Molecular switching devices

Organic compounds which show reversible color change by a photochemical reaction are potentially applicable to optical switching and/or memory materials. Azobenzenes and its derivatives are one of the most suitable candidates of photochemical switching molecular devices because of their well characterized photochromic behavior attributed to trans-cis photoisomerization reaction. Many works on photochromism of azobenzenes in monolayers LB films, and bilayer membranes, have been reported. Photochemical isomerization reaction of the azobenzene chromophore is well known to trigger phase transitions of liquid crystals [29-31]. Recently we have found the isothermal phase transition from the state VI to the state I of the cast film of CgAzoCioN+ Br induced by photoirradiation [32]. 

Multi-electron mechanisms of redox reactions. Switching molecular devices... 

The ability to switch a molecular unit on and off is a key component of an efficient molecular device, since it allows modulation of the physical response of such a device by external physical or chemical triggers. A molecular device, based on a trinuclear metal complex, shown in Figure 59, functions as an electroswitchable-photoinduced-electron-transfer (ESPET) device.616 Electrochemical switching of the redox state of a spacer intervening between a donor-acceptor pair can dictate the type of the observable charge separation and the lifetime of the resulting ion pair.616... 

One of the advances in the field of PET is the design of molecular devices, in which D and A pairs are ingeniously linked by covalent bridges (B) to form D-B-A dyads. Electron transfers between D and A across B in a controlled manner may thus display useful functionalities, such as molecular rectifiers [25], switches [26], biosensors [27], photovoltaic cells [28], and nonlinear optical materials [29]. Spacers that have been utilized are versatile, including small molecules, such as cyclohexane [30], adamantane [31], bicyclo[2.2.2]octane [32], steroids [33], and oligomers of... 

Kronemeijer AJ, Akkerman HB, Kudemac T, van Wees BJ, Feringa BL, Blom PWM, de Boer B (2008) Reversible conductance switching in molecular devices. Adv Mater 20(8) 1467-1473... 

Keywords Molecular Devices a Molecular Machines a Molecular Wires a Antenna Systems a Molecular Switches a Plug/socket Systems a Pseudorotaxanes a Rotaxanes a Catenanes a Supramolecuiar Chemistry a Photochemistry a Electrochemistry a Luminescence... 

In general, optically, electrically or chemically triggered switches would seem to be preferable to mechanically activated ones, as are photo-, electro- and chemo devices with respect to mechano devices and electronic or photonic computing with respect to mechanical computing. The ultimate in (nano)mechanical manipulation of a molecular device is represented by the realization of a bistable switch based on the motion of a single atom by means of the scanning tunnelling microscope [8.295] (see also Section 9.9). 

In principle any molecule able to exist in two reversible, switchable states can represents a molecular switch (bistable device) with potential to form part of molecular circuitry or act as molecular memory. An excellent component for switchable molecular devices is the 1,2-dithienylethene system, which has been exploited ingeniously by Lehn in a number of bistable systems.54 The core switching element is the transformation of the dithienylethene unit between two stable states as a function of the wavelength of incident radiation (Scheme 11.8). 

Balzani, V., Venturi, M., Credi, A. Molecular Devices and Machines. A Jorney into the Nanoworld, Wiley-VCH, Weinheim, 2003 b) Feringa, B.L. (ed.), Molecular Switches, Wiley-VCH, Weinheim, 2001 c) Raehm, L., Sauvage, J.-P. Molecular machines and motors based on transition metal-containing catenanes and rotaxanes, Struct. Bond. 99 (2001), 55-78. 

Two-terminal devices might seem more natural for the molecular-scale systems than three-terminal ones because of the technological difficulties in manipulating small structures. Furthermore, chemical assembly of molecular devices usually results in a periodic structure. This observation resulted in the idea to have a two-terminal switch, electronically reconfigurable, where a relatively high voltage (e.g. —2V or +2V in [62], which uses a 2-catenane-based molecule) (Fig. (7a)) is applied to close or open the switch, but a relatively low voltage to read (M). 1 V) [60]. These molecular switches [62], a mono-layer of rotaxane molecules, are not field-activated but can be described as small electro-chemical cells, which are characterized by... 

In conclusion, this book is intended as an overview of the principles behind and state-of-the-art in interfacial supramolecular chemistry. The book is suitable for researchers and graduate students and focuses on assemblies that demonstrate at least the potential to produce useful devices such as solar cells, electrochromic devices, molecular wires, switches and sensors which are addressable by using electrochemical and optical stimuli. Molecular materials for nanoscale molecular devices remain an intriguing conceptual possibility. 

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