No abstract

Electronic absorption and emission spectral characteristics of a ketocyanine dye have been studied in solution in the presence of lithium perchlorate. Absorption spectral studies indicate complex formation between lithium ion and the dye in the ground state. The value of the equilibrium constant along with the molar absorbance of the absorbing species has been determined for the dye-cation interaction. The energy of maximum fluorescence shifts toward the red with the addition of LiClO(4). Steady-state emission studies point to the existence of two emitting species, viz., the solvated and the complexed dye in equilibrium. The values of the equilibrium constant for the process have been determined in acetone and acetonitrile. Time-resolved studies in the picosecond domain in pure solvents reveal that the lifetime (tau) value increases as the solvation interaction increases. Time-resolved studies also indicate the presence of two emitting species in equilibrium.

No abstract

In the present work, we have studied the influence of a water-soluble neutral polymer (poly-N-vinyl pyrrolidin-2-one, PVP) on the Kamlet-Taft polarity parameters of sodium n-dodecyl sulfate (SDS) micelles. We have used pyrene as an independent dipolarity/polarizability (pi parameter) descriptor molecule. It has been found that the addition of polymer (0.1 wt % PVP) increases the pi value of SDS micelles, suggesting that PVP-SDS aggregates have a larger dipolarity/polarizability than that of SDS micelles. Linear solvation energy relationships involving the fluorescence transition energy of four structurally similar ketocyanine dyes have also been used to evaluate the polarity parameters. It is interesting to observe that the addition of polymer leads to a decrease in both the hydrogen-bond donation (alpha-parameter) and hydrogen-bond acceptance ability (beta-parameter) of the micellar aggregate formed by PVP-SDS, whereas the dipolarity/polarizability value shows an increasing trend. Moreover, convergent results have been obtained for the pi value for PVP-SDS aggregates, using pyrene as a pi descriptor and ketocyanine dyes as molecular probes.

No abstract