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Pi-Conjugated Porphyrin Nanorings

Final Report Summary - NANORING (Pi-Conjugated Porphyrin Nanorings)

Aim of this project was to get a deeper understanding of the p-delocalisation in a six-porphyrin nanoring. An informative method for the investigation of the p-delocalisation in extended p-system is to oxidise the molecule and to explor the resulting radical cation. The optical properties of radical cations can provide information about relative energy and symmetry of p-orbitals. Even more information can be aquired by electron paramagnetic resonance (EPR) measurements on radical species. The bandshape of continuous wave (CW)-EPR signals can provide information on the p-delocalisation by means of the hyperfine coupling of the unpaired electron with nuclei having a nuclear spin. In general, the bandwith of the EPR signal is decreasing by increasing p-system because the individual hyperfine couplings become smaller. Theories for the quantification of the p-delocalisation haven been developed for conjugated polymers and have already been used for the investigation of conjugated porphyrin systems. The work carried out in this project shows that the cyclic conjugated systems show an even more delocalised p-system than the linear oligomers. This could be observed in absorption as well as in CW-EPR measurements. For a more detailed and quantitative understanding of the CW-EPR results obtained so far, pulsed-EPR measurements on this samples and quantum chemical calculations were performed and the evaluation is in progress.