transitions involving the naphthyl groups in 5 and 6 were observed at approximately
270 and 360 nm, respectively. The signs of the CPL and the first Cotton CD band of
(R)-5 are both positive (+). Although the CD spectrum of (R,R)-6 is similar to that of
(R)-5, a weak negative (À) Cotton band was observed at the longest-wavelength
edge in the spectrum of (R,R)-6. Because the CPL sign of (R,R)-6 is negative (À),
this weak negative (À) Cotton CD band may be responsible for the negative (À) sign
of the CPL band. The |g CD | value at the first Cotton band (λ CD ¼ 330 nm) of 5 was
determined to be about 4.2 Â 10
–3 ; on the other hand, the |g CD | value of 6 at the first
Cotton CD band (λ CD ¼ 341 nm) is about 2.5 Â 10
–4 , which is smaller than that of
5 by a factor of 17. Since the dihedral angles of the binaphthyl units in 5 and 6 are
fixed, the opposite CD and CPL signs observed for (R)-5 and (R,R)-6, despite having
the same axial chirality, are due to the effects of the neighboring chiral binaphthyl
units in (R,R)-6.
In conclusion, the CPLs of chiral binaphthyl fluorophores can be controlled by
the number of neighboring chiral binaphthyl units, that is, by the effects of the
neighboring binaphthyl units.
2.5 Dependence of the Circularly Polarized Luminescence
(CPL) from Binaphthyl Units on External
Environmental Factors [24]
In Sects. 2.2 and 2.4, the CPL signs of chiral binaphthyl luminophores with the same
axial chirality were reported to be controllable by tuning the dihedral angle of the
binaphthyl unit and by employing the neighboring group effect between fluorescent
(a)
(b)
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
-40
-30
-20
-10
0
10
20
250 300 350 400 450 500
Absorbance
g
e
d
m
/
D
C
Wavelength / nm
-20
-10
0
10
20
330
340
350
360
g
e
d
m
/
D
C
Wavelength / nm
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
-40
-20
0
20
40
250 300 350 400 450 500
Absorbance
g
e
d
m
/
D
C
Wavelength / nm
-20
-10
0
10
20
330
340
350
360
g
e
d
m
/
D
C
Wavelength / nm
Fig. 2.10 CD (upper) and UV-Vis absorption (lower) spectra for (a) (R)-5 (red) and (S)-5 (black)
and for (b) (R,R)-6 (red) (S,S)-6 (black) in CHCl 3 (1.0 Â 10
À5 and (insets) 1.0 Â 10
À4
M)
18
Y. Imai
270 and 360 nm, respectively. The signs of the CPL and the first Cotton CD band of
(R)-5 are both positive (+). Although the CD spectrum of (R,R)-6 is similar to that of
(R)-5, a weak negative (À) Cotton band was observed at the longest-wavelength
edge in the spectrum of (R,R)-6. Because the CPL sign of (R,R)-6 is negative (À),
this weak negative (À) Cotton CD band may be responsible for the negative (À) sign
of the CPL band. The |g CD | value at the first Cotton band (λ CD ¼ 330 nm) of 5 was
determined to be about 4.2 Â 10
–3 ; on the other hand, the |g CD | value of 6 at the first
Cotton CD band (λ CD ¼ 341 nm) is about 2.5 Â 10
–4 , which is smaller than that of
5 by a factor of 17. Since the dihedral angles of the binaphthyl units in 5 and 6 are
fixed, the opposite CD and CPL signs observed for (R)-5 and (R,R)-6, despite having
the same axial chirality, are due to the effects of the neighboring chiral binaphthyl
units in (R,R)-6.
In conclusion, the CPLs of chiral binaphthyl fluorophores can be controlled by
the number of neighboring chiral binaphthyl units, that is, by the effects of the
neighboring binaphthyl units.
2.5 Dependence of the Circularly Polarized Luminescence
(CPL) from Binaphthyl Units on External
Environmental Factors [24]
In Sects. 2.2 and 2.4, the CPL signs of chiral binaphthyl luminophores with the same
axial chirality were reported to be controllable by tuning the dihedral angle of the
binaphthyl unit and by employing the neighboring group effect between fluorescent
(a)
(b)
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
-40
-30
-20
-10
0
10
20
250 300 350 400 450 500
Absorbance
g
e
d
m
/
D
C
Wavelength / nm
-20
-10
0
10
20
330
340
350
360
g
e
d
m
/
D
C
Wavelength / nm
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
-40
-20
0
20
40
250 300 350 400 450 500
Absorbance
g
e
d
m
/
D
C
Wavelength / nm
-20
-10
0
10
20
330
340
350
360
g
e
d
m
/
D
C
Wavelength / nm
Fig. 2.10 CD (upper) and UV-Vis absorption (lower) spectra for (a) (R)-5 (red) and (S)-5 (black)
and for (b) (R,R)-6 (red) (S,S)-6 (black) in CHCl 3 (1.0 Â 10
À5 and (insets) 1.0 Â 10
À4
M)
18
Y. Imai