stereospecific manner provides a useful basis for chiroptical
molecular switches and molecular memory elements.
This work was supported by the Zernike Institute for Advanced
Materials. Dr M. M. Pollard is gratefully acknowledged for
valuable discussions.
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In conclusion, all three individual atropisomers of a photo-
chromic diarylethene were isolated for the first time. While the
parallel meso form is photochemically inactive, the two anti-
parallel enantiomers are photochemically active and undergo
reversible ring-closure in a stereospecific process. The inherent
chirality that can be modulated in a fully reversible and
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16 The compounds 1o and 2o suffer from very low solubility in heptane
which makes their resolution difficult.
17 Ra and Sa indicate atropisomers of the open anti-parallel form, P,P and
M,M indicate helicities in the closed form, R and S indicate the
configuration of the stereogenic centres in the closed form.
18 For an analysis of the kinetic process, see supplementary material.
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Chem. Commun., 2007, 1745–1747 | 1747