Abstract There are numerous challenges to producing liquid crystal displays on plastic. We reviewed previous attempts to produce such displays and look at current state‐of‐the‐art approaches. We explore suitable materials for the construction of transmissive OTFT backplanes and examine modern methods of LCD production suitable for plastic substrates.
We have performed a detailed study of the photoluminescence from thin films of blue-light-emitting poly(9,9-dioctylfluorene) containing different fractions of planarized (\ensuremath{\beta}-phase) chains within the glassy polymer film. By choosing solvents with a range of polarities and boiling points we were able to cast films with reliable control of the relative amounts of \ensuremath{\beta}-phase chains present. We analyzed the emission spectra in terms of Franck-Condon progressions and found that, at low temperatures (8 K), the luminescence can be modeled accurately by considering two distinct contributions from the two phases present in the film. The Huang-Rhys parameter for the \ensuremath{\beta} phase is shown to be approximately half the value obtained for the glassy phase, in agreement with a more delocalized exciton in the \ensuremath{\beta} phase. Time-resolved photoluminescence measurements on a film containing roughly 25% of \ensuremath{\beta} phase reveal a fast transfer of excitations from the glassy to the \ensuremath{\beta} phase, indicating that the two phases are well intermixed. Assuming the transfer dynamics to be governed by dipole-dipole coupling, we obtain a F\"orster radius of $8.2\ifmmode\pm\else\textpm\fi{}0.6\mathrm{nm},$ significantly larger than the radius typically found for excitation transfer within the glassy phase. These results are consistent with the large spectral overlap between the emission of the glassy phase and the absorption of the \ensuremath{\beta} phase and explain why the latter dominates the emission even from films containing only a small fraction of \ensuremath{\beta}-phase chains.
Over the past several years, organic molecules exhibiting significant two-photon absorbance and subsequent up-converted fluorescence have been of intense interest for a wide variety of applications including data storage, imaging, and optical limiting. However, the establishment of structure−property relationships for some asymmetric molecules has been hindered by the sensitivity of these nonlinear optical properties to the local molecular environment and to the pulse width of the incident radiation. To understand the influence of the local molecular environment on the excited states of these two-photon-absorbing molecules, the linear absorbance, the single-photon-excited photoluminescence, and the two-photon-excited photoluminescence of a series of heterocyclic dyes are examined. The stabilization of the longest-lived one-photon-excited state by the local molecular environment can be described by mean field interactions with solvent molecules as given by the Lippert equation. Because the same stabilization dominates the two-photon-induced longest-lived excited state, the influence of the local molecular environment on the two-photon luminescence can be predicted using the Lippert equation and one-photon experiments. These results support models that suggest excited-state absorption is the primary cause of sensitivity of the "effective" two-photon cross-section to the pulse-width and the local molecular environment.
Plastic Logic has developed a process for organic TFT backplane deposition that is fully compatible with low glass transition temperature, inexpensive plastic substrates. We have combined backplanes made with this process with microencapsulated electrophoretic imaging films to make 50 and 100PPI displays that are flexible down to a radius of curvature of 5mm. This process is scalable and is being implemented in a pilot line for substrate sizes up to 350mm × 350mm.
The morphology of a conjugated polymer thin film determines how it will behave as an active layer in optoelectronic devices. The liquid crystalline phase present in some conjugated polymers offers a unique way of controlling the film morphology. For example, films in which the chains are aligned in a single direction can be fabricated by processing films on a templating layer and annealing them above the liquid crystalline melting point of the polymer. However, the ability to align to a templating layer will be influenced by the character of the as-cast film. This effect was examined by casting poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT) films from a range of both aromatic and chlorinated solvents on top of rubbed polyimide layers and aligning via the thermotropic melt. Measurements of the dichroic ratio as a function of annealing time revealed that films cast from high boiling point aromatic solvents like isodurene (ISO) and o-xylene (OXY) aligned well with a maximum dichroic ratio over 10. Films cast from toluene (TOL), a lower boiling aromatic solvent, exhibited a lower Dmax of only around 5, while the films cast from chloroform (CHL) and tetrachloroethane (TCE), both chlorinated solvents, exhibited very low dichroic ratios. The best alignment (Dmax = 15) was achieved when a F8BT film was annealed while still "wet", which proves that a plasticizer (in this case ISO molecules) can improve the mobility of the polymer chains as they initially align to the rubbed surface. However, it is unclear whether a plasticizing effect (from residual solvent) is responsible for the differences in the alignment observed in films that were dried before annealing, as Dmax for these samples did not directly correlate to the volatility of the solvent. Ellipsometric measurements showed that all the films that aligned well exhibited a much more dramatic densification upon annealing than those that did not align well. Since all the well-aligned films were cast from aromatic solvents, we believe that aromatic interactions between polymer and solvent is critical in spinning a film that will align well. These results will guide future efforts into improving molecular orientation of liquid crystalline polyfluorene films.
✓ The case of an aneurysm occurring at the site of fenestration of the supraclinoid portion of the left internal carotid artery (ICA) is reported. A 37-year-old woman presenting with subarachnoid hemorrhage was found to have bilateral ICA aneurysms at the level of the posterior communicating arteries (PCoA's). The patient underwent right-sided craniotomy with uneventful clipping of the right PCoA aneurysm, and attempted clip placement on the contralateral left ICA aneurysm. The follow-up angiogram revealed a residual dome on the left ICA aneurysm, which was noted to originate at the proximal end of a fenestration of the left supraclinoid ICA. This represents the third reported case of fenestration of the intracranial ICA associated with an aneurysm. Intracranial artery fenestrations and their embryological origins are also reviewed.
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