Charge-transfer complexes, work term

In many cases, the reactions of carbonyl compounds are interpreted in terms of the reactivity of the triplet carbonyl compound. However, the work on [123] in which a fluorescent excited charge-transfer complex was detected, and the finding that some amine radical cations react with the radical anions of carbonyl compounds to produce exciplex fluorescence (Zachariasse, 1974) shows that, although intersystem crossing in carbonyl compounds is usually highly efficient, they may participate in excited singlet-state reactions. 

Evaluation of the Work Term from Charge Transfer Spectral Data. The intermolecular interaction leading to the precursor complex in Scheme IV is reminiscent of the electron donor-acceptor or EDA complexes formed between electron donors and acceptors (21). The latter is characterized by the presence of a new absorption band in the electronic spectrum. According to the Mulliken charge transfer (CT) theory for weak EDA complexes, the absorption maximum hv rp corresponds to the vertical (Franck-Condon) transition from the neutral ground state to the polar excited state (22). 

The diffusion limit will obscure very fast rates of electron transfer (/cobs = for et d) [16]. Even if electron transfer is slow with respect to diffusion ( obs = et), work accompanies the formation of the precursor complex and/or separation of the successor complex (this is especially prevalent when the reactants and/or products are charged). Work term contributions to the observed rate of reaction can overwhelm the intrinsic factors that govern the electron transfer event [19]. For this reason, excluding special circumstances [20-26], intermolecular reactions are not ideal systems for examining the mechanistic details of electron transfer. 

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