To decrease aggregation phenomena and improve the luminescence of the blue-light-emitting
polymer polyfluorene, carbazole units were copolymerized to introduce disorder in the polymer backbone.
A “kink” linkage was introduced into the polyfluorene chain by forming a 9:1 and 7:3 copolymer with
the carbazole group at the 3,6 positions. The disordered polyfluorene was made though a Ni-catalyzed
reaction, which resulted in high yield and high molecular weight polymers. The structure and physical
properties were confirmed by NMR, SEC, UV absorption, photoluminescence, elemental analysis, and
quantum yield measurements. The copolymers exhibited better spectral properties both in solution and
in film compared to previously synthesized polyfluorene homopolymers. Annealing studies showed both
improved thermal and UV stability of the copolymer over previously reported homopolymers. Cyclic
voltammetry studies showed a slightly lower highest occupied molecular orbital (HOMO) than the
homopolymer.
We report the synthesis and characterization of dendritic thiophene derivatives with their unique supramolecular assembly into 2-D crystals, nanowires, and nanoparticle aggregates. The structure and size of the dendrons and dendrimers have been confirmed with various techniques, such as NMR, SEC, and MALDI-TOF-MS. The mass values were consistent with the mass observed by MALDI-TOF-MS, whereas SEC measurements also gave useful information on the hydrodynamic volume of the individual dendrimers. The interesting electrooptical properties were highlighted by very broad absorption spectra and narrower fluorescence consistent with their electrochemical behavior. The self-organization of the dendrimers on the solid substrate is dependent on the nature of the substrate, preparation methods, and the molecule-molecule and molecule-substrate interactions. Thus, 14T-1 and 30T both formed globular aggregates on mica surface, while 14T-1 also formed nanowires on graphite surface. On the other hand, the larger 30T was observed to form 2-D crystalline structures. By varying the alkyl chain length attached to 14T-1, we were also able to obtain 2-D crystals on graphite. This showed that the different symmetry of packing for 30T and 14T-1 is also dependent on several factors, such as the molecular shape, size, and the presence of noncovalent intermolecular interactions. The results demonstrated the unique ability of thiophene dendrimers to form nanostructures on surfaces.
[structure: see text] Thiophene dendrons and dendrimers were designed and synthesized using a convergent approach. Metal-mediated coupling reactions were used in the synthesis. A rational approach allowed the formation of alphaalpha, betabeta, and alphabeta linkages between the dendrons and thiophene units.
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