Effect of Conjugation Length on Photoinduced Charge-Transfer in π-Conjugated Oligomer-Acceptor Dyads

Handle URI:
http://hdl.handle.net/10754/623760
Title:
Effect of Conjugation Length on Photoinduced Charge-Transfer in π-Conjugated Oligomer-Acceptor Dyads
Authors:
Jiang, Junlin; Alsam, Amani Abdu; Wang, Shanshan; Aly, Shawkat Mohammede ( 0000-0002-0455-1892 ) ; Pan, Zhenxing; Mohammed, Omar F. ( 0000-0001-8500-1130 ) ; Schanze, Kirk S.
Abstract:
A series of -conjugated oligomer-acceptor dyads were synthesized that feature oligo(phenylene ethynylene) (OPE) conjugated backbones end-capped with a naphthalene diimide (NDI) acceptor. The OPE segments vary in length from 4 to 8 phenylene ethynene units (PEn-NDI, where n = 4, 6 and 8). Fluorescence and transient absorption spectroscopy reveals that intramolecular OPE NDI charge transfer dominates the deactivation of excited states of the PEn-NDI oligomers. Both charge separation (CS) and charge recombination (CR) are strongly exothermic (G0CS ~ -1.1 and G0CR ~ -2.0 eV), and the driving forces do not vary much across the series because the oxidation and reduction potentials and singlet energies of the OPEs do not vary much with their length. Bimolecular photoinduced charge transfer between model OPEs that do not contain the NDI acceptors with methyl viologen was studied, and the results reveal that the absorption of the cation radical state (OPE+•) remains approximately constant ( ~ 575 nm) regardless of oligomer length. This finding suggests that the cation radical (polaron) of the OPE is relatively localized, effectively occupying a confined segment of n 4 repeat units in the longer oligomers. Photoinduced intramolecular electron transfer dynamics in the PEn-NDI series was investigated by UV-visible femtosecond transient absorption spectroscopy with visible and mid-infrared probes. Charge separation occurs on the 1 – 10 ps timescale, with the rates decreasing slightly with increased oligomer length (βCS ~ 0.15 Å-1). The rate for charge-recombination decreases in the sequence PE4-NDI > PE6-NDI ~ PE8-NDI. The discontinuous distance dependence in the rate for charge recombination may be related to the spatial localization of the positive polaron state in the longer oligomers.
KAUST Department:
KAUST Solar Center (KSC); Physical Sciences and Engineering (PSE) Division
Citation:
Jiang J, Alsam AA, Wang S, Aly SM, Pan Z, et al. (2017) Effect of Conjugation Length on Photoinduced Charge-Transfer in π-Conjugated Oligomer-Acceptor Dyads. The Journal of Physical Chemistry A. Available: http://dx.doi.org/10.1021/acs.jpca.7b03547.
Publisher:
American Chemical Society (ACS)
Journal:
The Journal of Physical Chemistry A
Issue Date:
25-May-2017
DOI:
10.1021/acs.jpca.7b03547
Type:
Article
ISSN:
1089-5639; 1520-5215
Sponsors:
This work was partially supported by the National Science Foundation (Grant No. CHE-1504727). KSS also acknowledges the Welch Foundation for support. We also acknowledge many insightful discussions with John R. Miller (Brookhaven National Laboratory) which in part stimulated this work.
Additional Links:
http://pubs.acs.org/doi/abs/10.1021/acs.jpca.7b03547
Appears in Collections:
Articles; Physical Sciences and Engineering (PSE) Division; Solar and Photovoltaic Engineering Research Center (SPERC)

Full metadata record

DC FieldValue Language
dc.contributor.authorJiang, Junlinen
dc.contributor.authorAlsam, Amani Abduen
dc.contributor.authorWang, Shanshanen
dc.contributor.authorAly, Shawkat Mohammedeen
dc.contributor.authorPan, Zhenxingen
dc.contributor.authorMohammed, Omar F.en
dc.contributor.authorSchanze, Kirk S.en
dc.date.accessioned2017-05-31T10:09:30Z-
dc.date.available2017-05-31T10:09:30Z-
dc.date.issued2017-05-25en
dc.identifier.citationJiang J, Alsam AA, Wang S, Aly SM, Pan Z, et al. (2017) Effect of Conjugation Length on Photoinduced Charge-Transfer in π-Conjugated Oligomer-Acceptor Dyads. The Journal of Physical Chemistry A. Available: http://dx.doi.org/10.1021/acs.jpca.7b03547.en
dc.identifier.issn1089-5639en
dc.identifier.issn1520-5215en
dc.identifier.doi10.1021/acs.jpca.7b03547en
dc.identifier.urihttp://hdl.handle.net/10754/623760-
dc.description.abstractA series of -conjugated oligomer-acceptor dyads were synthesized that feature oligo(phenylene ethynylene) (OPE) conjugated backbones end-capped with a naphthalene diimide (NDI) acceptor. The OPE segments vary in length from 4 to 8 phenylene ethynene units (PEn-NDI, where n = 4, 6 and 8). Fluorescence and transient absorption spectroscopy reveals that intramolecular OPE NDI charge transfer dominates the deactivation of excited states of the PEn-NDI oligomers. Both charge separation (CS) and charge recombination (CR) are strongly exothermic (G0CS ~ -1.1 and G0CR ~ -2.0 eV), and the driving forces do not vary much across the series because the oxidation and reduction potentials and singlet energies of the OPEs do not vary much with their length. Bimolecular photoinduced charge transfer between model OPEs that do not contain the NDI acceptors with methyl viologen was studied, and the results reveal that the absorption of the cation radical state (OPE+•) remains approximately constant ( ~ 575 nm) regardless of oligomer length. This finding suggests that the cation radical (polaron) of the OPE is relatively localized, effectively occupying a confined segment of n 4 repeat units in the longer oligomers. Photoinduced intramolecular electron transfer dynamics in the PEn-NDI series was investigated by UV-visible femtosecond transient absorption spectroscopy with visible and mid-infrared probes. Charge separation occurs on the 1 – 10 ps timescale, with the rates decreasing slightly with increased oligomer length (βCS ~ 0.15 Å-1). The rate for charge-recombination decreases in the sequence PE4-NDI > PE6-NDI ~ PE8-NDI. The discontinuous distance dependence in the rate for charge recombination may be related to the spatial localization of the positive polaron state in the longer oligomers.en
dc.description.sponsorshipThis work was partially supported by the National Science Foundation (Grant No. CHE-1504727). KSS also acknowledges the Welch Foundation for support. We also acknowledge many insightful discussions with John R. Miller (Brookhaven National Laboratory) which in part stimulated this work.en
dc.publisherAmerican Chemical Society (ACS)en
dc.relation.urlhttp://pubs.acs.org/doi/abs/10.1021/acs.jpca.7b03547en
dc.rightsThis document is the Accepted Manuscript version of a Published Work that appeared in final form in The Journal of Physical Chemistry A, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see http://pubs.acs.org/doi/abs/10.1021/acs.jpca.7b03547.en
dc.titleEffect of Conjugation Length on Photoinduced Charge-Transfer in π-Conjugated Oligomer-Acceptor Dyadsen
dc.typeArticleen
dc.contributor.departmentKAUST Solar Center (KSC)en
dc.contributor.departmentPhysical Sciences and Engineering (PSE) Divisionen
dc.identifier.journalThe Journal of Physical Chemistry Aen
dc.eprint.versionPost-printen
dc.contributor.institutionDepartment of Chemistry and Center for Macromolecular Science and Engineering, University of Florida, P.O. Box 117200, Gainesville, Florida 32611-7200, United Statesen
dc.contributor.institutionDepartment of Chemistry, University of Texas at San Antonio, One UTSA Way, San Antonio, TX 78249en
kaust.authorAlsam, Amani Abduen
kaust.authorAly, Shawkat Mohammedeen
kaust.authorMohammed, Omar F.en
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