1.1 Porphyrins - Friedrich-Alexander-Universität Erlangen-Nürnberg

3 Discussion and Results
3.2.6.5 Comparative Studies
Since the characterization data of cycloketo-porphyrin systems 53, 57 and 58 is very closely
related to each other, they should be compared concerning not only basic characterization
data but also in terms of their photophysical and electrochemical properties. Before we go
into that matter, it shall again be started with theoretical aspects and visualizations based on
computational studies.
3.2.6.5.1 Computer-Assisted Simulations
To illustrate the effects of the implemented changes from 53 over 57 to 58 minimized
structures were calculated on the PM3 level being shown in Figure 32. 96,99
Figure 32. Minimum structures of 53, 57 and 58 (left to right) computed on the PM3 level
with given angular degrees for the dihedral angle between the Cmeso-Cα bond within the
porphyrin and the plane of the phenyl substituent.
Obviously, diminishing the steric demands of the tethered phenyl ring by going from 53 to
57 and shortening the tether itself, as done by going further to 58, force the annulated
phenyl ring to tilt further towards the porphyrin plane. This effect is most pronounced in 58
as then the phenyl ring becomes nearly coplanar with the porphyrin macrocycle. The more
pronounced rotation is thereby accompanied by a greater bending of the porphyrin core –
both cis standing phenyl substituents are pushed out of plane (see also Figure 14, p. 43).
Form the structural point of view, this should result in changes of the rotational barriers for
the non-tethered phenyl substituents. That effect is providing for example the already
presented bad resolution in the arylic areas of the 1 H-NMR spectra for 53 and 57.
From an electronic point of view, the orbital shapes and coefficients as well as the
corresponding energy levels will be affected as the porphyrin’s π-system will be more and
more “extended” as the tethered phenyl substituent comes into coplanarity. Therewith the
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