Aggregates solid state properties

Photoconducting and other solid state properties of materials are dependent both upon the intrinsic molecular properties of the material as well as the intermo-lecular interactions that occur in the solid state. The sharp and intense bands of squaraines for example become broad and red-shifted in the solid state [2]. Studies on aggregates can help in developing a molecular level understanding of their solid state properties. In view of this, the aggregation behavior of... 

Nonpolar block copolymers with functional polar groups combine the properties of a block copolymer with those of functionahzed homopolymers. End functionalized polymers can self-associate in solution in a manner analogous to low-molecular-weight surfactants, whereas the solid-state properties of the precursor polymer are greatly influenced by the presence of small amounts of polar groups since their aggregation persists in bulk [31]. The interaction of a polymer chain with a surface in solution can be altered and sometimes controlled by the nature and placement of specific functional groups. 

While these definitions and descriptors may be useM in systematizing molecular conformations, no safe correlations have ever been found between any of them and solid state properties of organic compounds. The seemingly inevitable conclusion is that as far as the smdy of molecular aggregation in condensed phases is concerned, these descriptors are too qualitative to be of any real use. Condensed phase properties depend on subtle details of the arrangement of the electron density in the molecule and between molecules, so that the true physics of the interaction must be considered. 

A main problem concerning the solid state electronic properties of PPPs is its tendency to form aggregates. One synthetic strategy for overcoming this problem is the transition from linear, one-dimensional systems to branched or dendritic, two-dimensional ones. 

The recent interest in substituted silane polymers has resulted in a number of theoretical (15-19) and spectroscopic (19-21) studies. Most of the theoretical studies have assumed an all-trans planar zig-zag backbone conformation for computational simplicity. However, early PES studies of a number of short chain silicon catenates strongly suggested that the electronic properties may also depend on the conformation of the silicon backbone (22). This was recently confirmed by spectroscopic studies of poly(di-n-hexylsilane) in the solid state (23-26). Complementary studies in solution have suggested that conformational changes in the polysilane backbone may also be responsible for the unusual thermochromic behavior of many derivatives (27,28). In order to avoid the additional complexities associated with this thermochromism and possible aggregation effects at low temperatures, we have limited this report to polymer solutions at room temperature. 

Nanosized supramolecular materials have received increasing attention during the last two decades. Their properties have been surveyed for their ability to form aggregates in the solution phase, which form channel-like arrays in the solid state, and which ultimately form single channels in planar bilayer membranes. These systems therefore illustrate, in general, the convergence of supramolecular selforganization and supramolecular function. 

S. Destri, M. Pasini, W. Porzio, G. Gigi, D. Pisignano, and C. Capolupo, Emission properties and solid-state aggregation in poly(fluorene-thiophene-5,5-dioxide) and in its model oligomer, Synth. Met., 138 289-293, 2003. 

Under normal conditions, matter can appear in three forms of aggregation solid, liquid, and gas. These forms or physical states are consequences of various interactions between the atomic or molecular species. The interactions are governed by internal chemical properties (various types of bonding) and external physical properties (temperature and pressure). Most small molecules can be transformed between these states (e.g., H2O into ice, water, and steam) by a moderate change of temperature and/or pressure. Between these physical states— or phases—there is a sharp boundary phase boundary), which makes it possible to separate the phases—for example, ice may be removed from water by filtration. The most fundamental of chemical properties is the ability to undergo such phase transformations, the use of which allows the simplest method for isolation of pure compounds from natural materials. 

If the externally imposed conditions of pressure and temperature permit a substance to be in the liquid state of aggregation, it possesses certain general properties. Contrary to a substance in the solid state, a liquid is fluid that is, it flows under the influence of forces and is characterized by its fluidity, or the recipro-... 

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