camphorquinone is predicted to be smaller because the molecule has a rigid structure. This is supported by the fact that although CD and CPL spectra associated with
n–πà transitions in carbonyl groups have been observed for both camphor and
camphorquinone, g abs and g lum for camphorquinone are closer than those for
camphor [2].
14.5.2 Lanthanoid Complexes
Figure 14.8 shows CPL and fluorescence spectra of the lanthanoid complex
(3-(trifluoromethylhydroxymethylene)-(+)-camphorate: Eu(facam) 3 ). Such complexes are widely used as LED materials because of their strong sharp emissions.
They also potentially possess an ability in applications such as 3D displays and
security markers. The synthesis and evaluation of lanthanoid complexes exhibiting
CPL are underway. It is generally known that forbidden transitions such as n–πÃ, d–
d, and f–f produce a larger g lum than allowed transitions such as π–πà [3]. Muller
et al. reported europium complexes with a large g lum of +1.38 [4]. In Fig. 14.8, it can
be seen that Eu(facam) 3 also exhibits a large g lum . It should be noted that
(+)-Camphor:
(-)-Camphor:
( )-Camphor:
(+)-Camphor
0
1
250
750
400 500 600
Wavelength [nm]
-2000
2000
CD [mdeg]
-0.1
0.1
0
gabs
0
0
0.1
g
lum
-0.02
0.02
-4
CPL [mdeg]
4
Ex wavelength: 280 nm
g
lum
-0.05
0.05
0
0.3
-40
CPL [mdeg]
40
Ex wavelength: 440 nm
CD/Abs
Wavelength [nm]
-400
400
CD [mdeg]
-0.05
0.05
0
0
250
650
400
500
2
0
g
abs
(1R)-(-)-Camphorquinone
(1R)-(-)-Camphorquinone:
(1S)-(+)-Camphorquinone:
CD/Abs
CPL/FL
CPL/FL
Abs
FL [Arb. Unit]
Abs
FL [Arb. Unit]
(a)
(b)
Fig. 14.7 CD, CPL, absorption, and fluorescence spectra of camphor (a) and camphorquinone (b)
316
S. Suzuki