Global mineralogical mapping of Mars by the Observatoire pour la Mineralogie, l'Eau, les Glaces et l'Activité (OMEGA) instrument on the European Space Agency's Mars Express spacecraft provides new information on Mars' geological and climatic history. Phyllosilicates formed by aqueous alteration very early in the planet's history (the “phyllocian” era) are found in the oldest terrains; sulfates were formed in a second era (the “theiikian” era) in an acidic environment. Beginning about 3.5 billion years ago, the last era (the “siderikian”) is dominated by the formation of anhydrous ferric oxides in a slow superficial weathering, without liquid water playing a major role across the planet.

Functional organic dyes provide a direct link between electronics and optics. The supramolecular packing of a given chromophore plays an important role in the functional properties of a material. A highly substituted, soluble quinacridone (see Figure) is presented for which the aggregation process can be directly probed by UV/vis spectroscopy. magnified image

The aggregation properties of derivatives of linear trans-quinacridone, an archetypal pigment, have been explored in two and three dimensions. The sparse solubility of the parent quinacridone pigment in common organic solvents can be traced back to the formation of a network of hydrogen bonds. Introducing aliphatic substituents on specific positions of the quinacridone core leads to an increased solubility without hampering the formation of intermolecular hydrogen bonds. With UV-Vis absorption, steady-state fluorescence, and infrared spectroscopy, the aggregation behavior of these substituted quinacridone derivatives is studied. On the basis of these data, models are proposed for the aggregate structure in solution. In addition, the two-dimensional ordering on graphite of these compounds and N,N′-dialkylated analogues has been investigated with scanning tunneling microscopy. The comparison between the two-dimensional organization and the solution data allows one to identify the extent of intermolecular interactions involved in the aggregation process.

This article describes the synthesis and thermal characterization of novel aryl‐substituted rod‐like homopolyimides. Synthetic aspects of monomer syntheses and one‐step polymer synthesis in m‐cresol are presented. Polyimides with rod‐like chain structure are based on monophenylated pyromellitic dianhydride (MPPMDA), diphenylated pyromellitic dianhydride (DPPMDA), and as rod‐like diamine units on phenylated para‐phenylene diamine and 1,1′‐binaphthyl‐4,4′‐diamine. As partial flexible units, which have the possibility to be converted into an extended chain conformation, commercially available 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (BPDA) and 3,4′‐oxydianiline (3,4′‐ODA) were used. The polyimides were investigated with respect to solution properties and thermal behavior. © 1993 John Wiley & Sons, Inc.