Department of Inorganic and Physical Chemistry , Indian Institute of Science , Bangalore 560012 , India.
Department of Chemical and Pharmaceutical Sciences , University of Trieste , Trieste 34127 , Italy.
J Am Chem Soc. 2018 Jun 27;140(25):7952-7960. doi: 10.1021/jacs.8b03946. Epub 2018 Jun 15.
Self-assembly of a cis-blocked Pd(II) 90° ditopic acceptor [ cis-(tmeda)Pd(NO)] (M) with a tetradentate donor L [benzene-1,4-di(4-terpyridine)] in 2:1 molar ratio yielded two isometric molecular barrels MB1 and MB3 in DMSO [tmeda = N, N, N' N'-tetramethylethane-1,2-diamine]. Exclusive formation of the symmetrical tetrafacial barrel (MB1) was achieved when the self-assembly was performed in aqueous medium. The presence of a large confined cavity makes MB1 a potential molecular container. Spiropyran (SP) compounds exist in stable closed spiro form in visible light and convert to transient open merocyanine (MC) form upon irradiation with UV-light or upon strong heating. The transient MC form readily converts to the stable closed SP form in visible light. MB1 has been employed as a safe container to store the planar and unstable merocyanine isomers (MC1/2) of different spiropyran molecules (SP1/2) [SP1/2 = 6-bromo-spiropyran and 6-nitrospiropyran] for several days. The transient MC forms (MC1 and MC2) were found to be stable inside the molecular container MB1 under visible light and even in the presence of different stimuli such as heat and UV light for a long time. Such stabilization of MC forms inside the confined cavity of MB1 is noteworthy. This phenomenon was generalized by utilizing a carbazole-based molecular barrel (MB2) as a host, which also showed a similar stabilization of transient MC form in visible light at room temperature. Moreover, reverse thermochromism was observed as a result of heating of the MC1 ⊂ MB2 complex, which de-encapsulates the guest in the form of SP1 to give a colorless solution. Moreover, both the host molecules (MB1, MB2) were capable of stabilizing transient MC2 even in the solid state. Such stabilization of transient MC forms in the solid state and transformation of SP forms to MC forms in the solid state in the presence of molecular barrel are remarkable, and these properties have been employed in developing a magic ink.
cis-（tmeda）Pd（NO）]（M）与四齿供体 L [苯-1,4-二（4-三吡啶）]以 2:1 的摩尔比自组装，在 DMSO 中得到两个等立体分子桶 MB1 和 MB3 [tmeda = N, N, N'N'-四甲基乙二胺]。当自组装在水介质中进行时，仅形成对称的四面桶（MB1）。大的受限腔的存在使 MB1 成为潜在的分子容器。螺吡喃（SP）化合物在可见光下以稳定的闭合螺环形式存在，在紫外线照射或强加热下转化为瞬态开式变色酸（MC）形式。瞬态 MC 形式在可见光下很容易转化为稳定的闭合 SP 形式。MB1 已被用作安全容器，可储存不同螺吡喃分子（SP1/2）[SP1/2 = 6-溴螺吡喃和 6-硝基螺吡喃]的平面和不稳定的变色酸异构体（MC1/2）数天。瞬态 MC 形式（MC1 和 MC2）在可见光下和甚至在存在不同刺激如热和紫外线的情况下在分子容器 MB1 内被发现是稳定的，这是值得注意的。这种 MC 形式在 MB1 的受限腔内的稳定现象被推广，利用咔唑基分子桶（MB2）作为主体，在室温下也显示出瞬态 MC 形式在可见光下的类似稳定化。此外，由于 MC1⊂MB2 配合物的加热，观察到反向热致变色，其以 SP1 的形式去封装客体，得到无色溶液。此外，主体分子（MB1、MB2）都能够即使在固态下也稳定瞬态 MC2。在固态下瞬态 MC 形式的稳定化以及在存在分子桶的情况下 SP 形式向 MC 形式的转化是显著的，这些性质已被用于开发魔术墨水。
