Dynamic disorder in stable and metastable thiophene. - I. N. M. R. lineshape study and structurally based interpretations

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Abstract
A proton wide-line N.M.R. study of crystalline thiophene has been undertaken using a high sensitivity F.T. spectrometer. Both stable and metastable phase sequences have been observed and phase transitions have been detected in very good agreement with our previous calorimetric studies [1]. Theoretical second moments have been calculated using the X-ray scattering data of André et al. [2]. Given the structural models, we have shown that the many different allowed configurations lead to a wide distribution of theoretical intermolecular second moments, suggesting very different local steric hindrances. All the known crystalline phases, from crystallization temperature down to 120 K and presumably lower, are orientationally disordered. The nature of this disorder was proven to be the in-plane molecular reorientation. The frequency of the motion is commensurate with the local field in a very wide range of temperatures indicating a wide distribution of correlation times. We suggest that this could be a signature for glassy crystalline-forming materials