Date of Award
Chemistry and Biochemistry
Surface enhanced Raman spectroscopy (SERS) is a chemical method gaining much popularity in recent years. With the use of a roughened metal surface or metal nanoparticles, surface plasmon resonances enhance the electromagnetic field allowing for increased Raman signal. Pyrimidine, having two lone pairs of electrons, is capable of charge transfer interactions contributing to a SERS chemical enhancement factor as well. It has recently been reported that hydrogen bonding with water results in the blue-shifting of certain normal modes of pyrimidine. By comparing experimental polarized Raman spectra with the results of electronic structure calculations, the origin of this blue-shifting was found to center around charge transfer from pyrimidine to water in the bulk mixtures. In this thesis, we show how weak, noncovalent interactions affect the SERS spectra of neat pyrimidine and pyrimidine solutions of both water and methanol using silver-island film substrates. We analyze the spectroscopic results by comparing both the Raman and SERS spectra of bulk pyrimidine and pyrimidine/solvent mixtures to theoretical predictions in order to deduce the mechanisms of the spectral shifts. SERS spectra of pyrimidine and pyrimidine solutions exhibit blue shifts in v 1 and v8b and a red shift at v8a due to charge transfer and the chemical enhancement from the silver island films. Multiple components in v1's spectra correspond to free pyrimidine, and one or two interactions with nitrogen atoms. Comparison of the experimental spectra suggests that interactions between pyrimidine and silver dominate interactions between pyrimidine and the solvent molecules. The magnitude of the blue shifts suggests charge transfer on the order of 35 and 80 milli electrons for one or two interactions, respectively.
McClellan, Annie Katherine, "Spectroscopic Study of Charge Transfer Induced Blue Shifting of Pyrimidine/Water Mixtures on Silver Substrate" (2013). Honors Theses. 92.