Resonance Raman process and photo-induced phase transition via 632.8 nm irradiation for diacetylene monocarboxylic acid derivative self-assembled layers on Ag surfaces

Photo-induced interfacial behaviors of a diacetylene monocarboxylic acid derivative 10,12-pentacosadiynoic acid (PCDA) on Ag substrates have been examined by means of surface enhanced Raman scattering (SERS) as a function of irradiation time upon excitation at 632.8 nm close to the blue phaseʹs maximum absorption at ∼625 nm. Photoreactions on a SERS-active spot appeared to differ from those on a SERS-inactive substrate. On a SERS-inactive Ag plate, laser excitation at 632.8 nm led to the exhibition of longer conjugation length blue phase PCDA than red phase via a resonance Raman process. On a roughened SERS active Ag plate, as the irradiation time elapsed, PCDA appeared to exhibit a blue-to-red phase transition even under excitation at 632.8 nm and the subsequent photo-degradation. Raman mapping of the CC stretching band intensity change at ∼1450 cm−1 for the blue phase, with respect to that at ∼1500 cm−1 for the red phase, can be utilized as a new method of photo-induced micro-patterning on SERS active surfaces.