Magnetic Field-Induced Switching of the Radical-Pair Intersystem Crossing Mechanism in a Donor鈭払ridge鈭扐cceptor Molecule for Artificial Photosynthesis

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• 作者：Michael T. Colvin ; Annie Butler Ricks ; Amy M. Scott ; Amanda L. Smeigh ; Raanan Carmieli ; Tomoaki Miura ; Michael R. Wasielewski
• 刊名：Journal of the American Chemical Society
• 出版年：2011
• 出版时间：February 9, 2011
• 年：2011
• 卷：133
• 期：5
• 页码：1240-1243
• 全文大小：807K
• 年卷期：v.133,no.5(February 9, 2011)
• ISSN：1520-5126

文摘

A covalent, fixed-distance donor鈭抌ridge鈭抋cceptor (D鈭払鈭扐) molecule was synthesized that upon photoexcitation undergoes ultrafast charge separation to yield a radical ion pair (RP) in which the spin鈭抯pin exchange interaction (2J) between the two radicals is sufficiently large to result in preferential RP intersystem crossing to the highest-energy RP eigenstate (T₊₁) at the 350 mT magnetic field characteristic of X-band (9.5 GHz) EPR spectroscopy. This behavior is unprecedented in covalent D鈭払鈭扐 molecules, and is evidenced by the time-resolved EPR (TREPR) spectrum at X-band of ^3*D鈭払鈭扐 derived from RP recombination, which shows all six canonical EPR transitions polarized in emission (e,e,e,e,e,e). In contrast, when the RP is photogenerated in a 3400 mT magnetic field, the TREPR triplet spectrum at W-band (94 GHz) of ^3*D鈭払鈭扐 displays the (a,e,e,a,a,e) polarization pattern characteristic of a weakly coupled RP precursor, similar to that observed in photosynthetic reaction center proteins, and indicates a switch to selective population of the lower-energy T₀ eigenstate.