Photoresponsive compounds

Commercial presensitized plates are formulated on two chief groups of photoresponsive compounds, namely, (1) diazo resins and diazo oxides, and (2) cinnamate resins, some of which have been... 

PhotocontroUed Transport Phenomenon in Lipid Bilayer Membranes. Photocontrolled ion transport across lipid bilayer membranes using photoresponsive compounds such as azobenzene derivatives has been of great interest for potential applications in optoelectronic devices and optical transducers. Most research has exploited membrane capacitance change because of the disruption of membrane structures resulting from photoisomerization of azoben-zene-containing compounds incorporated into the lipid bilayers. Others have used the volumetric change of azobenzene moieties associated with photoisomerization. 

Fig. 5.4 Molecular structures and photoisomerization of some photoresponsive compounds, a Azobenzene, b Overcrowed alkene. c Diarylethene. d Butadiene, e Spirooxazinc. f Fulgide...

Among various photoresponsive compounds, dithienylethene (DE) derivatives are the most feasible photochromic materials due to their outstanding fatigue resistance, thermal stability, and reversible properties [65-67]. Addition of this photoresponsive moiety into an aromatic conjugated polymer is attractive as a method of dynamic control of luminescence through photoisomerization-driven... 

FIGURE 5.3 Molecular structures and photoisomerization of photoresponsive compounds. 

Many families of organic and inorganic photoresponsive compounds have been discovered (He Yao, 2006 Irie, Sakemura, Okinaka, Uchida, 1995 Kumar Neckers, 1989). In comparison with photonic sensitive organic materials, inorganic photoresponsive compounds are comparatively few. Typical examples include the metal oxides (Mazurkevich Kobasa, 1997), alkali metal azides (Deb, 1963), sodalite (Williams, Hodgson, Brinen, 2006), mercury salts (Khalil, Rophael, Mourad,... 

Many photosensitive molecules are known to be transformed under photoirradiation into other isomers, which return to the initial state either thermally or photochemically. The isomerizations are always accompanied by certain physical and chemical property changes. The well-known organic photoresponsive compounds inclnde, among others, diarylethenes (Feringa et al., 1993 Uchida, Saito, Murakami, Nakamura, Me,... 

Photoresponsive polymers can be prepared by coupling photochromic compounds which undergo structural changes upon irradiation with light and subse-... 

For this puq)ose, the photoswitchable bis(crown ether)s 88 and 89 as well as the reference compound 90 have been synthesized. Compounds 88 and 89 are highly lipophilic derivatives of azobis(benzo-15-crown-5). The parent azobis crown ether was originally developed by Shinkai and its photoresponsive changes in complexation, extraction, and transport properties thoroughly examined. Compared to 87, more distinct structural difference between the cis and trans isomers can be expected for 88 and 89 because in the latter compounds the 15-crown-5 rings are directly attached to the azobenzene group. The photoequilibrium concentrations of the cis and trans forms and the photoinduced changes in the complexation constants for alkali metal ions are summarized in Table 7. 

The electron transfer from Ru(bpy)2+ to MV2+ is very rapid, the order being 10s—10 M-1 s . But the irradiation of an aqueous solution of both the compounds does not give a photoresponse at the electrode dipped in that solution, because the back electron transfer from MV+ to Ru(bpy)j+ is also very rapid thereby no photochemical products are accumulated in the photostationary state (Scheme 6), However, when Ru(bpy)2 + is modified on the electrode surface by utilizing polymer coating, the electrode shows photoresponse 95), Such a modification of the electrode makes it photoresponsive, to afford a new type of photodiode. 

In summary, it has been demonstrated that surface morphology is critically important in determining the performance of solar cells with layered compound semiconductors. Steps on structured surfaces of transition metal dichalcogenides have been identified as carrier recombination sites. The region defined by the depth of the space charge layer parallel to the van der Waals planes can be considered as essentially "dead" in the sense that its photoresponse is negligible. As the "step model" predicts, marked improvement in solar cell performance is found on samples with smooth surfaces. 

Compound 1 is an early example of a photoresponsive crown ether [2,3], 1 has a photofunctional azobenzene cap on an N2O4 crown ring, so that one can... 

Photodimerization of anthracene is also usable as a photochemical switch to create photoresponsive crown ethers. Photoirradiation of 3 in the presence of Li+ gives the photocycloisomer 4.[5,61 Compound 4 is fairly stable in the presence of Li+, but readily reverts to the open form 3 when Li+ is removed from the ring. 

Shinkai et al.111-151 synthesized a series of azobis(benzocrown ethers) called butterfly crown ethers , of which compounds 9 and 10 are examples. Their photoresponsive molecular motion resembles that of a flying butterfly. It was found that the proportion of their Z forms at the photostationary state increases remarkably with increasing concentration of Rb+ and Cs+, which interact with two crown rings in a 1 2 sandwich fashion. This is clearly due to the bridge effect of the metal cations with the two crowns, results that support the view that the Z forms make an intramolecular 1 2 complex with these metal cations. As expected, the Z forms extracted alkali metal cations with large ion radii more efficiently than did the corresponding E forms. In particular, the photoirradiation effect on 9 is quite remarkable for example, ( )-9 (n= 2) extracts Na+ 5.6 times more efficiently than (Z)-9 (n= 2), whereas (Z)-9(n= 2) extracts K+ 42.5 times more efficiently than ( )-9(n= 2). l ... 

Photoresponsive polymers can be obtained by introducing photochromic units, such as azobenzene or spiropyran groups, into the macromolecules of polymeric compounds. As described in Chapter 1 of this book, photochromic compounds can exist in two different states, such as two isomeric structures that can be inter-converted by means of a light stimulus, and the relative concentrations of which depend on the wavelength of the incident light. For instance, in azobenzene compounds, photochromism is due to trans-cis photoisomerization around the N=N double bond, while in spiropyran compounds photochromism involves interconversion between the neutral spiro form and the zwitterionic merocyanine form (Figure 1). 

The azo-modified, elastin-like polypeptide XIV illustrated in Scheme 9 exhibits a so-called inverse temperature transition" that is, the compound gives cross-linked gels that remain swollen in water at temperature below 25 °C but deswell and contract upon a rise of temperature. The trans-cis photoisomerization of the azo units, obtained through alternating irradiation at 350 and 450 nm, permits photomodulation of the inverse temperature transition.[S9] The result indicates that attachment of a small proportion of azobenzene chromophores is sufficient to render inverse temperature transition of elastin-like polypeptides photoresponsive, and provides a route to protein-based polymeric materials capable of photomechanical transduction. 

LB films of hairy-rod azo-poly(L-glutamate)s [Scheme 11, compounds XIX and XX (n = 2 and 6)] have been used to prepare photoresponsive waveguides. 931 These... 

The first example of a photoresponsive [2]rotaxane, published in 1997 by Nakashima and co-workers, is one of those cases [61]. Molecular shuttle E/Z-224+ consists of an a-cyclodextrin macrocycle, and a tetracationic thread containing an azobiphenoxy moiety, very closely related to azobenzene, and two bipyridinium stations. The well-known E-Z isomerizations of azobenzenes and the ability of cyclodextrins to bind lipophylic compounds in water are exploited in this system to achieve shuttling. When the azobiphenoxy station is in its trans form, E-224+, the cyclodextrin encapsulates it preferentially over the more hydrophilic bipyridinium station (Scheme 12). 

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