Molecular photoswitches

Reddy. D.R. Malya, B.G. A molecular photoswitch based on an axial-bonding type phosphorus(v) porphyrin. Chem. Commun. 2001, 117. 

Irie M, Fukaminato T, Sasaki T, Tamai N, Kawai T (2002) A digital fluorescent molecular photoswitch. Nature 420 759... 

As just mentioned, phosphorus porphyrins have unique photochemical properties. Their photophysics is also interesting. Emitter-quencher assemblies based on porphyrin building blocks have attracted attention due to their potential to serve as models in photosynthetic research (see [90] for an example) or for the development of photoswitches that could be used for the fabrication of molecular electronic/optical devices. In this context, Maiya and coworkers constructed a P(VI) porphyrin system 59b with two switchable azobenzene groups positioned in the apical positions of the pseudo-octahedral phosphorus atom [92]. Photoswitch ability (luminescence on/off) was demonstrated as... 

Nonadiabatic transitions definitely play crucial roles for molecules to manifest various functions. The theory of nonadiabatic transition is very helpful not only to comprehend the mechanisms, but also to design new molecular functions and enhance their efficiencies. The photochromism that is expected to be applicable to molecular switches and memories is a good example [130]. Photoisomerization of retinal is well known to be a basic mechanism of vision. In these processes, the NT type of nonadiabatic transitions play essential roles. There must be many other similar examples. Utilization of the complete reflection phenomenon can also be another candidate, as discussed in Section V.C. In this section, the following two examples are cosidered (1) photochromism due to photoisomerization between cyclohexadiene (CHD) and hexatriene (HT) as an example of photoswitching molecular functions, and (2) hydrogen transmission through a five-membered carbon ring. 

Liquid Membrane Ion-Selective Electrodes Response Mechanisms Studied by Optical Second Harmonic Generation and Photoswitchable lonophores as a Molecular Probe... 

IV. MOLECULAR PROBE FOR ISE MEMBRANE POTENTIALS BASED ON PHOTOSWITCHABLE AZOBIS(BENZO-15-CROWN-5) lONOPHORES [17]... 

If the photoequilibrium concentrations of the cis and trans isomers of the photoswitchable ionophore in the membrane bulk and their complexation stability constants for primary cations are known, the photoinduced change in the concentration of the complex cation in the membrane bulk can be estimated. If the same amount of change is assumed to occur for the concentration of the complex cation at the very surface of the membrane, the photoinduced change in the phase boundary potential may be correlated quantitatively to the amount of the primary cation permeated to or released from the membrane side of the interface under otherwise identical conditions. In such a manner, this type of photoswitchable ionophore may serve as a molecular probe to quantitatively correlate between the photoinduced changes in the phase boundary potential and the number of the primary cations permselectively extracted into the membrane side of the interface. Highly lipophilic derivatives of azobis(benzo-15-crown-5), 1 and 2, as well as reference compound 3 were used for this purpose (see Fig. 9 for the structures) [43]. Compared to azobenzene-modified crown ethers reported earlier [39 2], more distinct structural difference between the cis... 

This compound is also remarkable since it also exhibits a LIESST effect. As claimed by the authors, [Fe(qsal)2][Ni(dmit)2]3.CH3CN.H20 can indeed be classified as a prototypal photoswitchable SCO molecular conductor. ... 

Zhuang M, Emzerhof M (2005) Mechanism of a molecular electronic photoswitch. Phys Rev B 72(7) 073104... 

It is at present still difficult to correlate the absolute intensity of the SHG with the number of cationic complexes at the membrane surface. Therefore, a quantitative discussion, showing how the permselective uptake of primary cations forming SHG active complexes into the membrane side of the phase boundary corresponds to the increase in the membrane potential, is not possible yet. Lipophilic derivatives of photoswitchable azobis(benzo-15-crown-5) were recently shown as a molecular probe to determine photoinduced changes in the amount of the primary cation uptake into the membrane phase boundary in relation to the photoinduced EMF changes under otherwise identical conditions. 

Azobebzene undergoes trans-cis photoisomerization and this photoswitchable behavior can be used for the photoregulation of various molecular phenomena. A simple example is on-off photoregulation of ester hydrolysis by using an azoben-... 

This review surveys our studies devoted to the photoswitchable molecular receptors based on photochromic crown ethers. Photochromic systems described in the review may be classified into three groups according to the reaction types E,Z-isomerization, [2+2]-photocycloaddition reactions and electrocyclic reaction. It has proved the groups to be an especially suitable basis for photochromic systems, and promising for the industrial applications. 

Ushakov, E.N., Gromov, S.P., Buevich, A., Baskin, I.I., Fedorova, O.A., Vedernikov, A.I., Alfimov, M.V., Eliasson, B., Edlund, U. (1999) Crown-containing styryl dyes cation-induced self-assembly of multiphotochromic 15-crown-5 ethers into photoswitchable molecular devices, J. Chem. Soc., Perkin Trans. 2, 601-607. 

The photochromic chromophores can be classified into two categories, depending on the thermal stability of the photogenerated isomers. When photogenerated isomers are unstable and revert thermally to their initial isomer state in the dark, the chromophores are classified as T-type (thermally reversible type). Most photochromic chromophores belong to this type. The photogenerated blue color of 6-nitro-l, 3, 3 -trimethylspiro-[2H-l-benzopyran-2,2 -indoline], for example, disappears in less than half an hour even in high Tg polymer matrices.181 Such thermally unstable photochromic chromophores cannot be applied in photoswitchable molecular systems, because the switched states are unstable. For those applications, the characteristic of persistence, or in other words thermal irreversibility, is indispensable. 

Properties which change concomitantly with diarylethene derivative photoisomerization are geometrical structures, electronic structures, refractive indices, and chiral properties (when the molecules have chiral substituents). Table 1 shows how the above property changes are applied to various photoswitching molecular systems. Details of these photoswitching functions are described in Sections 2.3 to 2.6. 

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