Guest encapsulation in calixarenes: properties and reactivity of caged ions and molecules

The development of modern nanotechnologies is more challenging than ever. Understanding and controlling the properties at molecular level is at the base for creating new materials endowed with specific chemical and physical features. This work proposes new synthetic strategies in different fields of supramolecular chemistry, such as molecular receptors, photoresponsive materials, and catalysis. It can be summarised as follows. Chapter 1 describes the synthesis of upper-to-upper oriented calix[6]arene-based [3]rotaxane, as prototypes for the synthesis of molecular cages, as new containers for host-guest systems. The synthetic strategy adopted consists of a threading and capping approach applied to a two-station bis-viologen salt. The correct orientation of the components is obtained thanks to the unidirectional threading process of the templating axle. The effect of the distance between the two-station axle is also evaluated. The supramolecular-assisted synthesis of a series of head-to-head bis-calix[6]arene cages is reported in Chapter 2. This method involves the formation of oriented [3]pseudorotaxane complexes between the templating axle and two functionalized macrocycles. The clipping reaction with a proper linker leads to the formation of the cage. Preliminary studies on the complexation properties are also presented. The ability of a heteroditopic calix[6]arene macrocycle to form pseudorotaxane complexes with stilbazolium dyes is described in Chapter 3. This study evaluates the effect of the solvent polarity and the length of the alkyl chain inserted into the stilbazolium salt on the threading process. The non-palindrome nature of the calix[6]arene receptor cavity allows the formation of two orientational isomers with this asymmetric guest. The orientation adopted by the encapsulated guest inside the host cavity affects the optical properties of the former. The synthesis and characterization of stilbazolium-based [2]rotaxanes are presented in Chapter 4. The separation of the two orientational isomers is now possible as the complexes are interlocked species. This allows the straightforward study of the encapsulation and orientation effects on the spectroscopic properties of the isomers both in solution and in the solid state, which are remarkably enhanced with respect to the unencapsulated dye. Chapter 5 includes the synthesis of a series of new achiral and chiral digold(I) resorcin[4]arene-based cavitand complexes and their application in the cycloisomerization and alkoxycyclization reactions of 1,6-dienynes. The constrained environment and non-covalent interactions between the macrocycle and the substrate modify the outcome of the transformations.