Communication
doi.org/10.1002/chem.202100327
Chemistry—A European Journal
may be quite valuable for possible applications in the
chiroptical switching devices.[27] It is to note that an azahelicene
Keywords: azahelicenes
polarized luminescence · dehydrogenative coupling · X-ray
·
circular dichroism
·
circularly
involving an imidazole moiety was reported to show
a
structures
decreased dissymmetry factor upon an addition of TFA.[26d]
Thus, the effect of protonation to basic nitrogen on chiroptical
responses, in particular the jgCPL j values, is not straightforward
and details of observed enhancement in the current system are
remain to be elucidated.
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Finally, we paid our attention to the molecular packing
modes of helicenes 7 and 8 in their solid states. The molecules
of helicene 7 was found to make a unique one-directional
columnar structure in a helical manner, while those of 8 showed
a completely different packing mode (Figure S16 and S17). As
such, a semiconducting behavior was anticipated for the former
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In summary, we successfully obtained the enantiomerically
pure forms of a series of C2-symmetic π-extended azahelicenes
bearing the double indolo[3.2.1,-jk]carbazole scaffold by means
of palladium-mediated double dehydrogenative cyclization,
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chiroptical responses with ca. 6 times higher jgCD j and jgCPL
j
values compared with those from the non-pyridine azahelicene
7. Theoretical calculations confirmed that the pyridine nitrogen
effectively increases the magnetic versus electric contribution in
the relevant electronic transition, and thus, enhances the
dissymmetry factor values. Upon protonation of 8, a remarkable
red-shift of the emission with a considerable increase of the j
gCPL j value was observed, facilitating the chiroptical switching
applications. Besides, a p-type FET response was established
with helicene 7, due to its semiconducting property through
the columnar structure in its solid state. Our findings and
implications detailed above would provide valuable information
for designing novel azahelicenes and derivatives, with superior
optical, chiroptical, as well as electronic properties.
Acknowledgements
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This work was supported by JSPS KAKENHI Grant No. JP
17H06092 (Grant-in-Aid for Specially Promoted Research) to
M.M. and 17H03134 to K.N., and by CREST, JST, Japan (Grant
Number JPMJCR2001) to T.M. We thank Prof. N. Tohnai and
Prof. M. Suzuki/Mr. S. Torimitsu of Osaka University with the X-
ray analysis and FET measurement, respectively.
Conflict of Interest
The authors declare no conflict of interest.
Chem. Eur. J. 2021, 27, 7356–7361
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