This report describes photoluminescence studies of copper-containing [2]pseudorotaxanes that mimic elements of functioning molecular machines. Excitation with visible light induces a formal oxidation of the metal center and simulates an actuation process. In all four [2]pseudorotaxanes studied, the ring ligand is the same, but the thread ligand is variable, namely 2,9-di(anisol-4-yl)-1,10-phenanthroline (dap), 6,6′-di(anisol-4-yl)-2,2′-bipyridine (o-dabipy), 5,5′-di(anisol-4-yl)-2,2′-bipyridine (m-dabipy), or 8,8′-di(anisol-4-yl)-3,3′-bi-isoquinoline (dabiiq). The absorbance bandshapes suggest that aryl substituents extending from the core ligands engage in stacking interactions and induce a partially flattened structure in the ground state. More severe flattening occurs in the excited state and precludes the observation of emission if inter-ligand steric forces do not limit the distortion. Thus, the [2]pseudorotaxanes containing dap or o-dabipy as the thread ligand exhibit uncorrected emission maxima at around 720 nm in room-temperature dichloromethane, while the less constrained analogues, containing dabiiq or m-dabipy, are not emissive in fluid solution and barely exhibit a signal in rigid media. In dichloromethane, the luminescence quantum yields of the dap- and o-dabipy-containing systems are 6 × 10−4 and 4 × 10−4, and the excited-state lifetimes are 98 ns and 90 ns, respectively.
本报告介绍了对含铜 [2]pseudorotaxanes 的光致发光研究,这种化合物模仿了功能分子机器的元素。在可见光的激发下,金属中心会发生形式上的氧化,并模拟一个致动过程。在所研究的所有四种[2]赝轴烷中,环配体是相同的,但螺纹配体是可变的,即 2,9-二(茴香醇-4-基)-1,10-菲罗啉(dap)、6、6′-二(苯甲醚-4-基)-2,2′-联吡啶(o-dabipy)、5,5′-二(苯甲醚-4-基)-2,2′-联吡啶(m-dabipy)或 8,8′-二(苯甲醚-4-基)-3,3′-双异喹啉(dabiiq)。吸光带形状表明,从核心配体延伸出来的芳基取代基参与了堆叠相互作用,并导致基态结构部分扁平化。激发态的扁平化更为严重,如果配体间的立体力不限制畸变,就无法观察到发射。因此,含有 dap 或 o-dabipy 作为线配体的 [2]pseudorotaxanes 在室温二氯甲烷中显示出约 720 纳米的未校正发射最大值,而含有 dabiiq 或 m-dabipy 的限制较少的类似物在流体溶液中没有发射,在刚性介质中几乎没有信号。在二氯甲烷中,含有 dap 和 o-dabipy 的系统的发光量子产率分别为 6 × 10-4 和 4 × 10-4,激发态寿命分别为 98 ns 和 90 ns。