Interfacial Effects of the Photophysics of Rhodamine 6G Ultra-Thin Films on a Poly(methylmethacrylate) Surface

The absorbance, excitation, and emission spectra of ultra-thin films of slides are examined as a function of both PMMA and Rh6G thickness. The thickness of PMMA has a little effect on the absorption or emission properties of Rh6G. At low surface coverage, the spectral properties of Rh6G are dominated by isolated molecules. As the Rh6G thickness increases, there is no evidence for exciton formation. Instead, the Rh6G molecules aggregate, which is responsible for the observed absorption and emission spectra. The aggregates significantly quench the emission so that the maximum emission intensity is found just below a monolayer surface coverage. The lack of exciton formation, which is unexpected, is attributed to the surface morphology of PMMA, which has a periodic surface structure.