Electron spin polarization transfer from photogenerated spin-correlated radical pairs to a stable radical observer spin

Michael T. Colvin, Raanan Carmieli, Tomoaki Miura, Sabine Richert, Daniel M. Gardner, Amanda L. Smeigh, Scott M. Dyar, Sarah M. Conron, Mark A Ratner, Michael R Wasielewski

Research output: Contribution to journalArticle

25 Citations (Scopus)

Abstract

A series of donor-chromophore-acceptor-stable radical (D-C-A-R ) molecules having well-defined molecular structures were synthesized to study the factors affecting electron spin polarization transfer from the photogenerated D+•-C-A-• spin-correlated radical pair (RP) to the stable radical R. Theory suggests that the magnitude of this transfer depends on the spin-spin exchange interaction (2JDA) of D+•-C-A -•. Yet, the generality of this prediction has never been demonstrated. In the D-C-A-R molecules described herein, D is 4-methoxyaniline (MeOAn), 2,3-dihydro-1,4-benzodioxin-6-amine (DioxAn), or benzobisdioxole aniline (BDXAn), C is 4-aminonaphthalene-1,8-dicarboximide, and A is naphthalene-1,8:4,5-bis(dicarboximide) (1A,B-3A,B) or pyromellitimide (4A,B-6A,B). The terminal imide of the acceptors is functionalized with either a hydrocarbon (1A-6A) or a 2,2,6,6-tetramethyl-1-piperidinyloxyl radical (R ) (1B-6B). Photoexcitation of C with 416-nm laser pulses results in two-step charge separation to yield D+•-C-A -•-(R). Time-resolved electron paramagnetic resonance (TREPR) spectroscopy using continuous-wave (CW) microwaves at both 295 and 85 K and pulsed microwaves at 85 K (electron spin-echo detection) was used to probe the initial formation of the spin-polarized RP and the subsequent polarization of the attached R radical. The TREPR spectra show that |2JDA| for D+•-C-A-• decreases in the order MeOAn+• > DioxAn+• > BDXAn+• as a result of their spin density distributions, whereas the spin-spin dipolar interaction (dDA) remains nearly constant. Given this systematic variation in |2JDA|, electron spin-echo-detected EPR spectra of 1B-6B at 85 K show that the magnitude of the spin polarization transferred from the RP to R depends on |2JDA|.

Original languageEnglish
Pages (from-to)5314-5325
Number of pages12
JournalJournal of Physical Chemistry A
Volume117
Issue number25
DOIs
Publication statusPublished - Jun 27 2013

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Spin polarization
electron spin
Paramagnetic resonance
Amines
Electrons
polarization
1-Naphthylamine
Microwaves
Imides
Molecules
Photoexcitation
Exchange interactions
Chromophores
Hydrocarbons
Molecular structure
aniline
Laser pulses
Spectroscopy
echoes
electron paramagnetic resonance

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

Cite this

Electron spin polarization transfer from photogenerated spin-correlated radical pairs to a stable radical observer spin. / Colvin, Michael T.; Carmieli, Raanan; Miura, Tomoaki; Richert, Sabine; Gardner, Daniel M.; Smeigh, Amanda L.; Dyar, Scott M.; Conron, Sarah M.; Ratner, Mark A; Wasielewski, Michael R.

In: Journal of Physical Chemistry A, Vol. 117, No. 25, 27.06.2013, p. 5314-5325.

Research output: Contribution to journalArticle

Colvin, Michael T. ; Carmieli, Raanan ; Miura, Tomoaki ; Richert, Sabine ; Gardner, Daniel M. ; Smeigh, Amanda L. ; Dyar, Scott M. ; Conron, Sarah M. ; Ratner, Mark A ; Wasielewski, Michael R. / Electron spin polarization transfer from photogenerated spin-correlated radical pairs to a stable radical observer spin. In: Journal of Physical Chemistry A. 2013 ; Vol. 117, No. 25. pp. 5314-5325.
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AU - Gardner, Daniel M.

AU - Smeigh, Amanda L.

AU - Dyar, Scott M.

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AU - Ratner, Mark A

AU - Wasielewski, Michael R

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N2 - A series of donor-chromophore-acceptor-stable radical (D-C-A-R •) molecules having well-defined molecular structures were synthesized to study the factors affecting electron spin polarization transfer from the photogenerated D+•-C-A-• spin-correlated radical pair (RP) to the stable radical R•. Theory suggests that the magnitude of this transfer depends on the spin-spin exchange interaction (2JDA) of D+•-C-A -•. Yet, the generality of this prediction has never been demonstrated. In the D-C-A-R• molecules described herein, D is 4-methoxyaniline (MeOAn), 2,3-dihydro-1,4-benzodioxin-6-amine (DioxAn), or benzobisdioxole aniline (BDXAn), C is 4-aminonaphthalene-1,8-dicarboximide, and A is naphthalene-1,8:4,5-bis(dicarboximide) (1A,B-3A,B) or pyromellitimide (4A,B-6A,B). The terminal imide of the acceptors is functionalized with either a hydrocarbon (1A-6A) or a 2,2,6,6-tetramethyl-1-piperidinyloxyl radical (R •) (1B-6B). Photoexcitation of C with 416-nm laser pulses results in two-step charge separation to yield D+•-C-A -•-(R•). Time-resolved electron paramagnetic resonance (TREPR) spectroscopy using continuous-wave (CW) microwaves at both 295 and 85 K and pulsed microwaves at 85 K (electron spin-echo detection) was used to probe the initial formation of the spin-polarized RP and the subsequent polarization of the attached R• radical. The TREPR spectra show that |2JDA| for D+•-C-A-• decreases in the order MeOAn+• > DioxAn+• > BDXAn+• as a result of their spin density distributions, whereas the spin-spin dipolar interaction (dDA) remains nearly constant. Given this systematic variation in |2JDA|, electron spin-echo-detected EPR spectra of 1B-6B at 85 K show that the magnitude of the spin polarization transferred from the RP to R• depends on |2JDA|.

AB - A series of donor-chromophore-acceptor-stable radical (D-C-A-R •) molecules having well-defined molecular structures were synthesized to study the factors affecting electron spin polarization transfer from the photogenerated D+•-C-A-• spin-correlated radical pair (RP) to the stable radical R•. Theory suggests that the magnitude of this transfer depends on the spin-spin exchange interaction (2JDA) of D+•-C-A -•. Yet, the generality of this prediction has never been demonstrated. In the D-C-A-R• molecules described herein, D is 4-methoxyaniline (MeOAn), 2,3-dihydro-1,4-benzodioxin-6-amine (DioxAn), or benzobisdioxole aniline (BDXAn), C is 4-aminonaphthalene-1,8-dicarboximide, and A is naphthalene-1,8:4,5-bis(dicarboximide) (1A,B-3A,B) or pyromellitimide (4A,B-6A,B). The terminal imide of the acceptors is functionalized with either a hydrocarbon (1A-6A) or a 2,2,6,6-tetramethyl-1-piperidinyloxyl radical (R •) (1B-6B). Photoexcitation of C with 416-nm laser pulses results in two-step charge separation to yield D+•-C-A -•-(R•). Time-resolved electron paramagnetic resonance (TREPR) spectroscopy using continuous-wave (CW) microwaves at both 295 and 85 K and pulsed microwaves at 85 K (electron spin-echo detection) was used to probe the initial formation of the spin-polarized RP and the subsequent polarization of the attached R• radical. The TREPR spectra show that |2JDA| for D+•-C-A-• decreases in the order MeOAn+• > DioxAn+• > BDXAn+• as a result of their spin density distributions, whereas the spin-spin dipolar interaction (dDA) remains nearly constant. Given this systematic variation in |2JDA|, electron spin-echo-detected EPR spectra of 1B-6B at 85 K show that the magnitude of the spin polarization transferred from the RP to R• depends on |2JDA|.

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