Fluorescent dendrimer

Quantitative analysis of the results obtained has shown that a single eosin guest is sufficient to completely quench the fluorescence of any excited dansyl unit of the hosting dendrimer. Fluorescence lifetime measurements indicated that the dye molecules can occupy two different sites (or two families of substantially different sites) in the interior of the dendritic structure. 

They also investigated the quenching of the azobenzene dendrimer fluorescence by Eosin Y (2/,4/,5/,7/-tetrabromofluorescein dianion) [35]. It was concluded that Eosin Y was hosted in these dendrimers and Z-form dendrimers were more efficient hosts than E-form dendrimers. 

A luminescent unit extensively used to functionalize dendrimers is the so-called dansyl (5-dimethylamino-l-naphthalenesulphonamido group). Dendrimers (up to the third generation, compound 9) containing a single dansyl unit attached off center [39] show that this fluorescent unit, which is very sensitive to environment polarity, is progressively shielded from interaction with water molecules as the dendrimer generation increases. 

Luminescence experiments in dichloromethane solution indicated that the fluorescence of the phenylacetylene branches is quenched, whereas intense emission is observed from the binaphthol core. This antenna effect represents the first example of efficient (>99%) energy migration in an optically pure dendrimer. The fluorescence quantum yield increases slightly with increasing generation the values of 0.30,0.32, and 0.40 were obtained, respectively, for 10-12. 

Chiral dendrimers based on oligonaphthyl cores and Fr chet-type poly(aryl ether) dendrons have been investigated [44]. The absolute configuration of these dendrimers remains the same as that of their chiral cores. Both the nature of the core and the generation play a role in determining the fluorescence quantum yield. 

Poly(aryl ether) branches of generation 1 to 3 have been appended to a pho-totautomerizable quinoHne core to investigate the effect of dendritic architecture on the excited state intramolecular proton transfer [45]. The changes observed in the absorption and emission spectra on increasing dendrimer generation indicate that the dendritic branches affect the planarity of the core and therefore the efficiency of the excited state intramolecular proton transfer and of the related fluorescence processes. 

In a recent study, poly(aryl ether) dendritic branches terminated with triethyleneglycol chains were attached to Cgg [66] dendrimer 32 represents the fourth generation. The photophysical properties of these fullerodendrimers have been systematically investigated in three solvents, namely toluene, dichloromethane, and acetonitrile. On increasing dendrimer generation, it has been found that in each solvent (i) the maximum of the fullerene fluorescence band is red-shifted... 

Dye molecules can also be hosted into poly(propylene amine) dendrimers peripherally modified with OPV units [71]. In these systems, energy transfer from the OPV fluorescent units nm) to the enclosed dye molecules is... 

Dendritic hosts can be used in aqueous solution to encapsulate water-soluble fluorescent probes. Changes in the photophysical properties of these encapsulated probes are useful to understand the properties of the microenvironment created by the dendritic interior. For example, adamantyl-terminated poly(pro-pylene amine) dendrimers from the first to the fifth generation (36 represents the third generation) can be dissolved in water at pH<7 in the presence of -cyclodextrin because of encapsulation of the hydrophobic adamantyl residue inside the /1-cyclodextrin cavity and the presence of protonated tertiary amine units inside the dendrimer [72]. Under these experimental conditions, 8-anifi-... 

Dendrimers containing a polar surface and an apolar interior can work as hosts of hydrophobic fluorescent probes in aqueous environment. In particular. 

It has been demonstrated that dendrimers can be used also as fluorescent sensors for metal ions. Poly(propylene amine) dendrimers functionalized with dansyl units at the periphery like 34 can coordinate metal ions by the aliphatic amine units contained in the interior of the dendrimer [80]. The advantage of a dendrimer for this kind of application is related to the fact that a single analyte can interact with a great number of fluorescent units, which results in signal amplification. For example, when a Co ion enters dendrimer 34, the fluorescence of all the 32 dansyl units is quenched with a 32-fold increase in sensitivity with respect to a normal dansyl sensor. This concept is illustrated in Fig. 3. 

Fig. 2. Absorption solid line) and fluorescence bold line) spectra of Rd/dendrimer film. Inset is absorption spectra of the bared rhodamine B film...

Fig. 4. Fluorescence intensity as a function of the concentration of DCM-dendrimer mixture...

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