Probe Covalently Linked on the Dendrimer Surface

In order to study the molecular dynamics of the outer segments of a dendrimer, one pyrene moiety was selectively and covalently attached to one dendron of poly(aryl ester) dendrimers by Adams (in total three pyrene molecules per dendrimer) [24]. The fluorescence decay of pyrene in the THF solution of the labeled dendrimers provided details of the pyrene excimer formation, such as the excimer formation rate, the excimer decomposition rate constant and the equilibrium constant of the excimer formation. These parameters were utilized to evaluate the diffusional mobility of the dendrimer branches. 

Frechet et al [26] studied the microenvironment in dendritic molecules by covalently attaching a solvatochromic probe namely iV-methylamino-p- 

A similar approach was taken by Moore [27], utilizing poly(phenyl acetylene) dendrimers with a dimethylbenzene moiety attached at the core of the dendrimer. An anomalous shift (41 nm) in the fluorescence spectra of the probe in various nonpolar hydrocarbon solvents was observed for G5 and G6, but not for G1 to G4. This observation confirmed significant in the size and shape changes for these dendrimers between G4 and G5. 

Frechet and co-workers [32] studied the ability of the dendrimer shell to provide site isolation of the core porphyrin moiety, using benzene-terminated dendrimers Zn[G-n]4P (i.e. 6). From the cyclic voltammograms in CH2C12, the interfacial electron transfer rate between the porphyrin core and the electrode surface decreased with increasing dendrimer generation. However, small molecules like benzyl viologen could still penetrate the shell of 6 to access the porphyrin core as observed from the quenching of porphyrin fluorescence. Their results also revealed that the dendritic shell did not interfere electrochemically or photochemically with the porphyrin core moiety. 

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