1.1 Porphyrins - Friedrich-Alexander-Universität Erlangen-Nürnberg

3.2.3.5 Cyclic Voltammetry
-1.6
5 μA
Discussion and Results 3
Also the electrochemical behavior of the novel system 53 was investigated in comparison to
precursor system 40 and methyl pyropheophorbide a Me-33. The voltammograms are
assorted Figure 25.
53
40
Me-33
-1.4 -1.2 -1.0 -0.8 -0.6 -0.4 E (V) 0.8 1.0 1.2 1.4 1.6 1.8
Figure 25. Cyclic voltammograms of 53, its precursor 40 and methyl pyropheophorbide a
Me-33 in CH2Cl2 solution. Dashed-dotted lines stand for the positions of the half-wave
potentials of TPP 15 112 representing a standard 5,10,15,20-tetraphenylporphyrin.
The measurements were performed in CH2Cl2 (c = 10 -3 M) using tetra-n-butyl ammonium
hexafluorophosphate (c = 0.1 M) as supporting electrolyte at 25 °C in a three electrodes
arrangement with a gold disc electrode (0.07 cm 2 ), a platinum wire as counter electrode and
a Ag/AgCl-electrode (3 M NaCl) as reference. As scan rate 50 mV/s was chosen and ferrocene
was added as internal standard with E(Fc/Fc + ) = 0.53 V (see also paragraph 6.1). The thus
resulting half-wave potentials are included in Table 8. 96
The voltammogram of 53 clearly shows that both, two-step oxidation as well as two-step
reduction, are fully reversible as it is also the case for non-annulated standard porphyrin
systems like e.g. 15. The obtained half-wave potentials (E½) in the cathodic region are shifted
by approx. 0.3 V to higher values compared to 40, a non-annulated precursor of 53, or to
59