Chapter 7
Propeller Chirality: Circular Dichroism
and Circularly Polarized Luminescence
Tadashi Mori
Abstract Hexaarylbenzenes (HABs) and related highly substituted aromatic molecules possess unique propeller-shaped structure. The propeller chirality derived
therefrom turned out not to be a simple multiple combination of axial chirality. A
domino-like corporation between the radial aromatic blades is critical to produce the
highly enhanced chiroptical responses. More interestingly, such chirality can be
either static or dynamic depending on the sterical hindrance between the aromatic
blades. The latter systems could be easily controlled by subtle environmental factors
such as temperature, solvent, as well as pressure, and hence feasibly manipulatable.
The molecular systems with propeller chirality thus provide new design principle for
advanced and superior chiroptical materials, particularly those emit efficient circularly polarized light at desired wavelength and, in addition, are modulable and are
switched on-off at will.
7.1 Introduction
A propeller with uni-directionally twisted blades generates a forward or backward
thrust by inverting the rotating direction (Fig. 7.1, left pair). The same can be done
by switching the twist direction of the blades (Fig. 7.1, right pair). Certainly, such a
mechanical motif can be implemented in a molecule to afford a chiral molecular
propeller. Indeed, several propeller chiral molecules have been prepared using
benzene as a hub and aromatic rings as blades and their structures and inter-blade
interactions have been elucidated in some depth [1–6]. However, the dynamic
propeller chirality inversion and its chiroptical consequences have rarely befallen
to be the targets of intensive experimental and theoretical studies until very recently
[7, 8], making a keen contrast to molecular rotors and motors.
T. Mori (*)
Department of Applied Chemistry, Graduate School of Engineering, Osaka University, Suita,
Japan
e-mail: tmori@chem.eng.osaka-u.ac.jp
© Springer Nature Singapore Pte Ltd. 2020
T. Mori (ed.), Circularly Polarized Luminescence of Isolated Small Organic
Molecules, https://doi.org/10.1007/978-981-15-2309-0_7
151
Propeller Chirality: Circular Dichroism
and Circularly Polarized Luminescence
Tadashi Mori
Abstract Hexaarylbenzenes (HABs) and related highly substituted aromatic molecules possess unique propeller-shaped structure. The propeller chirality derived
therefrom turned out not to be a simple multiple combination of axial chirality. A
domino-like corporation between the radial aromatic blades is critical to produce the
highly enhanced chiroptical responses. More interestingly, such chirality can be
either static or dynamic depending on the sterical hindrance between the aromatic
blades. The latter systems could be easily controlled by subtle environmental factors
such as temperature, solvent, as well as pressure, and hence feasibly manipulatable.
The molecular systems with propeller chirality thus provide new design principle for
advanced and superior chiroptical materials, particularly those emit efficient circularly polarized light at desired wavelength and, in addition, are modulable and are
switched on-off at will.
7.1 Introduction
A propeller with uni-directionally twisted blades generates a forward or backward
thrust by inverting the rotating direction (Fig. 7.1, left pair). The same can be done
by switching the twist direction of the blades (Fig. 7.1, right pair). Certainly, such a
mechanical motif can be implemented in a molecule to afford a chiral molecular
propeller. Indeed, several propeller chiral molecules have been prepared using
benzene as a hub and aromatic rings as blades and their structures and inter-blade
interactions have been elucidated in some depth [1–6]. However, the dynamic
propeller chirality inversion and its chiroptical consequences have rarely befallen
to be the targets of intensive experimental and theoretical studies until very recently
[7, 8], making a keen contrast to molecular rotors and motors.
T. Mori (*)
Department of Applied Chemistry, Graduate School of Engineering, Osaka University, Suita,
Japan
e-mail: tmori@chem.eng.osaka-u.ac.jp
© Springer Nature Singapore Pte Ltd. 2020
T. Mori (ed.), Circularly Polarized Luminescence of Isolated Small Organic
Molecules, https://doi.org/10.1007/978-981-15-2309-0_7
151