Visible- and uv-excited optically detected magnetic resonance (ODMR), ESR, and light-induced ESR (LESR) study of C/sub 60/ and C/sub 70/ films and glasses

Summary form only given. The X-band ESR, LESR, and ODMR of C/sub 70/ molecules isolated in a toluene/polystyrene (C/sub 70/:T/PS) glassy matrix and C/sub 70/ films is compared to the ODMR of C/sub 60/ glasses and films. As in C/sub 60/:T/PS, the ODMR of the C/sub 70/ glasses consists only of a broad triplet exciton powder pattern at g /spl tilde/ 2; the half field resonance due to the /spl Delta/ = 2 transitions of this triplet is unobservable. In contrast to C/sub 60/:T/PS, the triplet powder pattern of C/sub 70/:T/PS is strikingly asymmetric, apparently due to the lower symmetry of C/sub 70/. The ODMR of C/sub 70/ films is also similar to that of C/sub 60/ films, and includes a narrow PL-enhancing polaron resonance (/spl Delta/H/sub 1/2/ /spl tilde/ 6 G) at g /spl tilde/ 2.0025 and narrow and broad triplet exciton powder patterns at full- and half-fields. The narrow triplet pattern, attributed to a triplet exciton delocalized over the entire molecule, is slightly narrrower than in C/sub 60/, consistent with a slightly larger exciton. The broad pattern observed in films but not in the glasses is similar to that observed in /spl pi/-conjugated polymers and is suspected to result from a triplet localized on a pentagon or hexagon adjacent to a neighboring molecule. While the half-field resonances are comparably intense in C/sub 60/, in C/sub 70/ the broad pattern is much weaker than the narrow (delocalized) exciton pattern. The effects of UV excitation, as well as UV-induced photopolymerization, will also be discussed.