First Experimental Evidence for the Diverse Requirements of Excimer vs Hole Stabilization in π-Stacked Assemblies
First Experimental Evidence for the Diverse Requirements of Excimer vs Hole Stabilization in π-Stacked Assemblies
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α-堆叠组件中准分子与空穴稳定性不同要求的第一个实验证据
DOI：
10.1021/acs.jpclett.6b01201
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发表时间：
2016
期刊：
影响因子：
--
通讯作者：
Reid, Scott A.
中科院分区：
文献类型：
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作者：
Reilly, Neil;Ivanov, Maxim;Uhler, Brandon;Talipov, Marat;Rathore, Rajendra;Reid, Scott A.
激子的形成、电荷的分离和传输是包括DNA在内的多种功能高分子材料和生物体系中的关键动力学事件。除了在货车德瓦耳斯接触的一对芳香族分子的必要的共面方法之外，对于激基缔合物与二聚体阳离子自由基的最佳稳定的重叠程度和必要的几何重组仍然没有解决。在这里，我们比较实验的动力学激基缔合物的形成（通过发射）和电荷稳定（通过阈值电离）的一种新的共价连接，cofacially堆叠芴二聚体（F2）与未连接的货车德瓦尔斯二聚体的芴，即（F）2。虽然测得的电离势是相同的，但在共价连接的F2中，受激异构体状态被稳定高达1030 kJ/mol。在理论的支持下，这项工作首次通过实验证明，准分子的最佳稳定需要具有最大重叠的完美的类π几何形状，而π堆叠聚集体中的空穴稳定在几何上的限制较少。
Exciton formation and charge separation and transport are key dynamical events in a variety of functional polymeric materials and biological systems, including DNA. Beyond the necessary cofacial approach of a pair of aromatic molecules at van der Waals contact, the extent of overlap and necessary geometrical reorganization for optimal stabilization of an excimer vs dimer cation radical remain unresolved. Here, we compare experimentally the dynamics of excimer formation (via emission) and charge stabilization (via threshold ionization) of a novel covalently linked, cofacially stacked fluorene dimer (F2) with the unlinked van der Waals dimer of fluorene, that is, (F)2. Although the measured ionization potentials are identical, the excimeric state is stabilized by up to ∼30 kJ/mol in covalently linked F2. Supported by theory, this work demonstrates for the first time experimentally that optimal stabilization of an excimer requires a perfect sandwich-like geometry with maximal overlap, whereas hole stabilization in π-stacked aggregates is less geometrically restrictive.