We report on the nanoscale structure and solvent-induced phase behavior of two, nearly similar π-conjugated hairy-rod polymers, branched side chain poly[9,9-bis(2-ethylhexyl)fluorene-2,7-diyl] (PF2/6) and linear side chain poly[9,9-dioctylfluorene-2,7-diyl] (PFO or PF8), in good and bad (or poor) solventssdeuterated toluene and deuterated methylcyclohexane (MCH)sat 20°C. Small-angle neutron scattering (SANS) measurements exploiting contrast variation with side chain deuterated PFO polyfluorene have been employed and complemented by optical absorption measurements. In toluene both PF2/6 and PFO adopt an elongated (rodlike) conformation containing predominantly only a single polymer chain (diameter of the order of 1 nm), which indicates dissolution down to the molecular level. In contrast, in MCH, PF2/6 shows an elongated structure while PFO forms sheetlike structures (characteristic thickness of 2-3 nm), thus dissolving down to the "colloidal" level. The elongated structure of PFO consists of individual polymer chains adopting dominantly a conformational isomer C R. The thickness of sheetlike PFO particles corresponds to that of around two polymer layers and side chain contrast variation gives an evidence for an even distribution of the backbones within the sheets. These sheets are potentially an initial stage of PFO crystallization and also contain conformational isomer C of those chains observed in the so-called beta-phase (or beta-sheets) in the solid state. The observed phenomena were not found to depend on concentration over the concentration range 5-10 mg/mL.

In this paper, we propose for the first time that the combination of a sol-gel derived diurethane crosslinked siloxane-based biohybrid host including short poly( -caprolactone) segments (PCL(530)) and lanthanide aquocomplexes incorporating β-diketonate ligands yields an effective protecting cage that efficiently encapsulates the emitting centers and reduces luminescence quenching. The results obtained using the Eu(tta) 3 (H 2 O) 2 (where ttais 2-thenoyltrifluoracetonate) complex demonstrate that 1 (2) carbonyl oxygen atoms of the host matrix enter the Eu 3+ coordination shell, thus replacing the labile water molecule-(s). The significant increase in the quantum efficiency q of the doped hybrid with respect to that of Eu(tta) 3 (H 2 O) 2 (44.2 versus 29.0%, respectively) reveals that complex anchoring to the PCL(530)-based host structure contributes to enhancement of the 5 D 0 quantum efficiency. However, when a complex that contains only strong chelating ligands, such as Eu(tta) 3 phen (where phen is 1,10-phenantroline), is incorporated into the same host medium, the effect is lost and the 5 D 0 nonradiative paths in the doped hybrid are higher than those existing in the complex itself. Under UVA exposure, the emission intensity of PCL(530)/siloxane/Eu(tta) 3 (H 2 O) 2 decreased 10% in 11 h, whereas that of PCL(530)/siloxane/Eu-(tta) 3 phen decreased 25% in the same period of time.

We report the fabrication of poly(p-phenylene vinylene) nanostructures by direct scanning near-field lithography of its soluble precursor. The technique is based on the spatially selective inhibition of the precursor solubility by exposure to the ultraviolet optical field present at the apex of scanning near-field fiber probes with aperture diameters between 40 and 80 nm (±5 nm). After development in methanol and thermal conversion under vacuum we obtain features with a minimum dimension of 160 nm. We demonstrate the use of the technique for the direct writing of two-dimensional photonic crystals with intentional defects and a periodicity relevant to applications in the visible range. Using a Bethe–Bouwkamp model, we then discuss the influence of probe size, tip-sample distance, and film thickness on the resolution of the lithographic process. We also discuss limitations to the resolution that can arise from physical properties of the lithographic medium.

Data are reported on the triplet states of a series of fluorene-based A-alt-B type alternating copolymers based on pulse radiolysis-energy transfer and flash photolysis experiments. From the pulse radiolysis experiments, spectra are given for eight copolymers involving phenylene, thiophene, benzothiadiazole, and oligothienylenevinylene groups. Quantum yields for triplet-state formation (PhiT) have been obtained by flash photolysis following laser excitation and in one case by photoacoustic calorimetry. In addition, yields of sensitized formation of singlet oxygen have been determined by time-resolved phosphorescence and are, in general, in excellent agreement with the PhiT values. In all cases, the presence of thiophene units is seen to increase intersystem-crossing quantum yields, probably because of the presence of the heavy sulfur atom. However, with the poly[2,7-(9,9-bis(2'-ethylhexyl)fluorene)-alt-1,4-phenylene] (PFP), thiophene S,S-dioxide (PFTSO2) and benzothiadiazole (F8BT) copolymers, low yields of triplet formation are observed. With three of the copolymers, the energies of the triplet states have been determined. With PFP, the triplet energy is virtually identical to that of poly[2,7-(9,9-bis(2'-ethylhexyl)fluorene)]. In contrast, with fluorene-thiophene copolymers PFaT and PF3T, the triplet energies are closer to those of thiophene oligomers, indicating that there is significant conjugation between fluorene and thiophene units but also that there is a more localized triplet state than with the homopolymers.

The polymer poly(9,9‐dioctylfluorene) (PF8) can be driven into a morphological form termed the β‐phase that has enhanced planarity and increased structural rigidity. We show that the β‐phase can be generated in two different fluorene oligomers; a fluorene pentamer, and a short (statistical) oligomer composed of chains having a maximum length of 19 monomer units. By comparing the energy of the zero‐zero phonon line in fluorescence from the β‐phase oligomers with that in the PF8 polymer, we show that the electronic conjugation length of the β‐phase is (30 ± 12) monomer‐units, a value consistent with the persistence length of the molecular chain.

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We report on the fabrication of photovoltaic cells, PVs, with controlled donor/acceptor interfaces using a process based on the phase separation between a cross-linkable polyfluorene and polystyrene. Robust, nanostructured columnar-grain layers of a conjugated cross-linked polymer, F8T2Ox1 (an oxetane-functionalized derivative of poly(9,9-dioctylfluorene-alt-bithiophene)) are obtained after removal of polystyrene. These layers are used, in combination with 1-(3-methoxycarbonyl)propyl-1phenyl-(6,6)C 61 (PCBM) deposited by spin coating, to define donor/acceptor interfaces, as PVs' active layers. The performance of these cells is dependent on the dimensions of the surface structures. In particular, a significant power conversion efficiency improvement is observed upon decrease of column diameter, reflecting an improvement of the exciton dissociation. We find, however, that these efficiencies still fall below those of the PVs based on blends of the same components, but are larger than the ones found for planar bilayer PVs. Furthermore, PVs based on blends of cross-linked F8T2Ox1 and PCBM showed enhanced efficiency and thermal stability with respect to PVs based on blends of PCBM and the non-cross-linkable analogue poly(9,9-dioctylfluorene-alt-bithiophene). Taking into account that the columnar-grain morphology is recognised as the ''ideal'' architecture for PVs' active layer provided the column radii are of the order of few nanometres, this work gives a new insight into how to achieve efficient organic photovoltaic cells through the use of cross-linkable conjugated polymers as the electron-donor component.

Hydrophilic polyanionic conjugated polyrotaxanes are readily synthesized in water by Suzuki coupling, but their high polarity and ionic nature limit the potential applications of these materials. Here, we demonstrate three methods for transforming these polar polyelectrolytes into nonpolar lipophilic insulated molecular wires. A water‐soluble polyfluorene‐alt‐biphenylene β‐cyclodextrin (CD) polyrotaxane was converted into nonpolar derivatives by methylation of the carboxylic acid groups with diazomethane and conversion of the hydroxyl groups of the CDs to benzyl ethers, trihexylsilyl ethers, benzoyl esters, and butanoate esters to yield polyrotaxanes that are soluble in organic solvents such as chloroform and cyclohexane. Elemental analysis, NMR spectroscopy, and gel permeation chromatography (GPC) data support the proposed structures of the organic‐soluble polyrotaxanes. The extents of reaction of the polyrotaxane CD hydroxyl groups were 55% for trihexylsilyl chloride/imidazole; 81% for benzyl chloride/sodium hydride; 72% for benzoyl chloride/pyridine/4‐dimethylaminopyridine; and 98% butanoic anhydride/pyridine/4‐dimethylaminopyridine. Alkylation, silylation, and esterification increase the bulk of the encapsulating sheath, preventing interstrand aggregation, increasing the photoluminescence efficiency in the solid state and simplifying the time‐resolved fluorescence decay. The organic‐soluble polyrotaxanes were processed into polymer light‐emitting diodes (PLEDs) from solution in nonpolar organic solvents, thereby excluding ionic impurities from the active layer.