Functional Dendrimers - Applications

This manuscript describes the dendritic macromolecules for optical and optoelectronic apph-cations, particularly stimulated emission, laser emission, and nonlinear optics. Dendrimers have been designed and synthesized for these applications based on simple concepts. A coreshell structure, through the encapsulation of active imits by dendritic branches, or a cone-shaped structure, through the step-by-step reactions of active imits, can provide particular benefits for the optical high-gain media and nonlinear optical materials. It also described experimental results that support the methods presented for designing and fabricating functionalized dendrimers for optoelectronic applications, and theoretical results that reveal the intermolecular electronic effect of the dendritic structure. 

After a variety of very different dendrimers had become available up to high generations, many groups directed their attention more and more to designing and synthesizing functionalized dendrimers, i.e., dendrimers adorned with functionalities that are intended to give them characteristic properties favourable for application purposes.14,141... 

In contrast to dendrimers built up from aliphatic chains, polyphenylene dendrimers exist as shape persistent nanoparticles as we have demonstrated above. The preparation of functionalized dendrimers is the key step towards various applications. 

In the search to develop new materials for immobilization of homogeneous transition metal catalyst to facilitate catalyst-product separation and catalyst recychng, the study of dendrimers and hyperbranched polymers for application in catalysis has become a subject of intense research in the last five years [68], because they have excellent solubility and a high number of easily accessible active sites. Moreover, the pseudo-spherical structure with nanometer dimensions opens the possibility of separation and recycling by nanofiltration methods. Although dendrimers allow for controlled incorporation of transition metal catalysts in the core [69] as well as at the surface [70], a serious drawback of this approach is the tedious preparation of functionalized dendrimers by multi-step synthesis. 

Another noteworthy difference between core- and periphery-functionalized dendrimers is that much higher costs are involved in the application of core-functionalized dendrimers due to their higher molecular weight per catalytic site. Furthermore, applications may be limited by the solubility of the dendrimer. (To dissolve 1 mmol of catalyst/L, 20 g/L of core-functionalized dendrimer is required (MW 20 000 Da, 1 active site) compared to 1 g/L of periphery-functionalized dendrimer (MW 20 000 Da, 20 active sites). On the other hand, for core-functionalized systems, the solubility of the dendritic catalyst can be optimized by changing the peripheral groups. 

Fio. 8. Application of a non-covalently functionalized dendrimer (see fig. 7) in a CFMR in the allylic amination of crotyl acetate and piperidine in dichloromethane (Koch MPF-60 NF membrane, molecular weight cut-off = 400 Da) (21). 

Jang W-D, Kataoka K. Bioinspired applications of functional dendrimers. J Drug Deliv Sci Technol 2005 15 19-30. 

The process utilizing supramolecular organization involves pore expansion in silicas. A schematic view of such micelles built from the pure surfactant and those involving in addition n-alkane is shown in Figure 4.9. Another example of pore creation provides a cross-linking polymerization of monomers within the surfactant bilayer [30]. As a result vesicle-templated hollow spheres are created. Dendrimers like that shown in Figure 4.10 exhibit some similarity to micellar structures and can host smaller molecules inside themselves [2c]. Divers functionalized dendrimers that are thought to present numerous prospective applications will be presented in Section 7.6. 

The many possibilities of directing the physical/chemical properties of a den-drimer by introduction of selected functional groups into the molecule lead to an great variety of potential applications of dendrimers. Depending upon the position and the nature of the functional units within the dendrimer structure, it is possible to distinguish between different types of functional dendrimers ... 

The LBL self-assembly onto the CD functionalized surface requires at least two complementary substrates in order that multiple layers can be built up upon repeated alternating applications of the substrates, until a desired thickness has been achieved. Reinhoudt and coworkers chose the self-assembled interaction between CD-modified gold nanoparticles and either adamantyl- or ferrocene-functionalized dendrimers, which in turn were composed either of poly(propyleni-mine) (PPI) or poly(amidoamine) (PAMAM) [118, 122]. 

Dendritic polymers can be covalently functionalized with organometallic complexes to obtain a dendritic catalyst with molecularly defined catalytic sites [5-7]. Moreover, a considerable number of reports on the applicability of functionalized dendrimers in catalysis have led to the idea of a dendritic effect on the catalyst activity/selectivity, which can either be positive or... 

We would like to report the synthesis of a star-shape poly(vinylmethyl-c6>-dimethyl)siloxane polymers functionalized in their exterior, which makes them especially suitable for application as catalytic supports. Similarly to catalysts bound to periphery-functionalized dendrimers [3] they offer regularly distributed and available catalytic sites. 

Over the years, molecular design has allowed the synthesis of functional dendrimers possessing metal and semiconductor nanoparticles, metal complexes and macrocycles, dyes and biologically important carrier molecules in various parts of the dentritic structures [31-39], Such dendrimers incorporating functional units are considered as supramolecular species [16, 21], Functional dendrimers have been proved to be very useful for specific applications [40, 41], Some examples of functional dendrimers are shown in Fig.5. 

The variety of the examples listed above documents that dendrimer chemistry has attained increasing interest. In this compilation of recent results the trend towards functional and application-oriented molecules including biochemically active, photoswitchable, and polymerlike dendrimers is particularly apparent. Dendrimers cross the boundaries of classical organic chemistry and as new materials will penetrate deeper into the topical fields of nanostructures , supramolecules and polymers in the future. Increasing industrial research on dendrimers and the commercial availability of PAMAM and polyamine dendrimers should stimulate further investigations in this field. 

Dendrimers represent a class of materials that combine unique features (well-defined macromolecular structure, monodispersity, and low viscosity) with remarkable properties such as encapsulation, catalysis, and chiroptical properties. Functionalized dendrimers are considered to be new materials with high potential applications. 

Chavan S A, Maes W, Gevers LEM, Wahlen J, Vankelecom IFJ, Jacobs PA, Dehaen W, De Vos DE. Porphyrin-functionalized dendrimers Synthesis and application as recyclable photocatalysts in a nanofiltration membrane reactor. Chem A Eur J 2005 11(22) 6754-6762. 

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