Molecular redox controlled switch

Photoinduced electron transfer processes involving electron donor (D) and acceptor (A) components can be tuned via redox reactions. Namely, the excited-state properties of fluorophores can be manipulated by either oxidation of electron donors or reduction of electron acceptors. Also, the oxidized and the reduced species show different properties compared to the respective electron donors and acceptors. By making use of these properties of electron donors and acceptors, a number of molecular switches and logic gates have been described in recent years. In the following, we will introduce these redox-controlled molecular switches according to the redox centers. 

R. Rathore, P. LeMagueres, S. V Lin-deman, J. K. Kochi, A Redox-controlled Molecular Switch Based on the Reversible C—C Bond Formation in Octa-methoxytetraphenylene, Angew. Chem. Int. Ed. 2000, 39, 809-812. 

Applying this new exciting transition metal dtc-based catenane high yielding synthetic procedure to the construction of novel redox-controlled molecular machines and switches is the subject of ongoing research within the group. 

Redox and Chemically Controlled Molecular Switches and Muscles... 

Furthermore, metals present additional intrinsic properties, such as redox reversibility, magnetism and luminescence. It is, therefore, possible to take benefit from these peculiarities for the design of redox-controlled NLO switches as illustrated in this chapter or for the elaboration of materials combining two or more properties. This latter field of research is in its infancy but it is possible to anticipate many improvements in the future for the elaboration of multifunctional molecular material optimising simultaneously all the wonderful capacities of metals. 

Another example of a photoredox molecular switch is based on a ferrocene-ruthenium trisbipyridyl conjugate, in which the luminescent form 4 switches to the non-luminescent form 5 upon electrochemical oxidation (Figure 2/bottom)171. Biological systems exploit the interplay of redox and molecular recognition to regulate a wide variety of processes and transformations. In an attempt to mimic such redox systems, Deans et al. have reported a three-component, two-pole molecular switch, in which noncovalent molecular recognition can be controlled electrochemically. x Willner et al. have reported on their research activities in developing novel means to achieve reversible photostimulation of the activities of biomaterials (see Chapter 6).[91 Recently, we have shown that it is possible to switch the luminescence in benzodi-furan quinone 6 electrochemically. 101 The reduction in THF of the quinone moiety... 

There has been a resurgence of interest in proton-coupled redox reactions because of their importance in catalysis, molecular electronics and biological systems. For example, thin films of materials that undergo coupled electron and proton transfer reactions are attractive model systems for developing catalysts that function by hydrogen atom and hydride transfer mechanisms [4]. In the field of molecular electronics, protonation provides the possibility that electrons may be trapped in a particular redox site, thus giving rise to molecular switches [5]. In biological systems, the kinetics and thermodynamics of redox reactions are often controlled by enzyme-mediated acid-base reactions. 

Fig. 8 (a) Chemical and stylized representation of the strategy of redox-mediated molecular brake passing from sulhde to sulfoxide and sulfone (b) an example of oxygen-flipped rotary switch (c) its stylized representation (d) X-ray structure of a bisarylanthracene peroxide (H atoms were omitted for clarity) (e) control of the frequency of molecular motions in rotaxanes of which annulus (macrocycle) contains a photoisomerizable dianthrylethane group (see text for details)... 

Over the past decade, cycIo6w(paraquat-p-phenylene) has been the benchmark compound in the design of molecular switches, in 7t-7t-stacking, and related dynamic processes and this continues in redox-controllable amphiphilic [2]rotaxanes <04CEJ155>. 

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