Dendrimer three-dimensional architecture

Dendrimers are macromolecules with a regular and highly branched three-dimensional architecture. The first example of an iterative synthetic procedure toward well-defined branched structures has been reported by Vogtle et al. [1], who named this procedure a cascade synthesis . The paper concerning den-... 

Dendrimers are a relatively new class of macromolecules different from the conventional linear, crosslinked, or branched polymers. Dendrimers are particularly interesting because of their nanoscopic dimensions and their regular, well-defined, and highly branched three-dimensional architecture. In contrast to polymers, these new types of macromolecules can be viewed as an ordered ensemble of monomeric building blocks. Their tree-like, monodispersed structures lead to a number of interesting characteristics and features globular, void-containing shapes, and unusual physical properties [107-111]. 

Dendrimers are a class of macromolecules whose application in NLO field has been considered recently [108]. Ideally, dendrimers are perfect monodisperse macro-molecules with a regular and highly branched three-dimensional architecture. Their monodisperse, tree-like nature determines interesting properties such as the formation of voids and nanostructures [109]. 

Other macromolecular architectures, such as linear polymers, and any comparisons that have been made were performed with polydisperse samples of significantly different repeat unit structure. For example, the unique melt viscosity behavior of polyether dendrimers was compared with linear polystyrene and not with monodisperse linear analogs containing the same number of polyether repeat units based on 3,5-dihydroxybenzyl alcohol (2). Because of this, important issues, such as i) effect of the numerous chain end functional groups, ii) the effect of branching and, iii) the development of a well defined three-dimensional architecture cannot be addressed and the underlying reason for these inherent differences remains a mystery. 

In addition to the one-dimensional wire-like compounds, a considerable number of two-dimensional and three-dimensional architectures have also been built, using the chemistry of the alkynyl units in an elegant manner, by the groups of Bunz [54], Diederich [55-57], de Meijere [58], Moore [59], Tykwinski [46, 47], Haley [60], Vollhardt [22-27] and others [61, 62]. In particular, a series of perylene-terminated phenylene ethynylene dendrimers with energy gradients was... 

Figure 1.14 Three-dimensional projection of dendrimer core-shell architecture for G = 4.5 poly(amidomine) (PAMAM) dendrimer with principal architectural components (I) core, (II) interior and (III) surface...

Embedding of pinacyanol in a three-dimensional polyphenylene dendrimer results in a red-shift of absorption (from 600 to 620 nm) and emission (from 625 to 648 nm) maxima and in an increase of the quantum yield from 9 x KT4 for free dye in water to 1.4 x 10 2 after insertion in the dendrimeric architecture [71]. This dendrimer was used to develop two FRET systems utilizing cyanine dyes as the donor (DTCI) and the acceptor (pinacyanol and 26a) molecules [72], The FRET system allows the time-resolved detection, where energy transfer can be observed at the single-molecule level. 

As defined, dendritic networks are considered to result from the one-, two-, and three-dimensional orientation of dendrimers thus ordering can be geometrically likened to rods surfaces or sheets and cubes, tetrahedrons, or spheres, respectively. Due to the broad scope and breadth of potential macromolecular architectures that can be obtained by application of different modes of connectivity, we will herein concentrate on networks constructed from the simplest dendritic structures, namely those that are pseudospheri-cal or globular. The principles that are presented here pertaining to network formation should be easily adaptable to non-spheroidal dendritic structures as well as macromolecular assemblies possessing only limited dendritic character. 

Dendrimers ) are macromolecules that exhibit a defined structure and not only a high degree of order but also a high degree of complexity. From a topological viewpoint, dendrimers contain three different regions core, branches, and surface (Fig. 1). A most important feature of dendrimer chemistry is the possibility to insert selected chemical units in predetermined sites of their architecture. Further, because of their three-dimensional structure, dendrimers exhibit internal dynamic cavities where ions or molecules can be hosted. 

STRUCnjRE Dendrimers are three-dimensional macromolecules consisting of three major architectural components a core, branch cells, and terminal groups. These products are constructed from repeat units called branch cells [e.g.,... 

STRUCTURE Dendrimers are three-dimensional macromolecules consisting of three major architectural components a core, branch cells, and terminal groups. These products are constructed from repeat units called branch cells [e.g., —CH2—CH2—CH2—N(CH2—CH2—012)2] iri concentric generations (G) surrounding various cores according to dendritic rules and principles, where = multiplicity of core N, = multiplicity of branch cell and Z = terminal groups (i.e., -CN or —CH2-NH2). 

Three-dimensional branched architectures, generally termed dendrimers, represent a class of synthetic macromolecules that have impacted dramatically on the field of organic and polymer chemistry and created a new branch in synthetic and material chemistry. For the last two decades, dendrimer research has been at the forefront of polymer research and was first postulated in the 1940s by Flory, a pioneer in polymer research and Nobel Laureate in 1974, who proved the existence of branched chains and their potential role in three-dimensional (3D) macromolecular architectures [446-448], In 1978, Vogtle et al. developed an iterative cascade method for the synthesis of low molecular weight branched amines [449]. The real expansion of the field started after Tomalia et al. [450] and Newkome et al. [451] discovered the starburst effect, which shed light on a new chemical arena. Since then, dendrimer chemistry has been diversified... 

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