Lutz Eggers

Helically twisted chiral cyanine dyes: Influence of chromophore length on observed and calculated rotatory strengths

Synthesis, chiroptical properties, and quantum-mechanical calculations of the monomethine dye 3 and of the trimethine dyes 7 and 11 are reported. In 3 and 11, the chromophore is forced into a twisted all-Z-conformation by steric interaction of the end groups in the former and the presence of a t-butyl group in the mesoposition of the latter, which is manifest in the UV/Vis spectra not only in the reduced intensity of the longest wavelength absorption, but also in the occurrence, at shorter wavelength, of a “cis-peak.” Chiral substitution of the end groups serves as chiral anchor to discriminate between otherwise enantiomeric forms and makes them amenable to chiroptical investigation. The results are in agreement with theoretically calculated chiroptical data based on helically twisted cyanine chromophores. They support the contention that not only the sense of the helix, but also its length determines the sign of the associated Cotton effect. Chirality 9:243–249, 1997.

A tolan substituted optically active spiropyran

Abstract A substituted optically active spiropyran with a tolan group in the 6′-position is described. Both the parent spiropyran and its derivative were separated by chiral HPLC and characterized by CD spectroscopy. There is a ‘diastereomeric switch’ at temperatures below −30°C , but the compound does not show liquid crystalline properties.