Gimeno Lea, Phelan Brian T, Sprague-Klein Emily A, Roisnel Thierry, Blart Errol, Gourlaouen Christophe, Chen Lin X, Pellegrin Yann
Université de Nantes, CNRS, CEISAM UMR6230, F-44000 Nantes, France.
Chemical Science and Engineering Division, Argonne National Laboratory, Lemont, Illinois 60439, United States.
Inorg Chem. 2022 May 16;61(19):7296-7307. doi: 10.1021/acs.inorgchem.1c03901. Epub 2022 May 4.
The steric strain around copper(I) in typical [Cu(NN)] complexes, where NN is a diimine ligand substituted in α-positions of the nitrogen atoms by R, is known to strongly impact the excited-state properties. Generally speaking, the larger the R, the longer the emission lifetime and the higher the quantum yield. However, the stability of the coordination scaffold can be at stake if the steric strain imposed by R is too large. In this work, we explore a way of fine-tuning the steric strain around Cu(I) to reach a balance between high emission quantum yield and stability in a highly bulky copper(I) complex. Taking stable [Cu(dipp)] and unstable [Cu(dtbp)] (where dipp and dtbp are, respectively, 2,9-diisopropyl-1,10-phenanthroline and 2,9-di--butyl-1,10-phenanthroline) as the boundary of two least and most sterically strained structures, we designed and characterized the nonsymmetrical ligand 2-isopropyl-9--butyl-1,10-phenanthroline (L1) and corresponding complex [Cu(L1)] (Cu1). The key experimental findings are that Cu1 exhibits a rigid tetrahedral geometry in the ground state, close to that of [Cu(dtbp)] and with an intermediate stability between that of [Cu(dipp)] and [Cu(dtbp)]. Conversely, the nonsymmetrical nature of ligand L1 leads to a shorter emission lifetime and smaller quantum yield than those of either [Cu(dipp)] or [Cu(dtbp)]. This peculiar behavior is rationalized through the in depth analysis of the ultrafast dynamics of the excited state measured with optical transient absorption spectroscopy and theoretical calculations performed on the ground and excited state of Cu1. Our main findings are that the obtained complex is significantly more stable than [Cu(dtbp)] despite the sterically strained coordination sphere. The nonsymmetrical nature of the ligand translates into a strongly distorted structure in the excited state. The distortion can be described as a rocking motion of one ligand, entailing the premature extinction of the excited state via several deactivation channels.
在典型的[Cu(NN)]配合物中，铜(I)周围的空间位阻应变（其中NN是在氮原子的α位被R取代的二亚胺配体）已知会强烈影响激发态性质。一般来说，R越大，发射寿命越长，量子产率越高。然而，如果R施加的空间位阻应变过大，配位骨架的稳定性可能会受到影响。在这项工作中，我们探索了一种微调铜(I)周围空间位阻应变的方法，以便在高度庞大的铜(I)配合物中实现高发射量子产率和稳定性之间的平衡。以稳定的[Cu(dipp)]和不稳定的[Cu(dtbp)]（其中dipp和dtbp分别是2,9 - 二异丙基 - 1,10 - 菲咯啉和2,9 - 二叔丁基 - 1,10 - 菲咯啉）作为两个空间位阻应变最小和最大的结构边界，我们设计并表征了不对称配体2 - 异丙基 - 9 - 叔丁基 - 1,10 - 菲咯啉（L1）和相应的配合物[Cu(L1)]（Cu1）。关键实验结果是，Cu1在基态呈现刚性四面体几何结构，接近[Cu(dtbp)]，并且稳定性介于[Cu(dipp)]和[Cu(dtbp)]之间。相反，配体L1的不对称性质导致其发射寿命比[Cu(dipp)]或[Cu(dtbp)]都短，量子产率也更小。通过对用光学瞬态吸收光谱测量的激发态超快动力学进行深入分析以及对Cu1的基态和激发态进行理论计算，解释了这种特殊行为。我们的主要发现是，尽管配位球存在空间位阻应变，但所得到的配合物比[Cu(dtbp)]稳定得多。配体的不对称性质在激发态转化为强烈扭曲的结构。这种扭曲可以描述为一个配体的摇摆运动，通过几个失活通道导致激发态过早猝灭。
