External Heavy-Atom Effects and Charge Transfer

External Heavy-Atom Effects and Charge Transfer 

Although some workers suggest that exchange interactions are dominant in determining the effects of external heavy atoms, experimental evidence at this point tends to favor charge transfer as the mechanism for external 

The best evidence for a charge-transfer exciplex (hetero excimer) has been provided by Thomaz and Stevens. They note a reduction in fluorescence yield of pyrene with increasing heavy-atom concentration and proposed the following set of reactions to explain their results  

A similar kinetic scheme with Q = A can be used to account for concentration quenching, where (AQ) = (AA), an excimer. Leonhardt and Wellerand Matoga, Okada, and Ezumi first proposed such a scheme to account for the quenching of fluorescence from aromatic hydrocarbons by IV-alkyl anilines. In addition, they observed a long-wavelength structureless emission from the excited hydrocarbon-aniline complex. The key step in the 

M- -Afl., kcal/ mole -AJ cal/ mole-°C Er, kcall mole D V, nsec nsec Ref. 

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