R ¼ Im 1
h j * μ 0
j i • 0
h jm
! 1
j i
where |0> and |1> are the ground and excited states under consideration, Im stands
for the imaginary part of the subsequent function, and μ and m are the electric and
magnetic dipole moment operators, respectively. In the second part of the CPL
history, a few labs undertook the development of the technique: the same Dutch
school, mainly Dekkers and Osterhoof [2, 3] and in Israel Gafni and Steinberg [4]
improved the experimental schemes; Richardson, Riehl and Dekkers [5, 6] developed the theory of CPL and treated a few interesting prototypical cases, advocating
the contribution from fine theoretical chemists [7]; recently, physical chemists like
Spano and Yamagata [8] focused on the treatment of aggregates. We would also like
to mention the contributions of Parker et al. [9, 10] and Brittain [11]. However, it is
in the last part of the CPL history that lot of interest was aroused among spectroscopists and physical chemists. This was originated by to several factors: (a) the
availability of novel optical elements and new design or update of the Gafni–
Steinberg scheme [12–14], with the appearance of commercial apparatuses
[15, 16]; (b) the possibility to run quantum mechanical calculations [17–19]; and
(c) vivid interest from material scientists, among the others [20, 21]. The recent
advancement and expansion of the technique, which approximately started around
2010, is now contemplating each year about 200–300 papers reporting CPL spectra;
the literature to be cited is interesting and quite sizeable. We have no intention to be
exhaustive here, but rather we wish to cite, at the beginning, some recent review
articles, written in this last period covering several aspects and attempting at defining
general themes in the set of problems defined through the CPL technique.
A separate treatment, while considering CPL, can be deserved to lanthanide
complexes; we may refer to reviews on the subject, among the others [9, 10, 22,
23]; we will not describe their work, since it is outside the focus of the present
chapter and we are mostly interested in small organic molecules and polymers or
aggregates thereof. For this reason we will refer to the review of Sánchez-Carnerero
et al. [24], who presented the first rather exhaustive collection of CPL data on purely
organic molecules and concluded that the maximum values for the observed g factor,
namely the ratio of the difference in circularly polarized emitted intensities to the
total emitted intensities (g lum ¼ ΔI/I, ΔI ¼ (I L À I R ) and I ¼ (I L + I R )/2), be of the
order of 10
–2 . An updated systematic classification of the CPL data of organic
molecules was provided recently by Mori et al. [25]. In that report the molecules
were classified in five groups, namely ketones, paracyclophane-based molecules
endowed with planar chirality, axially chiral biaryls, helicenes/helicenoids, and
chiral boron-dipyrromethene (BODIPY) derivatives. For each one of the above
groups of molecules, the authors looked not only at the magnitude of the g lum
ratio, but also at the ratio g lum /g abs (g abs ¼ Δε/ε, ε ¼ molecular absorption
coefficient); that review article may be defined as the first effort to discover a
common motif in the scattered behaviors of CPL data, namely that the closer the
latter ratio is to 1, the more undistorted the excited state is from the ground state.
Another recent review-type work has been presented by Fujiki et al. [26]. It is also
worth mentioning here the recent perspective article by Kawai et al. [27], which, in
its brevity, has though the virtue of a general review paper, tackling the issue of
220
G. Longhi and S. Abbate
h j * μ 0
j i • 0
h jm
! 1
j i
where |0> and |1> are the ground and excited states under consideration, Im stands
for the imaginary part of the subsequent function, and μ and m are the electric and
magnetic dipole moment operators, respectively. In the second part of the CPL
history, a few labs undertook the development of the technique: the same Dutch
school, mainly Dekkers and Osterhoof [2, 3] and in Israel Gafni and Steinberg [4]
improved the experimental schemes; Richardson, Riehl and Dekkers [5, 6] developed the theory of CPL and treated a few interesting prototypical cases, advocating
the contribution from fine theoretical chemists [7]; recently, physical chemists like
Spano and Yamagata [8] focused on the treatment of aggregates. We would also like
to mention the contributions of Parker et al. [9, 10] and Brittain [11]. However, it is
in the last part of the CPL history that lot of interest was aroused among spectroscopists and physical chemists. This was originated by to several factors: (a) the
availability of novel optical elements and new design or update of the Gafni–
Steinberg scheme [12–14], with the appearance of commercial apparatuses
[15, 16]; (b) the possibility to run quantum mechanical calculations [17–19]; and
(c) vivid interest from material scientists, among the others [20, 21]. The recent
advancement and expansion of the technique, which approximately started around
2010, is now contemplating each year about 200–300 papers reporting CPL spectra;
the literature to be cited is interesting and quite sizeable. We have no intention to be
exhaustive here, but rather we wish to cite, at the beginning, some recent review
articles, written in this last period covering several aspects and attempting at defining
general themes in the set of problems defined through the CPL technique.
A separate treatment, while considering CPL, can be deserved to lanthanide
complexes; we may refer to reviews on the subject, among the others [9, 10, 22,
23]; we will not describe their work, since it is outside the focus of the present
chapter and we are mostly interested in small organic molecules and polymers or
aggregates thereof. For this reason we will refer to the review of Sánchez-Carnerero
et al. [24], who presented the first rather exhaustive collection of CPL data on purely
organic molecules and concluded that the maximum values for the observed g factor,
namely the ratio of the difference in circularly polarized emitted intensities to the
total emitted intensities (g lum ¼ ΔI/I, ΔI ¼ (I L À I R ) and I ¼ (I L + I R )/2), be of the
order of 10
–2 . An updated systematic classification of the CPL data of organic
molecules was provided recently by Mori et al. [25]. In that report the molecules
were classified in five groups, namely ketones, paracyclophane-based molecules
endowed with planar chirality, axially chiral biaryls, helicenes/helicenoids, and
chiral boron-dipyrromethene (BODIPY) derivatives. For each one of the above
groups of molecules, the authors looked not only at the magnitude of the g lum
ratio, but also at the ratio g lum /g abs (g abs ¼ Δε/ε, ε ¼ molecular absorption
coefficient); that review article may be defined as the first effort to discover a
common motif in the scattered behaviors of CPL data, namely that the closer the
latter ratio is to 1, the more undistorted the excited state is from the ground state.
Another recent review-type work has been presented by Fujiki et al. [26]. It is also
worth mentioning here the recent perspective article by Kawai et al. [27], which, in
its brevity, has though the virtue of a general review paper, tackling the issue of
220
G. Longhi and S. Abbate