Superexchange contributions to distance dependence of electron transfer/transport: Exchange and electronic coupling in oligo(para-phenylene)- and oligo(2,5-thiophene)-bridged donor-bridge-acceptor biradical complexes

Martin L. Kirk, David A. Shultz, Daniel E. Stasiw, Geoffrey F. Lewis, Guangbin Wang, Candice L. Brannen, Roger D. Sommer, Paul D. Boyle

Research output: Contribution to journalArticlepeer-review

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Abstract

The preparation and characterization of three new donor-bridge-acceptor biradical complexes are described. Using variable-temperature magnetic susceptibility, EPR hyperfine coupling constants, and the results of X-ray crystal structures, we evaluate both exchange and electronic couplings as a function of bridge length for two quintessential molecular bridges: oligo(para-phenylene), β = 0.39 Å-1 and oligo(2,5-thiophene), β = 0.22 Å-1. This report represents the first direct comparison of exchange/electronic couplings and distance attenuation parameters (β) for these bridges. The work provides a direct measurement of superexchange contributions to β, with no contribution from incoherent hopping. The different β values determined for oligo(para-phenylene) and oligo(2,5-thiophene) are due primarily to the D-B energy gap, Δ, rather than bridge-bridge electronic couplings, H BB. This is supported by the fact that the HBB values extracted from the experimental data for oligo(para-phenylene) (HBB = 11 400 cm-1) and oligo(2,5-thiophene) (12 300 cm-1) differ by <10%. The results presented here offer unique insight into the intrinsic molecular factors that govern HDA and β, which are important for understanding the electronic origin of electron transfer and electron transport mediated by molecular bridges.

Original languageEnglish (US)
Pages (from-to)17144-17154
Number of pages11
JournalJournal of the American Chemical Society
Volume135
Issue number45
DOIs
StatePublished - Nov 13 2013

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