Molecular Interactions, Proton Exchange, and Photoinduced Processes Prompted by an Inclusion Process and a [2]Pseudorotaxane Formation

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• 作者：Amal Kumar Mandal ; Moorthy Suresh ; Manoj K. Kesharwani ; Monalisa Gangopadhyay ; Manoj Agrawal ; Vinod P. Boricha ; Bishwajit Ganguly ; Amitava Das
• 刊名：Journal of Organic Chemistry
• 出版年：2013
• 出版时间：September 20, 2013
• 年：2013
• 卷：78
• 期：18
• 页码：9004-9012
• 全文大小：517K
• 年卷期：v.78,no.18(September 20, 2013)
• ISSN：1520-6904

文摘

Appropriate design of the host and guest components allows formation of a novel [2]pseudorotaxane complex with an interrupted photoinduced electron transfer (PET)-coupled fluorescence resonance energy transfer (FRET) response. This is the first example of an inclusion complex with NO₆-based azacrown ether as the host unit (H). Different guest molecules (G1, G2, G3, and G4) with varying stopper size are used for the studies. Unlike G1, G2, and G3, G4 with a relatively bulkier stopper fails to form a [2]pseudorotaxane complex. Isothermal titration microcalorimetry measurements reveal a systematic increase in the association constant for H路G1, H路G2, and H路G3 with a change in the stopper size. Thermodynamic data suggest that the formation of H路G1/H路G2/H路G3 is exclusively driven by a large positive entropic gain (T螖S = 19.69/26.80/21.81 kJ路mol^鈥?), while the enthalpy change is slightly negative for H路G1/H路G3 (鈭?.61/鈥?.97 kJ路mol^鈥?) and slightly positive for H路G2 (螖H = 5.98 kJ路mol^鈥?). For these three inclusion complexes, an interrupted PET-coupled FRET response is observed with varying efficiency, which is attributed to the subtle differences in acidity of the NH₂⁺ unit of the guest molecules and thus the proton exchange ability between the host and respective guest. This is substantiated by the results of the computational studies.