El-Sayed rules
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[edit] El-Sayed rules
Intersystem Crossing (ISC) is a photophysical process involving an isoenergetic radiationless transition between two electronic states having different multiplicities. It often results in a vibrationally excited molecular entity in the lower electronic state, which then usually deactivates to its lowest vibrational level. ISC is forbidden by rules of conservation of angular momentum. As a consequence, ISC generally occurs on very long time scales.
However the El-Sayed’s rules state that the rate of intersystem crossing, e.g. from the lowest singlet state to the triplet manifold, is relatively large if the radiationless transition involves a change of orbital type.
Formulated by Prof. Mostafa. A. El-Sayed in 1960s, these rules are useful in photochemistry in understanding phosphorescence, vibrational relaxation, intersystem crossing, internal conversion and lifetimes of excited states in molecules.
[edit] References
El-Sayed, M.A., Acc. Chem. Res. 1968,1,8.
Lower, S.K.; El-Sayed, M.A., Chem. Rev.1966,66 ,199.
Mostafa Amr El-Sayed (8 May 1933 - , Egyptian-American, b. Zifta, Egypt)
Biographical References: McMurray, Emily J. (ed.), Notable Twientieth-Century Scientists, Gale Research, Inc.: New York, 1995.
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