Intramolecular Charge Transfer and Solvation Dynamics of Coumarin 152 in Aerosol-OT, Water-Solubilizing Reverse Micelles, and Polar Organic Solvent Solubilizing Reverse Micelles

Abstract

The relative retardation of intramolecular charge transfer (ICT) and the solvation dynamics of coumarin 152 in pure AOT, water, methanol, acetonitrile, and formamide reverse micelles have been investigated using picosecond time-resolved emission spectroscopy. The rate of ICT has been retarded almost 7 times at w 0 = 4 and 4 times at w 0 = 32 compared to that in pure water. The rate of retardation of ICT is also observed in the methanol and acetonitrile reverse micelles in comparison to that in pure methanol and acetonitrile. In pure AOT, the solvation time is 12.22 ns, but at w 0 = 4 of water reverse micelles the solvation time is 7.27 ns. The slow dynamics in methanol, acetonitrile, and formamide reverse micelles is also observed. The relative retardation of the ICT rate is much smaller compared to the several thousand fold decrease in the solvation dynamics in the pool of the reverse micelles. The w dependency of solvation time is observed for water and methanol reverse micelles, but it is little for acetonitrile and none for formamide reverse micelles. The various w dependencies of solvation dynamics in water, methanol, and acetonitrile reverse micelles are explained on the basis of the presence and the absence of hydrogen-bonding networks in water, methanol, and acetonitrile, respectively.

Influence of Confined Water on the Photophysics of Dissolved Solutes in Reverse Micelles

“…[6,30,43,46] Fluorescence experiments with suitable probes to understand the dynamics of the confined water molecules in RMs have shown that the nature of the water changes substantially as the size of the water droplet in RMs increases. [3,[15][16][17][18][19][20][21][22][23][24][25] In such studies, the possible uncertainty in the location of the probe in the heterogeneous media can sometimes impede inferences drawn on the structure and dynamics of the water confined in the nanoenvironment. [1] However, as long as the primary goal of a study is to understand the gross behavior of the water pool under nanoconfinement and to determine how it influences the properties of a solute dissolved inside the nanoenvironment, photophysical investigation with suitable fluorescent probes is possibly still the most useful option.…”

“…We also performed similar studies in which the polar protic solvent water was replaced by the polar aprotic solvent acetonitrile (ACN) for forming the RMs to obtain a generalized picture of the reverse micellar systems, if it prevails. [20,24,25,51] The selection of the two probes in the present study was based on the expected differences in their hydrophobicities and hence in their locations in the RMs, one preferring the polar water-like phase and the other the relatively less polar interfacial region. The chemical structures of the two probes and AOT are shown in Scheme 1.…”

Optical transition rates of a meso-substituted thiacarbocyanine in methanol-in-oil reverse micelles

“…Solvation dynamics of water and non-aqueous polar solvents in reverse micelles were demonstrated to depend on the molar ratio of solvent to surfactant [2,[10][11][12][13][14][15]. Shirota and Horie reported that the solvation dynamics were retarded by up to four orders of magnitude because of the presence of hydrogen-bonding network in reverse micelles [10].…”

“…The methanol-in-oil (m/o) dispersions were prepared using w 0 ¼ 2; 4 and 6, where w 0 is the molar ratio of dispersed methanol to surfactant [10,[12][13]. In the case of water-in oil microemulsions, w 0 values can be incorporated into an empirical formula to determine the radii of dispersed water droplets in oil [20].…”

Micellization of Cetyl Triphenyl Phosphonium Bromide Surfactant in Binary Aqueous Solvents

“…The micellization process of various ionic, non-ionic and gemini surfactants in aqueous-organic mixed solvent systems have been investigated [3][4][5][6][7][8][9][10][11][12]. The majority of fundamental studies on solvent effect of cationic surfactants have been made on alkyl trimethyl ammonium and alkyl pyridinum bromides.…”