Charge Injection and Transport in Metal-Containing Conducting Polymers: Spectroelectrochemical Mapping of Redox Activities

Electropolymerization of tris­(dioximate) cage complexes furnished metal-containing conducting polymers (MCPs) that deposit directly onto the electrode surface as uniform films. The injection of electrons into, or removal of electrons from, these electroactive materials proceeds via different pathways with different rates, the underlying molecular mechanisms of which were investigated by a combination of electrochemical, spectroscopic, and focused-ion-beam–scanning electron microscopy (FIB-SEM) cross-section analysis studies. For cobalt-containing polymers, both the metal centers and π-conjugated organic backbone work cooperatively as hopping stations for migrating holes, whereas the reduced polymer utilizes less-efficient self-exchange between cobalt­(II) and cobalt­(I) centers for electron transport. A small molecule model of such reductively doped polymer was prepared independently, which provided compelling electrochemical and spectroelectrochemical evidence to support the structural integrity of the metal centers upon redox switching. A well-defined metal-to-ligand charge transfer (MLCT) band of the n-doped polymer was exploited further as a straightforward spectroscopic tool to quantify the number of redox-active metal centers directly and to estimate the lower distance limit of diffusional charge transport across the bulk material.三（二肟）笼状配合物的电聚合反应可制备含金属导电聚合物（MCPs），该聚合物会以均匀薄膜的形式直接沉积于电极表面。向这类电活性材料注入电子或从中移除电子的过程，会通过不同路径以各异速率进行，其背后的分子机制已通过电化学、光谱学以及聚焦离子束-扫描电子显微镜（FIB-SEM）截面分析等多种研究手段组合开展探究。对于含钴聚合物而言，金属中心与π共轭有机骨架可协同作为迁移空穴的跳跃位点；而还原态聚合物则通过钴(II)与钴(I)中心之间效率较低的自交换过程实现电子传输。研究人员独立制备了这类还原掺杂聚合物的小分子模型，该模型提供了有力的电化学与光谱电化学证据，证实金属中心在氧化还原切换过程中保持结构完整性。研究人员进一步利用n型掺杂聚合物的特征明确的金属-配体电荷转移（MLCT）吸收带，将其作为简便的光谱学工具，可直接量化电活性金属中心的数量，并估算电荷在本体材料中扩散传输的最低距离限值。