Solvent-induced aggregation of optically active poly(phenylene ethynylene)s (PPEs) can follow different pathways, depending on the ability of the PPEs to stabilize the chiral macrostructure. A new approach has been developed that utilizes chirality in combination with ™pillarlike∫ structural elements for the first time to create strong electronic coupling systematically while maintaining high quantum yields. For more information see the following publication by Swager et al.

Stereodynamic complexes of copper were found to undergo inversion of a helical chiral element upon oxidation or reduction. The amino acid methionine was derivatized by the attachment of two chromophores to the nitrogen atom. The resultant ligands formed stable complexes with Cu(I) and Cu(II) salts. For a derivative of a given absolute chirality, the complexes afford nearly mirror image circular dichroism spectra. The spectral changes originate from reorientation of the nitrogen-attached chromophores due to a conformation interconversion driven by the exchange of a carboxylate for a sulfide ligand. The electrically induced chirality inversion coupled with strong interactions with polarized light is unique and may lead to novel chiral molecular devices.

[formula: see text] A circular dichroism technique has been applied to the absolute configurational assignment of acyclic alpha-amino acids and beta-amino alcohols with single stereogenic centers via a one-step derivitization procedure requiring microgram quantities of material. Metal ions fix the geometrical relationship of two chromophores, affording CD spectra that agree with theory on the basis of the expected conformation of the ligands in the metal complexes.

This manuscript describes the design, synthesis, and characterization of a coordination complex that demonstrates reversible interconversion between two redox states that show very different chiroptical properties. Reported here are three chiral N(4)-tetradentate ligands, prepared in enantiopure form by asymmetric synthesis, and their circular dichroic and other properties, as well as those of numerous Cu(I) and Cu(II) complexes. While the chiroptical spectra of the free ligands are unremarkable, the CD spectra of the complexes are very intense, and spectral features indicate that they derive from exciton coupling. Comparison of complexes with one, two, or three chromophores provides strong supportive evidence for this assignment, and semiquantitative correlation with intensity as rationalized by additivity. A Cu(I)(L)/Cu(II)(L) redox couple was identified that showed dramatically different circular dichroic properties that was further shown to be easily oxidized and reduced chemically between two states with remarkable retention of signal. A structural hypothesis for the interconversion is given and supported by a variety of spectroscopic evidence.

We report a method to determine the absolute configuration of alpha-amino acids by exciton coupled circular dichroism (ECCD). Naturally occurring amino acids were successfully derivatized with 2-bromomethylquinoline. Complexation of these conformationally flexible ligands with Cu(II) salts yielded defined propeller-like structures. The direction of the twist (i.e., the relative orientation of the chromophores to each other) is governed by the asymmetric amino acid carbon center. The transition moments of the chromophores couple and yield a bisignate circular dichroism spectrum, the sign of which corresponds to the absolute configuration of the chiral center of the amino acid. Enantiomeric excess (e.e.) of amino acid derivatives is linearly related to the differential extinction coefficient Delta(epsilon) and can be assessed easily utilizing a standard curve. This efficient, sensitive technique requires low analyte concentrations, offers several advantages over established methods, and could be applied in medicinal, pharmaceutical, or chemical retail and manufacturing industry.