Shape transition, dendrimer

Therefore, within the PAMAM family, the shapes of dendrimers span the range from stars to spheres. Small G3 dendrimers have a diffuse, open structure while large G10 dendrimers are spheres with a uniform interior, sharp outside transition, and low polydispersity. 

In the case of the PBisMPA-based family of dendrimers, the effect of the core has been investigated. It was fotmd that for 2-ethyl-2-(hydroxymethyl)-l,3-propanediol (TMP), a rather small trifunctional core, the shape transition occurs at generation 4, while the use of a tetrafunctional core, 2,2 -oxybis (methylene)bis(2-ethyl-1,3-propanediol) (di-TMP), shifts the transition to generation 3. A similar trend is observed when TPh is used as a core. ... 

The emission of the metal particles may thus originate from a band-to-band transition in the metal particle, which occurs at about 516 nm for gold [60, 119]. As stated above, the nature of the interaction of the dendrimer (PAMAM) host is still uncertain, there could be very strong electrostatic interactions that may play a part in the enhancement of the metal particles quantum efficiency for emission. However, one would expect that this enhancement would result in slightly distorted emission spectra, different from what was observed for the gold dendrimer nanocomposite. Further work is necessary to completely characterize the manner in which the dendrimer encapsulation enhances the emission of the metal nanoparticles. With further synthetic work in preparation of different size nanoparticles (in other words elongated and nonspherical shape particles, including nanorods) it may be possible to develop the accurate description of a... 

This behavior results from the appearance of a new interband transition corresponding to formation of intradendrimer Cu clusters. The measured onset of this transitions at 590 nm agrees with the reported value [121], and the nearly exponential shape is characteristic of a band-like electronic structure, strongly suggesting that the reduced Cu does not exist as isolated atoms, but rather as clusters [122]. The presence of metal clusters is also supported by loss of signal in the EPR spectrum [123] following reduction of the dendrimer Cu + composite. 

Junction parameter within the excitonic model Excitonic perturbation matrix element Transition oscillator strength Two-photon absorption transition strength N,N-Diethyl-4-(2-nitroethenyl)phenylamine Oligomer consisting of N monomers V-shape molecule with N monomers on branches g-generation dendrimer with N monomers on branches fluorene-fluorene junction... 

Intrinsic viscosity [ /] is a physical property (expressed in dL/g), which in essence is the ratio of volume to mass. As the generation number increases and transition occurs to a spherical shape, the volume of a spherical dendrimer increases in cubic fashion while its mass increases exponentially hence, the value of [//] must decrease once a certain generation is reached. This prediction has now been confirmed for many different dendrimer families [9, 116, 179]. Because of this feature, the soft particle dendron/dendrimer-based, [S-l]-type nano-elements are unique macromolecules that exhibit completely different physico-chemical properties (i.e., nano-periodic property patterns) compared to compositionaUy... 

---