Summary : Two series of derivatives containing C60 covalently linked to one and to two nitroxide groups have been investigated by EPR, ENDOR and time resolved EPR with pulsed laser excitation. In the first series, the sign of the electron exchange interaction between an unpaired electron spin and the spins of the triplet excited fullerene moiety has been determined. It is found that it depends on the overlap between the nitroxide unpaired electron wave function and the LUMO orbital of the C60 moiety. In the second series, magnitude and sign of the electron exchange interaction between the two nitroxide electron spins has been obtained from the EPR spectrum shape and the characteristics of the ENDOR spectra. The polarisation of the EPR lines observed when these derivatives are photoexcited by a laser light pulse is discussed in terms of C60 triplet annihilation by the nitroxide biradical triplet. Abstract : Nous avons étudié le spectres RPE, ENDOR et RPE resolu dan le temps de deux series de molecules ou C60 est lié avec un ou deux radicaux libres nitroxides. Pour la première serie le signe de l’interaction d’èchange electronique radical-état de triplet a eté determiné. Elle dépand de la superposition entre la fonction d’onde de l’electron désaccouplé du nitroxide et l’orbital LUMO du C60. Dans la deuxiemme serie, la valeur et le signe de l’interaction d’échange ont été obtenue a partir de la forme des spectres RPE et des caracteristiques du spectre ENDOR. La polarisation de RPE raies observè avec excitation laser est interprété suivant un model d’interaction triplet-triplet entre le triplet excité sur le C60 et le triplet formé par le deux nitroxides.
Intramolecular Exchange Interaction in many-spin systems. Determination of magnitude and sign by EPR, ENDOR and CIDEP effects due to the interaction with the excited triplet states
MAZZONI, MARTINA;FRANCO, LORENZO;CORVAJA, CARLO
2001
Abstract
Summary : Two series of derivatives containing C60 covalently linked to one and to two nitroxide groups have been investigated by EPR, ENDOR and time resolved EPR with pulsed laser excitation. In the first series, the sign of the electron exchange interaction between an unpaired electron spin and the spins of the triplet excited fullerene moiety has been determined. It is found that it depends on the overlap between the nitroxide unpaired electron wave function and the LUMO orbital of the C60 moiety. In the second series, magnitude and sign of the electron exchange interaction between the two nitroxide electron spins has been obtained from the EPR spectrum shape and the characteristics of the ENDOR spectra. The polarisation of the EPR lines observed when these derivatives are photoexcited by a laser light pulse is discussed in terms of C60 triplet annihilation by the nitroxide biradical triplet. Abstract : Nous avons étudié le spectres RPE, ENDOR et RPE resolu dan le temps de deux series de molecules ou C60 est lié avec un ou deux radicaux libres nitroxides. Pour la première serie le signe de l’interaction d’èchange electronique radical-état de triplet a eté determiné. Elle dépand de la superposition entre la fonction d’onde de l’electron désaccouplé du nitroxide et l’orbital LUMO du C60. Dans la deuxiemme serie, la valeur et le signe de l’interaction d’échange ont été obtenue a partir de la forme des spectres RPE et des caracteristiques du spectre ENDOR. La polarisation de RPE raies observè avec excitation laser est interprété suivant un model d’interaction triplet-triplet entre le triplet excité sur le C60 et le triplet formé par le deux nitroxides.
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