Single Molecule Spectroscopy Studies of Acid-Base Chemical Gradients Using Nile Red as a Probe of Local Surface...

Area of Science:

• Surface chemistry
• Spectroscopy
• Materials science

Background:

• Bifunctional acid-base materials are crucial for cooperative catalysis.
• Understanding local chemical properties on surfaces is essential for designing advanced materials.

Purpose of the Study:

• To investigate local acidity and basicity along chemical gradients on silica surfaces.
• To demonstrate the utility of Nile Red dye in single molecule spectroscopy for probing surface acid-base properties.

Main Methods:

• Preparation of acid-base gradients using 3-aminopropyl-trimethoxysilane on silica.
• Characterization using spectroscopic ellipsometry, contact angle measurements, and X-ray photoelectron spectroscopy.
• Single molecule spectroscopy with Nile Red dye for fluorescence imaging and spectral analysis.

Main Results:

• Nile Red emission spectra showed broad bimodal distributions that varied along the gradient.
• A gradual transition from basic aminosilane sites to acidic silanol sites was observed.
• Superlocalization microscopy revealed spatial correlations in acid-base properties over ~200 nm distances.

Conclusions:

• Single molecule spectroscopy with Nile Red is effective for mapping surface acid-base properties.
• The prepared gradients exhibit distinct chemical transitions relevant for catalytic applications.
• These findings contribute to the development of aminosilane-modified silica for bifunctional catalysis.