Molecular-level switching devices

A three-level switching device has been demonstrated in which photochromic properties are used to control electrical properties, and vice versa. Such a system has been realized in the form of thiophene bisphenol [90, 91]. Conversion of the open (8a) to the closed (8b) form of the thiophene was achieved by absorption of 312 nm light, and revered by absorption of 600 nm light. The bisphenol oxidation occurs at +0.735 V (vs. SCE), forming the closed-ring bisquinone, compound 8c. This species has large absorptions at 400 and 534 nm. The optical properties of the quinone phenol couple have previously been used in a bianthrone-based system [87]. The bisquinone (8c) cannot be converted to the open thiophene, and locks the system in the closed form. The thiophene has also been incorporated as a component in two-level molecular switches [99, 128] and switchable molecular wires [30]. 

Keywords Luminescence m Fluorescence m Phosphorescence a Sensors a Switches a Logic Gates a Supramolecular Systems a Truth Tables a Photoinduced Electron Transfer a Molecular-Level Devices... 

Switching devices that are reversible and work on the molecular level are essential features of nanomachinery. Control of the access to capsules, the transport of molecules in and out of the cavities, is desirable and we examined a well-established system that uses light as a switching device the cis-trans photoisomerization of azobenzenes [58, 59]. The azobenzenes have been applied in the supramolecular chemistry of crown ethers [60-62], cyclodextrins [63,64], and even proteins [65, 66]. The photoisomerization changes the shape in a predictable way and we used azobenzene photoisomerization in an indirect sense to control reversible encapsulation. 

The LB technique enables us to obtain ultrathin films with the structures and thicknesses controlled at the molecular level, which promises applications to various fields. One of the challenges is to construct a new type of switching device based on conductive LB films. For this purpose, a supramolecular system is used since the geometrical alignment of the functional units are defined by the molecular design of the supermolecules to be used. 

The need to improve the electrical communication between redox proteins and electrodes, and the understanding that the structural orientation at the molecular level of redox proteins and electroactive relay units on the conductive surfaces is a key element to facilitate ET, introduced tremendous research efforts to nano-engineer enzyme electrodes with improved ET functionalities. The present chapter addresses recent advances in the assembly of structurally aligned enzyme layers on electrodes by means of surface reconstitution and surface crosslinking of structurally oriented enzyme/cofactor complexes on electrodes. The ET properties of the nano-structured interfaces is discussed, as well as the possible application of the systems in bioelectronic devices such as biosensors, biofuel cell elements or optical and electrical switches. 

The idea that a single molecule or an assembly of molecules might function as an electronic device has been of interest since long ago [1-10]. In this regard, the molecular switch is one of the current approaches in molecular electronics. Bistability for the binary change of state in a molecular system is the prerequisite for an operational switch, according to Haddon and Lamola [11]. Furthermore, three additional essential conditions have to be fulfilled in order to get an operational molecular switch (i) the switching must be controllable, (ii) the state of the switch must be readable and (iii) the first two conditions must be executable at the molecular level. Kahn and Launay [12] defined molecular bistability as the property of a molecular system to evolve from one stable state to another stable state in a reversible and detectable fashion in response to an appropriate perturbation. 

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