Notably enantiopure bis(BODIPY)s of this type exhibit a strong and clearly
bisignated visible wavelength CD signals in solution (Fig. 6.27) [61].
The observed bisignalized dichroism is attributed to the formation of a molecular
helix, with a preferred helical conformation (Fig. 6.28), allowing near-degenerate
visible wavelength absorption transitions, due to the localization of two near identical
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absorption
Normalized absorption
Wavelength (nm)
[
] (deg cm 2
dmol -1
)
Fig. 6.27 UV-Vis absorption (down) and CD (up) spectra of bis(BODIPY)s (R,R)-36 (red), (S,S)36 (blue), and meso-36 (black) in CHCl 3 . A visible dichroic signal with strongly bisignalized
Cotton effect is observed for each enantiomer [adapted with permission from [61], published by the
Royal Society of Chemistry]
Negative couplet
Fig. 6.28 Computed helical
structure of (R,R)-36,
showing preferred
P configuration for the chiral
helix and negative
disposition for the involved
exciton couplet
6 BODIPY Based Emitters of Circularly Polarized Luminescence
139