Sukpattanacharoen Chattarika, Kumar Prashant, Chi Yun, Kungwan Nawee, Escudero Daniel
Department of Chemistry, KU Leuven, Celestijnenlaan 200F, B-3001 Leuven, Belgium.
Department of Chemistry, Faculty of Science and Graduate School, Chiang Mai University, Chiang Mai 50200, Thailand.
Inorg Chem. 2020 Dec 21;59(24):18253-18263. doi: 10.1021/acs.inorgchem.0c02780. Epub 2020 Dec 8.
The interplay between noncovalent interactions involving metal complexes may lead to the formation of aggregates (i.e., ground state dimers, trimers, -mers, etc.), and this is often linked to dramatic changes in their physical and chemical properties as compared to the original properties of the isolated units. Dimers and trimers can also be formed in the excited state potential energy surfaces, i.e., excimers. Excimers are short-lived but are also often characterized by different optical properties from those of the isolated units. Understanding the nature of noncovalent interactions and the presence or not of cooperativity effects in both aggregates and excimers is thus extremely important to rationalize these variations. In this study, we present computational investigations on isoquinolinyl pyrazolate Pt(II) complexes. Our results highlight that cooperativity effects between noncovalent interactions, which are modulated by sterically demanding substituents and metallophilic Pt···Pt interactions, are present only on certain investigated excimers. We use density functional theory (DFT) calculations to examine the cooperativity effects and the changes in the photophysical properties. Different descriptors of cooperativity effects between noncovalent interactions, including the synergetic, genuine nonadditive, and total interaction energies, were evaluated for a series of Pt(II) aggregates and excimers. In addition, energy decomposition analysis (EDA) calculations were performed to rationalize the origins of the cooperative effects. The cooperative effects in trimer excimers (in their lowest triplet excited state, i.e., T) led to shortened Pt···Pt contacts as compared to the trimer aggregates. Furthermore, this synergy between noncovalent interactions is ultimately responsible for the formation of the excimers and the striking changes in the measured photophysical properties. More in detail, we report a change in the character of the lowest-lying triplet excited state when going from dimer excimers (i.e., of mixed triplet ligand-centered and triplet metal-to-ligand charge transfer (LC/MLCT) character) to trimer excimers (i.e., of triplet metal-metal-to-ligand charge transfer (MMLCT) character). The EDA reveals that the total interaction energy on trimer excimers is subtly controlled by the electrostatic and dispersion terms.
涉及金属配合物的非共价相互作用之间的相互作用可能导致聚集体的形成（即基态二聚体、三聚体、多聚体等），与孤立单元的原始性质相比，这通常与它们的物理和化学性质的显著变化有关。二聚体和三聚体也可以在激发态势能面上形成，即准分子。准分子寿命短暂，但通常也具有与孤立单元不同的光学性质。因此，了解非共价相互作用的本质以及聚集体和准分子中协同效应的存在与否对于解释这些变化极为重要。在本研究中，我们展示了对异喹啉基吡唑酸根合铂（II）配合物的计算研究。我们的结果突出表明，由空间位阻较大的取代基和亲金属铂···铂相互作用调节的非共价相互作用之间的协同效应仅存在于某些研究的准分子中。我们使用密度泛函理论（DFT）计算来研究协同效应和光物理性质的变化。针对一系列铂（II）聚集体和准分子，评估了非共价相互作用之间协同效应的不同描述符，包括协同、真正非加和以及总相互作用能。此外，进行了能量分解分析（EDA）计算以解释协同效应的起源。与三聚体聚集体相比，三聚体准分子（处于其最低三重激发态，即T态）中的协同效应导致铂···铂接触缩短。此外，这种非共价相互作用之间的协同作用最终导致了准分子的形成以及所测量的光物理性质的显著变化。更详细地说，我们报告了从二聚体准分子（即具有混合的以配体为中心的三重态和三重态金属到配体电荷转移（LC/MLCT）特征）到三聚体准分子（即具有三重态金属 - 金属到配体电荷转移（MMLCT）特征）时最低三重激发态性质的变化。EDA表明，三聚体准分子上的总相互作用能受到静电和色散项的微妙控制。
