The inclusion complexations of rhodamine derivatives with native and 2,6-di-O-methylated β-cyclodextrins (β-CD and DM-β-CD) were studied spectrophotometrically. Rhodamine derivatives were shown to form 1:1 inclusion complexes with β-CDs by the continuous variation method. The structures of the inclusion complexes were characterized by 1H-1H rotating frame nuclear Overhauser effect spectroscopy (ROESY) NMR measurements. It was found that native β-CD encapsulates the xanthenyl ring of rhodamines into the cyclodextrin cavity, while DM-β-CD forms two group-in complexes (phenyl-in and xanthenyl-in (bidirectional (bimodal) inclusion complexes)) with rhodamines bearing moderately bulky functional groups. Furthermore, we demonstrated the unique thermodynamics for the group-inclusion complex formation by DM-β-CD. The quantum yields for the inclusion complexes of rhodamines were determined using a quantum measurement apparatus equipped with a half-moon unit. The results indicated that the cyclodextrin inclusion of rhodamines with the bulky amino substituents on the xanthenyl ring largely decreases the quantum yield values. Based on these results, the substituent effects on the fluorescence process for the cyclodextrin inclusion complexes of rhodamines were discussed. This study provides useful insights for the functional group recognition of native and modified β-CDs.

中文翻译：

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罗丹明衍生物与天然和 2,6-二-O-甲基化 β-环糊精的基团包合络合的表征

用分光光度法研究了罗丹明衍生物与天然和 2,6-二-O-甲基化 β-环糊精（β-CD 和 DM-β-CD）的包合络合。罗丹明衍生物通过连续变化方法与 β-CDs 形成 1:1 的包合物。包合物的结构通过 1H-1H 旋转框架核 Overhauser 效应光谱 (ROESY) NMR 测量表征。发现天然 β-CD 将罗丹明的呫吨环封装到环糊精腔中，而 DM-β-CD 与罗丹明形成两个基团络合物（苯基络合物和呫吨基络合物（双向（双峰）包合络合物））带有中等体积的官能团。此外，我们展示了 DM-β-CD 形成基团包合物的独特热力学。罗丹明包合物的量子产率是使用配备有半月单元的量子测量装置确定的。结果表明，在呫吨环上含有大量氨基取代基的罗丹明的环糊精大大降低了量子产率值。基于这些结果，讨论了取代基对罗丹明环糊精包合物荧光过程的影响。这项研究为天然和修饰的 β-CDs 的功能组识别提供了有用的见解。讨论了取代基对罗丹明环糊精包合物荧光过程的影响。这项研究为天然和修饰的 β-CDs 的功能组识别提供了有用的见解。讨论了取代基对罗丹明环糊精包合物荧光过程的影响。这项研究为天然和修饰的 β-CDs 的功能组识别提供了有用的见解。