In:
Proceedings of the National Academy of Sciences, Proceedings of the National Academy of Sciences, Vol. 102, No. 10 ( 2005-03-08), p. 3540-3545
Abstract:
The study of photoinitiated electron transfer in donor–bridge–acceptor molecules has helped elucidate the distance dependence of electron transfer rates and behavior of various electron transfer mechanisms. In all reported cases, the energies of the bridge electronic states involved in the electron transfer change dramatically as the length of the bridge is varied. We report here, in contrast, an instance in which the length of the bridge, and therefore the distance over which the electron is transferred, can be varied without significantly changing the energies of the relevant bridge states. A series of donor–bridge–acceptor molecules having phenothiazine (PTZ) donors, 2,7-oligofluorene (FL n ) bridges, and perylene-3,4:9,10-bis(dicarboximide) (PDI) acceptors was studied. Photoexcitation of PDI to its lowest excited singlet state results in oxidation of PTZ via the FL n bridge. In toluene, the rate constants for both charge separation and recombination as well as the energy levels of the relevant \documentclass[12pt]{minimal} \usepackage{amsmath}
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\begin{document} \begin{equation*}{\mathrm{FL}}_{n}^{+{\bullet}}\end{equation*}\end{document} bridge states for n = 1–4 are only weakly distance dependent. After the initial photo-generation of 1 (PTZ +· –FL n –PDI -· ), radical pair intersystem crossing results in formation of 3 (PTZ +· –FL n –PDI -· ) that recombines to give 3* PDI. The dependence of the 3* PDI yield on an applied magnetic field shows a resonance, which gives the singlet–triplet splitting, 2 J , of the radical ion pair. The magnitude of 2 J directly monitors the contribution of coherent charge transfer (superexchange) to the overall electron transfer rate. These data show that charge recombination through FL n is dominated by incoherent hopping at long distances.
Type of Medium:
Online Resource
ISSN:
0027-8424
,
1091-6490
DOI:
10.1073/pnas.0408940102
Language:
English
Publisher:
Proceedings of the National Academy of Sciences
Publication Date:
2005
detail.hit.zdb_id:
209104-5
detail.hit.zdb_id:
1461794-8
SSG:
11
SSG:
12
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