Rotational Reorientation Dynamics of Oxazine 750 in Polar Solvents

Experimental and Theoretical Rotational Diffusion Studies of 7DM4M1M1,8, N-2(1H)-one and 7A4T2H1B-2-one in Series of Alcohol Solvents: Stoke's-Einstein-Debye and Alavi-Waldeck Models

Rotational diffusion studies of two solutes 7-(dimethylamino)-4-methoxy-1-methyl-1,8-naphthyridin-2(1H)-one (7DM4M1M1,8, N-2(1H)-one) and 7-amino-4-(trifluoromethyl)-2H-1-benzopyran-2-one (7A4T2H1B-2-one) having equal volumes but different chemical natures are studied in series of alcohol solvents at 303 K using steady-state methods. HOMO-LUMO, Electron density, Molecular electrostatic potential (MEP), etc., are obtained from computational calculations using Gaussian 09 software. Rotational reorientation times of 7DM4M1M1,8, N-2(1H)-one solute molecule is found to be less than 7A4T2H1B-2-one solute molecule indicates it rotates slowly in chosen solvents. Stoke's-Einstein-Debye (SED) model with stick boundary conditions for the 7A4T2H1B-2-one solute molecule is modeled to describe mechanical friction. Polar solutes along with mechanical friction also experience dielectric friction. Both these frictions being non-separable, the Alavi-Waldeck (AW) model is studied for dielectric friction contribution to the total friction solute experiences in solvents. AW model effectively explains the observed dielectric friction in alcohol solvents.

An Experimental and Theoretical Test of Dielectric Friction Models Using Rotational Diffusion of 7-Diethylamino-2-H-1-Benzopyran-2-One in Non-associative Solvents

The rotational re-orientations times of the 7-DHB dye molecule have been examined in non-associative solvents (DMSO and Octanenitrile) by varying the temperature, by employing the Steady-State Fluorescence Depolarisation and Time-Correlated Single Photon Counting (TCSPC) techniques. Rotational re-orientations time values in DMSO are found larger by a factor of 1.136 than octanenitrile, which indicates that 7-DHB laser dye is experiencing higher friction in DMSO than octanenitrile. To determine mechanical friction Stokes Einstein's Debye theory (SED) -with a stick, slip boundary conditions parameters are used and found an interesting super slip trend. Point dipole models as Nee-Zwanzig (NZ) and van der Zwan-Hynes (ZH) fail to explain experimental dielectric friction observed trends. Alavi-Waldeck model successfully explains the observed dielectric friction trend in non-associative solvents.

Rotational Diffusion of Medium Sized 7-[Diethylamino]-2H-1-Benzopyran-2-One Molecule in Alcohols: Study of Temperature and Solvent Viscosity Effect

The rotational re-orientations times of the 7-[diethylamino]-2H-1-benzopyran-2-one (7-DHB) dye molecule have been examined in ethanol and octanol solvents when macroscopic solvent viscosity parameter is varied by varying the temperature, by employing the steady-state fluorescence depolarisation and Time-Correlated Single Photon Counting (TCSPC) techniques. Experimental observation shows that 7-DHB probe is experiencing higher friction in octanol compared to ethanol and rotates slower by a factor of 7.3. The hydrodynamic Stokes Einstein's Debye theory (SED) with a stick, slip boundary conditions parameters, quasi-hydrodynamic models (Dote-Kivelson-Schwartz and Geirer-Wirtz) were used to determine mechanical friction and found an interesting towards super slip trend. Dielectric frictional theories of point dipole, Nee-Zwanzig and van der Zwan-Hynes both models fail to describe experimentally observe dielectric friction trends. Evidently, both hydrodynamic and dielectric models failed to explain the examined behavior, even in the qualitative way in alcohols.