Chromophores dendronized

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]. 

In dichloromethane solutions, excitation of the chromophoric groups of the dendrons causes singlet-singlet energy transfer processes that lead to the excitation of the porphyrin core. It was found that the dendrimer 17, which has a spherical morphology, exhibits a much higher energy transfer quantum yield (0.8) than the partially substituted species 13-16 (quantum yield <0.32). Fluo-... 

Similar generation-dependent aggregation behavior was reported for a series of dendrons having a phosphate focal group and functionalized at the periphery with azobenzene chromophores in water (Zhang et al. 2007). In this system, the stability... 

Dendrimers with cyclam core unit (1,4,8,11-tetraazacyclotetradecane) and Fre-chet type dendrons, decorated with eight or 16 naphthyl units (Fig. 5.17) were examined for changes of their luminescence and absorption spectra during protonation [21]. The core unit itself is photoinactive, but can interact with photoactive groups in the dendritic branches, influencing the emission properties of the chromophore units and giving rise to the possibility of new emission bands. 

Recording numerous fluorescence spectra shows a bimodal distribution of the peak position due to conformational changes within the chromophore. Attaching polyphenylene dendrons to this perylene-diimide system influences this distribution and the position of the peaks. Here, SMS was used to monitor conformational interconversions on the single-molecule level. 

To maximize the dendritic effect, a chromophore 16 was recently modified further with multiple fluorinated dendrons (Scheme 10). The resulting dendritic chromophore 17 exhibits appreciably different properties, such as a blue-shifted absorp-... 

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