Synthesis and Characterization of A Pentiptycene-Enone-Derived Molecular Brake
Date Issued
2010
Date
2010
Author(s)
Chen, Ying-Chen
Abstract
In this thesis, the synthesis and brake performance of a new molecular system (1) that consists of a pentiptycene rotor and an indanone brake are reported. The rotation kinetics of the rotor was probed by both variable-temperature 1H and 13C NMR spectroscopy and DFT calculations, and the switching between the brake-on and brake-off states were conducted by a combination of photochemical and electrochemical isomerization. Due to a larger steric hindrance between the rotor and the brake units in Z-1 than E-1, rotation of the rotor is slowed down by 500-fold at room temperature (298 K) on going from E-1 to Z-1, corresponding to the brake-off and brake-on states, respectively. The E-1 → Z-1 photoisomerization in acetonitrile is efficient and reaches a 11:89 （E-1:Z-1）ratio in the photostationary state upon excitation at 290 nm, attributable to a larger isomerization quantum efficiency for E-1 vs Z-1. An efficient Z-1 → E-1 isomerization (96%) was also achieved through the radical anionic intermediates by electro chemical treatments. Consequently, the reversibility of E-Z switching of 1 is as high as 85%. The Z-1 → E-1 acid-catalyzed isomerization is also efficient (96%) through addition-elimination mechanism, but chemical energy is not as clean as light or electrical energy. Thus, we adopt alternating photochemical and electrochemical treatments to carry out consecutive E-Z switching of 1.
Subjects
molecular machine
isomerization
photochemistry
electrochemistry
Type
thesis
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