1.1 Porphyrins - Friedrich-Alexander-Universität Erlangen-Nürnberg

3 Discussion and Results
3.2.6.5.4 Photophysical Measurements
Also these data were gathered in cooperation with the group of Prof. Dr. B. RÖDER at Berlin.
The data obtained by steady-state fluorescence spectroscopy (see Figure 35) is very
consistent with the UV/Vis data as all compounds show a significant red-shift (λmax
determined at 450 nm is 709 nm and 701 nm for 53 and 57, respectively, compared to
778 nm for 58). Like their extinction coefficients, also their fluorescence quantum yields Φfl
are significantly lowered being determined 0.03 for 53 and 57 and 0.05 for 58 compared to
0.11 for TPP 15. 96
normalized fluorescence
88
1.0
0.8
0.6
0.4
0.2
0
600 700 800 900 λ [nm] 1000
Figure 35. Steady-state fluorescence
spectra of 53, 57 and 58 at an
excitation wavelength of 450 nm.
As already presented for 53, decay associated fluorescence spectroscopy reveals that also 57
and 58 are existing as discriminable tautomeric structures with different fluorescence life-
times and varying populations of the different species as Table 15 depicts. Obviously, the
ratio between the major tautomers A and B decreases with increasing level of distortion.
Table 15. Fluorescence life-times τ and proportions of present fluorophores P obtained from
DAFS analysis on 53, 57 and 58 in DMF. Excitation at 532 nm.
τA ± 0.02 a
τB ± 0.1 a τi ± 1 a,b P(A) ± 0.03 P(B) ± 0.02 P(i) ± 0.01 b Torsion c
53 1.15 3.3 10 0.90 0.09 0.01 35°
57 1.2 3.3 10 0.84 0.14 0.02 44°
58 1.6 3.6 10 0.75 0.24 0.01 75°
a
values given in ns a
b
“i” refers to an impurity present in the solution which cannot be excluded from DAFS analysis
c meso α
dihedral angle between the C -C -bond and the plane of the tethered phenyl substituent (see also Figure 32, p. 84)
Furthermore, ps-TAS was applied and singlet oxygen luminescence measurements were
conducted to obtain quantum yields for ISC, IC and 1 O2 generation (ΦΔ), respectively. The
results are summarized in Table 16.
53
57
58