Paraquat charge-transfer complexes

Polymer 102 was also used as a fluorescent chemosensory system in which the binding of paraquat leads to an attenuated emission intensity [211]. The same authors described related systems such as electrogenerated polymer 104. Although, addition of paraquat 105 to the monomer of 104 resulted in a charge-transfer complex, the binding properties of 104 were not reported [212]. 

Kim et al. reported a redox-driven molecular machine (Figure 46) based on a host-stabilized charge-transfer complex acting as a molecular loop lock. The molecular machine was based on a pseudorotaxane comprising a CB[8] ring and an axle component bearing a m-electron-deficient paraquat unit, a rr-electron-rich naphthalene unit. 

The X-ray crystal structures (Figure 7) of 6-[Diquat] and 9-[Paraquat] demonstrate that complex formation is aided not only by [C—H O] hydrogen bonding and [N O] electrostatic interactions but also by charge transfer stabilization between the ir electron rich aromatic rings in the molecular receptors and the ir electron deficient bipyridinium rings in the substrates. 

Deactivation of 2-naphthylamine singlet state by pyridines in enhanced by dipole moment and the ability to form hydrogen bonds. Picosecond laser spectroscopy shows charge transfer from the excited amine. The fluorescence of 2-iV,A -dimethylaminopyridine induced by p-nitroaniline is also caused by exciplex formation. The latter enhances triplet population of p-nitroaniline. The quenching of the fluoresence of carbazole and some derivatives by trichloroacetic acid and related compounds in fluid solutions has been studied by Johnson.A charge-transfer interaction is involved and the basicity of carbazole and derivatives determined. Charge transfer is also involved by quenching of carbazole by halocarbons. The A -isopropylcarbazole-dimethylterephthalate exciplex has been observed in PMMA films.Photoinduced electron-transfer in the p-phenylenediamine-paraquat complex yields the paraquat cation. ... 

A classic example of the formation of a macrocycle by a neutral template is that of the versatile host compound and component of molecular machines, the so-called blue box, or cyclobis paraquat-para-phenylene. Reaction of the horseshoe precursor with dibromo-para-xylene leads to the formation of a tricationic intermediate that is capable of binding the template molecule (Scheme 3), which closes the macrocycle to form the tetracationic cyclophane. The jT-ir interactions of the charge-transfer variety (the complex of the product and template is colored, whereas the components are not) assisted by the charge on ihe product are a major driving force in the process, as revealed in X-ray structures of complexes. It should be noted that the interaction is of the jr-n type assisted by the complementary positive charge on the bipyridinium residues and r-electron-rich nature of the template. This supramolecu-lar synthon can be used for other cyclophanes, catenanes, and rotaxanes (see Self-Assembly of Macromolecular Threaded Systems, Self-Assembled Links Catenanes, and Rotaxanes—Self-Assembled Links, Self-Processes). 

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