Photoinduced Hole Injection into a Self-Assembled π-Extended G-Quadruplex

Yi Lin Wu, Kristen E. Brown, Daniel M. Gardner, Scott M. Dyar, Michael R. Wasielewski

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15 Citations (Scopus)

Abstract

We have prepared a G-quadruplex (GQ-1) that incorporates an 8-(4′-aminophenylethynyl)guanine (GEAn) electron donor covalently attached to a 4-aminonaphthalene-1,8-imide (ANI) chromophore and a naphthalene-1,8:4,5-bis(dicarboximide) (NDI) electron acceptor (GEAn-ANI-NDI, 1). In the presence of KPF6 in tetrahydrofuran (THF), 1 self-assembles into a monodisperse, C4-symmetric GQ-1 with small spatial intraquadruplex overlap between the ANI-NDI units. Photoexcitation of monomeric 1 induces the two-step charge transfer GEAn-1∗ANI-NDI → GEAn+•-ANI-•-NDI → GEAn+•-ANI-NDI-• that occurs in τCS1 = 5 ps and τCS2 = 330 ps, respectively, while charge recombination in ca. 300 ns. Sharpening of the GEAn+• transient absorption and a shift of the ethynyl vibrational frequency in 1 were observed, concomitant with the stepwise electron transfer from ANI-• to NDI. Formation of GQ-1 from 1 in THF increases the secondary charge-shifting rate (τCS2 = 110 ps) and results in no change in ethynyl vibrational frequency. Charge recombination in GQ-1 is slowed by enhanced radical-pair intersystem crossing driven by the greater number of hyperfine couplings in the assembly. Moreover, time-resolved EPR spectroscopy shows that the spin-spin-exchange interaction (J) between the radicals of GEAn+•-ANI-NDI-• within GQ-1 is smaller than that of 1, suggesting that the spin (charge) density in GEAn+• is more dispersed in GQ-1. The spectroscopic results are consistent with hole sharing among the guanines within the G-quadruplex that is kinetically competitive with the formation of GEAn+•. This suggests that G-quadruplexes can serve as effective hole conduits in ordered donor-acceptor assemblies. (Graph Presented).

Original languageEnglish
Pages (from-to)3981-3990
Number of pages10
JournalJournal of the American Chemical Society
Volume137
Issue number11
DOIs
Publication statusPublished - Mar 25 2015

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ASJC Scopus subject areas

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

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