Toroidal delocalization of a single electron through circularly-arrayed benzophenone chromophores in hexakis(4-benzoylphenyl)benzene

- Toroidal electronic coupling amongst the six circularly-arrayed chromophores in hexaarylbenzenes.
- Formation of intramolecular exciplexes in hexaarylbenzenes.
- Electron delocalization by hopping over six circularly-arrayed benzophenones.

Molecules incorporating with multiple electro-active chromophores are actively sought owing to their potential to serve as energy- and charge-transport materials in the area of photovoltaics and energy storage devices. Herein we demonstrate that a hexaphenylbenzene derivative with six circularly-arrayed electroactive chromophores exhibits effective (toroidal) electronic coupling amongst the six benzophenone moieties. The hexaphenylbenzene-based monobenzoyl ppbBP and hexabenzoyl HBP afford the stabilization of triplet exciton by 4-5 kcal/mol, as compared to parent benzophenone, due to the formation of intramolecular exciplexes with the hexaphenylbenzene propeller. The HBP anion radical, generated by photoinduced electron transfer from a hindered tertiary amine, showed the presence of an intense charge-resonance transition, which was absent in the model compounds (such as ppbBP anion radical). The charge-resonance transition in HBP− evidences delocalization of an electron by hopping over six identical circularly-arrayed benzophenone moieties, which is highly reminiscent of the hole delocalization observed earlier in a number of hexaarylbenzene cation radicals.

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