title: Rotational Diffusion of a New Large Non Polar Dye Molecule in Alkanes.
abstract: Rotational reorientation times of a newly synthesized 2,5-bis(phenylethynyl)1,4-bis(dodecyloxy) benzene (DDPE) are experimentally determined in series of n-alkanes by employing steady state and time resolved fluorescence depolarization technique with a view to understand rotational dynamics of large non-polar solute molecule in non-polar solvents and few general solvents of different sizes and varying viscosity. It is observed that rotational reorientation times vary linearly as function of viscosity. The hydrodynamic stick condition describes the experimental results at low viscosities while the results tend to deviate significantly from it at higher viscosities. This is attributed to the possibility of long chains in solvents hosting a variety of chain defects (end-gauche, double-gauche, all-trans, kink, etc.) thereby reducing the effective length of the molecule, leading to a slightly reduced friction. The experimental results are compared with the predictions of Stokes-Einstein-Debye (SED) hydrodynamic theory as well as the quasi-hydrodynamic theories of Gierer-Wirtz (GW) and Dote-Kivelson-Shwartz (DKS). The predictions from these theories underestimate τr in the solvents employed in the study.
authors.affiliation: Laser Spectroscopy Programme, Department of Physics, Karnatak University, Dharwad, 580003, India.
authors.forename: Radha
authors.initials: R
authors.lastname: Goudar
authors.affiliation: Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bangalore, 560064, India.|Department of Chemistry, Indian Institute of Technology Jodhpur, Jodhpur, 342011, India.
authors.forename: Ritu
authors.initials: R
authors.lastname: Gupta
authors.affiliation: Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bangalore, 560064, India.|Centre for Nano and Soft Matter Sciences, Jalahalli, Bangalore, 560013, India.
authors.forename: Giridhar U
authors.initials: GU
authors.lastname: Kulkarni
authors.affiliation: Laser Spectroscopy Programme, Department of Physics, Karnatak University, Dharwad, 580003, India. him_lax3@yahoo.com.
authors.forename: Sanjeev R
authors.initials: SR
authors.lastname: Inamdar
keywords: Anisotropy; Rotational dynamics; SED hydrodynamics; Slip and stick behaviour