(with tilted blades) of HABs is essentially ignored. We have addressed this issue, at
least in part, by showing that both the propeller and doughnut structures with tilted
and orthogonal blades, respectively, are imperative in condensed phase, although the
latter maximizes the toroidal interaction [7, 8]. The relative importance, however,
can be controlled by changing the conditions employed.
7.3 Chiral Propeller Formation Driven by the Domino
Effect
The intramolecular point-to-propeller chirality transfer has been investigated by
introducing a point-chiral substituent to the para-position of 1–6 aromatic blades
in hexaphenylbenzene and by subsequently examining the chiroptical consequences
of the systematic peripheral modification [7, 8]. Thus, a series of HABs (H1–H6)
incorporating either methoxy or chiral alkyloxy (R
à O) group at the para-position of
each aromatic blade (Fig. 7.5) are prepared by the transition metal-catalyzed
trimerization of the corresponding acetylene derivatives or by the Diels-Alder
OMe
OMe
OMe
OMe
MeO
MeO
OR*
OR*
OR*
OR*
R*O
R*O
OR*
OR*
OMe
OMe
R*O
R*O
OMe
OMe
OR*
OMe
MeO
R*O
OR*
OMe
OMe
OMe
MeO
R*O
OMe
OMe
OMe
OMe
MeO
R*O
H0
H1
H2
H2P
H4
H6
R
R* =
O
Fig. 7.5 HABs with different number of chiral propeller blades
7 Propeller Chirality: Circular Dichroism and Circularly Polarized Luminescence
155