1.1 Porphyrins - Friedrich-Alexander-Universität Erlangen-Nürnberg

3 Discussion and Results
3.2.8.2.7 Blocking the Free Amine in 92 via BOC-Protection
To mimic the behavior of the sensitizer coupled to a PDT relevant substrate, it was decided
to transform the free amine into the corresponding t-butyl carbamate. The reaction, the
introduction of the so-called BOC protective group, could be easily accomplished under
standard conditions like it is depicted in Scheme 57.
122
O
N
NH HN
N
+
NH 2
O O
O O O
- CO 2
- tBuOH
O
N
NH HN
Scheme 57. Transformation of amino cycloketo-porphyrin 92 into is BOC-protected form 93.
Applied conditions: CHCl3/MeOH, NEt3, rt, 24 h.
The reaction provided the desired target in sufficient amounts to do full characterization and
also photophysical investigations.
The NMR spectra of 93 prove the successful transformation as in the 1 H NMR spectrum the
amine signal at 4.01 ppm disappears and a new signal for the carbamate proton shows up at
6.82 ppm while the corresponding t-butyl signal is detected at 1.62 ppm. The remainder
signals are observed at nearly identical positions. The BOC protective group is also clearly
observed in 13 C NMR spectrum providing resonances at 153.1, 81.0 and 28.4 ppm,
respectively.
92 93
The UV/Vis spectra appears analog to the one of nitro compound 91 as the spectral positions
are identical. The extinction coefficients show up slightly lower (approx. 20 %). The same
analogies are found for the fluorescence spectra. A comparative illustration is given in Figure
49. The fluorescence quantum yield Φfl for 93 was determined to be 0.03 and therewith
equal to the one of nitro compound 91. Measurements concerning the generation of singlet
oxygen delivered a quantum yield ΦΔ of 0.80 being pretty close to the values found for
primal cycloketo-porphyrin system 53 (ΦΔ = 0.85) 96 and nitro compound 91 (ΦΔ = 0.84).
N
O
NH
O