Electronic Excited-State Behavior of Rhodamine 3B in AOT Reverse Micelles Sensing Contact Ion Pair to Solvent Separated Ion Pair Interconversion

The amphiphile Aerosol OT (1,4-bis(2-ethylhexyl)sodium sulfosuccinate, AOT) forms, in reverse micellar nanoaggregates of water, RM, in isooctane, ion pairs (IPs) with the cationic fluorescent probe dye, rhodamine 3B, (3,6-bis(ethylamino)-9-[2-(ethoxycarbonyl)phenyl]-9H-xanthen-9-ylium, R3B), as eith...

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Bibliographic Details
Published in:The journal of physical chemistry. B 2010-08, Vol.114 (32), p.10417-10426
Main Authors: Ferreira, José A. B, Costa, Sílvia M. B
Format: Article
Language:English
Subjects:
Anisotropy
B: Surfactants, Membranes
Dioctyl Sulfosuccinic Acid - chemistry
Fluorescent Dyes - chemistry
Humans
Ions - chemistry
Micelles
Rhodamines - chemistry
Solvents - chemistry
Spectrometry, Fluorescence
Surface-Active Agents - chemistry
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Summary:The amphiphile Aerosol OT (1,4-bis(2-ethylhexyl)sodium sulfosuccinate, AOT) forms, in reverse micellar nanoaggregates of water, RM, in isooctane, ion pairs (IPs) with the cationic fluorescent probe dye, rhodamine 3B, (3,6-bis(ethylamino)-9-[2-(ethoxycarbonyl)phenyl]-9H-xanthen-9-ylium, R3B), as either contact ion pairs, CIPs, or solvent (water) separated ion pairs, SSIPs. The ground-state AOT R3B ion pairs’ equilibria as well as the dynamics of R3B electronic excited states show the progressive hydration of AOT− R3B+ toward solvent separated ion pairs, SSIPs as the characteristic reverse micelle parameter w 0 = [H2O]/[AOT] increases. The apparent limiting hydration constant of R3B ion pairs, K hyd = 2.8 ± 0.2, corresponds to full hydration of AOT, consistent with 1−3 water molecules per AOT polar head. Transient relaxations at w 0 = 0.2, with a 375 ± 15 ps decay at 550 nm decrease to 115 ± 15 ps at w 0 = 7.2 turning into corresponding rises at 588 nm. At higher w 0, water induced dynamics becomes faster. The lifetime is longer in RM with smaller w 0, due to the presence of CIPs that inhibit intrinsic nonradiative decay processes, which in contrast shorten the decay times at higher w 0, due to the presence of SSIPs. The pairs’ electronic excited-state properties are sensitive to viscosity and local polarity of the surrounding environment of the interfacial regions of AOT reverse micellar nanoaggregates.
ISSN:1520-6106
1520-5207
DOI:10.1021/jp100571t