Enhanced intersystem crossing in donor/acceptor systems based on zinc/iron or free-base/iron porphyrins
Artikel i vetenskaplig tidskrift, 2001

The deactivation pathways of the singlet excited state of a series of zinc or free-base donor porphyrins covalently linked by a bridge to a paramagnetic iron(III) chloride porphyrin acceptor have been studied. These donor-bridge-acceptor systems all share a similar geometry (25 Angstrom donor-acceptor center-to-center distance), but the bridges vary in electronic structure. In previously reported investigations of zinc/iron porphyrin systems, the fluorescence quenching of the donor has predominantly been assigned to electron transfer. However, for the porphyrin systems studied in this paper, we show that the dominant deactivation channels are enhanced intersystem crossing and singlet energy transfer. In both series, the intersystem crossing rate (S-1 --> T-1) of the donor moiety is almost doubled in the presence of a paramagnetic high-spin metal-porphyrin acceptor. The significant spectral overlap of the donor fluorescence and acceptor absorption in both series allows for efficient singlet energy transfer (Forster mechanism). Furthermore, the bridging chromophores mediate energy transfer and the enhancement is inversely dependent upon the energy gap between the donor and bridge excited states. Although Marcus theory predicts thermodynamically favorable electron transfer to occur in the systems investigated, the quenching rate constants were found to be independent of solvent polarity, and no charge-separated state could be detected, indicating very small electronic coupling for election transfer.


Kristine Kilså

Institutionen för fysikalisk kemi

Johan Kajanus

Institutionen för organisk kemi

Sven Larsson

Institutionen för fysikalisk kemi

A. N. Macpherson

Jerker Mårtensson

Institutionen för organisk kemi

Bo Albinsson

Institutionen för fysikalisk kemi

Chemistry - A European Journal

0947-6539 (ISSN) 1521-3765 (eISSN)

Vol. 7 10 2122-2133


Nanovetenskap och nanoteknik


Grundläggande vetenskaper



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