Benzyl ether type dendrons

Dendrimers are repeatedly branched molecules. The name comes from the Greek 8Ev8pov /dendron, which means tree. A series of stilbene dendrimers with a stilbene core and benzyl ether type dendrons has been synthesized and investigated... 

Photochemical and photophysical properties of a poly(propylene amine) dendri-mer (2) functionalized with -stilbene units have been studied [102]. Z-photoisome-rization and photocyclization of the Z-isomer of the stilbene units were investigated in air-equilibrated acetonitrile solutions. The quantum yields of the E Z photoisomerization reaction and the fluorescence quantum yield of the E were found to be equal to 0.30 and 0.014, respectively. Stilbene dendrimers prepared by coupling 4,4 -dihydroxystilbene with first-, second-, third-, or fourth-generation benzyl ether-type dendrons underwent photoisomerization with the same efficiency as that of 4,4 -dimethoxystilbene [103], The lifetime of the core structure was found to be shorter then 1 ns. According to [104], polyphenylene-based stilbene dendrimers, Gl, G2, and G3, underwent mutual cis-trans isomerization upon direct irradiation with 310 nm light at room temperature. In a solvent glass at 77 K, one-way cis-trans isomerization was observed for G2. 

In order to elucidate the dendrimer effects, the two-photon ionization process (308 and 266 nm) of stilbene dendrimers having a stilbene core and benzyl ether-type dendrons has been investigated in an acetonitrile 1,2-dichloroethane mixture [59]. 

Some features of the dendronized polymers obtained from the macromonomers of Table 1 will become important later in this article and are therefore emphasized in the following (1) Most of the macromonomers carry G1 or G2 dendrons. Exceptions are only (12) (G3), (16) (G3), (18) (G3 and G4), (23) (G4), (25) (G3), and (27) (G3 and G4) (2) Many dendrons are of the benzyl ether type whose terminal phenyl rings are either unsubstituted or have one to three long alkoxy or fluoroalkoxy chains. The corresponding polymers are important for a variety of reasons but are unreasonable candidates, of course, whenever chemical modification becomes an issue (3) This is where dendrons (7), (8), (10), (11), and potentially also (13) come into play which carry protected... 

Scheme 5.14. Poly(benzyl ether) dendrons have been attached to fullerenes via carbenoid-type chemistry.

The poly(benzyl ether) dendrimer synthesis is one of only a few convergent syntheses that can produce dendrons and dendrimers in reasonable yields up to the sixth generation. These dendrons, now frequently referred to as Frechet-type dendrons, have been utilized by a number of groups because they are... 

In 1996, Zimmerman and coworkers produced a seminal study in this field that first involved the synthesis of a series of Frechet-type benzyl ether dendrons (up to the fourth generation) that possessed a novel hydrogen... 

The stimuli-responsive supramolecular dendronized polymers produced by Stoddart and coworkers used a so-called hook-and-eye approach, harnessing the interaction between ammonium ions and crown ether receptor units (Scheme 10). The assembly was constructed by the addition of Frdchet-type benzyl ether dendrons with benzyl ammonium at the focal point (first to third generation, only G2 shown, 44, Figure 13) to either polystyrene (45, M 85kDa)- or polyacetylene (46, M 13kDa)-based polymers containing DB-24-C8 pendent eye groups. 

The Percec group has produced several libraries of structurally related LC dendrons including those based upon phenylpropyl, " biphenylpropyl, and benzyl ether dendrons, whereby each member of the library differs by generation and substitution pattern at each branch point. Analysis of the solid-state packing of each of the dendrons has allowed the group to develop a nano-periodic table to facilitate the prediction of solid-state structure from molecular connectivity of dendrons of this type. 

Scheme 69 Pd(ll) complexes of bis(pyrazolyl)alkane ligands containing benzyl or benzyloxycarbonyl or polyfaryl ether) Frechet-type dendron groups.

Oligothiophenes end-capped with polybenzyl ether dendrons were prepared by Frechet s group (Scheme 1.70) [508]. Benzyl ester-substituted quinquethiophene 5.65 was deprotected in basic medium to the carboxylic acid and converted to the corresponding acid chloride using oxalyl chloride. This was then connected to a G5-hydroxyl-terminated Frdchet dendron by ester linkages. Stille-type coupling of the terminally brominated quinquethiophene and 2,5-bis(trimethylstannyl)thiophene afforded the highly... 

Ethers are chemically and coordinatively more inert than amides. Indeed, Frechet-type polyether dendrimers prepared in solution demonstrate a broad spectrum of chemical and coordinative compatibilities. Accordingly, polyether dendron synthesis on solid support was developed, initially by Bradley and coworkers and later by Portnoy and Dahan Instead of the 3,5-dihydroxy benzyl alcohol derivatives used in the soluble Frechet-type dendrimers, a more SPOS suitable 3,5-bis(hydroxymethyl)phenol unit was conceived as a building block for the dendron construction. 

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