Specific and Nondestructive Detection of Different Diarylethene Isomers by NIR-SERS

This paper describes specific and nondestructive detection of two isomers of diarylethene derivative, namely 1,2-bis(5′-ethoxy-2′-(2″-pyridyl)thiazolyl)perfluorocyclopentene (DE) by surface-enhanced Raman scattering (SERS). UV and visible light irradiations transform reversibly DE between open-form (OF) and closed-form (CF) isomers, respectively. A mixture of poly(methyl methacrylate) and DE was spin-coated onto gold nanoparticles (GNP) aggregates, which support localized surface plasmon (LSP) in the near-infrared (NIR) region, leading to significant SERS enhancement when 785 nm laser excitation was used. SERS experiments showed that the SERS spectrum of the CF isomer is clearly distinguished from that of the OF isomer with a strong contrast. A comparison between photoisomerization kinetics obtained from SERS measurements recorded at 633 and 785 nm excitation revealed that excitation in the NIR enables less destructive detection of isomeric states compared to visible excitation. However, weak photoisomerization was detected even with the NIR excitation. We discuss possible mechanisms at the origin of the observed NIR ring-opening process.