Ox
+
-ZL crystal because DMP does not absorb light at the 495 nm excitation
wavelength used. It is shown as green line and bears an average fluorescence lifetime
of 1.71 ns. The decay of DMP, seen as red line in a DMP,Ox
+
-ZL crystal excited at
320 nm and observed at 470 nm, is more complex and has an average fluorescence
lifetime of 300 ps. The reason for this short lifetime is that energy transfer takes place
from excited DMP to Ox
+
. The reduction of the excited donor lifetime expectancy by
a factor of 6 means that 83% of the absorbed photons are transferred from excited
DMP to Ox
+ by means of FRET. Figure 29c reports on the second part of the
Luminescence dynamics, namely, the luminescence decay observed at different
position of a DMP,Ox
+
-ZL crystal, namely, outside of the crystal (d, yellow), at
the border at both sides (a, red), roughly at both phase boundaries DMP¦Ox
+ (b,
green), and in the middle (c, blue), upon excitation at 320 nm. The observation of the
emission was chosen above 660 nm to make sure that no DMP emission was
eventually mixed in. The yellow signal outside of the crystal is due to noise and
scattered photons. The red signal, observed at the border of the crystal, originates
from excited Ox
+ molecules that are very close to the DMP molecules. They have a
fast rise time and decay. The rise time is somewhat slower if we move further into the
crystal (green), and it is substantially delayed in the middle part of the crystal (blue).
The presence of a slow rise time and of a delayed decay shows that Ox
+
fluorescence
is excited via FRET through DMP. The spatial dependence of this effect beautifully
demonstrates the dynamics of the energy transfer and energy migration from the
border of the crystal to the center. The rise of the fluorescence intensity of an
acceptor excited via FRET by a donor can be well seen in a different experiment
made with Ox
+
,Py
+
-ZL composites similar to those shown in Fig. 26, where Py
+ is
the donor and Ox
+ the acceptor. This has been reported in Fig. 11 of [169]. The dyes
Ox
+ and Py
+ have been proven for being useful in many additional FRET experiments. We mention the transfer of electronic excitation energy between randomly
mixed dye molecules in the channels of zeolite [170] and optical spectroscopy
experiments on dye-ZL crystals organized as oriented monolayers [128], and we
⁄
ä
Fig. 29 (continued) profile on the left is observed when scanning the emission at 470 nm along the
crystal axis, upon excitation at 320 nm. That in the middle is observed when monitoring the
emission at 610 nm after excitation at 320 nm, while the profile on the right is seen when the
sample is excited at 490 nm. (b, c) show the luminescence decay of composites in a confocal
microscope excited with 1.2-ps pulses. (b) Decay observed as an average over the whole crystal.
Blue: Decay of the DMP fluorescence at 470 nm when a DMP-ZL sample is excited at 320 nm.
Green: Decay of the Ox
+ luminescence upon excitation at 495 nm and observation at 600 nm of a
DMP,Ox
+ -ZL composite. Red: Decay of the DMP luminescence observed at 470 nm when a DMP,
Ox
+ -ZL composite is excited at 320 nm. (c) Time- and space-resolved confocal microscopy results
for a DMP,Ox
+ -ZL composite. The decay of the Ox
+ emission is similar to that in (b) but with the
different regions indicated by different letters and colors (d, yellow; a, red; b, green; and c, blue).
The corresponding decay of the luminescence of Ox
+ (at λ ! 660 nm) when a DMP,Ox
+ -ZL
composite is excited at 320 nm at the positions indicated on the left [50]. Adapted with permission
from [50] Copyright Wiley VCH
Guests in Nanochannels of Zeolite L
55
+
-ZL crystal because DMP does not absorb light at the 495 nm excitation
wavelength used. It is shown as green line and bears an average fluorescence lifetime
of 1.71 ns. The decay of DMP, seen as red line in a DMP,Ox
+
-ZL crystal excited at
320 nm and observed at 470 nm, is more complex and has an average fluorescence
lifetime of 300 ps. The reason for this short lifetime is that energy transfer takes place
from excited DMP to Ox
+
. The reduction of the excited donor lifetime expectancy by
a factor of 6 means that 83% of the absorbed photons are transferred from excited
DMP to Ox
+ by means of FRET. Figure 29c reports on the second part of the
Luminescence dynamics, namely, the luminescence decay observed at different
position of a DMP,Ox
+
-ZL crystal, namely, outside of the crystal (d, yellow), at
the border at both sides (a, red), roughly at both phase boundaries DMP¦Ox
+ (b,
green), and in the middle (c, blue), upon excitation at 320 nm. The observation of the
emission was chosen above 660 nm to make sure that no DMP emission was
eventually mixed in. The yellow signal outside of the crystal is due to noise and
scattered photons. The red signal, observed at the border of the crystal, originates
from excited Ox
+ molecules that are very close to the DMP molecules. They have a
fast rise time and decay. The rise time is somewhat slower if we move further into the
crystal (green), and it is substantially delayed in the middle part of the crystal (blue).
The presence of a slow rise time and of a delayed decay shows that Ox
+
fluorescence
is excited via FRET through DMP. The spatial dependence of this effect beautifully
demonstrates the dynamics of the energy transfer and energy migration from the
border of the crystal to the center. The rise of the fluorescence intensity of an
acceptor excited via FRET by a donor can be well seen in a different experiment
made with Ox
+
,Py
+
-ZL composites similar to those shown in Fig. 26, where Py
+ is
the donor and Ox
+ the acceptor. This has been reported in Fig. 11 of [169]. The dyes
Ox
+ and Py
+ have been proven for being useful in many additional FRET experiments. We mention the transfer of electronic excitation energy between randomly
mixed dye molecules in the channels of zeolite [170] and optical spectroscopy
experiments on dye-ZL crystals organized as oriented monolayers [128], and we
⁄
ä
Fig. 29 (continued) profile on the left is observed when scanning the emission at 470 nm along the
crystal axis, upon excitation at 320 nm. That in the middle is observed when monitoring the
emission at 610 nm after excitation at 320 nm, while the profile on the right is seen when the
sample is excited at 490 nm. (b, c) show the luminescence decay of composites in a confocal
microscope excited with 1.2-ps pulses. (b) Decay observed as an average over the whole crystal.
Blue: Decay of the DMP fluorescence at 470 nm when a DMP-ZL sample is excited at 320 nm.
Green: Decay of the Ox
+ luminescence upon excitation at 495 nm and observation at 600 nm of a
DMP,Ox
+ -ZL composite. Red: Decay of the DMP luminescence observed at 470 nm when a DMP,
Ox
+ -ZL composite is excited at 320 nm. (c) Time- and space-resolved confocal microscopy results
for a DMP,Ox
+ -ZL composite. The decay of the Ox
+ emission is similar to that in (b) but with the
different regions indicated by different letters and colors (d, yellow; a, red; b, green; and c, blue).
The corresponding decay of the luminescence of Ox
+ (at λ ! 660 nm) when a DMP,Ox
+ -ZL
composite is excited at 320 nm at the positions indicated on the left [50]. Adapted with permission
from [50] Copyright Wiley VCH
Guests in Nanochannels of Zeolite L
55