The three–dimensional structure and the dynamic behavior of a molecule is important issue for regulating the molecular function or biological activity. Recently the development of functional molecular devices that undergo reversible conformational interconversion between two or more stable states when exposed to an external stimulus, such as light, electricity or a chemical reaction, has received much attention. In our investigations on the
cis conformational preference of aromatic
N–methylated amides, we found several aromatic amides altered the stable conformations depending on the external stimulus. Namely, 3,5–bis (dimethylamino) –
N–methylacetanilide (
6) existed in
cis form in CD
2Cl
2, while the addition of TFA–
d caused the conformational alteration into
trans form. Similarly,
N– (2,5–dihydroxyphenyl) –
N–phenylacetanilide (
8) and
N–phenylbenzohydroxamic acid (
12) changed the amide conformation by redox reaction or solvent properties, respectively.
N–Methylated pyridylamide also showed unique conformational properties. The stable conformation of the diamide
16 is solvent–dependent, and the acceptor number of the solvent seems to be significant. These pyridylamides and the oligomers changed the conformation by addition of acid. Further, we demonstrated the conformational change of the amide molecules could be detected by fluorescence spectra. These properties of the aromatic amides would be applied to the molecular switch or fluorescent sensors towards some external stimulus.
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