Redox activity switching

Redox-activated Switches for Dynamic Memory Storage... 

Metallodendrimers have attracted widespread interest for various sensing applications, such as ion detection, gas sensing, and redox-active switches, because of their polyvalent characteristics.220 Several recent examples of successful sensors using the metallodendrimers have appeared. 

It has been reported that the electrical properties of single molecules incorporating redox groups (e.g. viologens [114, 119, 120, 123, 124], oligophenylene ethynylenes [122, 123], porphyrins [111, 126], oligo-anilines and thiophenes [116, 127], metal transition complexes [118,128-132], carotenes [133], ferrocenes [134,135],perylene tetracarboxylic bisimide [93, 136, 137] and redox-active proteins [138-143]), can be switched electrochemically. Such experiments, typically performed by STM on redox-active molecules tethered via Au-S bonds between a gold substrate and a tip under potential control, allow the possibility to examine directly the correlation between redox state and the conductance of individual molecules. 

Several variants are discussed in the literature [18, 56, 57]. Figure 10 shows some cyclic voltammograms. The height of the second peak depends on the rate of the C-step. In chronoamperometry, the formation of a redox-active product leads to an increase in the apparent n during the experiment (e.g. from n = to n = 2). A plot of i vs. switches from a straight line for n = 1 at small t to the one for n = 2 at large t. 

As Figure 3 illustrates, redox active guests introduce PET processes almost by definition and luminescent on-off switching is the norm. However, the inhibitions outlined in Section 5 have not prevented the designers of switchable luminescent devices from exploring systems which bind redox active guests. The combined forces of inorganic coordination chemistry and supramolecular science have proved to be too attractive in many of these instances. It is to be hoped that some of this effort will filter across to the examination of more on-off systems like 17 and 18. 

Cu(II) is one of the best examples of a redox active guest, but apparently not when it is imprisoned in a cryptand such as 53. In this case, the Cu(II) is silent over a wide potential range during cyclic voltammetry. System 53 is designed as a lumophore-spacer-receptor system such as 28-30 and 33-34 in Section 1 with multiple lumophores. It also shows similar luminescence off-on switching with and even with Cu(II). The possibility of Cu(II) induced production of from moisture appears to have been ruled out. The absence of EET is a mystery which can only be dispelled by further studies on this interesting system. 

The insertion of a photosensitive group or of a redox active unit into the push-pull system 1 yields switchable molecular wires and push-pull molecules that contain a photo-switch or a redox switch S, as represented in 4. Compounds of such type containing for instance electroactive ferrocene groups and photosensitive metal complexes, have been synthesized. Some of them are shown in series 5 (Marczinke, B. Przibilla, K.J. Lehn, J.-M., unpublished data). 

The need to create functional nanosized architectures has led to the design and synthesis of surfactants that can be reversibly switched between two molecular states by incorporating redox-active or light sensitive functionalities.172,173,174,175,176,177,178 In these systems the ability to tune the properties of the surfactant by either controlling the potential applied to... 

Fabbrizzi s S[36] is unusual in using a nonmetallic, redox-active guest with a metal center serving as the receptor. An anionic nitrobenzoate guest is held by coordination of the carboxylate to the free apical position in Zn2+. The electron-deficient nitrobenzoate engages in PET with the anthracene fluorophore to switch the fluorescence OFF . 

Redox active ancillary ligands were first used to control lactide polymerizations using titanium complexes [51]. Very recently, Diaconescu and co-workers have reported derivatives of salen complexes incorporating a ferrocene unit which can be oxidized and reduced to switch the polymerization OFF and ON , respectively (Fig. 11) [52, 53],... 

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