Chapter 3
Circularly Polarized Luminescence from
Planar Chiral Compounds Based on [2.2]
Paracyclophane
Yasuhiro Morisaki
Abstract In this chapter, recent development on molecules emitting intense circularly polarized luminescence (CPL) based on planar chiral [2.2]paracyclophane is
described. Optical resolution routes of the planar chiral [2.2]paracyclophane compounds, optically active π-stacked molecules, and the CPL profiles are discussed. It
is suggested that the optically active higher-ordered structures, such as V-, X-,
triangle-, propeller-shaped structures, and so on, in the excited state are important
for intense CPL with large dissymmetry factors (g lum values).
3.1 Introduction
Cyclophanes are cyclic compounds containing at least one aromatic ring (arylene) in
the cyclic skeleton. They have been well studied, particularly in the field of organic
chemistry [1, 2]. A typical example of a cyclophane is [2.2]paracyclophane, which
was synthesized for the first time in 1949 by the pyrolysis of para-xylene [3]. Later,
in 1951, it was synthesized directly by the Wurtz-type intramolecular cyclization of
1,4-bis-bromomethylbenzene [4]. [2.2]Paracyclophane has a unique structure
consisting of two π-stacked benzene rings that are fixed in the para-position with
two ethylene chains. There are many studies on its synthetic routes, reactivities, and
physical properties, in the field of organic chemistry [1]. However, there are not
many examples where [2.2]paracyclophane is effectively utilized in the fields of
polymer chemistry and materials chemistry [5–16].
The two face-to-face benzene rings in close proximity (~3.0 Å apart) in [2.2]
paracyclophane completely suppress their rotational movement. The resulting [2.2]
paracyclophane becomes a planar chiral compound (Fig. 3.1) upon the introduction
of substituent(s) at appropriate position(s) of the benzene ring(s) [17–22]. Planar
chirality attained by [2.2]paracyclophane makes it structurally stable, because of
which this compound has been utilized as a chiral auxiliary or chiral ligand in the
Y. Morisaki (*)
School of Science and Technology, Kwansei Gakuin University, Sanda, Hyogo, Japan
e-mail: ymo@kwansei.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_3
31
Circularly Polarized Luminescence from
Planar Chiral Compounds Based on [2.2]
Paracyclophane
Yasuhiro Morisaki
Abstract In this chapter, recent development on molecules emitting intense circularly polarized luminescence (CPL) based on planar chiral [2.2]paracyclophane is
described. Optical resolution routes of the planar chiral [2.2]paracyclophane compounds, optically active π-stacked molecules, and the CPL profiles are discussed. It
is suggested that the optically active higher-ordered structures, such as V-, X-,
triangle-, propeller-shaped structures, and so on, in the excited state are important
for intense CPL with large dissymmetry factors (g lum values).
3.1 Introduction
Cyclophanes are cyclic compounds containing at least one aromatic ring (arylene) in
the cyclic skeleton. They have been well studied, particularly in the field of organic
chemistry [1, 2]. A typical example of a cyclophane is [2.2]paracyclophane, which
was synthesized for the first time in 1949 by the pyrolysis of para-xylene [3]. Later,
in 1951, it was synthesized directly by the Wurtz-type intramolecular cyclization of
1,4-bis-bromomethylbenzene [4]. [2.2]Paracyclophane has a unique structure
consisting of two π-stacked benzene rings that are fixed in the para-position with
two ethylene chains. There are many studies on its synthetic routes, reactivities, and
physical properties, in the field of organic chemistry [1]. However, there are not
many examples where [2.2]paracyclophane is effectively utilized in the fields of
polymer chemistry and materials chemistry [5–16].
The two face-to-face benzene rings in close proximity (~3.0 Å apart) in [2.2]
paracyclophane completely suppress their rotational movement. The resulting [2.2]
paracyclophane becomes a planar chiral compound (Fig. 3.1) upon the introduction
of substituent(s) at appropriate position(s) of the benzene ring(s) [17–22]. Planar
chirality attained by [2.2]paracyclophane makes it structurally stable, because of
which this compound has been utilized as a chiral auxiliary or chiral ligand in the
Y. Morisaki (*)
School of Science and Technology, Kwansei Gakuin University, Sanda, Hyogo, Japan
e-mail: ymo@kwansei.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_3
31