Sans contrast variation on a dendrimer host-guest complex

Small-angle neutron scattering (SANS) technique was used to study the configurational changes in an oligoethyleneoxy-functionalized poly(propyleneimine) dendrimer (host) when forming complexes with rose bengal (guest). Guinier fits to the scattering data recorded at max. contrast indicated a decrease in the radius of gyration (Rg = 2.2 nm) of the dendritic system after complex formation (Rg = 1.9 nm). The structure of the host system must fluctuate strongly with the endgroups revealing a significant amt. of backfolding. Moreover, SANS data indicated clear evidence for changes in the macromol

Structure of dendrimer-dye host-guest complexes as revealed by small-angle X-ray scattering

Small angle X-ray scattering (SAXS) expts. were performed on dil. aq. solns. of a new type of water-sol. ethyleneoxy-terminated poly(propyleneimine) dendrimer system. They reveal that the dimensions and d. distributions of the dendrimer are hardly affected by a change in the degree of protonation. This is in contrast to recent predictions regarding the structure of polyelectrolyte dendrimers but in line with the results of recent structural studies on charged PAMAM dendrimers. These dendrimer systems were applied as nanosized containers for guests like xanthene dyes. Structural studies with SAXS provide clear evidence for a complex formation but despite higher molar mass the max. dimensions of the complex are only slightly changed compared to the dendritic host. Since the radius of gyration represents the second moment of the electron d. distribution it appears to be very sensitive to changes in this distribution upon encapsulation of heavy-atom contg. guest mols. These are reflected in a decrease of the radius of gyration upon an increase of the guest-host ratio in the soln., a behavior that strongly indicates an accumulation of guest mols. in the center of the dendritic host. [on SciFinder (R)

The localization of guests in water-soluble oligoethyleneoxy-modified poly(propylene imine) dendrimers

Small-angle X-ray scattering measurements and UV/Vis titrations have been used to characterize a new water-soluble host¿–¿guest system based on oligoethyleneoxy-modified poly(propyleneimine) dendrimers. These experiments indicate that unique interactions between the host and guests lead to a specific location of the guests in the core of the dendrimers (see schematic representation)

Transfer of pi-conjugated columnar stacks from solution to surfaces

Three hydrogen-bonded oligo(p-phenylenevinylene)s, OPV3, OPV4, and OPV5, that differ in conjugation length have been synthesized and fully characterized. All three compds. contain chiral side chains, long aliph. chains, and a ureido-s-triazine hydrogen bonding unit. 1H NMR and photophys. measurements show that the OPV oligomers grow hierarchically in an apolar solvent; initially, dimers are formed by hydrogen bonds that subsequently develop into stacks by p-p interactions of the phenylenevinylene backbone with induced helicity via the chiral side chains. SANS measurements show that rigid cylindrical objects are formed. Stacks of OPV4 have a persistence length of 150 nm and a diam. of 6 nm. OPV3 shows rigid columnar domains of 60 nm with a diam. of 5 nm. Temp. and concn. variable measurements show that the stability of the stacks increases with the conjugation length as a result of more favorable p-p interactions. The transfer of the single cylinders from soln. to a solid support as isolated objects is only possible when specific concns. and specific solid supports are used as investigated by AFM. At higher concns., an intertwined network is formed, while, at low concn., ill-defined globular objects are obsd. Only in the case of inert substrates (graphite and silicium oxide) single fibers are visible. In the case of the repulsive surfaces (mica and glass), clustering of the stacks occurs, while, at attractive surfaces (gold), the stacks are destroye

An electron-deficient discotic liquid-crystalline material

Hexaazatriphenylene-hexacarboxy triimide 1 was synthesized and fully characterized using NMR, IR, UV/vis, and fluorescence spectroscopy. DSC and polarization microscopy showed compound 1 to be liquid crystalline over a large temperature range, while its specific mesophase (Col(ho)) could be determined via X-ray scattering experiments. Although the first reduction potential of 1 could not be measured directly, two closely related reference compounds 4 and 5 featured low first reduction potentials, suggesting the suitability of 1 as an acceptor material in photoinduced electron-transfer processes. The latter was confirmed via photoinduced absorption and fluorescence spectroscopy on mixed films of 1 and poly(3-hexylthiophene

Transfer of pi-conjugated columnar stacks from solution to surfaces

Three hydrogen-bonded oligo(p-phenylenevinylene)s, OPV3, OPV4, and OPV5, that differ in conjugation length have been synthesized and fully characterized. All three compds. contain chiral side chains, long aliph. chains, and a ureido-s-triazine hydrogen bonding unit. 1H NMR and photophys. measurements show that the OPV oligomers grow hierarchically in an apolar solvent; initially, dimers are formed by hydrogen bonds that subsequently develop into stacks by p-p interactions of the phenylenevinylene backbone with induced helicity via the chiral side chains. SANS measurements show that rigid cylindrical objects are formed. Stacks of OPV4 have a persistence length of 150 nm and a diam. of 6 nm. OPV3 shows rigid columnar domains of 60 nm with a diam. of 5 nm. Temp. and concn. variable measurements show that the stability of the stacks increases with the conjugation length as a result of more favorable p-p interactions. The transfer of the single cylinders from soln. to a solid support as isolated objects is only possible when specific concns. and specific solid supports are used as investigated by AFM. At higher concns., an intertwined network is formed, while, at low concn., ill-defined globular objects are obsd. Only in the case of inert substrates (graphite and silicium oxide) single fibers are visible. In the case of the repulsive surfaces (mica and glass), clustering of the stacks occurs, while, at attractive surfaces (gold), the stacks are destroye