Department of Chemistry , Michigan State University , East Lansing , Michigan 48824 , United States.
Inorg Chem. 2018 Sep 17;57(18):11633-11645. doi: 10.1021/acs.inorgchem.8b01772. Epub 2018 Aug 29.
A new low-spin (LS) cobalt(II) outer-sphere redox shuttle (OSRS) [Co(PY5Me)(CN)], where PY5Me represents the pentadentate ligand 2,6-bis(1,1-bis(2-pyridyl)ethyl)pyridine, has been synthesized and characterized for its potential application in dye-sensitized solar cells (DSSCs). Introduction of the strong field CN ligand into the open axial coordination site forced the cobalt(II) complex, [Co(PY5Me)(CN)], to become LS based upon the complex's magnetic susceptibility (1.91 ± 0.02 μ), determined by the Evans method. Interestingly, dimerization and subsequent cobalt hexacyanide cluster formation of the [Co(PY5Me)(CN)] monomer was observed upon long-term solvent exposure or addition of a supporting electrolyte for electrochemical characterization. Although long-term stability of the [Co(PY5Me)(CN)] complex made it difficult to fabricate liquid electrolytes for DSSC applications, short-term stability in neat solvent afforded the opportunity to isolate the self-exchange kinetics of [Co(PY5Me)(CN)] via stopped-flow spectroscopy. Use of Marcus theory provided a smaller than expected self-exchange rate constant of 20 ± 5.5 M s for [Co(PY5Me)(CN)], which we attribute to a Jahn-Teller effect observed from the collected monomer crystallographic data. When compared side-by-side to cobalt tris(2,2'-bipyridine), [Co(bpy)], DSSCs employing [Co(PY5Me)(CN)] are expected to achieve superior charge collection, which result from a smaller rate constant, k, for recombination based upon simple dark J- E measurements of the two redox shuttles. Given the negative redox potential (0.254 V vs NHE) of [Co(PY5Me)(CN)] and the slow recombination kinetics, [Co(PY5Me)(CN)] becomes an attractive OSRS to regenerate near IR absorbing sensitizers in solid-state DSSC devices.
一种新的低自旋（LS）钴（II）外球氧化还原穿梭物（OSRS）[Co（PY5Me）（CN）]，其中 PY5Me 代表五齿配体 2,6-双（1,1-双（2-吡啶基）乙基）吡啶，已被合成并表征，以评估其在染料敏化太阳能电池（DSSC）中的潜在应用。强场 CN 配体引入开放轴向配位位迫使钴（II）配合物[Co（PY5Me）（CN）]基于配合物的磁化率（1.91±0.02μ）成为 LS，通过 Evans 方法确定。有趣的是，在长期暴露于溶剂或添加支持电解质进行电化学表征后，观察到[Co（PY5Me）（CN）]单体的二聚化和随后的钴六氰化物簇形成。尽管[Co（PY5Me）（CN）]配合物的长期稳定性使其难以制造用于 DSSC 应用的液体电解质，但在纯溶剂中的短期稳定性为通过停流光谱法分离[Co（PY5Me）（CN）]的自交换动力学提供了机会。使用 Marcus 理论提供了一个小于预期的自交换速率常数 20±5.5 M s，对于[Co（PY5Me）（CN）]，我们将其归因于从收集的单体晶体学数据中观察到的 Jahn-Teller 效应。与钴三（2,2'-联吡啶）[Co（bpy）]相比，预计使用[Co（PY5Me）（CN）]的 DSSC 将实现更好的电荷收集，这是由于两种氧化还原穿梭物的简单暗 J-E 测量得到的较小的重组速率常数 k 所致。鉴于[Co（PY5Me）（CN）]的负氧化还原电位（0.254 V 对 NHE）和缓慢的重组动力学，[Co（PY5Me）（CN）]成为在固态 DSSC 器件中再生近红外吸收敏化剂的有吸引力的 OSRS。
