Journal
CHEMISTRY-A EUROPEAN JOURNAL
Volume 25, Issue 34, Pages 8003-8007Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.201901248
Keywords
circularly polarized luminescence; electronic circular dichroism; helicenes; heteroaromatization; push-pull chromophores
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Funding
- Swiss National Science Foundation [SNF 200020_159802]
- University of Pisa [PRA 2018-23]
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The synthesis and chiroptical properties of a series of enantiomerically pure, C-2-symmetrical carbo[6]helicene dimers are reported. Two helicene cores are connected through a buta-1,3-diyne-1,4-diyl linker or a heteroaromatic bridge and bear arylethynyl substituents at their 15-positions. This ensures the possibility of extended electronic communication throughout the whole molecule. The new chromophores exhibit intense ECD spectra with strong bands in the UV/Vis region well above 400 nm. The anisotropy factor g(abs) (defined as Delta epsilon/epsilon) reaches values up to 0.047, which are unusually large for single organic molecules. They also display blue fluorescence, with good quantum yields (phi(f)similar to 0.25). The emitted light is circularly polarized to an outstanding extent: in some cases, the luminescence dissymmetry factor g(lum)=2(I-L-I-R)/(I-L+I-R) attains values of |0.025|. To the best of our knowledge, such values are among the highest ever reported for non-aggregated organic fluorophores.
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