| Summary: | 碩士 === 國立臺灣大學 === 化學研究所 === 102 === We have adopted the rigid H-shaped pentiptycene scaffold as a four-bladed rotor
to create new light-controlled molecular brakes. In this thesis, a series of new
pentiptycene-derived molecular brakes 2OR, 2R and 2NR containing the well-known
photochromic azobenzene group were delveloped, and the substituent effect on the
photochemical and thermal isomerization was investagated.
The rotational rates and kinetic parameters of c-2 were probed by 2D-EXSY. The
results showed that the rotational rate of the brake-on state (c-2) is lower by ~109 fold
than the brake-off state (t-2). Furthermore, the brake can be switched off in two
different ways, i.e., photochemical and thermal switching. The overall
photoreversibility between t-2 and c-2 in hexane was as high as 55%. Further
improvement on switching efficiency can be achieved with themo reset from c-2 to
t-2 is achievable, which lead to a total efficiency of 75%. Compared to the previous
stilbene system, the total switching efficiency is enhanced by almost 375%.
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