A density functional theory and resonance Raman study of a benzotriazole dye used in surface enhanced resonance Raman scattering

Quantitative surface enhanced resonance Raman scattering (SERRS) requires effective adsorption of the analyte onto the metal surface. A range of dyes incorporating the benzotriazole group has been specifically designed to achieve this and they have proved successful labels for obtaining very sensitive analysis. However, if the spectra were more fully understood, the differences between the Raman spectrum in solution and on the surface could provide unique structural information on the nature of the surface layer. Using density functional theory (DFT) calculations the Raman and Infra-red (IR) spectra of the dye 3,5-dimethoxy-4-(6′-azobenzotriazolyl)-phenylamine (ABT-DMOPA) were assigned. A good correlation was found between the computed and experimental frequencies. Two competing isomers were compared and gave a largest error in fit for any clearly assigned band in the Raman spectrum of 41 cm−1 and an overall fit error of ∼15 cm−1. For the IR spectrum the largest error was 24 cm−1 with an overall fit error of ∼8 cm−1.Comparison of resonance Raman, SERS and SERRS spectra of the dye showed intensity changes which suggest the formation of a complex with silver on the surface. In the 1600–1630 cm−1 region, one vibration is reduced in intensity whilst one is greatly enhanced as surface attachment occurs, giving a good marker for surface attachment.