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R. Zugle et al. / Polyhedron 30 (2011) 1612–1619
the photosensitiser. That is if the triplet state of a photosensitiser is
populated, it can then interact with ground state triplet molecular
oxygen exciting it to its singlet excited state.
due to singlet oxygen production by complex 4. For complexes 5
and 6 there were no changes in the DPBF spectra even after long
period of light exposure in the presence of these complexes. That
is the DPBF was not degraded as evidence of the presence of singlet
state oxygen, due to lack of singlet oxygen production by these
complexes.
Compounds 5 and 6 have no observed triplet state population as
stated above, possibly due to the open-shell, paramagnetic nature
of Dy3+ and Er3+. In the case of compound 4 which gave a very high
triplet quantum yield, because of its closed-shell diamagnetic nat-
ure of Lu3+, there was evidence of its ability to generate singlet oxy-
gen with quantum yield of 0.71, which was detected by the
phosphorescence decay of singlet oxygen at 1270 nm in THF.
Fig. 7 shows the singlet oxygen decay curve profile for complex 4
in THF. This solvent was found to give better results for singlet oxy-
gen detection compared to DMSO. The latter was however em-
ployed for triplet state studies since it gave the best results.
However, even though direct comparison between UT and UD is
not appropriate due to the use of different solvents, the obtained
UD is reasonable and suggests that it is a potential photosensitiz-
ing agent.
4. Conclusion
In this work we have found that the type of phthalocyanine
complex (whether monomeric or oligomeric) with lanthanide ions
depend more on the particular metal rather than the phthalonitri-
le/metal ratio. The open-shell dysprosium bis-phthalocyanine
complex and the monomeric complex of the open-shell erbium
are neither fluorescent nor showed the ability to generate singlet
state molecular oxygen. On the other hand, the monomeric phtha-
locyanine complex of the close shell lutetium is a promising
photosensitizer.
To further demonstrate the ability of compound 4 to generate
singlet oxygen, 1,3-diphenylisobenzofuran (DPBF) was used as a
singlet oxygen quencher and its conversion by the singlet oxygen
was monitored by UV–Vis spectroscopy, Fig. 8. There were no
changes in the Q-band intensities during the process suggesting
that the phthalocyanine was not degraded, but DPBF degraded
Acknowledgements
This work was supported by the Department of Science and
Technology (DST) and National Research Foundation (NRF), South
Africa through DST/NRF South African Research Chairs Initiative
for Professor of Medicinal Chemistry and Nanotechnology as well
as Rhodes University.
0.25
0.20
0.15
0.10
0.05
0.00
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