PAPER www.rsc.org/pps | Photochemical & Photobiological Sciences Spectral properties and inclusion of a hetero-chalcone analogue in organized media of micellar solutions and beta-cyclodextrin M. Gaber, T. A. Fayed,* S. A. El-Daly and Y. S. El-Sayed Received 3rd September 2007, Accepted 27th November 2007 First published as an Advance Article on the web 13th December 2007 DOI: 10.1039/b713381b 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 b-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 b-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 (DS =−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. Introduction Organized media including micellar solutions and cyclodextrins (CDs) have been the subject of continuous interest. 1–4 These media are able to solubilize hydrophobic compounds in water and modify significantly their physicochemical properties. Amphiphilic molecules which self-assemble in solutions to form micelles are drawing the attention of chemists due to their importance as catalysts, solubility enhancers and detergents. 5,6 They are also used to simulate more complex environmental conditions present in larger bio-aggregates such as membranes. 7 Cyclodextrins are interesting microvesicles capable of encap- sulating a wide range of organic and inorganic compounds to form host–guest inclusion complexes. 8–12 CDs are cyclic oligosac- charides with a hydrophilic outer surface and a hydrophobic central cavity. The reduced polarity and restricted geometry of the cavity provide an interesting microenvironment for studying the energetics and dynamics of various photophysical processes of the encapsulated molecules. 13,14 Beta-cyclodextrin (b-CD), which is composed of 6 D-glucose units, is the most readily available and widely used amongst the three naturally occurring cyclodextrins. Chalcones are well known precursors of many naturally oc- curring pigments as flavones. They are used in many fields of applications such as UV-absorption filters in polymers, 15 in non- linear optics and holographic recording technologies 16 as well as Department of Chemistry, Faculty of science, Tanta University, 31527, Tanta, Egypt. E-mail: tfayed2003@yahoo.co.uk in food industry. 17 Also, they found potential applications as new drugs due to their wide spectrum of biological activities. 18,19 Chalcone derivatives containing amino-substituted phenyl groups exhibit fluorescence properties that depend on the physical and chemical nature of the medium. This is due to population of a highly dipolar intramolecular charge transfer (ICT) or twisted ICT (TICT) excited state as an emissive state. Therefore, the photophysical properties of donor–acceptor substituted chalcones have been widely investigated. 20–24 The high sensitivity of the ICT states to solvation, polarity and molecular mobility changes render such molecules to be efficient probes for their microenvi- ronments. In this respect, chalcone derivatives have been utilized as fluorescent probes for sensing of metal ions, 20,25–28 biological macromolecules 29–32 and microenvironment in micelles. 33 The present work deals with studying the absorption and emission characteristics of a hetero-chalcone derivative, namely; 3-(4 ′ -dimethylaminophenyl)-1-(2-thienyl)prop-2-en-1-one and ab- breviated as DMATP (Scheme 1), in aqueous micellar solutions of sodium dodecyl sulfate (SDS), cetyltrimethylammonium bromide (CTAB) and Triton X-100 (TX-100) as well as in b-CD solutions. Scheme 1 This journal is © The Royal Society of Chemistry and Owner Societies 2008 Photochem. Photobiol. Sci., 2008, 7, 257–262 | 257