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Influence of Anion Delocalization on Electron Transfer in a Covalent Porphyrin Donor-Perylenediimide Dimer Acceptor System Patrick E Hartnett, Catherine M. Mauck, Michelle A. Harris, Ryan M. Young, Yi-Lin Wu, Tobin J. Marks, and Michael R. Wasielewski J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.6b10140 • Publication Date (Web): 27 Dec 2016 Downloaded from http://pubs.acs.org on December 27, 2016
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Journal of the American Chemical Society
Influence of Anion Delocalization on Electron Transfer in a Covalent Porphyrin Donor-Perylenediimide Dimer Acceptor System Patrick E. Hartnett, Catherine M. Mauck, Michelle A. Harris, Ryan M. Young, Yi-Lin Wu, Tobin J. Marks,* and Michael R. Wasielewski* Department of Chemistry and Argonne-Northwestern Solar Energy Research (ANSER) Center, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, USA Abstract Photo-driven electron transfer from a donor excited state to an assembly of electronically coupled acceptors has been proposed to enhance charge transfer efficiency in functional organic electronic materials. However, the circumstances under which this may occur are difficult to investigate in a controlled manner in disordered donor-acceptor materials. Here we investigate the effects of anion delocalization on electron transfer using zinc meso-tetraphenylporphyrin (ZnTPP) as a donor and a perylene-3,4:9,10-bis(dicarboximide) dimer as the acceptor (PDI2). The PDI units of the dimer are positioned in a cofacial orientation relative to one another by attachment of the imide group of each PDI to the 4- and 5-positions of a xanthene spacer. Furthermore, the distal imide group of one PDI is linked to the para-position of one ZnTPP phenyl group to yield ZnTPP-PDI2. The data for the dimer are compared to two different ZnTPPPDI monomer reference systems designed to probe electron transfer to each of the individual PDI molecules comprising PDI2. The electron transfer rate from the ZnTPP lowest excited singlet state to PDI2 is increased by 50% relative to that in ZnTPP-PDI, when the data are corrected for the statistics of having two electron acceptors. Femtosecond transient IR absorption spectroscopy provides evidence that the observed enhancement in charge separation results from electron transfer producing a delocalized PDI2 anion. 1 ACS Paragon Plus Environment
Journal of the American Chemical Society
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INTRODUCTION Photoinduced charge separation is ubiquitous in organic materials ranging from models for photosynthetic reaction center proteins1-5 to organic photovoltaics (OPVs).6-10 If two or more electron acceptors are strongly electronically coupled, electron transfer may occur from a donor molecule to a molecular orbital delocalized over the acceptors. Moreover, if electron transfer occurs on a sub-picosecond time scale, this process may also be electronically coherent.11-13 Recently, it has been proposed that the electronic interaction of two or more electron acceptors can result in enhanced electron transfer rates and efficiencies that could favorably enhance charge generation and transport within functional organic materials7-10,14-15 One important example of this general problem has arisen in the field of organic photovoltaics (OPVs), many of which undergo exciton dissociation in
