Photochromic kinetic spectra and intermediates of BR-D96N

BR-D96N is a kind of genetically site-specific mutant 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 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 measuring the absorption dynamics at 407 nm 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.     

Synthesis and photochromic behavior of some azo-polysiloxanes modified with nucleobases or donor-acceptor groups

This paper presents the syntheses, characterization and photochromic behavior of some new azo-polysiloxanes modified with uracil, cytosine or nitro-phenolic groups. Taking into consideration the possibility of generating H-bonds or donor/acceptor interactions, this class of materials present a potential applicability in the immobilization of biomolecules and their nano-manipulations. Also, such compounds are capable of producing a fluid phase, with directional flowing capacity. For all these polymers, the molecular modeling simulations have shown disordered structures, which would generate amorphous phases, a very important aspect for molecules’ nano-manipulation. The photochromic behavior in the presence of UV irradiation was also evaluated.      

Photochromic dihetarylethenes. 9. Dithienylperfluorocyclopentenes: a quantum-chemical study

MNDO calculations of the open and cyclic forms of the molecules of three photochromic 1,2-di(3-thienyl)perfluorocyclopentene derivatives were carried out. Structural parameters as well as electronic and thermodynamic characteristics of the compounds studied were analyzed. The optimized geometric parameters of the open forms of the three molecules under study are in satisfactory agreement with the results of X-ray diffraction studies. Analysis of the effect of substituents on the electronic characteristics of the central fragment and on the composition of the frontier MOs suggests that it is more appropriate to use cyclic rather than open forms of the molecules for correlation analysis and for prediction of photochromism of dithienylperfluorocyclopentenes.     

Crystal shapes of cubic mesophases in pure and mixed carboxylic acids observed by optical microscopy

Two different cubic phases in pure (Ia3d cubic space group) and mixed (Im3m cubic space group) thermotropic carboxylic acids are observed by optical microscopy. In unpolarized light, the presence of the cubic phases is identified unambiguously by the observation of facetted single crystals with highly symmetrical shapes. The observed crystal habits are growth shapes, rather than equilibrium shapes. The facetting is described, both at the interfaces with air and with the isotropic liquid phase. The facets correspond to various reticular planes that are discussed in relation with crystallographic data.     

Spiropyrans and spirooxazines. 1. Synthesis and photochromic properties of 9"-hydroxy- and 9"-alkoxy-substituted spironaphthooxazines

A procedure was developed for phase-transfer catalyzed alkylation of 5-hydroxyindolenine and 9"-hydroxy-substituted spiro[indoline-2,3"-naphtho[2,1-b]oxazines] by alkyl halides. New 9"-hydroxy- and 9"-alkoxy-substituted spironaphthooxazines, spirooxazinyloxyacetic acids, and their esters containing substituents with different length of the carbon chain in the indoline moiety were synthesized. The influence of the substituents on the spectroscopic properties of the starting and colored forms and the kinetic characteristics of photochromic transformations of 9"-substituted spironaphthooxazines in solutions and polymeric films was investigated. The bipolar merocyanine forms of spirooxazines were found to produce H-aggregates.     

Polarization dependence on the holographic recording in spiropyran-doped polymers

We report on the photoinduced anisotropy in the holographic recording in spiropyran doped polymers as a result of the photoizomerization of spiropyran into merocyanine. Photoizomerization is achieved with UV polarized light ( = 355 nm) from the third harmonic of Q-switched Nd:YAG laser. After UV illumination a strong and broad polarization-dependent absorption peak centered 600 nm appears. Absorption holograms were recorded with low power He–Ne lasers with 2.2% output diffraction efficiency for polarization parallel to the polarization of the UV laser. The extremely long lifetime of the merocyanine states (12 days in the dark) and their high resolution makes this material promising as an optical memory element.     

Photo-controlled extraction and active transport of amino acids by functional reversed micelles containing spiropyran derivatives

In a reversed micellarn-decane solution, a spiropyran derivative 3,3-dimethyl-1-octadecyl-6-nitrospiro(2H-benzopyran-2,2-indoline) (PC18) showed normal photochromism, and the reversed micelles provided polar microenvironment increasing stability of a zwitterionic merocyanine (MC) form of PC18. Though the reversed micelles of tetraethyleneglycol dodecylether (TEGDE) alone inn-decane had relatively low ability to extract amino acid from aqueous solutions, the PC18-incorporated TEGDE reversed micelles inn-decane showed good photo-controlled extraction of zwitterionic amino acid under UV-irradiation and release under VIS-irradiation. Extent of the extracted amino acid was higher for tryptophane (Trp) bearing hydrophobic side chain than alanine (Ala), showing amino acid selectivity. Photo-driven active transport of amino acid across a liquid membrane was attained by the PC18-incorporated TEGDE reversed micellar carrier in a water/n-decane/water three-phase system, where one side of an aqueous/organic interface was irradiated by the UV-light and the other side by the VIS-light. When Trp and Ala were present in the aqueous solution, Trp was selectively transported.     

Optically active polymers containing side-chain azobenzene moieties: Photochromic and photoresponsive behavior of copolymers of N-(4-azobenzene) maleimide with (−)-menthyl vinyl ether and (+) (S)-2-methylbutyl vinyl ether

Photochromic behavior and photoisomerization kinetics of optically active copolymers of trans-N-(4-azobenzene) maleimide (ABM) with (?) -menthyl vinyl ether (MtVE) and (+) (S) -2-methylbutyl vinyl ether were studied by UV spectroscopy under irradiation at 348 nm. The resulting data have been compared with those of the corresponding copolymers containing also trans-N-(4-azobenzene) maleamic acid co-units as well as of low molecular weight model compounds. The photoresponsive behavior has been also investigated by circular dichroism measurements at various extents of photoisomerization. The results are discussed in terms of structural requirements of the macromolecules. © 1994 John Wiley & Sons, Inc.     

Chiral photochromic 2-(N-acyl-N-arylaminomethylene)benzo[b]thiophen-3(2H)-ones

Photochromic 2-(N-acyl-N-arylaminomethylene)benzo[b]thiophen-3(2H)-ones containing ortho-substituents in the N-phenyl ring were studied by X-ray diffraction analysis and ¹H NMR spectroscopy. It was established that these compounds have stable chiral structures due to hindered rotation of the phenyl ring around the C—N bond. The energy barrier to racemization evaluated by dynamic NMR spectroscopy is G ^# _{428 K} = 98 kJ mol^–1.     

Cuprous Halide Microcrystals Containing Photochromic Sol-Gel Glass

CuBr containing photochromic sol-gel glasses were synthesized by the introduction of CuBr dissolved in CH₃CN into a sol-gel of Al₂O₃-SiO₂ type. Microcrystals of CuBr were developed by a two step heat treatment, the first step in air initially at 280°C/2 h and then at 410°C/2 h for the removal of the organics and the second step at 700°C/2 h in nitrogen atmosphere for the reduction of the copper compounds to Cu₊. Photometric measurements of the small gel pieces show a distinct darkening of 24% and a remarkable fading at room temperature of 13% within 10 minutes.