Rotational Diffusion Dynamics of Fluorescein Derivatives in Binary Mixtures of Solvents: An Experimental and Computational Study.

With a view to understand the nature of solute solvent interactions, rotational reorientation times (τ) of three medium sized dipolar laser dyes viz., dichlorofluorescein (DCF), sodium fluorescein (SF) and kiton red (KR) in two binary mixtures namely, aqueous-DMSO and aqueous-1-propanol have been determined employing steady state fluorescence depolarization technique. The experimental results are analyzed in the light of SED hydrodynamic and of Gierer and Wirtz (GW) and Dote, Kivelson and Schwartz (DKS) quasihydrodynamic models.

Rotational diffusion of coumarins: a dielectric friction study.

The rotational diffusion of three probes: coumarin 522B (C522B), coumarin 307 (C307) and coumarin 138 (C138) with nearly identical size was studied at room temperature employing steady-state and time-resolved fluorescence anisotropy techniques in series of alcohols and alkanes. Experimental observations indicate faster rotation of C138 compared to the other two dyes in alcohols and a faster rotation of C522B than C307 in alkanes. The dielectric friction theories of Nee-Zwanzig (NZ) and van der Zwan-Hynes (ZH) were employed to estimate the friction experienced by the probes in alcohols, in addition to the mechanical friction calculated using Stokes-Einstein-Debye (SED) hydrodynamic with slip boundary condition and Dote-Kivelson-Schwartz (DKS) quasihydrodynamic theories.

Rotational diffusion of coumarins in aqueous DMSO.

The rotational dynamics of four structurally similar polar molecules viz., coumarin 440, coumarin 450, coumarin 466 and coumarin 151 has been studied in binary mixtures comprising of dimethyl sulphoxide and water at room temperature using the steady state fluorescence depolarization method and time correlated single photon counting technique. The binary mixtures are characterized by the fact that at a particular composition the viscosity (eta) of the solution reaches a maximum value that is higher than the viscosities of either of the two co-solvents.

Rotational diffusion of coumarins in alcohols: a dielectric friction study.

The rotational dynamics of three structurally similar polar molecules viz., coumarin 440, coumarin 151 and coumarin 450 has been studied in alcohols at room temperature using steady-state fluorescence depolarization method and time correlated single photon counting technique. The observed reorientation times of all the three probes are found to be longer than those predicted by Stokes-Einstein-Debye (SED) hydrodynamic theory with stick boundary condition and a deviation towards super-stick behavior is noted.

Solvent effect on absorption and fluorescence spectra of coumarin laser dyes: evaluation of ground and excited state dipole moments.

The effect of solvents on absorption and fluorescence spectra and dipole moments of coumarin 307 (C307) and coumarin 522B (C522B) have been studied extensively in various solvents, viz., general solvents, alcohols and binary mixtures (acetonitrile-benzene) at 298K. The bathchromic shift observed in absorption and fluorescence spectra of C307 and C522B with increasing solvent polarity indicates that transition involved are pi-->pi*.