nitroxide isomers based on 1 H NMR spectroscopy is very difficult.…”

“…10 Compounds 1 and 2 were synthesized following literature procedures. 8,11 Fortunately, the difference of the polarity of the isomers of 1 is sufficient to allow acceptable separation of four of the five major isomers using preparative TLC. Due to the low yield of the trans-1 isomer, we were only able to isolate and characterize this isomer using the larger available quantities of C 60 as the starting material.…”

Three‐Dimensional Intramolecular Exchange Interaction in a Curved and Nonalternant π‐Conjugated System: Corannulene with Two Phenoxyl Radicals

“…While many neutral diradical derivatives relevant to planar π‐conjugated systems have so far been investigated, studies on curved π‐conjugated neutral diradicals are limited to a single C 60 ‐based system in which [60]fullerene is linked to two nitroxide radicals 4. However, their intramolecular exchange interaction J through the C 60 skeleton was very weak (|${Jk{{- 1\hfill \atop {\rm B}\hfill}}}$ |<0.1 K)4b because of the small spin delocalization onto the C 60 π network from the nitroxide radicals with spin‐localized nature on the NO moieties. Therefore, in order to evaluate an intramolecular exchange interaction in a curved π‐conjugated system in a quantitative manner, synthesis and isolation of a stable neutral diradical derivative with extensively spin‐delocalized nature on its curved π‐conjugated system have been the focus of current attention in molecular magnetism and open‐shell chemistry 2.…”

Structures and electronic states of photoexcited states in a system of two nitroxide radicals linked to fullerene studied by two-dimensional pulsed nutation and time-resolved electron paramagnetic resonance spectroscopy

“…Therefore, the ground states of the bisadducts are a doublet in nature. The reported bisadducts of tetramethyl-pyrrolidine-1-oxyl in which the nitroxide radical is introduced into the pyrrolidine ring [29] in place of TEMPO showed typical EPR for biradicals with comparable exchange interactions IJNol to ]NA~sol. EPR spectra were analyzed on the basis of an intermediate coupling scheme of two spins, where the magnitude and sign of Jyo were determined.…”