Investigations of mechanical and dielectric friction: Rotational reorientation studies of 7-DHB, Qu-390, and C-6H molecules in polar solvents

Abstract

At the room temperature, the rotational re-orientations times of three probes 7-DHB, Qu-390, and C-6H have been examined in primary alcohol solvent series, by employing the steady-state fluorescence depolarisation and Time-Correlated Single Photon Counting (TCSPC) techniques. Experimental observation shows that C-6H probe rotates slower in solvents when compared to the other two probe molecules. 7-DHB and Qu-390 probes show relatively same rotational reorientation time with 10% of deviation. Hydrodynamic models - Stokes Einstein's Debye theory (SED) with a stick, slip boundary conditions limits, Quasi-hydrodynamic models - Dote-Kivelson-Schwartz and Geirer-Wirtz were, used to determine mechanical friction and the results are found interesting trend towards super stick behavior. Also, dielectric frictional theories - Nee-Zwanzig and van der Zwan-Hynes were used to examine dielectric friction. Both dielectric friction models, overestimate dielectric friction contributions for all the three probes is observed in alcohol series. Outcomes are explained in the context of the theoretical models, size effects were not noticed and the probability of hydrogen bonding among an amino functional group of the solute molecules and –OH functional group of the alcohols.