Formation of inclusion complexes between anionic surfactants, alkanesulfonates (« = 5-8, 10, 12) and alkyl sulfates ( = 8, 10, 12, 14, 16,18), and ß-cyclodextrin was studied by a fluorometric method using l-anilinonaphthalene-8-sulfonate (1,8-ANS) and 2-anilinonaphthalene-7-sulfonate (2,7-ANS) as probes. The association constants for 1:1 complexes of 1,8-ANS and 2,7-ANS with ß-CD were determined as 85 and 1500 M"1, respectively, at 25 °C. The first and second association constants of the surfactants with ß-CD were calculated from competitive binding data of the surfactants and the ANS's with ß-CD. The 2:1 ß-CD-surfactant complexes were formed with alkanesulfonates of > 10 and alkyl sulfates of > 8. The surfactanVi3-CD association was accompanied by a large increase in entropy, and hydrophobic binding appeared to contribute to a great extent to the association. Self-association of 1:1 complexes of surfactants of long hydrocarbon chains was also suggested.

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The intramolecualr charge transfer (CT) complex formation and photoinduced electron-transfer reactions in aromatic donor−viologen acceptor dyad systems linked by polymethylene linkage (-(CH2) n -) have been studied. The donors and the numbers of methylene unit in the linkages are 1-naphthoxyl with n = 3, 6, 8, and 10, 2-naphthoxyl with n = 3−10 and 12, and 2-dibenzofuranoyl with n = 3, 6, 8, and 10. The formation constants of the intramolecular CT complexes (K int) were determined from the absorbance of CT absorption by using the absorptivities of the complexes determined from the intermolecular complexation between the model donor compounds, the 1-aryloxy-3-aminopropanes, and dimethyl viologen. The K int values depend little on the length of the linkage and are about 0.2 for 1-naphthol and 2-naphthol derivatives, and 0.6 for dibenzofuranoyl derivatives. The addition of β-CD disrupts the formation of the intramolecular CT complexes. The 1:1 association constants of the dyad molecules with β-CD (K CD) were estimated from the dependence of the CT absorption on the concentration of β-CD. Complexation of the dyad molecules with β-CD or methylated β-CD (Me−β-CD) also enhances the fluorescence intensity of the excited-state aromatic donors. The 1:1 complexes further associate with CD molecules resulting further enhancement of fluorescence intensity. This was attributed to the extension of the dyad molecules in the CD complexes. The electron-transfer quenching rate constants in the CD complexes formed in the presence of 150 mM Me−β-CD were calculated from fluorescence lifetime data and found to vary exponentially with the length of the linkage. The apparent β value is 0.86 Å-1 (1.09/C−C bond), regardless of the nature of donor moieties. The distance dependence of reorganization energies (λ) of the CD complexes was evaluated. Comparing the λ value with ΔG° of the reaction, it appears that the reactions stay near the top of the Marcus curve. Comparison of the effects of Me−β-CD on steady-state fluorescence intensity and excited-state lifetime indicated that through-space/through-solvent electron transfer is the predominant quenching pathway in the molecules having the linkage shorter than heptamethylene chain and the quenching rate is fast enough to show a static-like behavior.

The dimerization and inclusion complexation equilibria of six phenothiazine (PN) dyes with cyclodextrins (R-, β-, and γ-CDs) in aqueous media have been studied using absorption and fluorescence spectroscopy. The PN dyes used in this study are thionine (TH), azure A (AZA), methylene blue (MB), toluidine blue (TB), new methylene blue (NMB), and 1,9-dimethylmethylene blue (DMMB). The dimerization constants (K D ) of the dyes having two methyl substituents at the phenothiazine ring (NMB and DMMB) are much greater than those of other dyes having unsubstituted rings, and the presence of methyl groups on the amine groups affects little the K D values. The positions of the monomer/dimer equilibria do not change with the presence of R-CD, while the addition of β-CD suppresses and γ-CD enhances the dimerization of the dyes except DMMB. The equilibrium constants for the inclusion complexation of the dye monomers and dimers with CDs are determined from the analysis of the dependence of the absorption spectra of the dye solutions on the concentrations of the CDs using a multiple-equilibrium scheme. The results indicated that, except DMMB, which has methyl groups at the 1-position of the fused phenothiazine ring, the dye monomers fit better to β-CD and the dimers fit snugly to γ-CD. The DMMB monomer is too large to fit in β-CD but forms stable complexes with γ-CD. It appears that the inclusion complexes of the dye monomers and dimers are formed by deep insertion of the phenothiazine rings into the cavities of the CDs, with the 2-methyl groups (in TB and NMB) and the amine groups protruding from the cavities of the CDs. Fluorescence spectroscopic studies indicate that the dye dimers are not fluorescent and inclusion of the monomer in β-CD results in a 3-5 times enhancement of fluorescence intensity. The determined equilibrium constants of the multipleequilibrium scheme of the dyes in CD media and fluorescent properties of the dyes can be used to control the dye aggregation and the photophysical and photochemical properties of the phenothiazine dyes for various applications.

Dimerization of radical cations of mono-6-(1-alkyl-4,4′-bipyridino)--cyclodextrins ( -CD-C n V •+ , n ) 6, 7, 8) formed via Ru(bpy) 3 2+ -sensitized photochemical reduction of -CD-C n V 2+ was studied spectroscopically, and the results were compared with those of methylalkyl viologens. Spectral characteristics of monomer and dimer of viologen radical cations were derived. The dimerization constants have been determined to be 4.0 × 10 4 M -1 for -CD-C 6 V •+ , 8.9 × 10 5 M -1 for -CD-C 7 V •+ , and 6.8 × 10 6 M -1 for -CD-C 8 V •+ . These values are 2-3 orders of magnitude greater than those for the corresponding methylalkyl viologen radical cations. The dimer formation is driven by a large enthalpy decrease and a moderate entropy increase. The dimerization is suppressed upon addition of -CD or amphiphilic molecules that are included into -CD. These results indicate that the dimers are stabilized by inclusion of the alkyl chain of the 1-alkyl-4,4′-bipyridino moiety of the -CD-C n V •+ molecule into the -CD cavity of the counter molecule. Association constants of -CD-C n V •+ with -CD and amphiphilic molecules have been determined from the dependence of dimerization constants on the concentrations of -CD or amphiphiles. The results suggested that the terminal methyl and ethyl groups of the alkyl chains of -CD-C 7 V •+ and -CD-C 8 V •+ , respectively, are included in the -CD cavities of the same molecules, and this intramolecular inclusion affects the association of -CD-C n V •+ with -CD and amphiphiles.