Spectral properties and inclusion of a hetero-chalcone analogue in organized media of micellar solutions and beta-cyclodextrin

Abstract

The absorption and fluorescence emission spectral properties of 3-(4'-dimethylaminophenyl)-1-(2-thienyl)prop-2-en-1-one, abbreviated as DMATP, have been investigated in organized media of aqueous micellar and beta-cyclodextrin (CD) solutions. While the absorption spectra are less sensitive to the nature of the added surfactant or CD, the characteristics of the intramolecular charge transfer (ICT) fluorescence are highly sensitive to the properties of the medium. The ICT maximum is strongly blue-shifted with a great enhancement in the fluorescence quantum yield on adding micellar or CD solutions. This indicates the solubilization of DMATP in the micellar core and formation of an inclusion complex with beta-CD. The critical micelle concentration (CMC) as well as the polarity of the micellar core of SDS, CTAB and TX-100 have been determined. The CMC values are in good agreement with the reported values while the polarity is lower indicating that DMATP molecules are incorporated in the micellar core not at the micellar interface. The inclusion constants of binding of DMATP in micellar or CD have been also determined. The thermodynamic parameters of formation of DMATP:CD inclusion complex have been calculated from the temperature dependence of the fluorescence spectra of the formed complex. The negative enthalpy and free energy of formation indicate that the inclusion process is energetically favorable. The highly negative value of formation entropy (DeltaS = -162.3 J mol(-1) K(-1)) reflects the high restrictions imposed on the movement of both the host and included guest molecules which is consistent with the increase of the fluorescence yield and blue shift of the fluorescence maximum.