A review on electronic spectral studies of charge transfer complexes

The electronic absorption spectra of several charge transfer (CT) interactions have showed appearance and/or disappearance of spectral bands in correlation with the lapse of time. Careful investigations of the structural formulae of the different species involved of such interactions including their intermediates and final products have led to provide adequate illustrations of the observed time-dependency. The different reported propositions which have explained this time-dependency observed in the UV/Visible spectral measurements of the interactions involving CT complexations have been surveyed, manifested and categorized. This review is not a literature survey for all CT interactions showed time-dependency but we believe that it reports all the different propositions (reaction pathways/mechanisms) which have been previously presented to reveal this time-dependency, however. Iodine (I2) as a typical σ-acceptor and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) as a typical π-acceptor have been selected for this study. Other conventional σ- and π-acceptors might follow, to some extent, one or more of the categories presented in this study.

► Some of the CT interactions involving I2 or DDQ acceptors are time-dependently.
► Effect of time on CT complexations has been reported and discussed.
► Different reactions mechanisms reported for time-dependently CT interactions have been manifested and categorized.
► Donor/acceptor interactions involving only CT complexations are time-independently.