Spin relaxation of fullerene $C70$ photoexcited triplet in molecular glasses: Evidence for onset of fast orientational motions of molecules in the matrix near 100 K Available to Purchase

Electron spin echo (ESE) was applied to study transversal spin relaxation of photoexcited triplet state of fullerene $C70$ molecules in glassy $o$-terphenyl and cis-/trans-decalin matrices (glass transition temperatures of 243 and 137 K, respectively). The relaxation rate $T2−1$ was found to increase sharply above 110 K in $o$-terphenyl and above 100 K in decalin. It is suggested that this increase arises from interaction of $C370$ pseudorotation with fast molecular librations in the matrix. Both these types of motion involve atomic vibrations and are uniaxial in their nature, the known literature data on Raman light scattering and others indicate that molecular librations may be thermally activated in glasses just near 100 K. The increase in $T2−1$ near 100 K is not observed for photoexcited triplet state of fullerene $C60$⁠, for which pseudorotation is not uniaxial. As the fullerene molecule has a size much larger than that for glass solvent molecules, it is likely that molecular librations in the matrix are of collective nature.