1.1 Porphyrins - Friedrich-Alexander-Universität Erlangen-Nürnberg

4 Summary
As the characterization data showed, the systems contain a distorted π-system arising from
the structural features being analogous to those already known for dodeca-substituted
porphyrins. But in contrast, the ones under investigation here turned out to be outstandingly
stable in configuration, as VT NMR spectroscopy demonstrated, and therewith represent
stable inherently chiral systems. The racemic mixtures which arose from synthesis have been
resolvable by chiral HPLC so that it was possible to characterize the individual enantiomers
by CD spectroscopy in cooperation with the group of G. BRINGMANN. Thus, for the first time,
we were able to describe stable inherently chiral porphyrin systems whose chirality is due to
a distorted π-system.
Via temperature-dependent NMR spectroscopy, it was also possible to show that the
lowering of symmetry is leading to the presence of distinguishable tautomers within mono-
exocyclic cycloketo-porphyrin system 53. Interestingly, those tautomers turned out to be
differentiable by photophysical means. So, in cooperation with the group of B. RÖDER, a novel
spectroscopic methodology for the detection and characterization of tautomeric porphyrin
structures could be developed.
Furthermore, the conducted photophysical experiments showed that the structural
elements and the thus arising deviation from planarity within the π-system is leading to an
enhanced spin-orbit-coupling providing a high intersystem crossing probability and hence,
an efficient excitation into triplet states. It was shown further on that the excitation energy
can be transferred onto present triplet oxygen nearly quantitatively and it was
demonstrated that the corresponding performance of the systems can be effectively tuned
via variations in the architecture of the exocycle as well as by degree and regiochemistry of
poly-annulation. Thus, novel singlet oxygen generators were made accessible captivating
through their high stability and outstanding quantum yields. Such systems are of great
interest for hygiene applications (e.g. for detoxification of water or air) and also for
medicinal means (foremost for applications in terms of the photodynamic therapy of cancer)
as, in comparison to pheophorbides, they exhibit a far higher stability, a better solubility and
an increased efficiency.
Also corresponding metal complexes (e.g. In(III)-53) and coupleable derivatives with
additional amino functionality (92) were made accessible without significant changes in the
photophysical performance. Those systems allowed investigations on completely novel
concepts of application. For example, it has been shown that the FÖRSTER resonance energy
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