Raman microspectroscopic study on polymerization and degradation processes of a diacetylene derivative at surface enhanced Raman scattering active substrates. 1. Reaction kinetics.

Raman microspectroscopy was applied to study the polymerization kinetics of the Langmuir−Blodgett (LB) films of 10,12-pentacosadiynoic acid (DA) adsorbed on surface enhanced Raman scattering (SERS) active Ag island films. A two-dimensional (2D) Raman microscopic image measured at 1520 cm-1 exhibits bright and dim spots with the diameter of several hundred nanometers. Raman microscopic spectra, measured by defocusing the excitation laser light (532 nm, diameter of ca. 10 μm) on the samples at room temperature, proved the occurence of the surface processes consisting of the formation of polydiacetylene (PDA) in the blue phase, its conversion to the red phase, and subsequent bleaching. These reactions were negligible under the same condition for the DA-LB films prepared on a smooth (i.e., SERS-inactive) Ag film, indicating that the 532-nm-induced polymerization and the bleaching process are enhanced by the SERS-active substrates. At low temperatures below −50 °C, the Raman microscopic measurements proved the...