Photo Induced Bleaching

I. PHOTOEXCITATION PHOTO-INDUCED ABSORPTION, PHOTO-INDUCED BLEACHING AND PHOTOCONDUCTIVITY Photo-excitation studies of conjugated semiconductor polymers were stimulated by the calculations of Su and Schrieffer (IJ. which demonstrated that in trans-fCH) an e-h pair should evolve into a pair... 

In summary, semiconductor polymers such as polyacetylene and polythiophene have experimentally demonstrated nonlinear optical processes (photo-induced absorption, photo-induced bleaching and photo-luminescence) with characteristic time scales in the picosecond range or faster. These phenomena are intrinsic and originate from the instability of these conjugated polymers toward structural distortion. 

Recently, the results of photoinduced absorption studies (i.e. excitation spectroscopy) of the emeraldine base polymer have been reported.22-24 Photoinduced absorptions were observed23 24 t 0.9eV, 1.4eV and 3.0 eV, accompanied by photo-induced bleaching at 1.8eV and at energies above 3.5 eV. The 1.4 and 3.0 eV photoinduced absorptions have been interpreted, by analogy with the absorption spectrum of the emeraldine salt, to the photoproduction of polarons in emeraldine base.24 Stafstrom et al25 concluded that positive and negative polarons,as well as positive bipolarons account very well for the 1.4 and 3.0 eV photoinduced absorptions. No specific explanation has been proposed for the 0.9 eV photoinduced peak. 

Spiro-oxazine (NOSH) photo-induced ring closure reactions were first described by Bohne et al., who used two-laser two-color excitation in the UV and visible regions [71,72]. In this work, they found that photoexciting the merocyanine in cyclohexane leads to a bleached product which recovers quantitatively to the merocyanine form over 30 xsec. The transient bleach state had an absorbance... 

Panchapakesan B (1990) Photo-induced reactions of lignin and lignin fragments Photooxidation of chlorinated organics in bleach plant effluents and brightness stability of high yield pulps. Ph.D. Thesis, North Carolina State University, Raleigh, North Carolina, USA... 

FIG. 5 Light scattering curves for isolated bovine rod outer segment disk membrane in aqueous sucrose of the indicated concentrations. ( ) unbleached and (O) bleached membranes. (Reprinted from T. Norisuye and H. Yu. Osmotically-induced and photo-induced deformations of disk membranes. Biochim. Biophys. Acta 477 441. Copyright 1977. With kind permission from Elsevier Science NL. Sara Burgerhartstraat 25. 1055 KV Amsterdam. The Netherlands.)... 

In addition to the 16 sunscreens approved in the United States, there are 2 non-sun-screen topical agents that are approved for the treatment of conditions related to photo-induced skin damage. These are tretinoin and hydroquinone. Both are prescription products. Tretinoin is approved as an adjunctive treatment for "mitigation of fine wrinkles, mottled hyperpigmentation, and tactile roughness of facial skin." Hydroquinone has been marketed for decades for bleaching of hy-perpigmented skin conditions. 

We found that there exists photo-induced anisotropy in fulgide-doped polymeric films M, which can be used in polarization holography application. When the colored states are irradiated by a linearly polarized 650 nm laser, the films returns to the bleached states and photo-induced anisotropy is produced during this process. The mechanism of photo-induced anisotropy in the fulgide films is the following HI anisotropic absorbing molecules of fulgide are immobilized randomly in the PMMA polymeric matrix, which shows... 

The fulgide material studied here is 3-indoly-benzylfulgimide, which was synthesized by the Stobbe condensation routine l l. The target compoimd of 3mg was dissolved in a 0.1ml 10% (by weight) PMMA-cyclohexanone solution. Then the solution was coated on a 1-mm thick K9 glass plane (0 25 mm x 1.5 mm) with a span coater and dried in air. The thickness of the film is determined to be about lOjim by microscopy of the cross section. The photochromic or photo-induced anisotropic paoperties of fulgides are due to a reversible photochromic (photoisomerization) reaction that occurs between one of the colorless E-form (bleached state) and the C-form (colored state). These are the two spectrally separated... 

A value of aUo/3 of about 0.4 eV is consistent with the measured values of AE obtained from photo-induced absorption measurements [25]. Associated with the formation of the mid-gap soliton absorption band is the loss of n and it band states and the bleaching of the n n interband transitions. 

Re. In principle, the blank is not fluorescing. However, one should subtract the Raman spectrum of the blank from the recorded fluorescence spectrum of the fluorophore. Therefore, the temperature should be the same for both spectra otherwise, an error could be induced in determining the real intensity of the fluorophore emission, f The principle of studying molecules diffusion in cells with the method of photo bleaching. 

Rf. We induce an irreversible photo-bleaching of fluorophore molecules within a specific region of the cell. The appearance of fluorescence in this area after a short time is the result of fluorophore diffusion from other cell areas to the irradiated area, g Why does an increase in temperature decrease the fluorescence quantum yield ... 

A 3D optical memory device can be based on different principles. Among them are the write once and read many times principle, based on TP initiated photopolymerization resulting in a photopolymer structure [242] or photo-bleaching of a fluorescent material [250]. The rewritable principle is based mainly on TP induced molecular change. This TP induced molecular change can be an isomerization reaction in the writing process and OP induced fluorescence in the reading process [119, 144, 247, 258],... 

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