Rotational Diffusion of Nondipolar and Charged Solutes in Alkyl-Substituted Imidazolium Triflimides: Effect of C2 Methylation on Solute Rotation

Influence of Viscosity and Temperature on Rotational Dynamics of 3-(1H-benzo[d]Imidazol-2-yl)-7-(Diethyl Amino)-2H-chromen-2-one (Polar Laser dye) in Highly Viscous Solvent: Low and High Viscous Range

Temperature-dependent rotational dynamics of 3-(1 H-benzo[d]imidazol-2-yl)-7-(diethyl amino)-2 H-chromen-2-one (3HBI-7D-2HChromen-2-one) has been studied in highly viscous glycerol solvent. Over the entire studied temperature range rotational reorientation time values vary linearly with temperature. Experimental obtained rotational results are analyzed using hydrodynamic and quasi-hydrodynamic models over the entire temperature range as well as low and high viscous range. 3HBI-7D-2HChromen-2-one rotational dynamics has been described using Stoke's-Einstein-Debye (SED) slip boundary conditions.

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.

Is Solute Rotation in an Ionic Liquid Influenced by the Addition of Glucose?

Fluorescence anisotropy measurements and molecular dynamics (MD) simulations have been performed to understand the specific interactions of two structurally similar nondipolar solutes, 2,5-dimethyl-1,4-dioxo-3,6-diphenylpyrrolo[3,4-c]pyrrole (DMDPP) and 1,4-dioxo-3,6-diphenylpyrrolo[3,4-c]pyrrole (DPP), with neat 1-butyl-3-methylimidazolium dicyanamide ([BMIM][N(CN)₂]) and also in the presence of glucose. It has been observed that the measured reorientation times of DMDPP in neat [BMIM][N(CN)₂] follow the predictions of the Stokes-Einstein-Debye hydrodynamic theory with slip boundary condition. Addition of glucose (0.075 and 0.15 mole fraction) has no bearing on the rotational diffusion of the solute apart from the viscosity related effects. In contrast, the reorientation times of DPP in neat [BMIM][N(CN)₂] obey stick boundary condition as the hydrogen bond donating solute experiences specific interactions with the dicyanamide anion. No influence of the additive can be noticed on the rotational diffusion of DPP at 0.075 mole fraction of glucose. However, at 0.15 mole fraction of glucose, the reorientation times of the solute at a given viscosity and temperature decrease by 15-40% compared to those obtained in the neat ionic liquid. MD simulations indicate that each DPP molecule hydrogen bonds with two dicyanamide anions in neat ionic liquid. The simulations also reveal that, at 0.15 mole fraction of glucose, the concentration of anions hydrogen bonded to glucose increases significantly; therefore, the percentage of solute molecules that can form hydrogen bonds with two dicyanamide anions decreases to 84, which leads to faster rotation of DPP.

Influence of C2-Methylation of Imidazolium Based Ionic Liquids on Photoinduced Spin Dynamics of the Dissolved ZnTPP Studied by Time-Resolved EPR

Unusual physical properties of ionic liquids (ILs) can be implemented in many different applications and are very sensitive to the structure of IL. In this work we investigate the spin dynamics of probe molecule Zn tetraphenylporphyrin (ZnTPP) dissolved in a series of ILs using time-resolved electron paramagnetic resonance (TR EPR). We compare the TR EPR characteristics in C2-methylated imidazolium-based ILs [bmmim]BF4 and [bmmim]PF6 and in their C2-protonated analogs [bmim]BF4 and [bmim]PF6 to assess the influence of C2-methylation. The corresponding TR EPR signatures are drastically different in the two types of ILs. The analysis of experimental data allows assumptions that the ZnTPP molecule is distorted in C2-methylated ILs, contrary to other organic media and C2-protonated analogs. The mobility of ZnTPP in C2-methylated ILs is smaller compared to that in C2-protonated analogs, implying different microenvironment formed around dissolved ZnTPP.

Dissolved chloride markedly changes the nanostructure of the protic ionic liquids propylammonium and ethanolammonium nitrate

The bulk nanostructure of 15 mol% propylammonium chloride (PACl) dissolved in propylammonium nitrate (PAN) and 15 mol% ethanolammonium chloride (EtACl) in ethanolammonium nitrate (EtAN) has been determined using neutron diffraction with empirical potential structure refinement fits.

Does addition of an electrolyte influence the rotational diffusion of nondipolar solutes in a protic ionic liquid?

Rotational diffusion of two structurally similar nondipolar solutes, 2,5-dimethyl-1,4-dioxo-3,6-diphenylpyrrolo[3,4-c]pyrrole (DMDPP) and 1,4-dioxo-3,6-diphenylpyrrolo[3,4-c]pyrrole (DPP), has been examined in ethylammonium nitrate-lithium nitrate (EAN-LiNO3) mixtures to understand the influence of added electrolyte on the local environment experienced by the solute molecules. The measured reorientation times of both DMDPP and DPP in EAN-LiNO3 mixtures fall within the broad limits set by the hydrodynamic slip and stick boundary conditions. The hydrogen bond accepting DMDPP and the hydrogen bond donating DPP experience specific interactions with the cation and anion of the ionic liquid, respectively. Addition of LiNO3 (0.1 and 0.2 mole fraction) to EAN induces only viscosity related effects on the rotational diffusion of the two nondipolar solutes. These observations suggest that the local environment experienced by DMDPP and DPP in EAN is not altered upon the addition of LiNO3. Our results are consistent with the structural details available in the literature for EAN-LiNO3 mixtures.