Addition of electron donors (e.g. tetramethyl-p-phenylenediamine, TMPD) to the solutions of bromosubstituted  organic molecules (e.g. CBr3NO2) in dichloromethane resulted in immediate appearance of absorption bands in the UV-Vis range related to 1:1 intermolecular complexes. X-ray crystallographic analysis revealed that these associates show short intermolecular contacts between electrophilic bromine atoms and electron-rich centers of nucleophiles, commonly referred to as halogen bonding. If the electrophile's LUMO were rather close to nucleophile's HOMO (as in CBr3NO2 /TMPD dyad), transient appearance of the intermolecular complexes was followed by the fast redox process leading to TMPD+. cation-radicals. With the larger HOMO/LUMO separation (e.g. in CBr3NO2 /TMPD dyad), cation-radicals were observed upon irradiation of the corresponding associates.  Following earlier analysis of the p-bonded precursor complexes,1 we demonstrate herein that electronic coupling, related to the halogen bonding,  plays a critical role in the thermal and photochemical electron transfer in these systems.[1] Rosokha, S.V.; Kochi, J.K. Acc. Chem. Res. 2008 , 641.

Halogen-bond-assisted thermal and photochemical electron transfer

245th National Meeting (2013)

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