Conformational Effects on Long-Range Electron Transfer: Comparison of Oligo-p-phenylene and Oligo-p-xylene Bridges
✍ Scribed by David Hanss; Oliver S. Wenger
- Publisher
- John Wiley and Sons
- Year
- 2009
- Tongue
- English
- Weight
- 518 KB
- Volume
- 2009
- Category
- Article
- ISSN
- 1434-1948
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✦ Synopsis
Abstract
Phototriggered intramolecular electron transfer across variable‐length oligo‐p‐phenylene and oligo‐p‐xylene bridges was investigated in seven molecules. For both types of bridges, charge transfer rates decrease exponentially with increasing number of spacer units. The distance decay parameter is 0.21 Å^–1^ for the phenylenes and 0.77 Å^–1^ for the xylenes. A simple analysis based on superexchange theory indicates that this difference is due to unequal electronic coupling between adjacent bridging units. On the basis of the experimental data, phenyl‐phenyl coupling is found to be roughly 7 times stronger than xylyl‐xylyl coupling. This difference in electronic coupling strengths can be explained satisfactorily on the sole basis of conformational effects. It is consistent with equilibrium torsion angles of 35–40° between two phenyls and 65–70° between two xylyls.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)