Δε ¼ ε L À ε R
ð14:1Þ
ΔI ¼ I L À I R
ð14:2Þ
ε extinction coefficient for left- (L ) and right-handed (R) circularly polarized light,
I fluorescence intensity of left- (L) and right-handed (R) circularly polarized light
CD and CPL signals are generally normalized by the averaged absorbance and the
averaged fluorescence intensity for a sample, and are expressed in terms of g abs and
g lum values:
CD : g abs ¼
2 ε L À ε R
ð
Þ
ε L þ ε R
ð14:3Þ
CPL : g lum ¼
2 I L À I R
ð
Þ
I L þ I R
ð14:4Þ
Both g abs and g lum take values between À2 and 2. When only left-handed
circularly polarized light is absorbed or emitted, the g value is +2, while when
only right-handed circularly polarized light is absorbed or emitted, it is À2.
The vertical axis in a CD or CPL spectrum is traditionally the ellipse angle θ
[mdeg]. Figure 14.2 shows the overall polarization trajectory for a mixture of leftand right-handed circularly polarized light. If there is a difference in the intensity of
the left- and right-handed polarized light, the overall trajectory is ellipse.
θ
Left-handed circularly
polarized light
Right-handed circularly
polarized light
Fig. 14.2 Ellipse angle (θ) for CD and CPL signals
14 Principles and Applications of Circularly Polarized Luminescence. . .
311