1.1 Porphyrins - Friedrich-Alexander-Universität Erlangen-Nürnberg

normalized fluorescence
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Discussion and Results 3
A special feature of those spectra is represented by the appearance of split SORET bands
observable as shouldered peaks in the spectra of 71 (462/483 nm) and of 68 & 70
(451/468 nm) while an almost separated band is detectable for 67 & 69 (454/490 nm and
455/489 nm). This seems to be again reflecting the regiochemistry as the spectral distance
between those two absorption is equivalent for corresponding pairs. The diagonal
positioning of the exocycles, providing the largest spectral distance of those two bands,
seems to be somehow special, as those spectra show the SORET band of lowest wavelength
(451 nm) but also the most red-shifted Q-band (731 nm). Thus, it can be concluded, that this
diagonal coupling of two exocyclic ketone moieties results in different perturbations of the
first and higher excited singlet states. That means, the S0 → S1 energy gap decreases
(bathochromic shift of Q-bands) whereas the energy difference between the ground state
and Sn states becomes bigger (hypsochromic shift of at least parts of the SORET region).
3.2.7.5 Photophysical Data
These data were obtained in cooperation with the group of Prof. Dr. B. RÖDER at Berlin. The
steady-state fluorescence spectra being depicted in Figure 40 are in good agreement with
the previously presented absorption spectra. The fluorescence maxima are detected at
810 nm for 71, at 775 nm 68 and 774 nm for 70, respectively, and at 731 nm for both 67 and
69 (all upon excitation at 532 nm). The obtained spectra of the investigated compounds
thereby not only show different bathochromic shifts but also different shapes. For 68, 70
and 71, the bands appear much broader than for the other two compounds being consistent
with the corresponding band-shapes of the highest Q-bands. Additionally, for those latter
ones, a vibronic shoulder at higher wavelengths is observed whereas that could not be
resolved for 68, 70 and 71.
67
68
69
70
71
Figure 40. Fluorescence spectra of
BCKPs 67-71 in DMF solution at an
excitation wavelength of 532 nm.
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