enhanced phosphorescence lifetime even at room temperature for 9-ethylcarbazole,
which tightly fits into the ZL channels. They reported dimer formation for anthracene and for naphthalene, as observed by excimer emission. The photo-physics of
anthracene and naphthalene in ZL was observed to be remarkably different from that
in solution and also different from that in large-pore faujasite zeolites where the
framework exerts only weak conformational control over the guest molecules
[177]. More attention has been devoted to the influence of co-cations on Brönsted
acidity and its impact on luminescence properties, as will be discussed in Sect. 7.3.
7.1 Absorption and Luminescence Spectra of Organic
Guest-ZL Composites
The conformational control of the ZL framework over the guest molecules leads to
enhanced luminescence yields for guests if conformational flexibility is responsible
for deactivation pathways [14]. The shape of the absorption spectra is often less
influenced by the host than one might perhaps expect. Figure 15 illustrates the
microscopically detailed picture of tb-DXP inside of the ZL channels, as established
using different experimental techniques and DFT modeling. This is an ideal situation
for a comparison of the absorption spectra of the perylene dyes tb-DXP (blue),
tb-DXT (green), and tb-DXQ in solution with the spectra of the corresponding
dye-ZL composites. We present it in Fig. 17. The finding that the vibronic structure,
known to be characteristic for perylene dyes in solution, Fig. 17a), is also present in
the ZL composites, Fig. 17b, reflecting an observation valid for many other dye-ZL
composites. We therefore discuss it in more detail by marking and comparing the
positions of the 0–0
0 , 0–1
0 , 0–2
0 , and 0–3
0 transitions, which can be identified easily
in spectra of diluted samples of these dyes, both in solution (Fig. 17a) and in the
dye-ZL samples (Fig. 17b). The broadening of the spectra of the dye-ZL composites
with respect to the solution spectra is smaller than one might expect. The uncertainty
of the band positions is small for the 0–0
0 transition. It increases with increasing
energy because the bands are not fully resolved. It also increases from tb-DXP to
tb-DXT to tb-DXQ but it is not larger in the dye-ZL composites. Their energy can be
sufficiently well determined to justify the conclusions presented below. We should
add that the same is seen for all 11 PDIs reported in [16]. The numerical values of the
positions and of the energy differences ΔΕ[ν
0
À (ν
0 + 1)] between the 0Àν
0 and the
0À(ν
0 + 1) transitions are reported in Table 5. The comparison of the spectra of the
dyes in solution and in ZL reveals that the broadening is small, that the shift
of the 0–0
0 transition is small, and that the vibronic pattern seen in solution is
preserved for the three dyes after intercalation into the nanochannels of ZL. This is
remarkable. The data collected in Table 5 allow the conclusion that the energy
difference ΔE[ν
0
À(ν
0 + 1)] between the 0Àν
0 and the 0À(ν
0 + 1) transitions is the
same in solution and in ZL, within the experimental uncertainty. These observations
signify that the part of the molecules responsible for the S 0 ! S 1 (π–πÃ) is not
34
G. Calzaferri
which tightly fits into the ZL channels. They reported dimer formation for anthracene and for naphthalene, as observed by excimer emission. The photo-physics of
anthracene and naphthalene in ZL was observed to be remarkably different from that
in solution and also different from that in large-pore faujasite zeolites where the
framework exerts only weak conformational control over the guest molecules
[177]. More attention has been devoted to the influence of co-cations on Brönsted
acidity and its impact on luminescence properties, as will be discussed in Sect. 7.3.
7.1 Absorption and Luminescence Spectra of Organic
Guest-ZL Composites
The conformational control of the ZL framework over the guest molecules leads to
enhanced luminescence yields for guests if conformational flexibility is responsible
for deactivation pathways [14]. The shape of the absorption spectra is often less
influenced by the host than one might perhaps expect. Figure 15 illustrates the
microscopically detailed picture of tb-DXP inside of the ZL channels, as established
using different experimental techniques and DFT modeling. This is an ideal situation
for a comparison of the absorption spectra of the perylene dyes tb-DXP (blue),
tb-DXT (green), and tb-DXQ in solution with the spectra of the corresponding
dye-ZL composites. We present it in Fig. 17. The finding that the vibronic structure,
known to be characteristic for perylene dyes in solution, Fig. 17a), is also present in
the ZL composites, Fig. 17b, reflecting an observation valid for many other dye-ZL
composites. We therefore discuss it in more detail by marking and comparing the
positions of the 0–0
0 , 0–1
0 , 0–2
0 , and 0–3
0 transitions, which can be identified easily
in spectra of diluted samples of these dyes, both in solution (Fig. 17a) and in the
dye-ZL samples (Fig. 17b). The broadening of the spectra of the dye-ZL composites
with respect to the solution spectra is smaller than one might expect. The uncertainty
of the band positions is small for the 0–0
0 transition. It increases with increasing
energy because the bands are not fully resolved. It also increases from tb-DXP to
tb-DXT to tb-DXQ but it is not larger in the dye-ZL composites. Their energy can be
sufficiently well determined to justify the conclusions presented below. We should
add that the same is seen for all 11 PDIs reported in [16]. The numerical values of the
positions and of the energy differences ΔΕ[ν
0
À (ν
0 + 1)] between the 0Àν
0 and the
0À(ν
0 + 1) transitions are reported in Table 5. The comparison of the spectra of the
dyes in solution and in ZL reveals that the broadening is small, that the shift
of the 0–0
0 transition is small, and that the vibronic pattern seen in solution is
preserved for the three dyes after intercalation into the nanochannels of ZL. This is
remarkable. The data collected in Table 5 allow the conclusion that the energy
difference ΔE[ν
0
À(ν
0 + 1)] between the 0Àν
0 and the 0À(ν
0 + 1) transitions is the
same in solution and in ZL, within the experimental uncertainty. These observations
signify that the part of the molecules responsible for the S 0 ! S 1 (π–πÃ) is not
34
G. Calzaferri