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Competition between superexchange-mediated and sequential electron transfer in a bridged donor-acceptor system
Mikael U Winters1, Karin Pettersson, Jerker Mårtensson
1Department of Chemistry and Bioscience, Chalmers University of Technology, 412 96 Gothenburg, Sweden.
Chemistry (Weinheim an Der Bergstrasse, Germany)
|December 4, 2004
Summary
Photoinduced electron transfer in donor-bridge-acceptor systems depends on solvent polarity and temperature. Direct electron transfer is favored in nonpolar solvents, while polar solvents enable both direct and sequential pathways, with the latter showing stronger temperature dependence.
Area of Science:
- Photochemistry
- Supramolecular Chemistry
- Physical Chemistry
Background:
- Photoinduced electron transfer (PET) is fundamental in chemical and biological processes.
- Donor-bridge-acceptor (DBA) systems are crucial for studying charge transfer mechanisms.
- Understanding the influence of solvent and temperature on PET is key to designing efficient molecular devices.
Purpose of the Study:
- To investigate the temperature and solvent effects on competing PET pathways in a porphyrin-based DBA system.
- To elucidate the mechanisms of sequential and direct superexchange-mediated electron transfer.
- To compare the kinetics of these pathways under varying conditions.
Main Methods:
- Fluorescence spectroscopy
- Transient absorption spectroscopy
- Systematic variation of solvent polarity (weakly polar to polar)
- Temperature-dependent measurements
Main Results:
- In weakly polar solvents, only direct electron transfer was observed, showing weak temperature dependence.
- In polar solvents, both direct and sequential electron transfer pathways were active.
- Sequential electron transfer exhibited strong temperature dependence in polar solvents.
- The long-range superexchange-mediated process was faster than the sequential process, despite greater donor-acceptor distance.
Conclusions:
- Solvent polarity dictates the dominant PET mechanism in DBA systems.
- Temperature significantly affects sequential electron transfer in polar environments.
- Superexchange can be a highly efficient electron transfer pathway, even over longer distances.