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Enhanced intersystem crossing in donor/acceptor systems based on zinc/iron or free-base/iron porphyrins

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). Vol. 7 (2001), 10, p. 2122-2133.
[Artikel, refereegranskad vetenskaplig]

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.



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Denna post skapades 2012-09-21. Senast ändrad 2017-10-03.
CPL Pubid: 163745

 

Institutioner (Chalmers)

Institutionen för fysikalisk kemi (1900-2003)
Institutionen för organisk kemi (1900-2003)

Ämnesområden

Nanovetenskap och nanoteknik
Kemi

Chalmers infrastruktur