1.1 Porphyrins - Friedrich-Alexander-Universität Erlangen-Nürnberg

3 Discussion and Results
Like Figure 20 depicts, the compound is not in compliance with KASHA’s rule 105 as the spectral
position and the shape of the fluorescence spectra depend on the excitation wavelength.
Time-dependent fluorescence spectroscopy in terms of time correlated single photon
counting (TCSPC) at 532 nm excitation wavelength elucidated a tri-exponential fluorescence
decay meaning that apparently three different fluorophores were present in the solution
under investigation. That can generally have many reasons, since it could be dealt with
impurities, different present conformations or even specific aggregates, like dimers. In order
to get a global analysis on the fluorescence kinetics, decay associated fluorescence
spectroscopy (DAFS) 106 was applied. The analysis 107 furnished the data on those three
components being displayed in Table 6.
Table 6. Results from DAFS analysis concerning fluorescence life-times τ and proportions P
of fluorophores A, B and C in the solution of seemingly pure 53. Excitation at 532 nm.
54
τA [ns] ± 0.02 τB [ns] ± 0.1 τC [ns] ± 1 P(A) ± 0.03 P(B) ± 0.02 P(C) ± 0.01
1.15 3.3 10 0.90 0.09 0.01
Further analysis on the obtained data made a correlation between the obtained DAFS
spectra and the initially recorded steady-state fluorescence spectrum possible. 107 Thus, the
original spectrum was split into three spectra representing the fluorescence spectra of the
contributing components A, B and C like it is shown in Figure 21.
amplitude
0.18
0.16
0.14
0.12
0.10
0.08
0.06
0.04
0.02
0
A A
B B
C C
sum sum
steady-state original exp.
700 770 λ [nm] 840
Figure 21. Steady-state and DAF spectra correlated. Excitation wavelength: 532 nm.