Chapter 4
Circularly Polarized Luminescence
in Helicene and Helicenoid Derivatives
Jeanne Crassous
Abstract In this chapter, we discuss the circularly polarized luminescence (CPL) of
helicene and helicenoid derivatives. The organic helicenic derivatives are classified
according to the type of atom (heteroatom or carbon) incorporated within the
helical backbone. Transition-metal complexes and chiroptical devices incorporating
helicene derivatives and exhibiting CPL activity are also presented.
4.1 Introduction
Circularly polarized luminescence (CPL) is a fascinating property of many classes
of chiral emissive molecules. The well-known luminescence dissymmetry factor
(g lum ) as a measure of the degree of circular polarization of emitted light is defined
as g lum ¼ 2ΔI/I ¼ 2(I L À I R )/(I L + I R ), where I L and I R denote the left- and righthanded circularly polarized emission intensities, respectively. Various types of chiral
fluorescent conjugated organic molecules exhibiting CPL are known and generally
possess g lum values on the order of 10
À4
–10
À2 [1–6]. Among them, helicenes are a
special class of chiral molecules which consist of n ortho-fused aromatic rings
combining a helical topology with an extended π-conjugation [7–9]. Since the first
preparation of enantioenriched helicenes in 1956 [10], their chirality has essentially
been characterized through their very large optical rotation (OR) values, and their
intense and characteristic electronic circular dichroism (ECD). In more rare cases,
vibrational circular dichroism (VCD) and Raman optical activity (ROA) of helicenes
have been measured. More recently, strong interest has grown on the elucidation of
the chirality-related emission properties of helicenes. Indeed, helicene derivatives
can be regarded as helically shaped polycyclic aromatic hydrocarbons (PAHs);
they thus usually display organic semiconducting behavior and are efficient chiral
emitters. With the development of circularly polarized emission techniques, the CPL
J. Crassous (*)
Univ Rennes, CNRS, ISCR (Institut des Sciences Chimiques de Rennes) - UMR6226, Rennes,
France
e-mail: jeanne.crassous@univ-rennes1.fr
© 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_4
53
Circularly Polarized Luminescence
in Helicene and Helicenoid Derivatives
Jeanne Crassous
Abstract In this chapter, we discuss the circularly polarized luminescence (CPL) of
helicene and helicenoid derivatives. The organic helicenic derivatives are classified
according to the type of atom (heteroatom or carbon) incorporated within the
helical backbone. Transition-metal complexes and chiroptical devices incorporating
helicene derivatives and exhibiting CPL activity are also presented.
4.1 Introduction
Circularly polarized luminescence (CPL) is a fascinating property of many classes
of chiral emissive molecules. The well-known luminescence dissymmetry factor
(g lum ) as a measure of the degree of circular polarization of emitted light is defined
as g lum ¼ 2ΔI/I ¼ 2(I L À I R )/(I L + I R ), where I L and I R denote the left- and righthanded circularly polarized emission intensities, respectively. Various types of chiral
fluorescent conjugated organic molecules exhibiting CPL are known and generally
possess g lum values on the order of 10
À4
–10
À2 [1–6]. Among them, helicenes are a
special class of chiral molecules which consist of n ortho-fused aromatic rings
combining a helical topology with an extended π-conjugation [7–9]. Since the first
preparation of enantioenriched helicenes in 1956 [10], their chirality has essentially
been characterized through their very large optical rotation (OR) values, and their
intense and characteristic electronic circular dichroism (ECD). In more rare cases,
vibrational circular dichroism (VCD) and Raman optical activity (ROA) of helicenes
have been measured. More recently, strong interest has grown on the elucidation of
the chirality-related emission properties of helicenes. Indeed, helicene derivatives
can be regarded as helically shaped polycyclic aromatic hydrocarbons (PAHs);
they thus usually display organic semiconducting behavior and are efficient chiral
emitters. With the development of circularly polarized emission techniques, the CPL
J. Crassous (*)
Univ Rennes, CNRS, ISCR (Institut des Sciences Chimiques de Rennes) - UMR6226, Rennes,
France
e-mail: jeanne.crassous@univ-rennes1.fr
© 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_4
53