Talk: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 rule states 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, this rule found in most chemistry textbooks is useful in photochemistry in understanding phosphorescence, vibrational relaxation, intersystem crossing, internal conversion and lifetimes of excited states in molecules.
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.
