Electron transfer in porphyrin—quinone cyclophanes studied on the pico- and femto-second time scale
✍ Scribed by W. Frey; R. Klann; F. Laermer; T. Elsaesser; E. Baumann; M. Futscher; H.A. Staab
- Publisher
- Elsevier Science
- Year
- 1992
- Tongue
- English
- Weight
- 429 KB
- Volume
- 190
- Category
- Article
- ISSN
- 0009-2614
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✦ Synopsis
Electron transfer in porphyrin-quinone cyclophanes is investigated by fluorescence and absorption spectroscopy with pico-and femto-second pulses. In nonpolar solvents, the S~ state of the porphyrin shows a lifetime from 300 ps up to several nanoseconds, depending upon the number of quinones and upon their electron affinity. Comparative measurements in polar solvents demonstrate very fast electron transfer on a time scale between 1 and 10 ps. The results are analyzed with the aid of quantum-chemical calculations which give the energy of the charge transfer states and the relevant coupling strengths. For nonpolar solvents, theory suggests fluctuation-induced charge separation and/or direct radiationless internal conversion from the porphyrin Sl to the ground state. In polar solution, the molecules exist in a tilted configuration with strong electronic coupling and charge transfer states well below the Sl level, resulting in fast electron transfer and subsequent charge recombination within 10-40 ps.