Dependence of Absorption and Emission Spectra on Polymorphs of Gold(I) Isocyanide Complexes: Theoretical Study with QM/MM Approach
Dependence of Absorption and Emission Spectra on Polymorphs of Gold(I) Isocyanide Complexes: Theoretical Study with QM/MM Approach
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DOI：
10.1021/acs.jpcc.8b10602
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发表时间：
2019-02-28
影响因子：
3.7
通讯作者：
Sakaki, Shigeyoshi
中科院分区：
文献类型：
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作者：
Aono, Shinji;Seki, Tomohiro;Sakaki, Shigeyoshi
我们用基于自洽点电荷的周期量子力学/分子力学(QM/MM)方法对晶体中苯基(苯基异氰酸酯)金(I)(PhNC)Au(Ph)1和苯基二甲基苯基异氰酸酯(I)Au(Ph)2进行了理论研究，以解释晶体中1和2吸收光谱和发射光谱的机械力化学变化。为了表征晶体中的1和2，比较了它们在晶体中的吸收光谱和发射光谱与在气相和CHCl3溶剂中的吸收光谱和发射光谱，其中采用三维参考作用点模型自洽场(3D-RISM-SCF)考虑了溶剂化效应。为了研究晶体中的磷光光谱，我们优化了晶体中三重态分子的几何构型，由于激发态布居一般很小，所以具有基态几何结构。QM/MM计算表明，1形成两个多态1b和1Y，2形成两个多态2b和2g，且1Y比1b更稳定，这与实验结果一致。在1b和2b中，配体到配体的电荷转移态是吸收中最低能量的激发态，而PhNC部分上的pi-pi*局域激发态是发射中最低能量的三重态。另一方面，在1Y和2G中，金属-配体电荷转移(MMLCT)态是吸收和发射中能量最低的激发态。两种晶体结构之间的这些特征差异是由于1Y和2G的Au-Au距离比1b和1Y的小得多，两个Au-PhNC基团之间的分子间扭角ETA分别比1b和2b的小得多；较短的Au-Au距离提高了由两个Au d(Sigma)轨道组成的反键轨道的能级，而较小的ETA角降低了由两个PhNC pi*轨道组成的成键轨道的能级，导致了MMLCT态的存在。QM/MM计算还揭示了Ph和PhNc面间的分子内扭角tau和Ph面上的CH-pi相互作用对吸收光谱有显著影响。在此基础上，讨论了气体、溶液和晶体之间吸收光谱和发射光谱的差异，实验观测到的激发光谱和发射光谱在晶体中的归属，以及由单晶到单晶相变引起的能量漂移。
We theoretically investigated phenyl(phenyl isocyanide) gold(I) (PhNC)Au(Ph) 1 and phenyl(dimethylphenyl isocyanide) gold(I) (dimPhNC)Au(Ph) 2 in crystal using our periodic quantum mechanics/molecular mechanics (QM/MM) method based on the self-consistent point charges to elucidate interesting mechano-chemical changes of absorption and emission spectra of 1 and 2 in crystal. To characterize 1 and 2 in crystal, their absorption and emission spectra in crystal were compared to those in gas phase and CHCl3 solvent, where a three-dimensional reference interaction site model self-consistent field (3D-RISM-SCF) was employed to incorporate solvation effect. To investigate the phosphorescence spectrum in crystal, we optimized the geometry of the molecule at the triplet state in crystal which had ground-state geometry because the population of the excited state is generally very small. The QM/MM calculations showed that 1 formed two polymorphs 1b and 1y, 2 formed two polymorphs 2b and 2g, and 1y was more stable than 1b, which agree with the experimental findings. In 1b and 2b, the ligand-to-ligand charge transfer state is the lowest-energy excited state in the absorption, and the pi-pi* locally excited state on the PhNC moiety is the lowest-energy triplet state in the emission. In 1y and 2g, on the other hand, the metal metal-to-ligand charge transfer (MMLCT) state is the lowest-energy excited state in both absorption and emission. These characteristic differences between two crystal structures arise from the geometrical features that the Au-Au distance is much shorter in 1y and 2g than in 1b and 1y and the intermolecular torsion angle eta between two Au-PhNC moieties is much smaller in 1y and 2g than in 1b and 2b, respectively; the short Au-Au distance raises the energy level of antibonding orbital consisting of two Au d(sigma) orbitals, and the small eta angle lowers the energy level of bonding orbital consisting of two PhNC pi* orbitals, leading to the presence of a lower-energy MMLCT state. The QM/MM calculations also disclosed intramolecular torsion angle tau between the Ph and PhNC planes and CH-pi interaction of the Ph plane significantly influence absorption spectrum. Based on those computational results, discussion is presented on the differences in absorption and emission spectra among gas, solution, and crystal, the assignments of experimentally observed excitation and emission spectra in crystal, and their energy shifts induced by single-crystal-to-single-crystal phase transition.