In Fig. 15.4, the CD spectrum of (M )-[6]carbohelicene ((M)-[6]CH) by our setup
is presented. (M )-[6]CH shows negative CD signal at 327 nm [18]. Note that
negative CD signal increased when the smaller θ-value was set. The increase in
S CD was proportional to the (sin(2θ))
À1 , as suggested in Eq. 15.13. Furthermore,
signals shown in the top part of Fig. 15.4 converged to the CD spectrum measured by
conventional CD polarimeter, within experimental error. This finding allows us to
obtain CD signals without lock-in detection by PEM usage.
At the end of this section, let us briefly comment on the circular birefringence
(CB) contribution on this CD measurement. Knowledge of the CB contribution is
needed for observation in CD measurements with elliptically polarized light
[14, 19]. Here, we described the CB signal by Jones calculus to give the zerothorder picture of this issue.
CB is described by the following Jones matrix:
M CB ¼
cos χ
sin χ
À sin χ cos χ
,
ð15:16Þ
where χ is the product of sample thickness (l ) and the phase shift due to CB, defined
by the asymmetric refractive index of media as
Fig. 15.4 Circular
dichroism spectra of [6]
helicene in toluene obtained
by our apparatus. (Top) θdependence of S CD . Inset:
CD intensity at 327 nm
plotted against (sin (2θ))
À1
.
(Bottom) CD spectrum by
our apparatus. CD spectrum
obtained by J-820 is also
shown for comparison
334
Y. Araki
is presented. (M )-[6]CH shows negative CD signal at 327 nm [18]. Note that
negative CD signal increased when the smaller θ-value was set. The increase in
S CD was proportional to the (sin(2θ))
À1 , as suggested in Eq. 15.13. Furthermore,
signals shown in the top part of Fig. 15.4 converged to the CD spectrum measured by
conventional CD polarimeter, within experimental error. This finding allows us to
obtain CD signals without lock-in detection by PEM usage.
At the end of this section, let us briefly comment on the circular birefringence
(CB) contribution on this CD measurement. Knowledge of the CB contribution is
needed for observation in CD measurements with elliptically polarized light
[14, 19]. Here, we described the CB signal by Jones calculus to give the zerothorder picture of this issue.
CB is described by the following Jones matrix:
M CB ¼
cos χ
sin χ
À sin χ cos χ
,
ð15:16Þ
where χ is the product of sample thickness (l ) and the phase shift due to CB, defined
by the asymmetric refractive index of media as
Fig. 15.4 Circular
dichroism spectra of [6]
helicene in toluene obtained
by our apparatus. (Top) θdependence of S CD . Inset:
CD intensity at 327 nm
plotted against (sin (2θ))
À1
.
(Bottom) CD spectrum by
our apparatus. CD spectrum
obtained by J-820 is also
shown for comparison
334
Y. Araki