The electronic coupling (HDA) between a donor and an acceptor in a Donor-Bridge-Acceptor (D-B-A) triad is a primary factor in determining intramolecular electron transfer rates and the efficiency of electron transport in single-molecule devices. This bridge-modulated electronic coupling can be evaluated effectively in the context of Anderson and McConnell superexchange models. When the D-B-A triad is comprised of a cross-conjugated π-system, electron transfer is slow and electronic conductance is weak relative to a conjugated triad. However, theory has suggested that the conductance in cross-conjugated triads can be varied with a suitable bridge probe, and thus such single molecule devices designed using the construct form the basis for quantum interference effect transistors. We have shown the utility of D-B-A biradicals at elucidating excited state contributions to HDA using a valence bond configuration model, and in particular we determined the operative π-superexchange pathway that turns on substantial electronic coupling in cross-conjugated triads. The electronic coupling in cross-conjugated triads is manifest in antiferromagnetic coupling between donor (metal semiquinone) and acceptor (nitronylnitroxide) spins in the ground state, in marked contrast to the ferromagnetic exchange observed in the π-conjugated analogues. Herein, we will present new results that further explore excited state electronic structure contributions to HDA in cross-conjugated D-B-A biradical complexes.

π-System superexchange in cross-conjugated donor-bridge-acceptor triads: Electronic structure contributions to quantum interference

249th National Meeting (2015)

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