Nonresonant and Resonant Surface-Enhanced Raman Scattering of N-Ethyl-N-(2-hydroxyethyl)-4-(4-nitrophenylazo) Aniline in Poly(methyl methacrylate) on Ag Films with Surface Roughness

Abstract

Abstract Nonresonant and resonant surface-enhanced Raman scatterings (SERS and SERRS) were studied for N-ethyl-N-(2-hydroxyethyl)-4-(4-nitrophenylazo) aniline (Disperse Red 1, or DR1) in poly (methyl methacrylate) on Ag films with surface roughness. DR1 is a chromophore that consists of azobenzene bridged between electron-donating amine and electron-accepting nitro groups, and it has attracted great attention because of its large molecular hyperpolarizability. DR1 hybridized with metal nanoparticles or nanostructures is promising as a building block for nonlinear plasmonics. Our experimental results demonstrated that the Raman cross sections were highly enhanced both at the molecular nonresonant and resonant excitation wavelengths. The spectroscopic properties of SERRS were taken from resonant Raman (RR), and the enhanced RR cross sections were attributed to electromagnetic enhancements due to surface plasmons (SP). The SERS spectrum was also similar to the RR spectrum, rather than the non-resonant Raman (NR) spectrum, even at the molecular non-resonant excitations. A diagram of energy levels was drawn for the DR1/Ag interfaces by using ultraviolet-visible linear absorption and ultraviolet photoelectron spectroscopic data. The enhanced NR cross sections were explained in terms of the electromagnetic enhancements, as well as the metal-to-molecular charge-transfer, by using the energy diagram.