A novel, amphiphilic, conjugated block copolymer is described, which was prepared by a Suzuki-type cross-coupling of 2-bromo-[9,9-bis(2-ethylhexyl)fluorene]-7-pinacolato boronate as an AB-type monomer and monobromo-substituted poly[3-(6-bromohexyl)thiophene] (Br-P3BrHT) as a polymeric end capper in the key step. PF-P3PHT (P2; PF = poly(9,9-dialkylfluorene); P3PHT = poly[3-(6-diethylphosphonato-hexyl)thiophene]) as the amphiphilic target polymer was then generated in a polymer-analogous conversion of the alkyl bromide side chains of the PF-P3BrHT (P1) precursor into polar alkyl phosphonate groups by reaction with triethyl phosphite. P2 shows a strong influence of the solvent polarity on the optical spectra (absorption, emission). Treatment of solutions of P2 in tetrahydrofuran (THF), a nonselective solvent, with increasing amounts of solvents that are selective for the polar polythiophene blocks (water) or the nonpolar polyfluorene blocks (hexane), respectively, results in the formation of two different types of core-shell aggregates, which show rather different optical properties (photoluminescence quenching, excitation energy transfer).
We report a straightforward two-step synthesis toward conjugated DAD-type triblock copolymers
with both electron-donor (D) and electron-acceptor (A) blocks. Cyano-substituted poly(phenylenevinylene) (CN−PPV) prepolymers with two bromide end groups hereby act as the central electron-acceptor building block and
are generated under Yamamoto conditions. The dibromo prepolymers are finally coupled with monobromo-terminated regioregular poly(3-hexylthiophene) (P3HT), which is selected as the electron-donor block (D). The
molecular weight of the different blocks, especially the acceptor block, can be controlled by adjusting the
polymerization time and the substitution pattern (degree of alkyl substitution) of the monomers. Elemental analysis,
NMR, DSC, and optical spectroscopy prove that the DAD conjugated triblock copolymers. Atomic force microscopy
(AFM) images of one triblock copolymer (P3HT1−HCNPPV−P3HT1) exhibit the formation of regular nanosized
mesostructures in thin films. The resulting conjugated triblock copolymer shows a distinctly different morphology
as compared to a corresponding polymer blend. A covalent connection of donor (P3HT) and acceptor (CN−PPV) blocks is a favorable way to control the scale length of nanostructure formation.
A quantitative thermal conductivity measurement technique, the method, is applied in a scanning thermal microscope (SThM) with a resistive probe for the determination of thermal properties with a high spatial resolution in the nanometre range. With this set-up the quantitative thermal conductivity of materials can be determined with a deviation of less than 2%. Using gold as the reference material, the local thermal conductivities of silver and a CVD diamond film have been measured with a spatial resolution of approximately 30 nm.
The hole mobility and power conversion efficiency of bulk heterojunction solar cells based on P3HT‐type donor polymers and the soluble fullerene derivative [6,6]‐phenyl C61 butyric acid methyl ester (PCBM) as an acceptor both show a strong sensitivity to the introduction of interchain branches into the P3HT backbones. Branched B‐P3HT copolymers display a distinctly decreased hole mobility and reduced solar cell power conversion efficiency with increasing amount of interchain 3.3′‐bithiophene branches within the polythiophene macromolecules. The results illustrate the primary importance of proper solid state packing towards optimum charge transport and solar cell performance.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.