Super-fluorinated materials

Liquid Crystals. Based on worldwide patent activity, numerous compounds containing fluoroaromatic moieties have been synthesized for incorporation into liquid crystals. For example, fluoroaromatics are incorporated in ZLI-4792 and ZLI-4801-000/-100 for active matrix displays (AMD) containing super fluorinated materials (SFM) (186,187). Representative stmctures are as follows. 

Scheme 4.11 Examples of typical super-fluorinated materials (SFM) used in the current generation of active matrix LCD. The liquid crystals 7-13 have positive dielectric anisotropy, compounds 14 and 15 have negative dielectric anisotropy. The approximate orientation of the molecular dipole moment for the two classes of material is indicated by arrows.

Shortly after the commercial introduction of the first active matrix LCD in 1989 it became clear that cyano-based liquid crystals of the second generation (e.g. 3-6) cannot be used for this application. Even after extensive purification, the voltage holding ratio of this type of material is too low. The stringent reliability requirements could, on the other hand, be easily fulfilled with super-fluorinated materials (SFM), such as those depicted in Scheme 4.11. For this reason - with in-plane switching (IPS) technology as the only exception - only SFM are currently used in AM-LCD. 

NFPy N-fluoro pyridinium SFM super-fluorinated materials... 

K later they determined that the drop was a fluke, that subtle shifts in resistance in the contacts between the electrical leads and the sample, and not in the sample itself, were responsible. Sumitomo Electric Industries of Japan came in with 300° K (no confirmation]. In Michigan, researchers at Energy Conversion Devices announced that part of a synthetic material made of fluorine (a highly dangerous yellow gas), yttrium, barium, and copper oxide had superconducted at 45° to 90° F. (The part that super-conducted, it turned out, represented less than 1 percent of the material tested, and the samples were far too small to lose all resistance. It is incredibly difficult to identify the exact portion of any material that shows superconductivity and then produce a pure sample of it.) In New Delhi, at the National Physical Laboratory, scientists saw evidence of superconductivity in material heated to 80° F, but the electrical signals were misleading, an artifact of the measurement process. 

Current photoresists cannot be used for 157 nm technology, mainly because their transmittance at 157 nm is too low. Although materials with aromatic substructures are quite useful for the 248-nm process, only purely aliphatic polymers are employed in the current 193 nm technology. For an illuminating wavelength of 157 nm, even the absorptivity of most aliphatic compounds is too high. Therefore, only partially fluorinated polymers with absorption characteristics carefully optimized by experiment [10] and molecular modeling [11] can be used. The solubility switch after illumination is usually achieved by addition of a photo-activatable super-acid (e.g. a diaryl iodonium hexafluoroantimonate) [12], which typically cleaves an add-labile tert-butyl ester in the polymer (Scheme 4.9). 

By analogy with nitrile-based liquid crystals, the most simple SFM (super-fluori-nated materials) carry one terminal fluorine substituent on an aromatic moiety. 

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