EPR of Exchange-coupled Oligomers

Electron Paramagnetic Resonance, Volume 18 The Royal Society of Chemistry, 2002 

Conti et aV have studied the bis-nitroxide fulleropyrrolidine 6 by CW and time-resolved (TR-)EPR. The CW spectrum of 6 in toluene solution reveals that the exchange between the nitroxides expressed as J/g is temperature dependent from ca. 2 mT at 350 K to ca. 3.5 mT at 250 K. More importantly, an excited S = 2 state is observed by TR-EPR upon photoexcitation. This is a rare example of spin states of higher than triplet multiplicity being observed by TR-EPR. 

Lahti and co-workers are using nitrene radicals as components in large spin molecules and for molecular electronics. They have investigated the photolysis products of a series of 2,4,6-triazidopyridines (7-10) in 2-methyl-THF (mTHF) at 77 K, and have interpreted the spectra in terms of the complex mixture of mono-. 

The same group have investigated covalently linked nitrene-radical species 13-15, generated from the corresponding azido species at 77 K in mTHF. In each case S = 3/2 spectra are observed. The axial (D) and rhombic ( ) ZFS 

Lahti and other co-workers have also studied the triazene moiety as a triangular linker promoting ferromagnetic coupling between three 2,4,6-nitrox-ide or 2,4,6-phenoxyl radicals (16,17), monitored by their S = 3/2 EPR spectra at 77 K. 

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Critical reviews of applications involving the design of spin-traps, advances in spin-labelling, paramagnetic centres on solid surfaces, exchange-coupled oligomers and radicals in flavoenzymes highlight the detailed and sophisticated information provided by EPR in areas of particular contemporary interest. 

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