Dynamics of meso-chiral interconversion in butterfly-shape overcrowded alkene rotor tunable by solvent properties.

Control over dynamic motion at the molecular level and stimuli-responsiveness are important issues for making nano-motors, nano-actuators or nano-sensors. Elucidation of dynamics of molecular rotational motion is an essential part and still challenging area of research. In this report, demonstration of reversible diastereomeric interconversion of a molecular rotor composed of overcrowded butterfly-shape alkene ( FDF ) is given. Its inherent dual rotatory motion (two rotors, one stator) with interconversion between two diastereomers, chiral  trans - FDF  and meso  cis - FDF  forms, has been examined in detail upon varying temperatures and solvents. The free energy profile of 180 °  revolution of one rotor part has a bimodal shape with unevenly positioned maxima (i.e. transition states).  FDF  in aromatic solvents adopts preferentially meso  cis -conformation, while in non-aromatic solvents a chiral  trans -conformation is more abundant. Additionally, moderate correlations between the  trans - FDF / cis - FDF  ratio and solvent parameters, such as refractive index, polarizability, and viscosity were found. The results presented here have implementations in several fields of organic chemistry, such as design of artificial molecular machines, asymmetric/stereoselective reactions and solvent properties scales.