Chromophoric molecular switches

L. Gobbi, P. Seiler, F. Diederich, A Novel Three-Way Chromophoric Molecular Switch pH and Light Con-trollale Switching Cycles , Angew. Chem Int. Ed. Engl 1999,38, 674-678. 

Scheme 11.10 Pseudorotaxane-based, chemically driven chromophoric molecular switch.

Recently, Diederich and co-workers have made use of the DHA-VHF system for designing a three-way chromophoric molecular switch, which can be controlled by pH, light, and heat.1371 The system is based on a molecule with three addressable subunits, that can undergo individual, reversible switching cycles. These processes... 

Scheme 3. Three-dimensional switching diagram of TEE-DHA-DMA hybrid derivative trans-12a, a three-way chromophoric molecular switch. Six out of eight possible states can be attained [23c],...

Gobbi, L., Seiler, R, and Diederich, E, A novel three-way chromophoric molecular switch pH and Hght controllable switching cycles, Angew. Chem. Int. Ed. Engl, 38, 674,1999. 

The sterically overcrowded alkenes shown in Scheme 6 have been exploited in our group since, from the perspective of molecular switches design, they combine a number of attractive structural features. Steric interactions between the groups attached to the central olefmic bond force these molecules to adapt a non-planar helical shape. The chirality of these so-called inherently dissymmetric alkenes 3, is therefore the result of distortion of the entire molecular structure. Beside the heli-cene-like geometry, both a cis- and a trans-stilbene chromophore are present in the same molecule. 

Because of their rich redox properties, NLO chromophores featuring transition metal complexes are among the best candidates for the role of NLO molecular switches, and the majority of examples reported up to now concerns metal-based chromophores in which the NLO response is modified by a chemical (or electrochemical) oxidation/reduction sequence. Several examples of reversible proton- or photon-driven switching of 0 will also be discussed in the following. 

Even the concept of molecular switch is an important topic from a variety of perspectives ranging from the modelling of biological processes to the design of devices for molecular electronics. The idea of switching directly the NLO properties has recently been envisioned [151]. Lamere et al. have reported on the synthesis and characterization of a boronate chromophore built up from two push-pull NLO sub-units in a quasi-free rotation around a chemical axis. They discussed on the possibility to use such a system as a molecular NLO switch induced by an electric field [152]. 

Chromophores can be classified in two categories reversible and irreversible. Reversible chromophores, often named molecular switches, undergo... 

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]. 

Figure 11. Schematic representation of the concept of a Figure 10 A, B, and C are suitably chosen chromophoric three-pole supramolecular switching of energy transfer. The groups. For more details, see the text, cartoons correspond to the molecular components shown in...

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