TY - JOUR
T1 - Electron spin polarization transfer from photogenerated spin-correlated radical pairs to a stable radical observer spin
AU - Colvin, Michael T.
AU - Carmieli, Raanan
AU - Miura, Tomoaki
AU - Richert, Sabine
AU - Gardner, Daniel M.
AU - Smeigh, Amanda L.
AU - Dyar, Scott M.
AU - Conron, Sarah M.
AU - Ratner, Mark A.
AU - Wasielewski, Michael R.
PY - 2013/6/27
Y1 - 2013/6/27
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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U2 - 10.1021/jp4045012
DO - 10.1021/jp4045012
M3 - Article
C2 - 23721288
AN - SCOPUS:84879678662
SN - 1089-5639
VL - 117
SP - 5314
EP - 5325
JO - Journal of Physical Chemistry A
JF - Journal of Physical Chemistry A
IS - 25
ER -