and negative ΔS for (M)3 [6]CH
à in addition to the weak signal near 420 nm with
opposite ΔS signs with respect to the 620-nm peak. The ΔS values can be
transformed to Δε values by Eq. 15.13. To evaluate the initial concentration of
3 [6]CH
à , the ε values of T n
T 1 absorption with the comparison method, which
gives the ε value at 660 nm to be (1.1 Æ 1.5) Â 10
4 M
À1 cm
À1 [11].
The transient absorption spectrum of
3 [6]CH
à in the 100–150 ns region measured
with an image-intensifier is shown in Fig. 15.5 (bottom), in which the T n
T 1
absorption peak appears at 650 nm [19], with weak peaks at 400 nm, in addition to
the 330-nm peak in the ultraviolet region. The average concentration of
3 [6]CH
à in
the 1–11 μs interval was evaluated as 1.3 Â 10
À6 M in this time regime from the
estimated ε 660 (¼ (1.1 Æ 1.5) Â 10
4 M
À1 cm
À1 ) value. Employing the
3 [6]CHÃ-concentration in the 1–11 μs interval, the CD spectrum in Δε is depicted, as shown
in Fig. 15.5 (middle). The main CD peak at 620 nm exhibits a positive sign for
(P)3 [6]CH
à and a negative sign for (M )3 [6]CH
à in a mirror image. For (P)3 [6]
CH
à , several CD peaks appear; i.e., negative 420-nm CD, positive 380-nm CD,
Fig. 15.5 (a) Anisotropy
(gà ¼ Δε/ε) factor and (b)
TRCD spectra accumulated
during 1–11 μs interval after
laser excitation of (P)- (red)
and (M )3
[6]CH
à (blue) in
toluene at RT monitored
with an image-intensifier.
Azimuth of retarder θ ¼ 15
.
(c) Transient absorption
spectrum of
3
[6]CH
à in
toluene at RT (reprinted
from Kuronuma et al. [11])
336
Y. Araki