Correlation between molecular reorientation dynamics of ionic probes in polar fluids and dielectric friction by picosecond modulation spectroscopy

Abstract

done with the system 0.03 m CTAB + 0.04 and 0.08 m K(Br:Cl). The results for R(90) and Z)app are plotted against the bromide molar fraction XBr in Figure 10, a and b. At 0.04 m both systems have small aggregates and the difference in all properties is small and monotonic from = 0 to 1. At 0.08 m K(Br:Cl), J?(90) and Z>app are almost constant up to XBr = 0.6. At higher bromide content the growth is reflected in both properties. The parameter µ2/ 21 2 is related to the polydispersity of the system.17 It has been mentioned that the polydispersity of spherical aggregates is smaller than for large cylin order to investigate the correlations between orientational relaxation times (rrot) and properties of the single-solvent or binary systems. A sequence of normal and substituted alcohols, dimethyl sulfoxide, formamide, TV-methylformamide, and dimethylformamide has been investigated. While good agreement with hydrodynamic-based theories is seen for the pure alcohol systems, the binary propanol-H20 systems show a surprising curvilinear dependence of rrot vs. beyond the realms of any expectations in simple hydrodynamic responses, as has been shown previously. If a dielectric friction model is applied, then these curvilinear profiles are predicted at least qualitatively. The successful ingredients of such a model are discussed and its limitations assessed for its application to polar fluids, given the poor agreement with the relaxation times or trends in the dimethyl sulfoxide and amide solvents.

Rotational diffusion of the 7-diethylamino-4-methylcoumarin C1 dye molecule in polar protic and aprotic solvents

“…They studied the rotational diffusion of these solutes in alcohols, amides, DMSO and water-alcohol binary systems by pumpprobe polarisation anisotropy. 20,21 They observed that the rotational times in the alcohols are much longer than for the other solvents, similar to our case. Following the MK treatment of the dielectric friction coefficient they derived the following expression of the correlation time where and D r is the rotational diffusion constant (11) (12) (13) (14) We have used these equations, the NZ theory ([eq.…”

“…The two pioneering works of Eisenthal and coworkers 1,2 have triggered off a large number of similar studies of picosecond depolarisation of either the absorbance or the fluorescence of various dye molecules in different solvents, many testing more or less directly the validity of a linear τ R = f(η/T) dependency, either only within the "stick" limit, [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] or considering also the "slip" limit. [28][29][30][31] Interestingly, most papers have reported qualitative accordance with the prediction of a linear η/Tdependency, but only when varying η for a restricted class of solvents (protic, aprotic, n-alcohols, etc.)…”

“…The most important deviations from simple SED predictions have been found in binary mixtures, where an extreme non-linear dependency of τ R on viscosity seems to be the rule. 20,21,27 One has thus come to the conclusion that SEDtheory is flawed by serious drawbacks but that it seems to work quite well for a given solute in a certain class of solvents. Refined models have been developed through the years in order to better describe the rotational diffusion in various solvents, one may mention the solvent attachment model or dielectric friction theory.…”

Rotational dynamics of pyrrolopyrrole derivatives in alcohols: Does solute–solvent hydrogen bonding really hinder molecular rotation?

“…4,11,35 Recent investigations, however, attributed the observed slower reorientation times to electrical aspects of the solute-solvent coupling known as the dielectric friction. The rotational dynamics of a number of polar solutes in polar solvents have been studied to stress the importance of dielectric friction [15][16][17][18][19][20][21][22][23][24][25][32][33][34][35][36] and also to test various theories of dielectric friction. [26][27][28][29][30][31] Since almost all the probe molecules used in these investigations have functional groups like CvO, NH, and NH 2 , chemical intuition tells us that these groups form hydrogen bonds with protic and aprotic solvents.…”

Inhomogeneous rotational dynamics of a rodlike probe in 1-propanol

“…5,28 -35 These theories have been carefully compared to experimental data [36][37][38][39][40][41][42][43][44][45][46] as well as with molecular dynamics ͑MD͒ simulations. 6,47-50 Although quantitative agreement between theory and experiment has not always been Rotational correlation times, R , reduced correlation times, R /, and initial anisotropy values, r 0 , obtained from fits of polarized fluorescence decays.…”