Novel, all-conjugated polyelectrolyte block copolymers of the rod-rod type can be generated in a ''grafting from'' scheme and exhibit a preferred tendency to self-assemble into layered aggregates both in solution and the solid state. Here, the rigid-rod structure of the individual, complex macromolecules favours the formation of low-curvature vesicular and lamellar aggregates. Our poly(9,9-dialkylfluorene)-b-poly [3-(6-ammoniumhexyl)thiophene] (PF2/6-b-P3TMAHT and PFO-b-P3TMAHT, where PF2/6 and PFO denote 2-(ethyl)hexyl and linear octyl alkyl pendant groups, respectively), and poly(9,9-dialkylfluorene)-b-poly[3-(6-pyridylhexyl)thiophene] (PF2/6-b-P3PyHT and PFO-b-P3PyHT) polyelectrolyte diblock copolymers allow for simple and reliable control of the occurring self-organisation process and the resulting nano-scaled architectures. They are, therefore, promising candidates for application as the active layer in electronic devices or as functional membranes (e.g. for sensor applications). Moreover, the electronic properties of the materials (especially the excitation energy transfer between both blocks) strongly depend on the aggregation state present. Aggregation can be further controlled via addition of oppositely charged surfactants resulting in the formation of ordered polyelectrolyte/surfactant complexes.
Phosphorescence and delayed fluorescence of polyfluorene polymer films doped with cyclooctatetraene (COT) and anthracene are studied by means of time-resolved photoluminescence (PL) measurements. The occurrence of an anomalous nonvertical triplet energy transfer in solid conjugated polymer films is demonstrated for the first time employing the "nonvertical" COT triplet acceptor, which appears to behave similarly to conventional vertical triplet acceptors, such as anthracene. Both dopant molecules are found to efficiently quench the host phosphorescence of the polymer without affecting the host fluorescence--this can be attributed to the large singlet-triplet (S(1)-T(1)) splitting of these molecules. This S(1)-T(1) splitting is exceptionally large in COT due to its low-lying relaxed triplet state, which is capable of accepting host triplet excitations. In contrast to anthracene, the triplet lifetime of the COT molecules is reasonably short, thus making a fast deactivation of the triplet excitations possible. This suggests that nonvertical triplet scavengers might be promising candidates for quenching the host triplet excitations in future electrically pumped fluorescence organic lasers, which suffer from excessive triplet-state losses.
We report on the feasibility and process parameters of nanoimprint lithography to fabricate low refractive index passive optical devices. Diffraction gratings printed in polymethylmethacrylate (PMMA) exhibit a sharp dispersion with a full width at half maximum of about 20 nm. Waveguides were printed in polystyrene (PS) on silicon oxide and had losses between 8-20 dB cm −1 at wavelengths between 650-400 nm, respectively. Finally, one-dimensional photonic structures were also printed in PS and their transmission and morphology characterized. The expected Bragg peak was observed in transmission and atomic force microscopy images have shown a good pattern transfer. A square lattice was printed in PMMA and more than 40 print cycles were obtained, i.e., potentially more than 1000 imprints from one master stamp.
Novel dye-terminated, hyperbranched polytruxenes and polytruxene-block-polythiophene multiblock copolymers have been synthesized in a simple "AB(2) + A" approach. Photoexcitation into the higher energy polytruxene absorption band results in an efficient excitation energy transfer to the peripheral dye or polythiophene blocks.
We study relations among the side-chain asymmetry, structure, and order-disorder transition (ODT) in hairy-rod-type poly(9,9-dihexylfluorene) (PF6) with two identical side chains and atactic poly(9-octyl-9-methylfluorene) (PF1-8) with two different side chains per repeat. PF6 and PF1-8 organize into alternating side-chain and backbone layers that transform into an isotropic phase at T ODT (PF6) and T
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