Photoluminescence-detected magnetic resonance (PLDMR) studies of matrix isolated molecules and films of C 60 and C 70

Abstract

The X-band spin 1 2 photoluminescence-detected magnetic resonance (PLDMR) of C 60 and C 70 isolated in a toluene/polystyrene matrix and various films is reviewed. The fluorescence (F)-enhancing triplet resonances of the isolated molecules are attributed to ground-state repopulation by a nonradiative triplet state delocalized over the molecule. The phosphorescence-detected resonance of C 70 glasses is due to the direct radiative decay of the long-lived triplets. Its strong temperature dependence results apparently from a dynamic Jahn-Teller effect. The PLDMR of C 60 and C 70 films is similar, and includes a narrow F-enhancing spin 1 2 resonance (ΔH 1 2 ∼8G) at g∼2.0025 and narrow and broad triplet patterns at full- and half-fields. The spin 1 2 resonance is discussed in relation to polaron recombination or a radical-triplet pair mechanism. The narrow triplet pattern, attributed to a triplet delocalized over the molecule, is slightly narrower than in C 60, consistent with a slightly larger exciton. The broad pattern is similar to that observed in π-conjugated polymers and is believed to result from a triplet localized on a pentagon or hexagon adjacent to a neighboring molecule.