Rigid rod complexes

Pentanedionates, with Ru and Os half-sandwiches, 6, 483 Pentanuclear silver(I)-rhenium(I) alkynyl rigid-rod complex, preparation, 2, 229-230... 

Many complex systems have been spread on liquid interfaces for a variety of reasons. We begin this chapter with a discussion of the behavior of synthetic polymers at the liquid-air interface. Most of these systems are linear macromolecules however, rigid-rod polymers and more complex structures are of interest for potential optoelectronic applications. Biological macromolecules are spread at the liquid-vapor interface to fabricate sensors and other biomedical devices. In addition, the study of proteins at the air-water interface yields important information on enzymatic recognition, and membrane protein behavior. We touch on other biological systems, namely, phospholipids and cholesterol monolayers. These systems are so widely and routinely studied these days that they were also mentioned in some detail in Chapter IV. The closely related matter of bilayers and vesicles is also briefly addressed. 

Although liquid crystalline phases can be formed from entirely rigid units such as rods and ellipsoids, all liquid crystal molecules are partially flexible objects which can change their shape in a variety of ways. The extension of rigid-rod theories to account for flexibility is complex and has been the object of considerable effort for several years. It is now clear that simply relaxing the assumption of molecular rigidity is expected to have profound effects on phase behaviour. 

Even larger, conjugated systems were synthesized by employing both difunctional isocyanides and difunctional alkynes. In all the cases, the components have structural rigidity, which lends rigid-rod character to the complexes prepared from them. Many of the complexes are associated via intermolecular aurophilic contacts, which appear to have a distinct influence on the photophysical behavior, but are as yet not a necessary condition for luminescence (Scheme 51).196... 

The adsorption of diatomic or dimeric molecules on a suitable cold crystalline surface can be quite realistically considered in terms of the dimer model in which dimers are represented by rigid rods which occupy the bonds (and associated terminal sites) of a plane lattice to the exclusion of other dimers. The partition function of a planar lattice of AT sites filled with jV dimers can be calculated exactly.7 Now if a single dimer is removed from the lattice, one is left with two monomers or holes which may separate. The equilibrium correlation between the two monomers, however, is appreciable. As in the case of Ising models, the correlation functions for particular directions of monomer-monomer separation can be expressed exactly in terms of a Toeplitz determinant.8 Although the structure of the basic generating functions is more complex than Eq. (12), the corresponding determinant for one direction has been reduced to an equally simple form.9 One discovers that the correlations decay asymptotically only as 1 /r1/2. 

There have been only a few reports on crown ethers laterally attached to rod-like molecules in the last few years. Nevertheless, very interesting compounds have been synthesized in the past. The general problem of this compound class is the flexible crown ether itself that can destroy the mesomorphic properties when attached laterally. Making the rigid rod longer can circumvent this problem. Another way to obtain stable mesophases is the complexation with suitable salts. 

Barigelletti F et al (1993) Luminescence properties of rigid rod-like binuclear ruthenium(II)-osmium(II) terpyridine complexes - electronic interaction through phenyl bridges. JCS Chem Commun 942-944... 

Rigid-rod bisiridium(III) cr-diyne complexes have also been prepared from Vaska s complex and the bisphenyliodonium triflates of butadiyne and 1,2- and 1,4-diethynylben-zenes45. The reactions were conducted in acetonitrile and, under such conditions, the products are doubly charged bimetallic salts in which acetonitrile occupies one coordination... 

The mechanism by which the condensin complex organizes chromosomes during mitosis into their fully compacted and stable structure is currently unresolved. Several studies in multiple organisms have established that inactivation of condensin does not result in completely decondensed chromosomes but in compacted chromosomes that are not properly structured into rigid rods (42). The identity of those factors that mediate chromosome compaction in the absence of condensin is unknown. These... 

Despite their inherent electronic advantages, CT complexes and radical cation salts tend to be brittle and unprocessable. This problem might be overcome by the incorporation of oligomeric tetrathiafulvalenes in polymers, whereby the TTFs can be part of a main-chain or side-chain polymer. The key concern thereby is to achieve the suitable packing of the donor moieties, which is, of course, less perfect than in the crystalline state. Remarkably, the rigid-rod poly-TTF 164 could be made recently by a precursor route in which 164 is made by dimethyl disulfide extrusion of the precursor polymer (scheme 39). The electrical conductivity after iodine doping amounts to 0.6 S/cm [221]. Other examples of TTF-containing polymers, either in the backbone [222] or in the side-chain [223], are summarized in chart 25. 

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