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Helically twisted chiral cyanine dyes: Influence of chromophore length on observed and calculated rotatory strengths
Author(s) -
Eggers Lutz,
Kolster Klaus,
Buss Volker
Publication year - 1997
Publication title -
chirality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.43
H-Index - 77
eISSN - 1520-636X
pISSN - 0899-0042
DOI - 10.1002/(sici)1520-636x(1997)9:3<243::aid-chir7>3.0.co;2-g
Subject(s) - chromophore , cyanine , chemistry , chirality (physics) , enantiomer , steric effects , circular dichroism , cotton effect , wavelength , crystallography , photochemistry , stereochemistry , optics , chiral symmetry , physics , quantum mechanics , nambu–jona lasinio model , fluorescence , quark
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. © 1997 Wiley‐Liss, Inc.