Isomerization Reaction of mer- to fac-Tris(2-phenylpyridinato-N,C2′)Iridium(III) Monitored by Using Surface-Enhanced Raman Spectroscopy

We developed a new method by enclosing the complex tris(2-phenylpyridinato-N,C2′)Iridium(III), Ir(ppy)3 with surfactant cetyltrimethylammonium bromide (CATB), coated with a thin layer of silica then bonded to the surface of silver nanoparticle. These samples were used to acquire surface-enhanced Raman scattering (SERS) spectra. The thickness of silica layer was controlled to have efficient phosphorescence quenching and Raman enhancement by metal nanoparticle. The SERS spectra of fac- and mer-Ir(ppy)3, recorded at 633 nm excitation, display distinct ring breathing mode features because the total symmetric vibrational bands were enhanced. This provides a convenient means to differentiate these isomers with great sensitivity and to study their isomerization process. A direct conversion reaction of mer- to fac- isomerization is identified with time constant 3.1 min when mer was irradiated with Xe light. Via thermal activation, under moderate conditions (pH 5.5 and 343 K), we observed an intermediate particula...