Host-guest systems compounds

For host/guest systems, tri(acryloxyethyl)trimelletate (7), a liquid trifunctional monomer was employed. This compound is easily and rapidly crosslinked to a tough solid by photopolymerization in the presence of a suitable sensitizer and activator, for example 8 and 9. This particular initiator system is useful because the sensitizer 8 is partially bleached out during irradiation, which allows the light to penetrate the sample as polymerization proceeds. 

Unfortunately, 7 is a poor solvent for donor-acceptor compounds, and a maximum of 1 wt % concentration was achieved for 1. Limited solubility is a common problem with host-guest systems we found however, that the solubility of donor-acceptor stilbene and azobenzene compounds can be improved considerably by die attachment of bulky side-groups such as butyl or allyl to the chromophores. In this way, loading levels above 15 wt % were possible for certain compounds. On the other hand, simple cyclic side-groups such as pyrrolidino (12) led to poorly soluble materials (Figure 1). 

These descriptions, while helpful, are by their nature noncomprehensive and there are many exceptions if such definitions are taken too literally. The problem may be linked to the definition of organometallic chemistry as the chemistry of compounds with metal-to-carbon bonds . This immediately rules out Wilkinson s compound, RhCl(PPh3)3, for example, which is one of the most important industrial catalysts for organometallic transformations known in the field. Indeed, it is often the objectives and thought processes of the chemist undertaking the work, as much as the work itself, which determine its field. Work in modern supramolecular chemistry encompasses not just host-guest systems but also molecular devices and machines, molecular recognition, so called self-processes ... 

An enormous work done in the field of polypeptides and proteins by Scheraga and coworkers includes calculations of both conformational energies and enzyme-substrate interactions for this special class of compounds 11 "13 . This kind of calculations on host-guest systems is well documented elsewhere and is not considered within the scope of this article. 

In order to describe the interaction energies of large host-guest systems for each atom pair i-j, a corresponding similar atom pair has to be selected from the model systems. Furthermore, the atomic net charges have to be calculated or estimated on the basis of a model compound. 

This thinking applies, in particular, when planning the design of a chiral three-dimensional supramolecular host-guest system, since the mutual interaction of the two distinct complementary molecular units or coordination entities is necessary. Examples of this methodology include the above-described anionic, tris-chelated transition metal oxalato complexes [Mzl(ox)3/6 which form the host system together with the cationic, tris-chelated transition metal diimino complexes, e.g. [M(bpy)3]21/31, bpy = 2,2 -bipyridine, which play the role of the guest compounds. 

A particularly interesting family of host-guest systems [1] is that in which a linear guest is threaded through the cavity of a macrocyclic host (Figure 1). A compound which exhibits such a supramolecular structure is usually called pseudorotaxane [2], with reference to the name rotaxane (see Volume III, Part 2, Chapter 7) used to indicate the species in which the ring is prevented to dethread by the presence of bulky stoppers at the ends of the linear guest. 

The presence or absence of extra-zeolite guest material has been frequently inferred by intensity data. Considerable BE increases of the guest cation in intrazeolite locations, which have been reported with several host-guest systems (e.g.,Mo03, WO3 [196, 198],MoS2 [77],Mo(CO)6 and other carbonyl compounds... 

The question of guest exchange in inclusion compounds received little attention, despite that fact that such processes are important for sensing and catalysis based on inclusion. However, a number of host-guest systems with organic and metal-containing hosts that entrap volatile guests were recently studied.The host l,l,6,6-tetraphenyl-2,4-diyne-1.6-diol H) forms inclusion compounds with tetrahydrofuran (THF), and thiophene (THIO), and we analyzed the dynamics of the reaction ... 

A useful approach for the synthesis of highly ordered host-guest systems is based on the use of macrocycles. One of these systems makes use of the couple cyclo[12]thiophene 9 and Ceo fullerene, which are a ring-shaped p-type and a spherical n-type organic semiconductor, respectively [41, 55], Compound 9 and Ceo self-assemble on HOPG as demonstrated by STM imaging (Figure 13.3). The deposition was realized... 

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