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Excited state proton transfer in ionic liquid mixed micelles.
Tridib Mondal1, Atanu Kumar Das, Dibyendu Kumar Sasmal
1Department of Physical Chemistry, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700 032, India.
The Journal of Physical Chemistry. B
|September 25, 2010
Summary
Excited state proton transfer (ESPT) in room temperature ionic liquid (RTIL) mixed micelles shows altered kinetics compared to water. RTIL concentration and counterion type significantly influence ESPT rates within these complex micellar structures.
Area of Science:
- Physical Chemistry
- Supramolecular Chemistry
- Photochemistry
Background:
- Excited state proton transfer (ESPT) is a fundamental photophysical process.
- Room temperature ionic liquids (RTILs) offer unique solvent properties.
- Triblock copolymers form micelles that can encapsulate various molecules.
Purpose of the Study:
- To investigate the ESPT dynamics of pyranine (HPTS) within RTIL-P123 mixed micelles.
- To understand how RTIL concentration and type affect ESPT kinetics.
- To correlate micelle structure and solvation dynamics with proton transfer rates.
Main Methods:
- Femtosecond up-conversion spectroscopy was employed to monitor ultrafast dynamics.
- Mixed micelles were formed using Pluronic P123 and two different RTILs: [pmim][Br] and [pmim][BF(4)].
- Hydrodynamic diameter measurements indicated significant changes in micelle size with RTIL concentration.
Main Results:
- ESPT in P123 micelles was significantly slower (65 ps) than in water (5 ps).
- RTIL addition modulated ESPT rates, with faster initial transfer at low concentrations.
- ESPT time constants increased with RTIL concentration, attributed to micelle penetration by RTILs.
- The [pmim][BF(4)] counterion resulted in slower ESPT compared to [pmim][Br] due to its hydrophobicity and structural effects.
Conclusions:
- The kinetics of ESPT are highly sensitive to the microenvironment within RTIL-P123 mixed micelles.
- Solvation dynamics, particularly ultrafast components, play a crucial role in inducing proton transfer.
- The choice of RTIL counterion impacts ESPT, highlighting the importance of specific ion-solvent interactions.
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