Intermolecular dendrimer interactions

JM Lupton, IDW Samuel, R Beavington, PL Burn, and H Bassler, Control of charge transport and intermolecular interaction in organic light-emitting diodes by Dendrimer generation, Adv. Mater, 13 258-261, 2001. 

Except for some regions indicated by arrows, most of the surface consists of small domains of various sizes, as seen in Figure 12.4 (b). Low generation members (i.e. G = 0-3) in the PAMAM dendrimer series appear to exist as floppy open, plate-like molecules in which the dendrimer branches can easily interpenetrate each other and establish intermolecular interactions [19],... 

Fig. 29 Effect of the linker chain lengths on the intermolecular interaction of catalytic dendrimers immobilized on silica supports [62]...

As a general statement it can be concluded that macromolecular conformations different fi om the predominant coil structure are still the exception. Defined spherical secondary-structures have not been obtained by means of noncovalent interactions, since there is no synthetic concept available, distinguishing between inter- and intra-molecular interactions. Formation of globular structures by linear macromolecules is still a privilege of biomolecules where intermolecular interactions are counteracted by well-coordinated intermolecular interactions [50,51]. Synthetic nanospheres can be obtained by the stepwise synthesis of dendrimers [15] or by polymerization of microgels [52] (see below). 

A pronounced influence of pH and added electrolyte on the charge interactions between dendrimers with ionizable groups is expected in aqueous solution. Briber et al. ° investigated the intermolecular interactions between PAMAM dendrimers in concentrated solutions using SANS and SAXS techniques. They showed that the molecules develop large scale interactions which can be screened by the addition of excess acid or electrolyte. SANS studies of the structural... 

Briber, R.M. Bauer, B.J. Hammouda, B. Tomalia, D.A. Small-angle neutron scattering from solutions of dendrimer molecules intermolecular interactions. Polym. Mater. Sci. Eng. 1992, 67, 430-431. 

As with chromophores, the steric encapsulation of a dendrimer core can be utilized to prevent intermolecular interactions between redox active sites. A number of different redox active core moieties have been investigated, including, iron—sulfide clusters,9394 bis(terpyridine)iron(II) complexes,92 tris-(bipyridine)ruthenium(II) complexes,330 zinc porphyrins,252 oligothienylenevinylenes,331 fullerenes,236,332 ferrocenes,333-336 oligothiophenes,322 oligonaphtha-lenes,337 and 4,4 -bipyridinium.338... 

This chapter presents a selective glimpse of this dynamic family of spherical macromolecnles for newcomers to the topic in order to help them better appreciate the field that has been extensively reviewed elsewhere. This chapter is divided into several parts to emphasize the structmal diversity and their potential applications. First, a study of the internal structure of the dendritic architecture, emphasizing the different types, followed by a study of their interactions with other molecules or atoms, such as in the case of host-guest chemistry, molecular recognition, or encapsulation inside the dendrimer. Finally, there is a small section that will address the intermolecular interactions of dendrimers and dendrons to either themselves or other nano-objects. In this past quarter century, tens of thousands of papers have been published producing a wide variety of different dendritic architectures with varied structural components capable of novel supramolecular interactions. Therefore, only an overview describing their structure with representative examples and practical purposes will be discussed, when appropriate. 

G2, to G3, and to G4, the effective enhancement was 10%, 36%, and 35% larger than the value estimated by the simple addition of monomeric values. The enhancement included the local field effect due to the screening electric field generated by neighboring molecules. Assuming the chromophore-solvent effect on the second-order susceptibility is independent of the number of chro-mophore units in the dendrimers, p enhancement can be attributed to the inter-molecular dipole-dipole interaction of the chromophore units. Hence, such an intermolecular coupling for the p enhancement should be more effective with the dendrimers composed of the NLO chromophore, whose dipole moment and the charge transfer are unidirectional parallel to the molecular axis. 

For a complete quantitative description of the solvent effects on the properties of the distinct diastereoisomers of dendrimers 5 (G = 1) and 6 (G = 1), a multiparameter treatment was used. The reason for using such a treatment is the observation that solute/solvent interactions, responsible for the solvent influence on a given process—such as equilibria, interconversion rates, spectroscopic absorptions, etc.—are caused by a multitude of nonspecific (ion/dipole, dipole/dipole, dipole/induced dipole, instantaneous dipole/induced dipole) and specific (hydrogen bonding, electron pair donor/acceptor, and chaige transfer interactions) intermolecular forces between the solute and solvent molecules. It is then possible to develop individual empirical parameters for each of these distinct and independent interaction mechanisms and combine them into a multiparameter equation such as Eq. 2, "... 

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