A Comparative Study on the Photophysical and Photochemical Properties of Dyes in the Presence of Low Generation Amino‐terminated Polyamidoamine Dendrimers

Abstract

The photophysical and photochemical properties of the xanthene dyes mercurochrome (MCr) and eosin-Y (Eos); and the phenazine dye safranine-O (SF) are evaluated in the presence of amino-terminated polyamidoamine (PAMAM) dendrimers of low generations. The dendrimers produce a red shift in the UV-vis absorption spectra of the dyes, which increases with concentration and the size of the PAMAM molecule. The Stern-Volmer plots of fluorescence quenching for xanthenic dyes present a downward curvature. It is ascribed to a static mechanism involving a dye-dendrimer binding. A nonlinear fitting of the SV plots allows the calculation of the binding constants. For SF, the fluorescence is only slightly quenched by PAMAMs and the SV plots are linear. The binding constants are in the order K bind (SF) ( K bind (Eos) < K bind (MCr). The difference must be due to important specific structural effects. A decrease in the triplet lifetime and an increase in the absorption of the semireduced form of the dyes are observed in the presence of dendrimers. While for the two xanthene dyes, the rate constants reach the diffusional limit for G2 and G3, for SF they are one order of magnitude lower. This is explained by a different quenching mechanism of the two types of dyes.

New Dye/Dendrimer Photoinitiating Systems Operating under Visible Radiation: Eco‐Friendly Synthesis of Highly Viscous Polymers

“…In previous works, we demonstrated that under visible LED light xanthene dye/PAMAM couples generate radicals with high efficiency because amino groups in the dendrimer structure act as electron donors to excited dyes. [15][16][17] In addition, we found that the strong dye/PAMAM binding is a key factor in the electron transfer process. Such features along with the water solubility of PAMAM make these dye/dendrimer combinations excellent candidates for their use in solvent-free formulations, thus reducing the environmental impact of typical PIs.…”

“…In previous works, we demonstrated that under visible LED light xanthene dye/PAMAM couples generate radicals with high efficiency because amino groups in the dendrimer structure act as electron donors to excited dyes [15–17] . In addition, we found that the strong dye/PAMAM binding is a key factor in the electron transfer process.…”