Electron Spin Polarization Transfer from Photogenerated Spin-Correlated Radical Pairs to a Stable Radical Observer Spin
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- 作者：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
- 刊名：The Journal of Physical Chemistry A
- 出版年：2013
- 出版时间：June 27, 2013
- 年：2013
- 卷：117
- 期：25
- 页码：5314-5325
- 全文大小：549K
- 年卷期：v.117,no.25(June 27, 2013)
- ISSN：1520-5215
文摘
A series of donor鈥揷hromophore鈥揳cceptor鈥搒table radical (D鈥揅鈥揂鈥揜鈥?/sup>) molecules having well-defined molecular structures were synthesized to study the factors affecting electron spin polarization transfer from the photogenerated D+鈥?/sup>鈥揅鈥揂鈥撯€?/sup> spin-correlated radical pair (RP) to the stable radical R鈥?/sup>. Theory suggests that the magnitude of this transfer depends on the spin鈥搒pin exchange interaction (2JDA) of D+鈥?/sup>鈥揅鈥揂鈥撯€?/sup>. Yet, the generality of this prediction has never been demonstrated. In the D鈥揅鈥揂鈥揜鈥?/sup> 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鈥?b>3A,B) or pyromellitimide (4A,B鈥?b>6A,B). The terminal imide of the acceptors is functionalized with either a hydrocarbon (1A鈥?b>6A) or a 2,2,6,6-tetramethyl-1-piperidinyloxyl radical (R鈥?/sup>) (1B鈥?b>6B). Photoexcitation of C with 416-nm laser pulses results in two-step charge separation to yield D+鈥?/sup>鈥揅鈥揂鈥撯€?/sup>鈥?R鈥?/sup>). 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鈥揺cho detection) was used to probe the initial formation of the spin-polarized RP and the subsequent polarization of the attached R鈥?/sup> radical. The TREPR spectra show that |2JDA| for D+鈥?/sup>鈥揅鈥揂鈥撯€?/sup> decreases in the order MeOAn+鈥?/sup> > DioxAn+鈥?/sup> > BDXAn+鈥?/sup> as a result of their spin density distributions, whereas the spin鈥搒pin dipolar interaction (dDA) remains nearly constant. Given this systematic variation in |2JDA|, electron spin鈥揺cho-detected EPR spectra of 1B鈥?b>6B at 85 K show that the magnitude of the spin polarization transferred from the RP to R鈥?/sup> depends on |2JDA|.