Bridge-dependent electron transfer in porphyrin-based donor-bridge-acceptor systems

Kilså, Kristine,1972Chalmers tekniska högskola,Chalmers University of Technology (author)

Photoinduced electron transfer in donor-bridge-acceptor systems with zinc porphyrin (or its pyridine complex) as the donor and gold(III) porphyrin as the acceptor has been studied. The porphyrin moieties were covalently linked with geometrically similar bridging chromophores which vary only in electronic structure. Three of the bridges are fully conjugated pi -systems and in a fourth, the conjugation is broken. For systems with this bridge, the quenching rate of the singlet excited state of the donor was independent of solvent and corresponded to the rate of singlet energy transfer expected for a Forster mechanism. In contrast, systems with a rr-conjugated bridging chromophore show a solvent-dependent quenching rate that suggests electron transfer in the Marcus normal region. This is supported by picosecond transient absorption measurements, which showed formation of the zinc porphyrin radical cation only in systems with pi -conjugated bridging chromophores. On the basis of the Marcus and Rehm-Weller equations, an electronic coupling of 5-20 cm(-1) between the donor and acceptor is estimated for these systems. The largest coupling is found for the systems with the smallest energy gap between the donor and bridge singlet excited states. This is in good agreement with the coupling calculated with quantum mechanical methods, as is the prediction of an almost zero coupling in the systems with a nonconjugated bridging chromophore.

Kajanus, Johan,1967Chalmers tekniska högskola,Chalmers University of Technology (author)
Macpherson, A. N.Umeå universitet,Kemiska institutionen (author)
Mårtensson, Jerker,1965Chalmers tekniska högskola,Chalmers University of Technology(Swepub:cth)jerker (author)
Albinsson, Bo,1963Chalmers tekniska högskola,Chalmers University of Technology(Swepub:cth)balb (author)
Chalmers tekniska högskolaKemiska institutionen (creator_code:org_t)

In:Journal of the American Chemical Society: American Chemical Society (ACS)123:13, s. 3069-30801520-51260002-7863

By the author/editor: Kilså, Kristine, ...; Kajanus, Johan, ...; Macpherson, A. N ...; Mårtensson, Jerk ...; Albinsson, Bo, 1 ...

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