Growing interest in the use of first-row transition metal complexes in a number of applied contexts—including but not limited to photoredox catalysis and solar energy conversion—underscores the need for a detailed understanding of their photophysical properties. A recent focus on ligand-field photocatalysis using cobalt(III) polypyridyls in particular has unlocked unprecedented excited-state reactivities. Photophysical studies on Co(III) chromophores in general are relatively uncommon, and so here we carry out a systematic study of a series of Co(III) polypyridyl complexes in order to delineate their excited-state dynamics. Compounds with varying ligand-field strengths were prepared and studied using variable-temperature ultrafast transient absorption spectroscopy. Analysis of the data establishes that the ground-state recovery dynamics are operating in the Marcus inverted region, in stark contrast to what is typically observed in other first-row metal complexes. The analysis has further revealed the underlying reasons driving this excited-state behaviour, thereby enabling potential advancements in the targeted use of the Marcus inverted region for a variety of photolytic applications.

人们对在许多应用领域（包括但不限于光氧化还原催化和太阳能转换）中使用第一排过渡金属配合物越来越感兴趣，这凸显了详细了解其光物理性质的必要性。最近对使用钴（III）聚吡啶的配体场光催化的关注特别释放了前所未有的激发态反应性。一般来说，对 Co(III) 发色团的光物理研究相对较少，因此我们对一系列 Co(III) 聚吡啶配合物进行了系统研究，以描绘它们的激发态动力学。使用变温超快瞬态吸收光谱制备并研究了具有不同配体场强度的化合物。对数据的分析表明，基态恢复动力学在马库斯倒置区域中运行，与其他第一行金属配合物中通常观察到的情况形成鲜明对比。该分析进一步揭示了驱动这种激发态行为的根本原因，从而使马库斯倒置区域在各种光解应用中的针对性使用取得了潜在的进展。