Department of Chemistry, Graduate School of Science, Hiroshima University, Higashi-Hiroshima 739-8526, Japan.
Phys Chem Chem Phys. 2010 Apr 14;12(14):3559-65. doi: 10.1039/b924822f.
The conformation and complex formation with guest molecules have been investigated for jet-cooled dibenzo-24-crown-8-ether (DB24C8) by laser induced fluorescence (LIF), UV-UV hole-burning (UV-UV HB), and IR-UV double-resonance (IR-UV DR) spectroscopy. The results are compared with the results of dibenzo-18-crown-6-ether (DB18C6) and analyzed by density functional theory (DFT) calculations at the B3LYP/6-31+G* level. Five conformers are identified for DB24C8 under jet-cooled conditions, and the structure of the major isomer is determined to be a boat form, similar to the case of DB18C6. Two molecules (water and methanol) are investigated as the guest species for the encapsulation experiment. DB24C8 hardly encapsulates a water molecule, different from the case of DB18C6 in which a water molecule is efficiently captured. However, it is likely that larger (water)(n) clusters can be captured in the DB24C8 cavity. The different feature in the complex formation between DB24C8 and DB24C8 with the water molecules are attributed to a larger cavity size of DB24C8 than that of DB18C6. For methanol, two kinds of DB18C6-(methanol)(1) isomers are identified by IR-UV DR spectroscopy; one is the "OH...pi" H-bonded isomer, characteristic of methanol with one OH group, and the other is the "OH...O" H-bonded ones. These results indicate the multiple H-bond formation to the oxygen atoms of the ether ring may play an important role in the complexes of DB24C8 or DB18C6 with water.
已通过激光诱导荧光（LIF）、紫外-紫外光烧孔（UV-UV HB）和红外-紫外双共振（IR-UV DR）光谱研究了喷射冷却的二苯并-24-冠-8-醚（DB24C8）与客体分子的构象和络合。将结果与二苯并-18-冠-6-醚（DB18C6）的结果进行了比较，并通过密度泛函理论（DFT）计算在 B3LYP/6-31+G*水平上进行了分析。在喷射冷却条件下，确定了 DB24C8 的 5 种构象，并且主要异构体的结构确定为船形，类似于 DB18C6 的情况。选择两种分子（水和甲醇）作为包合实验的客体物种。DB24C8 几乎不包合水分子，与 DB18C6 不同，后者可以有效地捕获水分子。但是，DB24C8 腔中可能会捕获更大的（水）（n）簇。DB24C8 与 DB24C8 与水分子形成的复合物的不同特征归因于 DB24C8 的腔尺寸大于 DB18C6。对于甲醇，通过 IR-UV DR 光谱鉴定了两种 DB18C6-（甲醇）（1）异构体；一种是具有一个 OH 基团的甲醇的“OH...pi”氢键异构体，另一种是“OH...O”氢键异构体。这些结果表明，与醚环的氧原子形成多重氢键可能在 DB24C8 或 DB18C6 与水的配合物中起重要作用。
