We investigated the single chain motions of monodisperse polyisobutylene chains in the melt by neutron spin echo spectroscopy. Thereby a wide range in momentum space over a large dynamic range was covered. Motional processes from the center of mass diffusion, the Rouse dynamics to the more local relaxation processes which limit the validity of the standard Rouse model, were elucidated. The observed dynamic structure factors were analyzed in terms of relevant theoretical approaches addressing the limiting factors of the Rouse model. We found that other than claimed in the literature effects of local chain stiffness-they were treated in terms of the all rotational states model and a bending force model-cannot account for the experimental observations. It appears that additional damping effects related to an internal viscosity of the chain have to be involved, in order to explain the experimental results.

By optical excitation of molecular triplet states along with selective population of their spin sublevels nuclear spin polarization can be generated up to a level far above the Boltzmann equilibrium. This effect known as Optical Nuclear Polarization (ONP) has been applied for the investigation of dynamical processes in solid state matrices in the following three ways: (i) The efficiency of the ONP process and its dependency on an external magnetic field is affected by the fluctuation of local fields which is correlated to molecular motions. (ii) By pulsed irradiation of light and radio‐frequencies one can achieve a temporal resolution of the polarization process; in this way the time evolution of the spin order of the molecular states involved in the optical excitation cycle can be mapped out. (iii) The high nuclear polarization makes time resolved NMR measurements on solid state systems feasible which cannot be studied by conventional techniques because of insufficient sensitivity, e.g. guest molecules in low concentrations or isotopes with small natural abundance. The three methods, which cover together a time range between 10−12 and 103 seconds are illustrated by experiments on various organic crystals.

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A gain in detection sensitivity of more than three orders of magnitude has been achieved in high resolution solid state 2H NMR of monocrystalline systems by applying optical nuclear polarization (ONP) via excited triplet states. The method is demonstrated for crystals of fluorene doped with optically active guest molecules which have localized triplet states and for the 1: 1 mixed crystal of anthracene/tetracyanobenzene with excitonic states. The factors determining the efficiency of ONP are discussed and compared to the case of proton spin systems.

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