186800-70-4Relevant academic research and scientific papers
Synthesis, self-assembly, and characterization of supramolecular polymers from electroactive dendron rodcoil molecules
Messmore, Benjamin W.,Hulvat, James F.,Sone, Eli D.,Stupp, Samuel I.
, p. 14452 - 14458 (2007/10/03)
We report here the synthesis and self-assembly of a series of three molecules with dendron rodcoil architecture that contain conjugated segments of oligo(thiophene), oligo(phenylene-vinylene), and oligo(phenylene). Despite their structural differences, all three molecules yield similar self-assembled structures. Electron and atomic force microscopy reveals the self-assembly of the molecules into high aspect ratio ribbon-like nanostructures which at low concentrations induce gelation in nonpolar solvent. Self-assembly results in a blue-shifted absorption spectrum and a red-shifted, quenched fluorescence spectrum, indicating aggregation of the conjugated segments within the ribbon-like structures. The assembly of these molecules into one-dimensional nanostructures is a route to π-π stacked supramolecular polymers for organic electronic functions. In the oligo(thiophene) derivative, self-assembly leads to a 3 orders of magnitude increase in the conductivity of iodine-doped films due to self-assembly. We also found that electric field alignment of these supramolecular assemblies can be used to create arrays of self-assembled nanowires on a device substrate.
α-Amino acids and N-protected α-amino aldehydes by stereoselective additions of a chiral vinyllithium reagent to sulfonylimines
Braun, Manfred,Opdenbusch, Kersten
, p. 141 - 154 (2007/10/03)
The chiral vinyllithium reagent (S)-1b, readily generated from dibromoalkene (S)-1a by bromine/lithium exchange, adds stereoselectively to mesitylsulfonylimines 2a-f so that the diastereomers 3 are obtained in ≥98% d.e. after column chromatography. The bromoalkenes 3a-d are submitted to ozonolysis in methanol to give α-mesitylsulfonylamino esters (S)-8a-d which can be hydrolyzed to deliver N-protected α- amino acids in >95% e.e. On the other hand, α-mesitylsulfonylamino aldehydes 12a-d are available when bromoalkenes 3a, d-f are first debrominated (→ 11a-d) and subsequently ozonized. In order to avoid reacemization, the aldehydes 12a-d are not purified but submitted to a Mukaiyama-type aldol addition whereby hydroxyesters 15a-d are formed as single diastereomers in a chelate-controlled reaction. The relative configuration of the esters 15a-d is proven by conversion into the oxazolidinones 16a-d whose optical purity is determined to exceed 92% e.e. by 1H-NMR measurements in the presence of chiral shift reagents. The sulfonylimine 21a and a series of para-substituted derivatives 21b-h are also allowed to react with the vinyllithium reagent 1b to give mixtures of diastereomers 22/23. The logarithms of the diastereomeric ratios 22:23 correlate with Hammett's σ-values. VCH Verlagsgesellschaft mbH, 1997.
