Light induced manganese oxidation and long-lived charge separation in a Mn2II,II-RuII (bpy)3-acceptor triad
Light induced manganese oxidation and long-lived charge separation in a Mn2II,II-RuII (bpy)3-acceptor triad
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DOI：
10.1021/ja055243b
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发表时间：
2005-12-14
影响因子：
15
通讯作者：
Hammarström, L
中科院分区：
文献类型：
--
作者：
Borgström, M;Shaikh, N;Hammarström, L
用时间分辨光学和电子顺磁共振研究了Mn-2(II)-R-II-NdI三元化合物(1)([Mn-2(Bpmp)(OAc)(2)](+)，BPMP=2，6-bis[bis(2-pyridylmethyl)aminomethyl]-4-methyiphenolate和OAc=乙酸酯，R-II=三联吡啶Ru(II)，Ndi=萘二亚胺)中的光致电子转移反应。配合物1是第一个合成连接的电子给体-敏化剂-受体三元化合物，其中锰配合物扮演给体的角色。用EPR光谱直接研究了氧化锰二聚体络合物(Mn2(II III))和还原的萘二亚胺(NDI中心点-)受体基团的光诱导生成，用光学光谱跟踪了[Ru(Bpy)(3)](2+)中间态和NDI中心点自由基在较宽温度范围内的动力学演化.在室温下，NDI-自由基的平均寿命约为600亩S，比以前报道的基于[Ru(Bpy)(3)](2+)光敏剂的三元化合物的寿命至少长2个数量级。在140K时，这种分子内复合明显减慢，显示出0.1-1的S寿命，这与光合作用反应中心中许多自然发生的电荷分离态相当。研究发现，这种长的复合寿命可以用异常大的重组能(约为2.0 eV)来解释，这是由于锰络合物有很大的内部重组。这使得尽管有很大的驱动力(-Delta G度=1.07 eV)，复合反应仍然被强烈地激活。因此，当电荷分离态能量较高时，锰络合物的固有性质也有利于在“马库斯正常区”产生长寿命的电荷分离。
The photoinduced electron-transfer reactions in a Mn-2(II.II)-R-II-NDI triad (1) ([Mn-2(bpmp)(OAc)(2)](+), bpmp = 2,6-bis[bis(2-pyridylmethyl)aminomethyl]-4-methyiphenolate and OAc = acetate, R-II = trisbipyridine ruthenium(II), and NDI = naphthalenediimide) have been studied by time-resolved optical and EPR spectroscopy. Complex 1 is the first synthetically linked electron donor-sensitizer-acceptor triad in which a manganese complex plays the role of the donor. EPR spectroscopy was used to directly demonstrate the light induced formation of both products: the oxidized manganese dimer complex (Mn-2(II.III)) and the reduced naphthalenediimide (NDI center dot-) acceptor moieties, while optical spectroscopy was used to follow the kinetic evolution of the [Ru(bpy)(3)](2+) intermediate states and the NDI center dot- radical in a wide temperature range. The average lifetime of the NDI- radical is ca. 600 mu s at room temperature, which is at least 2 orders of magnitude longer than that for previously reported triads based on a [Ru(bpy)(3)](2+) photosensitizer. At 140 K, this intramolecular recombination was dramatically slowed, displaying a lifetime of 0.1-1 s, which is comparable to many of the naturally occurring charge-separated states in photosynthetic reaction centra. It was found that the long recombination lifetime could be explained by an unusually large reorganization energy (lambda approximate to 2.0 eV), due to a large inner reorganization of the manganese complex. This makes the recombination reaction strongly activated despite the large driving force (-Delta G degrees = 1.07 eV). Thus, the intrinsic properties of the manganese complex are favorable for creating a long-lived charge separation in the "Marcus normal region" also when the charge separated state energy is high.