Department of Chemistry, Graduate School of Advanced Science and Engineering, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8526, Japan.
J Phys Chem A. 2023 Apr 13;127(14):3210-3220. doi: 10.1021/acs.jpca.3c01447. Epub 2023 Apr 4.
This study investigated the geometric and electronic structures of dibenzo-21-crown-7 (DB21C7) and dibenzo-24-crown-8 (DB24C8) complexes with alkali metal ions, identified as M(DB21C7) and M(DB24C8) (M = Na, K, Rb, and Cs), respectively. We observed the ultraviolet photodissociation (UVPD) spectra of these complexes under cold (∼10 K) gas-phase conditions. The conformations of the M(DB21C7) and M(DB24C8) complexes were determined by comparing the UVPD spectra with the calculated electronic transitions of the local-minimum forms. The interactions between the electronic excited states of the two benzene chromophores in the M(DB21C7) and M(DB24C8) complexes were examined and compared with those of previously studied complexes (dibenzo-15-crown-5 (DB15C5) and dibenzo-18-crown-6 (DB18C6)). The S-S and S-S electronic excitations of the M(DB21C7) complexes were almost localized in one of the benzene rings. In contrast, the closed conformers of the M(DB24C8) (M = K, Rb, and Cs) complexes were delocalized over the two chromophores for electronic excitations, exhibiting strong electronic interactions between the benzene rings. For the M(DB24C8) complexes (M = K, Rb, and Cs), the short distance between the benzene rings (∼3.9 Å) led to a strong interaction between the benzene chromophores. We conclude that this strong interaction in the M(DB24C8) complexes correlates strongly with the broad absorption in the UVPD spectra, suggesting the presence of an intramolecular excimer for the K(DB24C8), Rb(DB24C8), and Cs(DB24C8) complexes.
本研究调查了二苯并-21-冠-7（DB21C7）和二苯并-24-冠-8（DB24C8）与碱金属离子形成的配合物的几何和电子结构，分别鉴定为 M（DB21C7）和 M（DB24C8）（M = Na，K，Rb 和 Cs）。我们在冷（约 10 K）气相条件下观察了这些配合物的紫外光解（UVPD）光谱。通过将 UVPD 光谱与局部最小形式的计算电子跃迁进行比较，确定了 M（DB21C7）和 M（DB24C8）配合物的构象。检查了 M（DB21C7）和 M（DB24C8）配合物中两个苯环发色团的电子激发态之间的相互作用，并将其与先前研究的配合物（二苯并-15-冠-5（DB15C5）和二苯并-18-冠-6（DB18C6））进行了比较。M（DB21C7）配合物中电子激发的 S-S 和 S-S 跃迁几乎局限于一个苯环中。相比之下，M（DB24C8）（M = K，Rb 和 Cs）配合物的封闭构象在两个发色团上电子激发时离域，两个苯环之间表现出强烈的电子相互作用。对于 M（DB24C8）配合物（M = K，Rb 和 Cs），苯环之间的短距离（约 3.9 Å）导致苯环发色团之间的强烈相互作用。我们得出结论，这种 M（DB24C8）配合物中的强烈相互作用与 UVPD 光谱中的宽吸收强烈相关，表明 K（DB24C8）、Rb（DB24C8）和 Cs（DB24C8）配合物存在分子内激基复合物。
