Molecular association of benzene with a new cyclophane receptor
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Host/guest interactions in the cyclophane-2/benzene system have been investigated by absorption and fluorescence spectroscopy in dichloromethane. The cyclophane serves as a host and the benzene as a guest. Absorption and fluorescence titration experiments are carried out by holding either the concentration of the host or guest constant while varying the concentration of the other component. When the concentration of benzene is kept constant, an isostilbic point at 288 nm is observed in the fluorescence spectral data, suggesting that only two absorbing species are present in equilibrium. Keeping the concentration of cyclophane-2 constant while increasing the concentration of benzene results in a hyposchromic shift of the emission peaks in the range 275–360 nm. The shift is attributed to interaction of the cyclophane with benzene. The average association constant of cyclophane-2 with benzene, K a = 425 ± 54 M−1, obtains from fitting the absorption and the fluorescence spectral data to the Bourson et al. equation using non-linear regression analysis.
KeywordsAromatic compounds Association constant Cyclophane Host/guest complexation
This work was financially supported by the NSF-MRI grant-0421228 and the Materials Characterization Center at Western Kentucky University. CD and RG wish to acknowledge the KY NSF-EPSCoR Scholar Program, and the NSF-REU Grant EAR-035361 for support of their research. The research conducted at Texas Tech University was supported by Grant D-0775 from The Welch Foundation.
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