Correlating proton transfer dynamics to probe location in confined environments

Area of Science:

• Physical Chemistry
• Photochemistry
• Supramolecular Chemistry

Background:

• Proton transfer dynamics are sensitive to the molecular environment.
• Reverse micellar systems offer tunable microenvironments for studying chemical reactions.
• The photoacid 8-hydroxypyrene-1,3,6-trisulfonic acid (HPTS) is a model system for photoinduced proton transfer.

Purpose of the Study:

• To investigate the influence of reverse micellar environments on HPTS proton transfer dynamics.
• To elucidate the location of HPTS within different reverse micellar systems.
• To correlate molecular location with proton transfer efficiency.

Main Methods:

• Ultrafast time-resolved transient absorption spectroscopy.
• Time-resolved anisotropy decays.
• Two-dimensional Nuclear Magnetic Resonance (2D NMR) spectroscopy (specifically 2D NOESY).

Main Results:

• In anionic AOT reverse micelles, HPTS proton transfer dynamics resemble those in aqueous solution.
• 2D NOESY NMR confirmed HPTS is in the water pool of AOT micelles, showing no interaction with AOT.
• In cationic CTAB reverse micelles, ultrafast transient absorption showed no HPTS photoinduced proton transfer.
• 2D NOESY NMR revealed HPTS embeds within the interface of CTAB micelles, interacting with CTAB.

Conclusions:

• The microenvironment within reverse micelles critically controls HPTS proton transfer.
• HPTS location (water pool vs. interface) dictates its photochemical reactivity.
• Complementary spectroscopic techniques are essential for understanding structure-function relationships in complex systems.