Dendrimers excited state quenching

Self-assembly of functionalized carboxylate-core dendrons around Er +, Tb +, or Eu + ions leads to the formation of dendrimers [19]. Experiments carried out in toluene solution showed that UV excitation of the chromophoric groups contained in the branches caused the sensitized emission of the lanthanide ion, presumably by an energy transfer Forster mechanism. The much lower sensitization effect found for Eu + compared with Tb + was ascribed to a weaker spectral overlap, but it could be related to the fact that Eu + can quench the donor excited state by electron transfer [20]. 

Ru(bpy)2(CN)2] to Nd3+ can be assumed to be equal to the efficiency of the quenching of the [Ru(bpy)2(CN)2] emission (ca. 90%) because quenching by electron transfer can be ruled out in view of the Nd3+ redox properties. No evidence of energy transfer in the adduct from the naphthyl-localized 7) excited state of the dendrimer to the lowest 3MLCT state of [Ru(bpy)2(CN)2] has been found since no change in the Tx lifetime at 77 K has been observed. 

Encapsulation of a Ru atom into a caged [109, 110] or hemicaged [299] tris-bipyridine ligand extends the MLCT excited state lifetime and improves photostability relative to [Ru(bpy)3] ", while retaining the fast (diffusion controlled) bimolecular excited state electron transfer reactivity. In contrast, the [Ru(bpy)3] + in the core of a dendrimer [248] has about the same inherent lifetime as the free complex but the rate of electron transfer quenching rapidly decreases with increasing the number and size of dendrimer branches. 

Poly(propyleneamine) dendrimers of generations 1 and 4 (89) functionalized with azobenzene groups were investigated as hosts for eosin Y (eosin = 2, 4, 5, 7 -tetrabromofluorescein dianion) in DMF solution [159]. The peripheral azobenzene groups can be switched by light excitation from the E to the Z form. The fluorescent excited state of eosin is reductively quenehed by the tertiary amine units present in the dendrimer structure. This electron transfer quenching takes place with a static... 

Aida and coworkers synthesized water-soluble poly(phenyleneethynylene) wrapped with poly(benzyl ether) dendrimer frameworks bearing negatively exterior surfaces, as a photosensitizer [130]. The wrapping of the conjugated backbone suppressed self-quenching of the excited state. The negatively charged surface incorporated to form a spatially separated donor-... 

The steady state absorption and fluorescence spectra of both dendrimer generations 1 and 2 are depicted in Fig. 2. The former are merely superpositions of the absorption spectra of both chromophores involved. In the fluorescence, however, the peryleneimide part is almost completely quenched compared to the model compound. Instead, the fluorescence at wavelengths longer than 650 nm almost completely resembles the emission spectrum of the terrylene-diimide model compound 3. This feature is a strong indication that within these dendrimers the excitation energy is efficiently transferred from the peryleneimide to the terrylenediimide. 

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