Tada Kohei, Kawakami Takashi, Hinuma Yoyo
Research Institute of Electrochemical Energy (RIECEN), Department of Energy and Environment, National Institute of Advanced Industrial Science and Technology (AIST), 1-8-31 Midorigaoka, Ikeda, Osaka 563-8577, Japan.
RIKEN Center for Computational Science, Kobe, Hyogo 650-0047, Japan.
Phys Chem Chem Phys. 2023 Nov 8;25(43):29424-29436. doi: 10.1039/d3cp02988c.
The analysis of the diradical state of functional open-shell molecules is important for understanding their physical properties and chemical reactivity. The diradical character is an important factor in the functional elucidation and design of open-shell molecules. In recent years, attempts have been made to immobilise functional open-shell molecules on surfaces to form devices. However, the influence of surface interactions on the diradical state remains unclear. In this study, the physisorption structures of -benzyne, which is a typical diradical molecule, on MgO(001) and SrO(001) surfaces are used as models to investigate how the diradical character is affected by physisorption. This is done using approximate spin-projected density functional theory calculations with dispersion correction and plane-wave basis (AP-DFT-D3/plane-wave calculations). The diradical character change (Δ) due to adsorption can be categorised into three factors, namely the change due to the distortion of the diradical molecule (Δ), the interaction between neighbouring diradical molecules (Δ), and molecule-surface interactions (Δ). In all the calculated models, physisorption reduced the diradical character (Δ < 0), and the contribution of Δ was the largest among the three factors. The calculated results show that adsorption induces electron delocalisation to π-conjugated orbitals and intramolecular charge polarisation, both of which contribute to reducing the occupancy of singly occupied molecular orbitals. This indicates that the diradical character of -benzyne is reduced by the stabilisation of the resonance structures. Furthermore, geometry optimisation of the surfaces shows that the chemical-soft surface (SrO) varies the diradical character more significantly than the chemical-hard surface (MgO). This study shows that the open-shell electronic state and stack structure of diradical molecules can be controlled through the analysis of the surface diradical state.
对功能性开壳分子的双自由基态进行分析，对于理解其物理性质和化学反应性至关重要。双自由基特性是开壳分子功能阐释和设计中的一个重要因素。近年来，人们尝试将功能性开壳分子固定在表面以形成器件。然而，表面相互作用对双自由基态的影响仍不明确。在本研究中，以典型双自由基分子对 - 苯炔在MgO(001)和SrO(001)表面的物理吸附结构为模型，研究物理吸附如何影响双自由基特性。这是通过使用带有色散校正和平面波基组的近似自旋投影密度泛函理论计算（AP-DFT-D3/平面波计算）来完成的。由于吸附导致的双自由基特性变化（Δ）可分为三个因素，即双自由基分子畸变引起的变化（Δ）、相邻双自由基分子之间的相互作用（Δ）以及分子 - 表面相互作用（Δ）。在所有计算模型中，物理吸附降低了双自由基特性（Δ < 0），并且在这三个因素中，Δ的贡献最大。计算结果表明，吸附诱导电子离域到π共轭轨道和分子内电荷极化，这两者都有助于降低单占据分子轨道的占有率。这表明 - 苯炔的双自由基特性通过共振结构的稳定而降低。此外，表面的几何优化表明，化学性质较软的表面（SrO）比化学性质较硬的表面（MgO）对双自由基特性的影响更显著。本研究表明，通过分析表面双自由基态，可以控制双自由基分子的开壳电子态和堆积结构。
