Intramolecular Charge Transfer Processes in Confined Systems. Nile Red in Reverse Micelles^†

Abstract

Intramolecular charge transfer (ICT) processes of the neutral fluorescence probe, nile red, I, confined in the water pool of aerosol-OT (AOT) reverse micelle in n-heptane, is studied using picosecond emission spectroscopy. Utilizing the solvatochromism of nile red, only those probe molecules inside the reverse micelle are selectively excited. It is observed that while in aqueous solutions the lifetime (τf) of nile red is 650 ps, inside the reverse micelles τf increases to 3.73 ns in reverse micelle and to 2.06 ns at the highest water content of the microemulsion (w o = 32). With increase in the water-to-surfactant ratio, w o, as the water pool swells in size, the lifetime and quantum yield of emission decrease and the rate of the ICT process of nile red increases. However, the magnitude of the change (at most 8 times) in the rate of the ICT process of nile red compared to that of ordinary water is much smaller than the several thousandfold decrease observed in the solvation dynamics of water in the water pool relative to bulk water. It is proposed that while the solvation dynamics in the water pool is governed by the dielectric relaxation time, dynamics of the ICT process is controlled by the static polarity of the medium.

Energy Gap Dependence of the Nonradiative Decay Rate Constant of 1-Anilino-8-naphthalene Sulfonate in Reverse Micelles

“…7,[13][14][15][16][17][18][19][20][21] As an example, Cho et al reported that ANS in reverse AOT micelles exhibited a double exponential decay: short component=0.3 -0.6 ns and long component=2.6 -5.1 ns at w 0 =4 -33.…”

“…As one of the several advantages of a reverse AOT micellar system, the size of the water pool can be controlled precisely at the nanometer level through the molar ratio of water to AOT: 7 Therefore, size effects on chemical and physical properties in nanometer dimensions can be studied by the use of reverse AOT micelles. Indeed, reverse AOT micelles have been studied by various techniques such as fluorescence spectroscopy [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] , NMR 22,23 , ESR 24,25 , IR [26][27][28] , and so on. [29][30][31][32] These studies demonstrated that polarity [8][9][10] , viscosity 11 , pH 12 , and other properties 30,32 of the water pool in the micelles were different from those in the bulk state and were dependent on the w 0 value.…”

“…Particularly, recent time-resolved fluorescence spectroscopy has provided invaluable information about the structures and dynamical behavior of water molecules inside the micelles. 7,[13][14][15][16][17][18][19][20][21] It is noteworthy that these studies are essentially based on the changes in the fluorescence properties of a probe molecule with the size of the water pool. However, we supposed that detailed discussions on the fluorescence characteristics should be based on photophysical parameters represented by the radiative and nonradiative rate constants of a probe molecule.…”

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].…”

Quantitative determination of the surfactant-induced split ratio of influenza virus by fluorescence spectroscopy

“…We attribute the shortest lifetime t 1 to NR populations in a relatively hydrophilic micro-environment (corresponding to peak 3 from multi-peak fitting), possessing a lifetime close to the literature value of 0.650 ns for NR in aqueous buffer. 18 The slightly longer lifetime t 2 is attributed to NR populations that are bound to the various features mentioned above for peak 2, while the longest lifetime t 3 is attributed to NR molecules bound to viral membranes (peak 1 from multipeak fitting).…”