Light Directs Monomer Coordination in Catalyst-Free Grignard Photopolymerization

Eliot F. Woods; Alexandra J. Berl; Leanna P. Kantt; Christopher T. Eckdahl; Michael R. Wasielewski; Brandon E. Haines; Julia A. Kalow

doi:10.1021/jacs.1c09595

Light Directs Monomer Coordination in Catalyst-Free Grignard Photopolymerization

Eliot F. Woods, Alexandra J. Berl, Leanna P. Kantt, Christopher T. Eckdahl, Michael R. Wasielewski, Brandon E. Haines^*, Julia A. Kalow^*

^*Corresponding author for this work

Chemistry

Research output: Contribution to journal › Article › peer-review

7 Scopus citations

Abstract

π-Conjugated polymers can serve as active layers in flexible and lightweight electronics and are conventionally synthesized by transition-metal-mediated polycondensation at elevated temperatures. We recently reported a photopolymerization of electron-deficient heteroaryl Grignard monomers that enables the catalyst-free synthesis of n-type π-conjugated polymers. Herein, we describe an experimental and computational investigation into the mechanism of this photopolymerization. Spectroscopic studies performed in situ and after quenching reveal that the propagating chain is a radical anion with halide end groups. DFT calculations for model oligomers suggest a Mg-templated SRN1-type coupling, in which Grignard monomer coordination to the radical anion chain avoids the formation of free sp2 radicals and allows C-C bond formation with very low barriers. We find that light plays an unusual role in the reaction, photoexciting the radical anion chain to shift electron density to the termini and thus enabling productive monomer binding.

Original language	English (US)
Pages (from-to)	18755-18765
Number of pages	11
Journal	Journal of the American Chemical Society
Volume	143
Issue number	44
DOIs	https://doi.org/10.1021/jacs.1c09595
State	Published - Nov 10 2021

Funding

This research was supported in part through the computational resources and staff contributions provided for the Quest high performance computing facility at Northwestern University, which is jointly supported by the Office of the Provost, the Office for Research, and Northwestern University Information Technology. This work was supported by funding from the Air Force Office of Scientific Research Young Investigator Program (J.A.K., FA9550–18–1–0159), a 3 M Non-Tenured Faculty Award (J.A.K.), the National Science Foundation under the Graduate Research Fellowship Program (A.J.B. and C.T.E., DGE-1842165), the NSF Centers for Chemical Innovation (M.R.W., CHE-1925690), and Westmont College (B.E.H.). This work made use of NMR and MS instrumentation at the Integrated Molecular Structure Education and Research Center (IMSERC) at Northwestern, which has received support from the NSF (NSF CHE-9871268); Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (NSF ECCS-1542205); the State of Illinois; and the International Institute for Nanotechnology.

ASJC Scopus subject areas

General Chemistry
Biochemistry
Catalysis
Colloid and Surface Chemistry

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@article{ce38b37fb83c4b698d5ac96331f5e547,

title = "Light Directs Monomer Coordination in Catalyst-Free Grignard Photopolymerization",

abstract = "π-Conjugated polymers can serve as active layers in flexible and lightweight electronics and are conventionally synthesized by transition-metal-mediated polycondensation at elevated temperatures. We recently reported a photopolymerization of electron-deficient heteroaryl Grignard monomers that enables the catalyst-free synthesis of n-type π-conjugated polymers. Herein, we describe an experimental and computational investigation into the mechanism of this photopolymerization. Spectroscopic studies performed in situ and after quenching reveal that the propagating chain is a radical anion with halide end groups. DFT calculations for model oligomers suggest a Mg-templated SRN1-type coupling, in which Grignard monomer coordination to the radical anion chain avoids the formation of free sp2 radicals and allows C-C bond formation with very low barriers. We find that light plays an unusual role in the reaction, photoexciting the radical anion chain to shift electron density to the termini and thus enabling productive monomer binding.",

author = "Woods, {Eliot F.} and Berl, {Alexandra J.} and Kantt, {Leanna P.} and Eckdahl, {Christopher T.} and Wasielewski, {Michael R.} and Haines, {Brandon E.} and Kalow, {Julia A.}",

note = "Funding Information: This research was supported in part through the computational resources and staff contributions provided for the Quest high performance computing facility at Northwestern University, which is jointly supported by the Office of the Provost, the Office for Research, and Northwestern University Information Technology. Funding Information: This work was supported by funding from the Air Force Office of Scientific Research Young Investigator Program (J.A.K., FA9550–18–1–0159), a 3 M Non-Tenured Faculty Award (J.A.K.), the National Science Foundation under the Graduate Research Fellowship Program (A.J.B. and C.T.E., DGE-1842165), the NSF Centers for Chemical Innovation (M.R.W., CHE-1925690), and Westmont College (B.E.H.). This work made use of NMR and MS instrumentation at the Integrated Molecular Structure Education and Research Center (IMSERC) at Northwestern, which has received support from the NSF (NSF CHE-9871268); Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (NSF ECCS-1542205); the State of Illinois; and the International Institute for Nanotechnology. Publisher Copyright: {\textcopyright} 2021 American Chemical Society.",

year = "2021",

month = nov,

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doi = "10.1021/jacs.1c09595",

language = "English (US)",

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AU - Woods, Eliot F.

AU - Berl, Alexandra J.

AU - Kantt, Leanna P.

AU - Eckdahl, Christopher T.

AU - Wasielewski, Michael R.

AU - Haines, Brandon E.

AU - Kalow, Julia A.

N1 - Funding Information: This research was supported in part through the computational resources and staff contributions provided for the Quest high performance computing facility at Northwestern University, which is jointly supported by the Office of the Provost, the Office for Research, and Northwestern University Information Technology. Funding Information: This work was supported by funding from the Air Force Office of Scientific Research Young Investigator Program (J.A.K., FA9550–18–1–0159), a 3 M Non-Tenured Faculty Award (J.A.K.), the National Science Foundation under the Graduate Research Fellowship Program (A.J.B. and C.T.E., DGE-1842165), the NSF Centers for Chemical Innovation (M.R.W., CHE-1925690), and Westmont College (B.E.H.). This work made use of NMR and MS instrumentation at the Integrated Molecular Structure Education and Research Center (IMSERC) at Northwestern, which has received support from the NSF (NSF CHE-9871268); Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (NSF ECCS-1542205); the State of Illinois; and the International Institute for Nanotechnology. Publisher Copyright: © 2021 American Chemical Society.

PY - 2021/11/10

Y1 - 2021/11/10

N2 - π-Conjugated polymers can serve as active layers in flexible and lightweight electronics and are conventionally synthesized by transition-metal-mediated polycondensation at elevated temperatures. We recently reported a photopolymerization of electron-deficient heteroaryl Grignard monomers that enables the catalyst-free synthesis of n-type π-conjugated polymers. Herein, we describe an experimental and computational investigation into the mechanism of this photopolymerization. Spectroscopic studies performed in situ and after quenching reveal that the propagating chain is a radical anion with halide end groups. DFT calculations for model oligomers suggest a Mg-templated SRN1-type coupling, in which Grignard monomer coordination to the radical anion chain avoids the formation of free sp2 radicals and allows C-C bond formation with very low barriers. We find that light plays an unusual role in the reaction, photoexciting the radical anion chain to shift electron density to the termini and thus enabling productive monomer binding.

AB - π-Conjugated polymers can serve as active layers in flexible and lightweight electronics and are conventionally synthesized by transition-metal-mediated polycondensation at elevated temperatures. We recently reported a photopolymerization of electron-deficient heteroaryl Grignard monomers that enables the catalyst-free synthesis of n-type π-conjugated polymers. Herein, we describe an experimental and computational investigation into the mechanism of this photopolymerization. Spectroscopic studies performed in situ and after quenching reveal that the propagating chain is a radical anion with halide end groups. DFT calculations for model oligomers suggest a Mg-templated SRN1-type coupling, in which Grignard monomer coordination to the radical anion chain avoids the formation of free sp2 radicals and allows C-C bond formation with very low barriers. We find that light plays an unusual role in the reaction, photoexciting the radical anion chain to shift electron density to the termini and thus enabling productive monomer binding.

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IS - 44

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Light Directs Monomer Coordination in Catalyst-Free Grignard Photopolymerization

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