Supramolecular order

The following sections contain a review of many of the varied synthetic systems that have been developed to date utilising noncovalent interactions to form assembhes of molecules. These sections are loosely demarcated according to the most important type of noncovalent interactions utilized in conferring supramolecular order (ie, van der Waal s interactions, electrostatic interactions, and hydrogen bonds). For extensive reviews, see References 1,2,4—6,22,46,49,110—112. Finally, the development of self-assembling, self-replicating synthetic systems is noted. 

It has been shown frequently that without the presence of strong intermolecular interactions, discotic molecules are highly mobile in the liquid crystalline state.1 They undergo both lateral as well as rotational translations, resulting in the absence of positional order. Similarly, such discotics also freely rotate in the columnar aggregates they form in solution. This lack of positional order in the columns accounts for the absence of chiral or helical supramolecular order. We will demonstrate this characteristic using results obtained for triphenylenes. 

Scheme 16. 2,3,9,10-Tetra(dodecyloxy)quinacridone 53 is an attractive example for supramolecular ordering of chro-mophores.

D.A.M. Egbe, B. Carbonnier, L. Ding, D. Miihlbacher, E. Birckner, T. Pakula, F.E. Karasz, and U.-W. Grummt, Supramolecular ordering, thermal behaviour, and photophysical, electrochemical, and electroluminescent properties of alkoxy-substituted yne-containing poly(phenylene-viny-lene)s, Macromolecules, 37 7451-7463, 2004. 

This review will focus on systems that are able to adopt supramolecular order in both intra- and intermolecular fashion. Because of this,para-phenylene ethynylenes (pPE)s will not be covered in this review. However, there are several excellent reviews of pPE synthesis, structure, and function in the recent literature that discuss the intermolecular order of those systems [7-15]. Similarly, phenylene ethynylene macrocycles, which form a wide range of supramolecular aggregates with interesting stacking behavior, will not be covered but have been extensively reviewed [16-22]. 

Figure 7. Electron micrographs of intermediate stages of supramolecular order...

Fig. 57 Generation of large lamellar periodicities via supramolecular ordering of DBSA/ P4VP-PS composites. Reprinted with permission from [209]...

We have discussed the synthesis of dendritic boxes possessing a unimolecular compartmented structure in which guest molecules are physically locked. Evidence is presented that the encapsulation is dominated by the architecture of the dendrimer and that some supramolecular ordering is present. Furthermore, a shape-selective liberation of guests can be accomplished by a two-step process. 

SUPRAMOLECULAR ORDERING AND SELF-ASSEMBLY OF DISSOLVED POLYMERS... 

The role of the supramolecular order of LBK films on the photoreorientation of azobenzene moieties upon polarized irradiation was investigated in detail. It was found that the photo(re)orientation proceeds reaclily in disordered, spin-coated films of azobenzene polymer 34 or azobenzene-containing polypeptide 38, whereas the photoreorientation is hindered in highly ordered LBK films of these polymers. In the case of polyacrylaerylat 34 and polypeptides 38 with shorter spacers (n = 2), the photoreorientation proceeds readily after the structure of the LBK film has been randomized by UV irradi-... 

Vesicles (Latin vesicula, bladder) are sealed, extremely thin (< 10 nm), often spherical membraneswhich enclose aqueous or other solvent volumes of approximately 10 -10 nm. Aggregation numbers are in the order of 10 -10. The monomers are held together by the same solvophobic effects which produce micelles, and solvation forces together with membrane undulations prevent crystallization. The state of the vesicle membrane is therefore also essentially of a fluid character. Supramolecular ordering within vesicle membranes is negligible. 

Multilayered scrolls, which are commonly formed from water-insoluble lipids upon swelling, offer no possibilities for supramolecular ordering and most of their molecular constituents have no contact with water. Furthermore, the position of dissolved or surface-attached functional molecules can neither be fixed nor determined with any certainty. Thinner surfactant rods are more promising. 

The complexation of 42 (R=Me) with poly(acrylic acid) (PAA) results in a mesomorphously ordered material consisting of hexagonally-ordered ion-rich cylindrical rods containing the PAA embedded in a polystyrene matrix. This complex represents a new type of a polymeric hybrid material with a supramolecular ordered nanostructure [83]. 

Section V—A has dealt with the formation of supramolecular polymers by nonspecific arene—arene stacking, which generally results in irregular or loose stacking. The use of additional steric interactions in these structures allowed for a control over supramolecular order or helicity. In this section we will discuss columnar supramolecular polymers formed by the more specific intermolecular hydrogen bonds. 

---