Rotational dynamics of nonpolar laser dyes

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

“…The dielectric friction can be modeled using continuum theories of NeeZwanzig (NZ) (Nee and Zwanzig, 1970), which treats the solute as a point dipole rotating in a spherical cavity, Alavi-Waldeck (AW) (Alavi and Waldeck, 1991b;1993) model which is an extension of the NZ theory where the solute is treated as a distribution of charges instead of point dipole and the semiempirical approach of van der Zwan and Hynes (vdZH) (van der Zwan and Hynes, 1985) in which fluorescence Stokes shift of the solute in a given solvent is related to dielectric friction. Conversely, the results of neutral and nonpolar solutes deviate significantly from the hydrodynamic predictions at higher viscosities (Waldeck et al, 1982;Canonica et al, 1985;Phillips et al, 1985;Courtney et al, 1986;Ben Amotz and Drake, 1988;Roy and Doraiswamy, 1993;Williams et al, 1994;Jiang and Blanchard, 1994;Anderton and Kauffman, 1994;Brocklehurst and Young, 1995;Benzler and Luther, 1997;Dutt et al, 1999;Ito et al, 2000;Inamdar et al, 2006). These probes rotate much faster than predicted by the SED theory with stick boundary condition and are described by either slip boundary condition or by quasihydrodynamic theories.…”

“…It is also noted that the quasihydrodynamic description is adequate for small solutes of 2-3 Å radius in case of GW theory whereas, the DKS model with experimental value in alcohols fail beyond the solute radius of 4.2 Å. Our earlier work on rotational dynamics of exalite probes E392A (r = 5.3 Å), and E398 (r = 6.0 Å), yielded striking results (Inamdar et al, 2006), in that, these large probes rotated much faster than slip hydrodynamics and followed subslip trend in alcohols. The quest to understand the influence of size of solute on rotational dynamics is continued with three nonpolar solutes viz., Exalite 404 (E404), Exalite 417 (E417) and Exalite 428 (E428), which may further fill the gap between the existing data.…”

“…In the two limiting cases of hydrodynamic stick and slip for a nonspherical molecule, the value of C follows the inequality, 0< C ≤ 1 and the exact value of C is determined by the axial ratio of the probe. It is observed that the experimentally measured rotational reorientation times of number of the nonpolar solutes (Waldeck et al, 1982;Canonica et al, 1985;Phillips et al, 1985;Courtney et al, 1986;Ben Amotz and Drake, 1988;Roy and Doraiswamy, 1993;Williams et al, 1994;Jiang and Blanchard, 1994;Anderton and Kauffman, 1994;Brocklehurst and Young, 1995;Benzler and Luther, 1997;Dutt et al, 1999;Ito et al, 2000;Inamdar et al, 2006) could be described by the SED theory with slip boundary condition (subslip behavior). For a homologous series of solvents such as alcohols or alkanes, the normalized reorientation times decreased as the size of the solvent is increased.…”

“…Most of the nonpolar probes so far studied have the radii of 2.5 Å to 5.6 Å (Inamdar et al, 2006) and a transition towards stick boundary condition is evident with increase in size of the solute. Most of the medium sized neutral nonpolar molecules rotate faster in alcohols compared to alkanes, which is in contrast to that of smaller neutral solutes.…”

“…G ( = 1 . 1 4 ) i s a n instrumental factor that corrects for the polarization bias in the detection system (Inamdar et al, 2006) and is given by…”