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Intrinsic photogeneration of long-lived charges in a donor-orthogonal acceptor conjugated polymer

Efficient charge photogeneration in conjugated polymers typically requires the presence of a second component to act as electron acceptor. Here, we report a novel low band-gap conjugated polymer with a donor/orthogonal acceptor motif: poly-2,6-(4,4-dihexadecyl-4H-cyclopenta [2,1-b:3,4-b′]dithiophene...

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Autores principales: Shaikh, Jordan, Congrave, Daniel G., Forster, Alex, Minotto, Alessandro, Cacialli, Franco, Hele, Timothy J. H., Penfold, Thomas J., Bronstein, Hugo, Clarke, Tracey M.
Formato: Online Artículo Texto
Lenguaje:English
Publicado: The Royal Society of Chemistry 2021
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8208312/
https://www.ncbi.nlm.nih.gov/pubmed/34194707
http://dx.doi.org/10.1039/d1sc00919b
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author Shaikh, Jordan
Congrave, Daniel G.
Forster, Alex
Minotto, Alessandro
Cacialli, Franco
Hele, Timothy J. H.
Penfold, Thomas J.
Bronstein, Hugo
Clarke, Tracey M.
author_facet Shaikh, Jordan
Congrave, Daniel G.
Forster, Alex
Minotto, Alessandro
Cacialli, Franco
Hele, Timothy J. H.
Penfold, Thomas J.
Bronstein, Hugo
Clarke, Tracey M.
author_sort Shaikh, Jordan
collection PubMed
description Efficient charge photogeneration in conjugated polymers typically requires the presence of a second component to act as electron acceptor. Here, we report a novel low band-gap conjugated polymer with a donor/orthogonal acceptor motif: poly-2,6-(4,4-dihexadecyl-4H-cyclopenta [2,1-b:3,4-b′]dithiophene)-alt-2,6-spiro [cyclopenta[2,1-b:3,4-b′]dithiophene-4,9′-fluorene]-2′,7′-dicarbonitrile, referred to as PCPDT-sFCN. The role of the orthogonal acceptor is to spatially isolate the LUMO from the HOMO, allowing for negligible exchange energy between electrons in these orbitals and minimising the energy gap between singlet and triplet charge transfer states. We employ ultrafast and microsecond transient absorption spectroscopy to demonstrate that, even in the absence of a separate electron acceptor, PCPDT-sFCN shows efficient charge photogeneration in both pristine solution and film. This efficient charge generation is a result of an isoenergetic singlet/triplet charge transfer state equilibrium acting as a reservoir for charge carrier formation. Furthermore, clear evidence of enhanced triplet populations, which form in less than 1 ps, is observed. Using group theory, we show that this ultrafast triplet formation is due to highly efficient, quantum mechanically allowed intersystem crossing between the bright, initially photoexcited local singlet state and the triplet charge transfer state. Remarkably, the free charges that form via the charge transfer state are extraordinarily long-lived with millisecond lifetimes, possibly due to the stabilisation imparted by the spatial separation of PCPDT-sFCN's donor and orthogonal acceptor motifs. The efficient generation of long-lived charge carriers in a pristine polymer paves the way for single-material applications such as organic photovoltaics and photodetectors.
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spelling pubmed-82083122021-06-29 Intrinsic photogeneration of long-lived charges in a donor-orthogonal acceptor conjugated polymer Shaikh, Jordan Congrave, Daniel G. Forster, Alex Minotto, Alessandro Cacialli, Franco Hele, Timothy J. H. Penfold, Thomas J. Bronstein, Hugo Clarke, Tracey M. Chem Sci Chemistry Efficient charge photogeneration in conjugated polymers typically requires the presence of a second component to act as electron acceptor. Here, we report a novel low band-gap conjugated polymer with a donor/orthogonal acceptor motif: poly-2,6-(4,4-dihexadecyl-4H-cyclopenta [2,1-b:3,4-b′]dithiophene)-alt-2,6-spiro [cyclopenta[2,1-b:3,4-b′]dithiophene-4,9′-fluorene]-2′,7′-dicarbonitrile, referred to as PCPDT-sFCN. The role of the orthogonal acceptor is to spatially isolate the LUMO from the HOMO, allowing for negligible exchange energy between electrons in these orbitals and minimising the energy gap between singlet and triplet charge transfer states. We employ ultrafast and microsecond transient absorption spectroscopy to demonstrate that, even in the absence of a separate electron acceptor, PCPDT-sFCN shows efficient charge photogeneration in both pristine solution and film. This efficient charge generation is a result of an isoenergetic singlet/triplet charge transfer state equilibrium acting as a reservoir for charge carrier formation. Furthermore, clear evidence of enhanced triplet populations, which form in less than 1 ps, is observed. Using group theory, we show that this ultrafast triplet formation is due to highly efficient, quantum mechanically allowed intersystem crossing between the bright, initially photoexcited local singlet state and the triplet charge transfer state. Remarkably, the free charges that form via the charge transfer state are extraordinarily long-lived with millisecond lifetimes, possibly due to the stabilisation imparted by the spatial separation of PCPDT-sFCN's donor and orthogonal acceptor motifs. The efficient generation of long-lived charge carriers in a pristine polymer paves the way for single-material applications such as organic photovoltaics and photodetectors. The Royal Society of Chemistry 2021-05-10 /pmc/articles/PMC8208312/ /pubmed/34194707 http://dx.doi.org/10.1039/d1sc00919b Text en This journal is © The Royal Society of Chemistry https://creativecommons.org/licenses/by-nc/3.0/
spellingShingle Chemistry
Shaikh, Jordan
Congrave, Daniel G.
Forster, Alex
Minotto, Alessandro
Cacialli, Franco
Hele, Timothy J. H.
Penfold, Thomas J.
Bronstein, Hugo
Clarke, Tracey M.
Intrinsic photogeneration of long-lived charges in a donor-orthogonal acceptor conjugated polymer
title Intrinsic photogeneration of long-lived charges in a donor-orthogonal acceptor conjugated polymer
title_full Intrinsic photogeneration of long-lived charges in a donor-orthogonal acceptor conjugated polymer
title_fullStr Intrinsic photogeneration of long-lived charges in a donor-orthogonal acceptor conjugated polymer
title_full_unstemmed Intrinsic photogeneration of long-lived charges in a donor-orthogonal acceptor conjugated polymer
title_short Intrinsic photogeneration of long-lived charges in a donor-orthogonal acceptor conjugated polymer
title_sort intrinsic photogeneration of long-lived charges in a donor-orthogonal acceptor conjugated polymer
topic Chemistry
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8208312/
https://www.ncbi.nlm.nih.gov/pubmed/34194707
http://dx.doi.org/10.1039/d1sc00919b
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