Although the planar chiral molecules discussed above emit intense CPL in a
dilute solution, their fluorescence quantum yield is basically lowered in the solid
state due to the general aggregation-caused quenching. The problem of quenching
can be overcome by introducing Fréchet-type dendrons [50, 51] into the X-shaped
molecules [52]. Figure 3.17 shows the third-generation dendrimer 14, and the CPL
spectrum of the thin film. The Φ PL of 14 was estimated to be 0.65, which is almost
the same as the value of 0.66 observed in the dilute solution. This was because of the
X-shaped core being isolated by the dendrons. The CPL |g lum | value of 14 was
1.8 Â 10
–3 . A thin film emitting CPL with high intensity, high efficiency, and high
dissymmetry factor could be obtained because of the light-harvesting effect of the
benzene rings of the dendrimer.
Recently, catalytic system that enables chemoselective Sonogashira-Hagihara
coupling was developed [35]. The combination of Pd 2 (dba) 3 /P
t
Bu 3 reacted predominantly with Ar-Br instead of Ar-OTf; thus, 4,7,12-tribromo-15trifluoromethanesulfonyl[2.2]paracyclophane (Fig. 3.6) was converted to the
corresponding triyne (Fig. 3.18). This triyne could be used as a chiral building
block to obtain the X-shaped molecules 15, which consisted of heterogeneous
π-electron systems could be obtained. The optical properties were almost identical
to those of the X-shaped molecule 16, and they were excellent CPL emitters [53]. It
is possible to layer heterogeneous π-electron systems possessing various electronaccepting and electron-donating groups.
350
400
450
500
550
600
650
700
I
L –I
R / a.u.
Intensity / a.u.
Wavelength / nm
(R p )-5
(S p )-5
CPL
PL
D
Fig. 3.14 CPL and PL
spectra of (R p )- and (S p )-5 in
CHCl 3 (10 Â 10
–6
M)
3 Circularly Polarized Luminescence from Planar Chiral Compounds Based on. . .
43
dilute solution, their fluorescence quantum yield is basically lowered in the solid
state due to the general aggregation-caused quenching. The problem of quenching
can be overcome by introducing Fréchet-type dendrons [50, 51] into the X-shaped
molecules [52]. Figure 3.17 shows the third-generation dendrimer 14, and the CPL
spectrum of the thin film. The Φ PL of 14 was estimated to be 0.65, which is almost
the same as the value of 0.66 observed in the dilute solution. This was because of the
X-shaped core being isolated by the dendrons. The CPL |g lum | value of 14 was
1.8 Â 10
–3 . A thin film emitting CPL with high intensity, high efficiency, and high
dissymmetry factor could be obtained because of the light-harvesting effect of the
benzene rings of the dendrimer.
Recently, catalytic system that enables chemoselective Sonogashira-Hagihara
coupling was developed [35]. The combination of Pd 2 (dba) 3 /P
t
Bu 3 reacted predominantly with Ar-Br instead of Ar-OTf; thus, 4,7,12-tribromo-15trifluoromethanesulfonyl[2.2]paracyclophane (Fig. 3.6) was converted to the
corresponding triyne (Fig. 3.18). This triyne could be used as a chiral building
block to obtain the X-shaped molecules 15, which consisted of heterogeneous
π-electron systems could be obtained. The optical properties were almost identical
to those of the X-shaped molecule 16, and they were excellent CPL emitters [53]. It
is possible to layer heterogeneous π-electron systems possessing various electronaccepting and electron-donating groups.
350
400
450
500
550
600
650
700
I
L –I
R / a.u.
Intensity / a.u.
Wavelength / nm
(R p )-5
(S p )-5
CPL
PL
D
Fig. 3.14 CPL and PL
spectra of (R p )- and (S p )-5 in
CHCl 3 (10 Â 10
–6
M)
3 Circularly Polarized Luminescence from Planar Chiral Compounds Based on. . .
43