Synthesis and Photoisomerization of Azocalixarenes with Dendritic Structures

Azo group(s) in selected macrocyclic compounds

Azobenzene derivatives due to their photo- and electroactive properties are an important group of compounds finding applications in diverse fields. Due to the possibility of controlling the trans-cis isomerization, azo-bearing structures are ideal building blocks for development of e.g. nanomaterials, smart polymers, molecular containers, photoswitches, and sensors. Important role play also macrocyclic compounds well known for their interesting binding properties. In this article selected macrocyclic compounds bearing azo group(s) are comprehensively described. Here, the relationship between compounds' structure and their properties (as e.g. ability to guest complexation, supramolecular structure formation, switching and motion) is reviewed.

Spectroscopic properties of some new azo-azomethine ligands in the presence of Cu(2+), Pb(2+), Hg(2+), Co(2+), Ni(2+), Cd(2+) and Zn(2+) and their antioxidant activity

Due to their potential applicability as selective receptors in optical sensors, two novel azo Schiff-base derivatives I and II are synthesized and characterized with FT-IR, (1)H NMR and elemental analysis techniques. The optical response of azo groups of I and II towards Ni(2+), Co(2+), Cu(2+), Pb(2+), Hg(2+), Zn(2+) and Cd(2+) metal ions is studied in DMSO by UV-vis spectroscopy. The absorption spectra of both compounds with cations show marked changes. In solution, azo Schiff-base I produces a cation induced 95nm blue shift for Cu(2+) ion from 555nm to 460nm with remarkable color change from red to yellow. Whereas no significant color change is observed upon addition of studied metal cations to the solution of ligand II or other metal ions to the solution of ligand I. Furthermore, Job's plot indicate 1:1 binding-stoichiometry for I with Cu(2+) ion and Benesi-Hildebrand plot is used for the determination of its association constant. Therefore receptor I is highly specific for copper ions in DMSO solution. Finally, the study of antioxidant properties of I and II with DPPH method reveals high and significant activities.

Reversible photocontrolled disintegration of a dimeric tetraurea-calix[4]pyrrole capsule with all-trans appended azobenzene units

The light-induced trans-to-cis-isomerization of a single azobenzene moiety triggers the disintegration of a dimeric tetraurea calix[4]pyrrole capsule.

Optical spectroscopy studies of the complexation of bis(azophenol)calix[4]arene possessing chromogenic donors with Ni2+, Co2+, Cu2+, Pb2+ and Hg2+

Due to their potential applicability as selective receptors in electrochemical or optical sensors, a bis(azophenol)calix[4]arene derivative H(2)L has been investigated. The complexation properties of this molecule towards Ni(2+) and Co(2+) metal ions has been studied. It is revealed that this ligand exhibits tetradentate with N(2)O(2) core when bound to Ni (II) or Co (II) metal ion. The optical response of azo groups of H(2)L towards Ni(2+), Co(2+), Cu(2+), Pb(2+) and Hg(2+) metal ions has been investigated in DMSO by UV-vis spectroscopy. The absorption spectra of calix[4]arene with cations show marked changes, especially for Co(2+) ion. Furthermore, Job's plot indicate 1:1 binding-stiochiometry for calix[4]arene with Co(2+) ion and Benson-Hilderbrand plot is used for the determination of its association constant. The investigation of UV-vis spectra of chromogenic calix[4]arene in different solvents shows that cis-trans isomerization of azo groups probably depends on kind of solvent. Also the different between the polarity and viscosity of organic solvents used is likely responsible for the changes of the band shape of the spectra.

Supramolecular dendrimers: convenient synthesis by programmed self-assembly and tunable thermoresponsivity

We report here the noncovalent synthesis of thermosensitive dendrimers. Short oligoguanosine strands were linked to the focal point of a dendron by using "click chemistry", and quadruplex formation was used to drive the self-assembly process in the presence of metal ions. The dynamic nature of these noncovalent assemblies can be exploited to create combinatorial libraries of dendrimers as demonstrated by the co-assembly of two components. These supramolecular dendrimers showed thermoresponsive behavior that can be tuned by varying the templating cations or the number of guanines in the oligonucleotide strand.