Chapter 5
Structural Control of Fluorescent Helicates
for Improved Circularly Polarized
Luminescence Properties
Taku Hasobe
Abstract This chapter focuses on the structural and photophysical control of
fluorescent helicene derivatives and related homoleptic zinc(II) helicates for
improved circularly polarized luminescence properties. Our synthetic strategy
enables to significantly enhance the fluorescence quantum yield (Φ FL ) of helicene
derivatives for observation of circularly polarized luminescence (CPL). Moreover,
the zinc(II) helicate also demonstrated unusually strong chiroptical responses with
absorption and luminescence dissymmetry factors such as |g abs | ¼ 0.20 at 615 nm
and |g lum | ¼ 0.022 at 660 nm, respectively. The g lum profiles significantly expanded
up to ca. 850 nm.
5.1 Introduction
π-Conjugated molecules generally possess the characteristic optical and electronic
behaviors concerning the fundamental properties and advanced applications
[1, 2]. These are dependent on the electronic structures of molecules. Especially,
the conformational distortion of π-electron units enforced by an intramolecular
and/or intermolecular steric hindrance and electronic interaction trigger the chirality,
which is seen in biological molecular assemblies. Such helical topology of these
molecules with distinctive photophysical properties provide good possibilities for
various functionalities such as separation [3], chiroptical, and electronic properties
[4, 5].
Helicene derivatives are among the unusual organic dye molecules composed of
ortho-condensed aromatic rings that form the peculiar screwed π-conjugated structures [6]. These molecular systems have been investigated in various research fields
such as supramolecular assemblies [7–9], fluorescent sensors [10], and liquid crystals [11–14] because of the nonplanar conformations. As is well known, these
T. Hasobe (*)
Department of Chemistry, Faculty of Science and Technology, Keio University, Yokohama,
Japan
e-mail: hasobe@chem.keio.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_5
99
Structural Control of Fluorescent Helicates
for Improved Circularly Polarized
Luminescence Properties
Taku Hasobe
Abstract This chapter focuses on the structural and photophysical control of
fluorescent helicene derivatives and related homoleptic zinc(II) helicates for
improved circularly polarized luminescence properties. Our synthetic strategy
enables to significantly enhance the fluorescence quantum yield (Φ FL ) of helicene
derivatives for observation of circularly polarized luminescence (CPL). Moreover,
the zinc(II) helicate also demonstrated unusually strong chiroptical responses with
absorption and luminescence dissymmetry factors such as |g abs | ¼ 0.20 at 615 nm
and |g lum | ¼ 0.022 at 660 nm, respectively. The g lum profiles significantly expanded
up to ca. 850 nm.
5.1 Introduction
π-Conjugated molecules generally possess the characteristic optical and electronic
behaviors concerning the fundamental properties and advanced applications
[1, 2]. These are dependent on the electronic structures of molecules. Especially,
the conformational distortion of π-electron units enforced by an intramolecular
and/or intermolecular steric hindrance and electronic interaction trigger the chirality,
which is seen in biological molecular assemblies. Such helical topology of these
molecules with distinctive photophysical properties provide good possibilities for
various functionalities such as separation [3], chiroptical, and electronic properties
[4, 5].
Helicene derivatives are among the unusual organic dye molecules composed of
ortho-condensed aromatic rings that form the peculiar screwed π-conjugated structures [6]. These molecular systems have been investigated in various research fields
such as supramolecular assemblies [7–9], fluorescent sensors [10], and liquid crystals [11–14] because of the nonplanar conformations. As is well known, these
T. Hasobe (*)
Department of Chemistry, Faculty of Science and Technology, Keio University, Yokohama,
Japan
e-mail: hasobe@chem.keio.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_5
99