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A detailed description of the thermal relaxation processes in MEH−PPV is reported. Bulk methods such as DMTA were employed in conjunction with other techniques that probe molecular motions, such as fluorescence spectroscopy, thermal stimulated current, and 13C NMR. From the two main transitions observed (glass transition process at 340 K and β-relaxation between 200 and 220 K), it was demonstrated that the first is strongly correlated with the dissociation of a fluorescent emissive interchain complex and that the second relaxation involves movements of the lateral substituents of the polymer backbone and, more specifically, their CH2 groups. NMR dipolar chemical shift correlation experiments pointed an increasing gain in mobility through the side chain, the lateral carbons close to the aromatic ring being more rigid than those located more distant from the main polymer chain. A kinetic model involving the dissociation of interchains to re-form intrachain excitons was proposed to explain the profiles of the photoluminescence spectra at higher temperatures.

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Solid-state nuclear magnetic resonance methods were used to study molecular dynamics of MEH-PPV at different frequency ranges varying from 1 Hz to 100 MHz. The results showed that in the 213 to 323 K temperature range, the motion in the polymer backbone is predominantly slow ͑Hz-kHz͒ involving small angle librations, which occurs with a distribution of correlation times. In the side chain, two motional regimes were identified: Intermediate regime motion ͑1-50 kHz͒ for all chemical groups and, additionally, fast rotation ͑ϳ100 MHz͒ for the terminal CH 3 group. A correlation between the motional parameters and the photoluminescent behaviors as a function of temperature was observed and is discussed.

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Measurements of the 13C, 7Li, and 1H nuclear magnetic resonance (NMR) of the nanocomposite formed by the intercalation of lithium and diethylamine in molybdenum disulfide, Li0.1MoS2[(C2H5)2NH]0.2, are reported. The strong Li−Li dipolar interaction strength, calculated from the 7Li NMR decoupling data, suggests the formation of lithium clusters. The dimensional restriction of the available space between the host layers supports a hypothesis that is based on the formation of Li3 clusters stabilized by amine ligands. The lithium relaxation is mainly due to the interaction between the quadrupolar moment of the 7Li nuclei and the fluctuating electric field gradient at the site of the nucleus, produced by the surrounding charge distribution. The dynamical parameters obtained from the 7Li temperature dependence of the spin−lattice relaxation indicate a high lithium mobility, which is attributed to the fast exchange motion of the lithium ions between the coordination sites within each Li3 aggregate. The 1H line shape and relaxation data support the proposed structural model for the lithium−diethylamine cluster. Numerical analysis of the 1H line shape indicates that the intercluster dipole−dipole interactions are responsible for most of the spectral broadening. 1H spin−lattice relaxation is mainly governed by hydrogen nuclei in the less-mobile CH2 and in the fast-relaxing CH3 groups in the diethylamine molecule.