Issue 8, 2016

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

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 (<10 ps) from the guest to the PBI in CH2Cl2. 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.

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

Supplementary files

Article information

Article type
Edge Article
Submitted
09 Apr 2016
Accepted
06 May 2016
First published
18 May 2016
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY license

Chem. Sci., 2016,7, 5428-5434

Author version available

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

P. Spenst, R. M. Young, M. R. Wasielewski and F. Würthner, Chem. Sci., 2016, 7, 5428 DOI: 10.1039/C6SC01574C

This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. You can use material from this article in other publications without requesting further permissions from the RSC, provided that the correct acknowledgement is given.

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