Principles of Fluorescence Spectroscopy

254 DYNAMICS OF SOLVENT AND SPECTRAL RELAXATION
Figure 7.29. Time-resolved emission spectra of ASM encapsulated
C102. Top, fluorescence upconversion. Bottom, TCSPC. Revised and
reprinted with permission from [80]. Copyright © 2002, American
Chemical Society. Courtesy of Dr. Edward W. Castner, Jr. from the
Rutgers University, NJ.
an additional rate of deactivation, resulting in more rapid
intensity decays for BABP than for BABAPH (Figure 7.32,
lower panel).
The TRES were also used to determine the timedependent
center of gravity (ν cg (t)) and the time-dependent
half width (∆ν cg (t)). The results of least-squares fitting of
the TRES line shapes are shown in Figure 7.32. The dramatic
difference in spectral shape between BABP and
BABAPH is seen in the middle panel. The spectral width of
the restrained analogue BABP is independent of time,
whereas BABAPH shows an increase in spectral width. The
data are consistent with rotation of the dibutylamino group
in BABP to allow a larger charge separation than in
BABAPH. The larger charge separation results in a new
Figure 7.30. Hemicyanine dyes 2-(sulfonatobutyl)-7-(dibutylamino)-
2-azaphenanthrene (BABAPH) and 1-(sulfonatobutyl)-4-[4'-(dibutylamino)phenyl]pyridine
(BABP). Reprinted with permission from
[81]. Copyright © 1996, American Chemical Society.
Figure 7.31. Normalized time-resolved emission fluorescence
spectra of BABAPH and BAPH in butanol, 25°C, at time delays
of 20, 50, 150, and 2000 ps after excitation (from right to left).
The data are fitted by the log-normal spectral-shape functions.
Reprinted with permission from [81]. Copyright © 1996,
American Chemical Society.
species emitting at longer wavelengths, and thus the
increase in spectral half width of BABAPH. In this case the
TRES provided an explanation for the different spectral
shifts displayed by these similar molecules.