R. S. Hartman

A test of continuum models for dielectric friction. Rotational diffusion of phenoxazine dyes in dimethylsulfoxide

Rotational diffusion times for three mechanically similar phenoxazine dyes with differing electronic properties were measured. These studies probe the importance of dipole/dipole and ion/dipole couplings to the friction. The experimental results are compared with the predictions of available continuum theories of dielectric friction. Future directions for a more realistic model of dielectric friction are discussed.

The influence of wave vector dependent dielectric properties on rotational friction. Rotational diffusion of phenoxazine dyes

The rotational diffusion of three mechanically similar phenoxazine dyes possessing distinct electrical properties was studied in isopropanol. The results, along with previously presented results from other polar solvents, were analyzed in terms of continuum theories for rotational dielectric friction. It was found that a continuum based theory can account for the observed rotational relaxation dynamics, but only with realistic modeling of the solute charge distribution (not a point dipole), and by accounting for both frequency and wave vector dependences of the solvent dielectric properties.

Optically heterodyned polarization spectroscopy. Measurement of the orientational correlation function

Polarization spectroscopy has been developed as a useful method for the investigation of molecular reorientation in both liquid phase solutions and in the gas phase. This technique has the advantage of measuring a single particle orientational correlation function directly but the disadvantage of averaging over rotation in all electronic states. Described and characterized herein is a variant of this technique, optically heterodyned polarization spectroscopy, which is able to disentangle various contributions to the signal and determine the rotational relaxation of the solute molecule in different electronic states independently. This work also demonstrates the measurement of the normalized value of the orientational correlation function at time zero, r(0), without extensive normalization of laser parameters. Lastly, various technical advantages of the optically heterodyned method are discussed.

PROBING SOLUTE-SOLVENT ELECTROSTATIC INTERACTIONS: ROTATIONAL DIFFUSION STUDIES OF 9,10-DISUBSTITUTED ANTHRACENES

The rotational diffusion of 9,10-disubstituted anthracenes is studied in various solvents. By systematic variation of the anthracene functionalities the influence of the electrostatic properties of the solute on the solute–solvent frictional coupling is investigated. These studies explore the range of validity of continuum based dielectric friction models for describing the frictional coupling. It is found that a continuum model of the solvent with an extended charge distribution for the solute is adequate in unassociated solvents, but does not adequately describe the friction in the associated solvent, benzyl alcohol.

Rotational diffusion of organic solutes: the role of dielectric friction in polar solvents and electrolyte solutions

Abstract Experimental and computer simulation studies of the rotational relaxation of organic solutes in polar organic solvents and electrolyte solutions are used to investigate the role of solute-solvent dielectric friction. These studies are used to explore the boundaries of applicability for continuum based models of the dielectric frictional coupling and to identify the important molecular mechanisms that define these boundaries. These investigations explore the importance of the solute charge distribution, solvent structure, ion pairing, and hydrogen bonding.

Rotational Diffusion of Phenoxazine Dyes: Characterization of Molecular Friction

Relative contributions of mechanical, dielectric, and specific solute/solvent interactions to molecular friction in liquids are evaluated by measuring solute reorientation times for phenoxazine dyes.