Rational design and in-situ FTIR analyses of colorimetrically reversibe polydiacetylene supramolecules

The colorimetric reversibility of polydiacetylene supramolecules, derived from a variety of functionalized diacetylenic lipids, has been subjected to detailed investigation. In an earlier effort, it was shown that polydiacetylene vesicles prepared from PCDA-mBzA 1, bearing terminal m-carboxyphenyl-amido groups, display complete reversibility upon thermal stimulation [J. Am. Chem. Soc. 2003, 125, 8976]. The origin and nature of reversible thermochromism in these systems have been elucidated in-situ in the current studies by using polydiacetylene supramolecules, prepared from analogues of PCDA-mBzA 1. Issues related to the effects of (1) internal amide groups, (2) headgroup aromatic interactions, (3) lengths of the hydrophobic alkyl chains, and (4) terminal carboxylic groups on the colorimetric reversibility of the polydiacetylene supramolecules have been probed. The results demonstrate that well-developed hydrogen-bonding and aromatic interactions between headgroups are essential for complete recovery of the length of the conjugated T-electron chain following thermal stimulus. The results of this comprehensive investigation allow for the first time the rational design of reversible colorimetric sensors based on polydiacetylene supramolecules.