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*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

34 Scopus citations

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 (US)
Pages (from-to)5314-5325
Number of pages12
JournalJournal of Physical Chemistry A
Volume117
Issue number25
DOIs
StatePublished - Jun 27 2013

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

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