Host-guest complexation of cationic xanthene dyes with cucurbit[7]uril

The macrocyclic host, cucurbit[7]uril (CB7) is known to be a very selective host for cationic guests. Additionally, CB7 has also been shown to have beneficial effects on the photophysical properties of cationic organic fluorophores, particularly cationic dyes of the xanthene family, including various rhodamines and pyronins. Examples of the beneficial effects include increased fluorescence intensity, protection from photobleaching and the prevention of nonspecific adsorption and aggregation.;We have chosen to study the ability of CB7 to affect changes in the spectroscopic properties of cationic xanthene dyes using bulk ensemble measurements and single molecule spectroscopy. To investigate the ability of CB7 to affect chromophore-chromophore interactions in multichromophoric systems, flexible C6 and C12 tethered rhodamine B dyads were prepared and the effects of CB7 on their spectroscopic properties in aqueous solution were studied. Results obtained from these studies provide evidence for the ability of CB7 to convert a cationic tethered dyad from a non-fluorescent H-dimer form to a fluorescent J-dimer form upon complexation. A fluorescent rhodamine B propargyl ester was prepared and covalently attached to the glass surface by a 1,2,3-triazole linkage following a 1,3-dipolar cycloaddition "click" reaction facilitated by a well defined homogeneous copper (I) catalyst. The effects of CB7 on the spectroscopic properties of the surface attached dyes in aqueous solution were studied using UV-Vis absorbance and steady-state fluorescence spectroscopy. Results from these studies provide evidence for the ability of CB7 to disrupt cationic dye aggregation and enhance the fluorescence of surface attached dye molecules.;Preliminary investigations were also preformed into the covalent functionalization of silica nanoparticles with cationic dyes and the effects of CB7 on the photophysical properties of the dye functionalized nanoparticles suspended in aqueous solution. Results from these studies provide evidence for the ability of CB7 to disrupt cationic dye aggregation and enhance the fluorescence of dye molecules attached to the surface of silica nanoparticles.;It is anticipated that this work will lead to the development of bright and long-lived fluorescent probes for single molecule fluorescent spectroscopy applications and encourage additional studies of more sophisticated multichromophoric systems to promote the development of new photonic materials and devices based on CB7 mediated host-guest chemistry.