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Keywords:

  • molecular motions;
  • organic chromophores;
  • phase transitions;
  • dielectrics

Abstract

Molecular motion associated with rotational and orientational phase transitions is one of the prominent structural strategies for assembling the functional materials such as artificial motors and tunable molecular dielectrics. Here, a new organic chromophore molecule, 4-N,N-dimethylamino-4′-N′-methylstilbazolium trifluoromethanesulfonate (complex 1), which undergoes an exceptional order-disorder phase transition at 322 K, is successfully synthesized. The single crystal X-ray diffraction analysis, thermal analysis, and dielectric measurements are used to characterize its dielectric dynamic behaviors. The results reveal that 1 behaves as a molecular rotator with the obviously distorted bipyramidal geometry of trifluoromethanesulfonate anions. In addition to its disorderings, two very distinct motions of the anionic moieties are confirmed, namely the “earth rotation” of partial units and the “earth revolution” of the whole molecule. Such unique molecular motions are found to be mainly responsible for the order–disorder phase transition together with the abrupt dielectric anomaly and anisotropy. The charge-transfer cationic parts enhance the molecular motions behaving as the stator and give rise to its excellent third-order nonlinearities. The concept may allow for the remote control of molecular events to explore functional materials in organic chromophores.