Electron Spin Polarization Transfer from Photogenerated Spin-Correlated Radical Pairs to a Stable Radical Observer Spin
Electron Spin Polarization Transfer from Photogenerated Spin-Correlated Radical Pairs to a Stable Radical Observer Spin
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DOI：
10.1021/jp4045012
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发表时间：
2013-06-27
影响因子：
2.9
通讯作者：
Wasielewski, Michael R.
中科院分区：
文献类型：
--
作者：
Colvin, Michael T.;Carmieli, Raanan;Wasielewski, Michael R.
合成了一系列具有明确分子结构的给体 - 生色团 - 受体 - 稳定自由基（D - C - A - R - •）分子，以研究影响从光生D⁺• - C - A⁻•自旋相关自由基对（RP）到稳定自由基R•的电子自旋极化转移的因素。理论表明，这种转移的程度取决于D⁺• - C - A⁻•的自旋 - 自旋交换相互作用（2J(DA)）。然而，这一预测的普遍性从未得到证实。在此描述的D - C - A - R - •分子中，D为4 - 甲氧基苯胺（MeOAn）、2,3 - 二氢 - 1,4 - 苯并二氧杂环己烯 - 6 - 胺（DioxAn）或苯并双二氧杂环戊烯苯胺（BDXAn），C为4 - 氨基萘 - 1,8 - 二羧酰亚胺，A为萘 - 1,8:4,5 - 双（二羧酰亚胺）（1A，B - 3A，B）或均苯四甲酸二酰亚胺（4A，B - 6A，B）。受体的末端酰亚胺用烃（1A - 6A）或2,2,6,6 - 四甲基 - 1 - 哌啶氧基自由基（R•）（1B - 6B）官能化。用416 nm激光脉冲对C进行光激发导致两步电荷分离，产生D⁺• - C - A⁻• - （R•）。在295 K和85 K使用连续波（CW）微波以及在85 K使用脉冲微波（电子自旋回波检测）的时间分辨电子顺磁共振（TREPR）光谱用于探测自旋极化RP的初始形成以及所连接的R•自由基的后续极化。TREPR光谱表明，由于它们的自旋密度分布，D⁺• - C - A⁻•的|2J(DA)|按MeOAn⁺• > DioxAn⁺• > BDXAn⁺•的顺序减小，而自旋 - 自旋偶极相互作用（d(DA)）几乎保持不变。鉴于|2J(DA)|的这种系统性变化，在85 K下1B - 6B的电子自旋回波检测EPR光谱表明，从RP转移到R•的自旋极化程度取决于|2J(DA)|。
A series of donor-chromophore-acceptor-stable radical (D-C-A-R-center dot) molecules having well-defined molecular structures were synthesized to study the factors affecting electron spin polarization transfer from the photogenerated D+center dot-C-A(-center dot) spin-correlated radical pair (RP) to the stable radical R-center dot. Theory suggests that the magnitude of this transfer depends on the spin-spin exchange interaction (2J(DA)) of D+center dot-C-A(-center dot). Yet, the generality of this prediction has never been demonstrated. In the D-C-A-R-center dot 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-center dot) (1B-6B). Photoexcitation of C with 416-nm laser pulses results in two-step charge separation to yield D+center dot-C-A(-center dot)-(R-center dot). 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-center dot radical. The TREPR spectra show that vertical bar 2J(DA)vertical bar for D+center dot-C-A(-)center dot decreases in the order MeOAn(+center dot) > DioxAn(+center dot) > BDXAn(+center dot) as a result of their spin density distributions, whereas the spin-spin dipolar interaction (d(DA)) remains nearly constant. Given this systematic variation in vertical bar 2J(DA)vertical bar, 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-center dot depends on vertical bar 2J(DA)vertical bar.