Guest and solvent modulated photo-driven charge separation and triplet generation in a perylene bisimide cyclophane

Peter Spenst, Ryan M. Young, Michael R Wasielewski, Frank Würthner

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28 Citations (Scopus)

Abstract

Cofacial positioning of two perylene bisimide (PBI) chromophores at a distance of 6.5 Å in a cyclophane structure prohibits the otherwise common excimer formation and directs photoexcited singlet state relaxation towards intramolecular symmetry-breaking charge separation (τCS = 161 ± 4 ps) in polar CH2Cl2, which is thermodynamically favored with a Gibbs free energy of ΔGCS = -0.32 eV. The charges then recombine slowly in τCR = 8.90 ± 0.06 ns to form the PBI triplet excited state, which can be used subsequently to generate singlet oxygen in 27% quantum yield. This sequence of events is eliminated by dissolving the PBI cyclophane in non-polar toluene, where only excited singlet state decay occurs. In contrast, complexation of electron-rich aromatic hydrocarbons by the host PBI cyclophane followed by photoexcitation of PBI results in ultrafast electron transfer (2Cl2. The rate constants for charge separation and recombination increase as the guest molecules become easier to oxidize, demonstrating that charge separation occurs close to the peak of the Marcus curve and the recombination lies far into the Marcus inverted region.

Original languageEnglish
Pages (from-to)5428-5434
Number of pages7
JournalChemical Science
Volume7
Issue number8
DOIs
Publication statusPublished - 2016

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ASJC Scopus subject areas

  • Chemistry(all)

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