1.1 Porphyrins - Friedrich-Alexander-Universität Erlangen-Nürnberg

O
N
NH HN
N
Discussion and Results 3
This process would allow the utilization of light of different wavelengths since the excitation
could then be accomplished indirectly via the donor dye and FRET and still directly via the
acceptor itself. This would not only broaden the “active window” for excitation but also
provide the possibility to tune the wavelength for excitation without the need to change the
sensitizer (=acceptor) in structure but by selection of an appropriate donor. This can lead to
an improved performance of PDT systems and also to applications in detoxification devices
for purification of air or water.
To clarify, whether the concept could be working, a model compound has to be designed in
which two photoactive dyes are brought into close proximity by a covalent linkage. As the
two different photosensitizer classes used within this thesis represent a carboxylic acid
derivative (pyropheophorbide a 33) and an amine (cycloketo-porphyrin 92) it seemed
obvious to simply try to couple both to obtain a conjugate.
3.2.9.2 Approaching a Novel Photosensitizing Systems by Conjugation of Amino
O
N
NH HN
N
Cycloketo-Porphyrin 92 and Pyropheophorbide a 33
The coupling reaction to obtain the desired two-dye conjugate was conducted under
standard condition utilizing the carbodiimide method. Both dyes were reacted with 1-ethyl-
3-(3-dimethylaminopropyl)-carbodiimide (EDC) assisted by N-hydroxysuccinimid (NHS) and
N,N-4-dimethylaminopyridine (DMAP) in DMF like it is shown in Scheme 59.
+
NH 2
HO
O
N
O
N
H N
H
N
92 33 94
HN
O
N
O
N
H N
H
N
Scheme 59. Formation of two-dye conjugate 94 from monomeric photosensitizers 33 and
92. Applied conditions: 1. EDC, NHS, DMAP (catalytic) in DMF, rt, 24 h, 2. add. EDC and 92, rt,
24 h.
The reaction proceeded well to give conjugate 94 in good isolated yield (69 % based on 33)
as pure and stable compound with a molecular weight of 1368.75 g·mol -1 providing a single
125