Photoinduced change

Imura, K. and Okamoto, H. (2008) Ultrafast photoinduced changes of eigenfunctions of localized plasmon modes in gold nanorods. Phys. Rev. B, 77, 041401(R) (4 pages). 

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... 

Griffiths, D. W., Bain, H., Dale, M. F. B. (1995). Photoinduced changes in the total chlorogenic acid content of potato Solanum tuberosum) tubers. J. Sci. Food Agric., 68, 105-110. 

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. 

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. 

Photoinduced Changes in Phase Boundary Potentials. The photoinduced membrane potentials were measured by using PVC matrix liquid membranes in contact with a polypyrrole-coated Pt electrode [dibutyl phthalate (DBP) as the membrane solvent]. The polypyrrole layer allows to obtain a stable and sample-in-dependent potential drop between Pt and the PVC membrane. The phase boundary potential at the interface of a membrane containing ionophore and an aqueous RbCl or KCl solution could be reversibly altered by UV and visible light irradiation, as shown for ionophore 89 in Figure 23a,b. The values of the photoinduced potential... 

The most unique and intriguing features of chalcogenide vitreous semiconductors are the photoinduced changes appearing as a nearly parallel shift of the optical absorption edge to lower energy (so-called photodarkening effect) after irradiation... 

At room temperature, the amorphous Se (a-Se) films exhibit very slight but definite photodarkening. The effect consists of a decrease of transmission (—2% in magnitude) after illumination, which was spontaneously restored as excitation was switched off It was found that the restoration period increases with the arsenic concentration. In other words, the photoinduced changes are transient (dynamic) and not permanent. 

Very important is the observed similarity between the light-induced changes in pure amorphous Se and Se containing Sb or As additives. The similarity is possibly the clue to a more general understanding of various photoinduced changes, photocrystallization, and compositional dependency in chalcogenide vitreous semiconductors. Further experiments would be very helpful in this context. 

In solution the cfl complexes of Ni11 are characterized by several rapid equilibria between species having different coordination numbers and/or geometries. Upon irradiation, these equilibria are perturbed and can be studied by relaxation techniques. A number of photoinduced changes have been investigated in this manner including square planar/tetrahedral, four-coordinate/five-coordinate and four-coordinate/six-coordinate interconversions.138... 

Photooxidation occurs at potentials well negative of the anodic wave. As dimer formation occurs photo-currents (0.1-3.9 yA) can be detected, implying photoinduced change transfer. 

A polymer of I-a,y-diaminobutanoic acid almost quantitatively substituted with azobenzene units in the side chains [Scheme 5, VIII(n= 2)] was not completely soluble in HFP when the sample was kept in the dark. The initial, slightly turbid solution became clear on irradiation at 360 nm and the consequent photoconversion of the azo moieties from their trans to the cis configuration (for photosolubility effects see Section 13.2.3). The cis polymer was found to adopt an essentially random coil conformation. Exposure to 460 nm light and the consequent back-isomerization of the azo units to about 70/30 trans-cis isomeric composition gave rise to a reversible photoinduced change from random coil to a-helical structure (helix content, about 60%).1411... 

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