Rotational Diffusion of Coumarins: A Dielectric Friction Study

Abstract

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. The observed reorientation times for the three probes do not follow the trend predicted by dielectric friction theories of NZ and ZH. The dipole moments determined from solvatochromic techniques were found to be different for the three probes.

Translational and Rotational Diffusion of Two Differently Charged Solutes in Ethylammonium Nitrate–Methanol Mixture: Does the Nanostructure of the Amphiphiles Influence the Motion of the Solute?

“…However, this type of behavior has been reported for various polar molecules in polar solvents. 60,61 Now, the C obs value of Fl-Na (2.04) is much higher than the value obtained for R6G (1.60) in neat CH 3 OH. A closer look at the molecular structure of the Fl-Na reveals that it has carboxylate (COO − ), carbonyl (CO), and ONa groups.…”

Rotational Dynamics of Nonpolar and Dipolar Molecules in Polar and Binary Solvent Mixtures

“…7. The reorientation times of C522B, C307 in alcohols and alkanes and C138 in alcohols (Mannekutla et al, 2010) are summarized in Tables 6 and 7. The τ r values obtained in alkanes clearly show that C522B rotates faster compared to C307.…”

“…Steady-state anisotropy (<r>), fluorescence lifetime (τ f ) and rotational reorientation time (τ r ) of coumarins in alcohols at 298K (the maximum error in the fluorescence life times is less than ±50 ps) (Mannekutla et al, 2010) a Viscosity data is from Inamdar et al, 2006 Table 7. Steady-state anisotropy (<r>), fluorescence lifetime (τ f ) and rotational reorientation time (τ r ) of coumarins in alkanes at 298K for C522B and C307 (the maximum error in the fluorescence life times is less than ±50 ps) (Mannekutla et al, 2010) The probes C522B and C138 have shown coincidentally similar interactions. In C138, aminomethyl group being free contributes more to the charge separation through resonance-whereas in C522B this resonance contribution is sluggish, comparatively.…”