9.3 CPL of Chirally Arranged Achiral Luminophores
Through Chiral Spacers
An achiral luminophore has an advantage with regard to the fluorescence efficiency
compared to a chirally distorted luminophore such as a helicene. A strategy to
provide a chiral environment on an achiral luminophore is the chiral arrangement
of two or more luminophores. When two luminophores are linked through a
chiral spacer, the luminophores take a chiral orientation. Then, the luminophores
interact each other, and the electronic state of a luminophore is chirally perturbed
by the other luminophore. Various skeletons providing chiral orientation have
been developed in the field of asymmetric catalysts. The most famous one is a
chiral binaphthyl moiety. A binaphthyl has axial chirality since the free rotation
about the bond linking the naphthyl rings is restricted due to the steric effect of
hydrogen atoms at the 8 and 8
0 positions. Thus, each naphthalene takes a chiral
orientation. Fujiki, Imai, and coworkers have developed CPL of simple and extended
binaphthyls 11–18 (Fig. 9.5) [19–27]. The CPL properties of the binaphthyl
derivatives depend on the dihedral angle of binaphthyl, the topology of the
neighboring groups, the position of binaphthyl linkage, and the π-extension of
the binaphthyl unit. The binaphthyl derivatives other than 14 (nonfluorescent)
and 17 (CPL-inactive) exhibited CPL with g lum values within the range of
(1.5–0.8) Â 10
À3 and with fluorescent quantum yields within the range of 15–25%.
O
O
N
N
O
H
O
O
O
N
N
OH
H
O
O
O
N
N
O
H
O
O
O
N
N
O
H
O
H
H
H
in CHCl 3
(M)-10
Fig. 9.4 CPL-active trimeric disk of the phthalhydrazide-functionalized [7]helicene-like
compound (M )-10
9 Circularly Polarized Luminescence of Chirally Arranged Achiral Organic. . .
201
Through Chiral Spacers
An achiral luminophore has an advantage with regard to the fluorescence efficiency
compared to a chirally distorted luminophore such as a helicene. A strategy to
provide a chiral environment on an achiral luminophore is the chiral arrangement
of two or more luminophores. When two luminophores are linked through a
chiral spacer, the luminophores take a chiral orientation. Then, the luminophores
interact each other, and the electronic state of a luminophore is chirally perturbed
by the other luminophore. Various skeletons providing chiral orientation have
been developed in the field of asymmetric catalysts. The most famous one is a
chiral binaphthyl moiety. A binaphthyl has axial chirality since the free rotation
about the bond linking the naphthyl rings is restricted due to the steric effect of
hydrogen atoms at the 8 and 8
0 positions. Thus, each naphthalene takes a chiral
orientation. Fujiki, Imai, and coworkers have developed CPL of simple and extended
binaphthyls 11–18 (Fig. 9.5) [19–27]. The CPL properties of the binaphthyl
derivatives depend on the dihedral angle of binaphthyl, the topology of the
neighboring groups, the position of binaphthyl linkage, and the π-extension of
the binaphthyl unit. The binaphthyl derivatives other than 14 (nonfluorescent)
and 17 (CPL-inactive) exhibited CPL with g lum values within the range of
(1.5–0.8) Â 10
À3 and with fluorescent quantum yields within the range of 15–25%.
O
O
N
N
O
H
O
O
O
N
N
OH
H
O
O
O
N
N
O
H
O
O
O
N
N
O
H
O
H
H
H
in CHCl 3
(M)-10
Fig. 9.4 CPL-active trimeric disk of the phthalhydrazide-functionalized [7]helicene-like
compound (M )-10
9 Circularly Polarized Luminescence of Chirally Arranged Achiral Organic. . .
201