Stimuli-responsive host-guest systems decorated with hemithioindigo and spiropyran units

Identifier:  TDX:2976

Handle: https://hdl.handle.net/20.500.11797/TDX2976

Authors:  Moncelsi, Giulia

Abstract:
The aim of the research work included in this doctoral thesis is the design and synthesis of stimuli-responsive host-guest systems in which photoswitchable units are covalently incorporated into either the receptor’s or the guest’s scaffold. We use two photoswitches with distinct properties, hemithioindigos and spiropyrans, and two types of macrocyclic scaffolds based on calix[4]arene and calix[4]pyrrole. We study how light-irradiation and acid-base treatments induce the isomerization of the molecular switch. We were especially interested in coupling the isomerization processes with the binding affinity and the encapsulation properties of unimolecular receptors and supramolecular capsules, respectively. First, we describe the synthesis and photochemical characterization of two hemithioindigos featuring a terminal N-oxide moiety. We probe their Z/E reversible photoisomerization with visible light (λ = 450 nm) and we provide a detailed study of the 1:1 binding and its effect on the switching of the Z- and E-HTI isomers into the polar aromatic cavity of a super aryl-extended calix[4]pyrrole receptor in organic solvent. Next, we design and synthesize two tetraurea calix[4]arenes decorated with four hemithioindigo units at the upper rim. We describe the synthetic efforts to obtain these receptors and we investigate their dimerization in a variety of non-polar organic solvents and in the presence of tetramethyl phosphonium salts. We also report the tentative photoisomerization of the tetraureas in the monomeric state and involved in aggregates. Finally, we synthesize a stimuli-responsive tetraurea calix[4]arene featuring four appended spiropyran groups at its upper rim, which self-assembles into a homo- or heterodimeric capsule, the latter in the presence of a calix[4]pyrrole counterpart and a suitable N-oxide templating guest. The self-assembly, self-sorting, photo- and acidochromic studies of the capsular systems in chlorinated solvents are discussed. Our results suggest that the acid-base treatments are reversible and augur well for the transport and release of molecular cargo.