Controlling electron transfer in donor-bridge-acceptor molecules using cross-conjugated bridges

Annie Butler Ricks, Gemma C. Solomon, Michael T. Colvin, Amy M. Scott, Kun Chen, Mark A. Ratner, Michael R. Wasielewski

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Abstract

Photoinitiated charge separation (CS) and recombination (CR) in a series of donor-bridge-acceptor (D-B-A) molecules with cross-conjugated, linearly conjugated, and saturated bridges have been compared and contrasted using time-resolved spectroscopy. The photoexcited charge transfer state of 3,5-dimethyl-4-(9-anthracenyl)julolidine (DMJ-An) is the donor, and naphthalene-1,8:4,5-bis(dicarboximide) (NI) is the acceptor in all cases, along with 1,1-diphenylethene, trans-stilbene, diphenylmethane, and xanthone bridges. Photoinitiated CS through the cross-conjugated 1,1-diphenylethene bridge is about 30 times slower than through its linearly conjugated trans-stilbene counterpart and is comparable to that observed through the diphenylmethane bridge. This result implies that cross-conjugation strongly decreases the π orbital contribution to the donor-acceptor electronic coupling so that electron transfer most likely uses the bridge σ system as its primary CS pathway. In contrast, the CS rate through the cross-conjugated xanthone bridge is comparable to that observed through the linearly conjugated trans-stilbene bridge. Molecular conductance calculations on these bridges show that cross-conjugation results in quantum interference effects that greatly alter the through-bridge donor-acceptor electronic coupling as a function of charge injection energy. These calculations display trends that agree well with the observed trends in the electron transfer rates.

Original languageEnglish (US)
Pages (from-to)15427-15434
Number of pages8
JournalJournal of the American Chemical Society
Volume132
Issue number43
DOIs
StatePublished - Nov 3 2010

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ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

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