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Raman microspectroscopic study on polymerization and degradation processes of a diacetylene derivative at surface
K Itoh1, T Nishizawa, J Yamagata
1Department of Chemistry, School of Science and Engineering, Waseda University, Shinjuku-ku, Tokyo 169-8555, Japan. itohk@waseda.jp
The Journal of Physical Chemistry. B
|July 21, 2006
Summary
Surface-enhanced Raman scattering (SERS) active silver films significantly enhance the polymerization of 10,12-pentacosadiynoic acid (DA) into polydiacetylene (PDA). This study reveals simultaneous polymerization and degradation pathways on SERS substrates, even at low temperatures.
Area of Science:
- Materials Science
- Spectroscopy
- Chemical Kinetics
Background:
- Langmuir-Blodgett (LB) films of 10,12-pentacosadiynoic acid (DA) are model systems for studying polymerization.
- Surface-enhanced Raman scattering (SERS) can amplify Raman signals from adsorbed molecules.
- The polymerization of DA into polydiacetylene (PDA) can yield different phases (blue and red) with distinct properties.
Purpose of the Study:
- To investigate the polymerization kinetics of DA-LB films on SERS-active substrates using Raman microspectroscopy.
- To elucidate the role of SERS in the polymerization and degradation processes of DA.
- To analyze the influence of temperature on the polymerization and degradation pathways.
Main Methods:
- Raman microspectroscopy was employed to monitor the polymerization of DA-LB films on SERS-active Ag island films.
- Two-dimensional (2D) Raman microscopic imaging and spectral analysis were performed at room temperature and low temperatures (below -50 °C).
- Kinetic analysis was conducted by tracking the intensity changes of characteristic Raman bands for blue and red PDA phases.
Main Results:
- SERS-active substrates significantly enhanced the 532-nm-induced polymerization of DA and subsequent bleaching compared to SERS-inactive substrates.
- At room temperature, polymerization proceeded through blue to red PDA phases, followed by bleaching, while at low temperatures, bleaching was suppressed.
- Kinetic analysis revealed at least two simultaneous surface reaction pathways: sequential formation of blue and red PDA, and formation followed by degradation of PDA.
Conclusions:
- SERS substrates, particularly 'hot spots', dramatically influence the polymerization and degradation kinetics of DA-LB films.
- Simultaneous polymerization and degradation processes occur on SERS-active sites, even at sub-zero temperatures.
- Raman microspectroscopy is a powerful tool for studying surface-confined reactions and the role of SERS in chemical transformations.
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