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Published on: August 13, 2019
Transient Brewster angle reflectometry of spiropyran monolayers
Sergey Gorelik1, Song Hongyan, Martin J Lear
1Institute of Materials Research and Engineering, A*STAR (Agency for Science, Technology and Research), 3 Research Link, Singapore117602.
Summary
Brewster angle reflectometry precisely measures changes in molecular monolayers. This technique quantizes spiropyran to merocyanine conversion and its reversal, offering insights into thin film dynamics.
Area of Science:
- Materials Science
- Physical Chemistry
- Spectroscopy
Background:
- Molecular monolayers are crucial in advanced materials.
- Spiropyran and merocyanine isomers exhibit distinct optical and electronic properties.
- Monitoring molecular transformations in thin films is essential for device development.
Purpose of the Study:
- To develop and validate Brewster angle reflectometry for analyzing molecular monolayers.
- To quantify the photoinduced conversion of spiropyran to merocyanine and its subsequent reversal.
- To assess the potential of this technique for non-intrusive probing of thin film dynamics.
Main Methods:
- Brewster angle reflectometry was employed to monitor changes in absorbance and refractive index.
- Fresnel equations were analytically solved to correlate reflectometry data with absorption.
- Transient measurements using a single laser pulse were performed.
Main Results:
- The method is sensitive to changes in both real and imaginary parts of the refractive index.
- Spiropyran photoconversion to merocyanine occurred with an efficiency of approximately 0.1.
- Photochemical reversion efficiencies ranged from 0.03-0.2, showing site dependence.
- Thermal reversion from merocyanine to spiropyran was found to be slow.
Conclusions:
- Brewster angle reflectometry is a sensitive tool for real-time monitoring of molecular monolayer transformations.
- The technique allows for non-intrusive probing of thin film properties without sample photobleaching.
- This method provides quantitative data on photochemical and thermal reactions in molecular films.
