Photoinduced charge separation involving an unusual double electron transfer mechanism in a donor-bridge-acceptor molecule

Scott E. Miller, Aaron S. Lukas, Emily Marsh, Patrick Bushard, Michael R Wasielewski

Research output: Contribution to journalArticle

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Abstract

A series of rodlike donor-bridge-acceptor (D-B-A) molecules was synthesized to study the role of bridge energy levels on electron transfer (ET) rates. In these compounds, a 4-aminonaphthalene-1,8-imide (ANI) electron donor is linked to a 1,8:4,5-naphthalenediimide acceptor (NI) via the 1,4 positions on a phenyl bridge. The phenyl bridge is substituted at the 2 and 5 positions with methyl or methoxy groups to yield ANI-diMe-NI and ANI-diMeO-NI. These molecules differ only in the energy levels of the bridge molecular orbitals. Other parameters affecting ET rates such as donor-acceptor distance, orientation, and driving force are constant between the two systems. The rate constants for charge separation (CS) and charge recombination (CR) within ANI-diMeO-NI in toluene are 32 and 1400 times larger, respectively, than the corresponding rate constants for ANI-diMe-NI. Solvents of higher polarity diminish these differences in rate constants, making them comparable to those observed for ANI-diMe-NI. The relative energies of the ion pair states suggest that it is possible for the reaction 1*D-B-A → D-B+-A- to occur via a double electron-transfer process that is somewhat analogous to Dexter energy transfer. The lowest excited singlet state of the donor, 1*ANI, possesses about 70% charge-transfer character, so that significant positive charge is localized on its amine nitrogen, whereas significant negative charge is localized on its naphthalene-1,8-imide ring. Electron transfer from the naphthalene-1,8-imide ring of 1*ANI to NI is concomitant with electron transfer from the p-dimethoxybenzene bridge to the electron-deficient amine nitrogen atom in 1*ANI. A series of reference molecules in which the p-dimethoxybenzene bridge moiety is attached only to ANI or NI alone is used to establish the structural and electronic requirements for this unusual charge separation mechanism.

Original languageEnglish
Pages (from-to)7802-7810
Number of pages9
JournalJournal of the American Chemical Society
Volume122
Issue number32
DOIs
Publication statusPublished - Aug 16 2000

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1-Naphthylamine
Imides
Electrons
Molecules
Rate constants
Naphthalene
Electron energy levels
Amines
Nitrogen
Molecular orbitals
Excited states
Energy transfer
Toluene
Charge transfer
naphthalenediimide
Atoms

ASJC Scopus subject areas

  • Chemistry(all)

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Photoinduced charge separation involving an unusual double electron transfer mechanism in a donor-bridge-acceptor molecule. / Miller, Scott E.; Lukas, Aaron S.; Marsh, Emily; Bushard, Patrick; Wasielewski, Michael R.

In: Journal of the American Chemical Society, Vol. 122, No. 32, 16.08.2000, p. 7802-7810.

Research output: Contribution to journalArticle

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