Structural effects on photoinduced electron transfer in carotenoid-porphyrin-quinone triads
- Arizona State Univ., Tempe, AZ (United States)
meso-Polyarylporphyrins are often used as components of molecules that mimic photosynthetic reaction centers by carrying out photoinduced electron-transfer reactions. Studies of these systems have raised questions concerning the role of alkyl substituents at the `{beta}-pyrrolic` positions on the porphyrin periphery in limiting {pi}-{pi} overlap between the macrocycle and the aryl rings. The degree of overlap affects electronic coupling and, therefore, the rates of electron-transfer reactions. There is also evidence that when the linkages joining porphyrins to electron-acceptor or -donor moieties contain amide bonds, the sense of the amide linkage may strongly affect electron-transfer rate constants. In this study, three carotenoid-porphyrin-quinone molecular triads and various model compounds have been prepared, and electron-transfer has been studied using time-resolved emission and absorption techniques. The results show that steric hindrance due to methyl groups at the {beta}-pyrrolic positions reduces electron-transfer rate constants by a factor of approximately 1/5. In addition, amide-containing donor-acceptor linkages having the nitrogen atom attached to the porphyrin meso-aryl ring demonstrate electron-transfer rate constants approximately 30 times larger than those for similar linkages with the amide reversed, after correction for thermodynamic effects. 52 refs., 7 figs., 2 tabs.
- DOE Contract Number:
- FG03-93ER14404
- OSTI ID:
- 501886
- Journal Information:
- Journal of Physical Chemistry B: Materials, Surfaces, Interfaces, amp Biophysical, Vol. 101, Issue 3; Other Information: PBD: 16 Jan 1997
- Country of Publication:
- United States
- Language:
- English
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