Hash-Mark-Shaped Azaacene Tetramers with Axial Chirality

The tetramers of azapentacene derivatives
with unique hash mark
(#)-shaped structures were prepared in a quite facile manner. The
#-shaped tetramers are optically active due to possessing extended
biaryl skeletons, and the structure of the tetramer composed of four
dihydrodiaza­pentacene (DHDAP) units (1) was investigated
as the first example of this kind of molecule. The tetramer 1 showed characteristic chiroptical properties reflecting
its orthogonally arranged quadruple DHDAP moieties, as well as redox
activity. The solution of enantiopure 1 exhibited intense
circularly polarized luminescence (CPL) with a dissymmetry factor
of 2.5 × 10–3. The absolute configuration of
the enantiomers of 1 was experimentally determined by
X-ray crystal analysis for the dication salt of the enantiomer of 1 with SbCl6– counterions. The
solutions of enantiopure 12+·2­[SbCl6–] also showed NIR circular dichroism (CD)
spectra over the entire range from visible to 1100 nm, enabling the
modulation of the chiroptical properties by redox stimuli.