Comparison of nitrogen core and ethylenediamine core starburst dendrimers through photochemical and spectroscopic probes

The surface properties of ammonia core and ethylenediamine core poly(amidoamine) starburst dendrimers (N-SBD and EDA-SBD, respectively) were comparatively investigated, by employing photochemical and spectroscopic probes. Photoinduced electron-transfer quenching of tris-(2,2'-bipyridyl)ruthenium(II) chloride by methyl viologen on the SBD, monitored by fluorescence spectroscopy, was utilized to probe the negatively charged dendrimer surface. Electron-transfer quenching was found to be enhanced when the donor and acceptor are adsorbed on later generation dendrimers. Adsorption and aggregation of organic dyes, such as methylene blue and fluorescein, on negatively and positively charged dendrimers, respectively, were studied by applying UV-vis and fluorescence spectroscopy. The aggregation of the dyes depended strongly on the SBD generation. For the later generation SBDs, aggregation was found to occur more readily. Both photochemical and probe techniques allowed nearly identical conclusions for the external surface of the two different core dendrimers (N-SBD and EDA-SBD); i.e., the surface properties of both dendrimer types change qualitatively at approximately generation 3 from an "open" to a "closed" structure, as predicted by computational investigations of the full generations. These results suggest that earlier findings from applications involving N-SBD can be applied to more readily available EDA-SBD.