Encounter complex charge-transfer interactions

This chemoluminescence results from interaction of 156 (generated from 155 under thermal conditions) and 1,3-DIBF (formed in a minor amount from 156). The first step is the formation of an encounter complex. Electron transfer generates a peroxide radical anion of 156 and a radical cation of 1,3-DIBF. Cleavage of the 0-0 bond in the radical anion of 156 forms an o-dibenzoylbenzene radical anion. Annihilation of the oppositely charged ions gives an excited singlet of 1,3-DIBF (with subsequent fluorescence) (82JA1041). 

Because of the low excess energy, a multi-collision interaction leads to an encounter situation combined with structural optimization to something like an asymmetric charge transfer complex which here is identical with an encounter complex. Then the delayed electron transfer takes place, as mentioned above. This can be well illustrated in terms of the quantum-chemically calculated electron and charge distributions of the involved orbitals as shown in Fig. 8. 

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