Prescription for optimizing holograms in LiNbO3 : Fe : Mn

The photorefractive holographic dynamics of grating formation in photochromic doubly doped LiNbO3:Fe:Mn crystal is studied numerically and analytically in terms of the two-center model of Kukhtarev Et al. [Ferroelectrics 22, 949 (1979)]. The relations among the recorded and fixed space-charge fields and the doping densities, the oxidation-reduction states of the fields, and the intensities of UV-sensitizing and red recording beams are studied. Important conditions and effects are feued, and an optimal prescription for material doping and oxidation-reduction processing is suggested in which the crystal can be strongly oxidized and the Mn-doping density is smaller than the Fe-doping density. (C) 2000 Optical Society of America. OCIS codes: 050.7330, 190.5330, 090.2900.

Dipole assisted photogated switch in spiropyran grafted polyaniline nanowires

In this work we show dipole-assisted photogated switching by covalent grafting of photoactive molecules to conducting polymers. Photochromic spiropyran molecules were covalently attached to polyaniline (PANI) nanowires via N-alkylation reaction to the quinoic part of PANI. Upon irradiation with ultraviolet light spiropyran transformed to a large dipole containing molecule, merocyanine form. We show that this transformation leads to a substantial (ca. 2 orders of magnitude) increase in conductance of the photochromic PANI nanowires, which were evident by an increase in field-effect mobility and calculated band gap narrowing of the system. Finally, this transformation was found to be fully reversible with no significant photofatigue. © 2011 American Chemical Society.

Kinetic spectra of light-adaptation dark-adaptation and M-intermediate of BR-D96N

BR-D96N is a kind of genetically site-specific mutants of bacteriorhodopsin (BR) with obvious photochromic effect. Compared to the wild type BR, the lifetime of M state of BR-D96N is prolonged to several minutes so that the photochromic kinetics and the intermediates formation can be studied by the conventional spectra analysis. In the experiment, the absorption spectra of the sample at different time after light illumination are measured with spectrophotometer. By fitting and analyzing the variation of the spectra, we suppose that there are three main states in the, photochromic process, i.e., B state (light-adapted state), M state and D state (dark-adapted state). The absorption spectra of the B state, M state and D state are extracted from the experimental data based on this three-state model and the spectra at various time are fitted with the least-square method. So, the variations of population percentages of the M state, B state and D state are obtained and the M state and B state lifetimes are estimated. In another way, from the measurement of the absorption dynamics at 407 and 568 nm, the M state and B state lifetimes are also obtained by two exponential data fitting, which give coincident results with those of the spectra analysis. (C) 2003 Elsevier Science B.V. All rights reserved.

Optical image contrast reversal using bacteriorhodopsin films

The implementation of image contrast reversal by using a photochromic material of Bacteriorhodopsin (BR) films is demonstrated with two methods based on the optical properties of BR. One is based on the absorption difference between the B and M states. Images recorded by green light can be contrast reversed readout by violet light. The other is based on the photoinduced anisotropy of BR when it is excited by linear polarization light. By placing the BR film between two crossed polarizers (i.e. a polarizer and an analyser), the difference of polarization states of the recorded area and the unrecorded area can be detected, and thus different contrast images can be obtained by rotating the polarization axis of the analyser.

Bleaching kinetics of indoly-benzylfulgimide in PMMA

Indoly-benzlfulgimide belongs to the photochromic fulgide family and follows photochemical first order kinetics. Its bleaching kinetics is investigated at 633 nm and 640 nm by spectroscopy, by the time dependence of transmission and of diffraction from holographically induced gratings. The non-exponential decay law resulting for diffraction experiments with a Gaussian beam profile is calculated and verified experimentally. For a quasi-homogeneous beam profile the time constant determined from diffraction decay is half the one for absorbance decay. The photochemical reaction rate of indoly-benzylfulgimide in PMMA is (3.9 +/- 0.3) cm(2)/J at 650 nm. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Absorbance kinetics of dye-doped systems with photochemical first order kinetics

Often it is assumed that absorbance decays in photochromic materials with the time dependence of the photochemical kinetics, i.e. exponentially for first order kinetics. Although this may hold in the limiting case of vanishing absorbance, deviations are to be expected for realistic samples, because the local photochemical kinetics slows down with increasing initial absorption and penetration depth of the radiation. We discuss the theory of the kinetics of initially homogeneous photochromic samples and derive analytical solutions. In extension of Tomlinson's theory we find an analytical solution that holds with good approximation even for samples that exhibit a small residual absorption in the saturation limit. The theoretical time dependence of the absorbance originating from photochemical first order kinetics of dye-doped systems is compared with experimental data published by Lafond et al. for fulgides doped in different polymer matrices. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Synthesis and application on parallel image storage of bisfurylfulgide

A bisfurylfulgide, E, E-3,4-bis[1-(2,5-dimethyl-3-furyl)ethylidene]-3,4-dihydrofuran-2,5-dione, is synthesized by Stobbe condensation reaction. The molecular structure of target compound is confirmed by single crystal X-ray crystallography analysis. It shows that the distances between two possible reaction sites of molecule are 0.3394 and 0.3406 nm respectively, which is favorable to photocyclization. The photochromic properties of this compound in different solvents are investigated, and the result shows that the compound exhibits excellent photochromic behavior. The primary result of applied research on parallel image storage is also presented.

Optical image processing using the photoinduced anisotropy of pyrrylfulgide

A synthesized photochromic compound-pyrrylfulgide-is prepared as a thin film doped in a polymethylmethacrylate (PMMA) matrix. Under irradiation by UV light, the film converts from the bleached state into a colored state that has a maximum absorption at 635 nm and is thermally stable at room temperature. When the colored state is irradiated by a linearly polarized 650 nm laser, the film returns to the bleached state; photoinduced anisotropy is produced during this process. Application of optical image processing methods using the photoinduced anisotropy of the pyrrylfulgide/PMMA film is described. Examples in non-Fourier optical image processing, such as contrast reversal and image subtraction and summation, as well as in Fourier optical image processing, such as low-pass filtering and edge enhancement, are presented. (c) 2006 Optical Society of America.

Influence of polarization orientation of violet light on the diffraction efficiency of bacteriorhodopsin

When a grating is recorded in a bacteriorhodopsin film by two linear parallel polarized beams together with anauxiliary violet light, the diffraction efficiency has a dependence on the polarization orientation of the violet light as well as its intensity. A method for calculating the diffraction efficiency of gratings in bacteriorhodopsin is proposed based on the two-state photochromic model, considering the saturation effect and the polarization status of all the involved lights. It is found that the polarization orientation of the violet light produces an approximate-cosine and an approximate-sine modulation on the steady-state diffraction efficiency separately at low and high intensities, respectively. The parallel polarized violet light can improve the steady-state diffraction efficiency to a larger degree than the perpendicularly polarized violet light when both are at their optimal intensities. The optimal intensity for the parallel polarized violet light is lower than that of the perpendicular polarized one. Thus, the improvement of the steady-state diffraction efficiency is less sensitive to the intensity of perpendicular polarized violet light than to that of parallel polarized violet light. (C) 2008 Optical Society of America.

Effect of reconstruction beam polarization on the kinetics of anisotropic gratings in bacteriorhodopsin

Anisotropic gratings are recorded on bacteriorhodopsin films by two parallelly polarized beams, and the effect of the polarization orientation of the reconstructing beam on the diffraction efficiency kinetics is studied. A theoretical model for the diffraction efficiency kinetics of the anisotropic grating is developed by combining Jones-matrix and photochromic two-state theory. It is found that the polarization azimuth of the reconstructing beam produces a cosine modulation on the kinetics of the diffraction efficiency, being positive at the peak efficiency and negative for steady state. By adding auxiliary violet light during grating formation, the saturation of the grating can be restrained. As a result, the negative cosine modulation for the steady-state diffraction efficiency changes to a positive one. In addition, the steady-state diffraction efficiency is increased appreciably for all reconstructing polarization orientations. (c) 2008 Optical Society of America.

Spectral relationship of photoinduced refractive index and absorption changes in fulgide films

Fulgides are one kind of organic photochromic compound, which are famous for their thermal irreversibility. In this report, from the difference spectra of the absorption A() of one kind of pyrrylfulgide, the spectral refractive index change n() was calculated by the Kramers-Kronig relation (KKR), and a good correlation of theoretically derived values and the experimental values of the n measured by a modified Michelson interferometer was found. Further, it is demonstrated that it was possible to calculate the spectral dependence of diffraction efficiency from the easily accessible absorption changes. This method will be a useful tool for the characterization and optimization of fulgide films. The results show that the diffraction efficiency is high at 488 and 750 nm, where the absorption is very small, so we can realize non-destructive reconstruction.

Photo- and Thermo-Chromic Study of the Ethylenediamine Trimolybdate

The ethylenediamine trimolybdate (ENTMo) can show unusually photochromic and thermochromic properties and there exists in the difference of chromic mechanisms, which has been proved in our previous work [I]. In this paper, X-ray powder diffraction (XRD), Fourier transform infrared (FTIR) and laser Raman spectroscopy (LRS) of the colored samples are characterized and analyzed in detail. The crystal structure, the inorganic skeleton and the microenvironment of center ions of the colored samples do not substantively change except distortion. The color difference of the photochromic and the thermochromic samples is discussed and that the difference of reduction sites result in their different chromic mechanisms is suggested.

Synthesis of a series of chiral copolymers with azo groups and investigations of reversible liquid crystalline alignment induced by the LB films of these materials

A series of liquid crystalline copolymers, poly{2-hydroxyethyl methacrylate}-co-{6-[4-(S-2-methyl-1-butyloxycarbonylphenylazo)phenoxy]hexyl methacrylate} with an azobenzene moiety as photoreactive mesogenic unit, was prepared and investigated by using DSC, polarized optical microscopy and X-ray diffraction. The results show that these polymers exhibit smectic phases. Z-type Langmuir-Blodgett films of these copolymers were successfully deposited onto calcium fluoride and quartz. Reversible homeotropic and planar liquid crystal alignments were induced by using the photochromism of the LB films of one of the copolymers containing 20.6 mol % of the azo unit.

Oligo switches: photoresponsive oligonucleotide conjugates by solid-supported click chemistry

Photoresponsive oligonucleotides (ONs) incorporating isoxazole-linked azobenzene (AB) moieties were prepared by resin-supported nitrile oxide-alkyne cycloaddition (NOAC) chemistry. The thermal and photochromic properties of the modified ONs were significantly influenced by the extent of pi-conjugation between the isoxazole and the AB modules.

Controlled Self-assembly of p-Phenyleneethynylene Derivatives to Diverse Supramolecular Architectures

Regional Research Laboratory