Photochemical reaction kinetics in optically dense media: The influence of thermal reactions

The kinetics of photochemical reactions in optically dense media essentially free from diffusion was considered. The photochromic isomerization A ↔ B was studied as an example. If thermal isomerization is possible, a stationary state is achieved in time determined by rate constants for the thermal reactions. The concentration wave profile is changed during the photochemical reaction propagation. Low values of thermal reaction constants and decrease in sample optical density during photochemical isomerization were found to be essential for maximal wave penetration into the sample. Sharp concentration gradients of A and B can be observed when both the optical density is increased during photochemical isomerization and the quantum yield of the direct photochemical reaction A → B is higher than that of the reverse photochemical reaction B → A.     

Photo-induced Conversion of Furylfulgide Single Crystal Under High Pressures

We have studied pressure effects on single crystal of photochromic furylfulgide for researching the possibility of photo-induced structural change. Pressure dependence of the absorption spectra was investigated up to 8.2 GPa at room temperature. Pressure-induced conversion to C-form molecules was observed at 8.2 GPa in single crystal composed only of E-form molecules, while at 5.7 GPa in single crystal containing small amount of C-form ones. Photochromic reaction was observed under high pressure as well as the ambient pressure. The dependence of absorption intensity due to C-form molecules suggests the possibly of cooperative structural change in furylfulgide single crystal at 5.5 GPa.     

Sensitivity and Resolution Development of Spiropyran‐based Molecular Photoswitches

The phenylazo moiety and its donor‐ and acceptor‐substituted derivatives are studied as effective auxochromes to improve their sensitivity and resolution for distinguishing between the spiro (SP; OFF) and mero (ON) forms in molecular photoswitching applications. Thus, 13 azospiropyran derivatives were synthesized and their spectroscopic and photokinetic behaviors were studied. The quality of photochromic reactions of the synthesized photochromic compounds were compared using a dose–response model. Interestingly, by replacing the nitro group in 6‐nitrospiropyran (ε = 0.42 × 10⁴ M^?1 cm^?1) with a simple phenylazo moiety, the SP form is still colorless and the color intensity of the merocyanine (MC) form is improved desirably by extending the conjugation length ( 1a , ε = 1.35 × 10⁴ M^?1 cm^?1). The presence of a hydrophilic OH group or a CH₃ group at the para position of phenylazo moiety revealed more or less the same photochromic properties as 1a . The OCH₃ group substituted at position 6 of the phenylazo moiety at the para position of the azobenzene moiety effectively increased the photochromic properties with the maximum k‐value for SP to MC switching. Meanwhile, Cl, Br, COOH, and NO₂ groups at the para position of the azobenzene moiety revealed the reduction in photochromic properties compared to 1a .     

一类西弗碱基光致异构化分子在不同基底上的表面增强拉曼光谱(英文)

由水杨醛衍生得到的Schiff碱由于其具有起因于受激分子内质子转移的光致 (热致 )变色性质而受到了人们的重视 .本文利用表面增强拉曼光谱研究了该类化合物在金、银基底及银溶胶表面上的拉曼光谱 ,比较了不同基底对吸附分子结构的影响     

Synthesis, chiroptical properties and photoinduced birefringence of optically active methacrylic copolymers bearing side-chain bisazoaromatic moieties

Three series of optically active photochromic copolymers, deriving from methyl methacrylate (MMA) and the chiral bisazoaromatic monomers (S)-3-methacryloyloxy-1-[4′-phenylazo-(4-azobenzene)]-pyrrolidine [(S)-MPAAP], (S)-3-methacryloyloxy-1-[4′-cyanophenylazo-(4-azobenzene)]-pyrrolidine [(S)-MPAAP-C] and (S)-3-methacryloyloxy-1-[4′-nitrophenylazo-(4-azobenzene)]-pyrrolidine [(S)-MPAAP-N], have been prepared and characterized in solution and in the solid state with the aim to evaluate the effect on their chiroptical and thermal properties originated by the insertion of inactive MMA groups along the main chain. The optical activity displayed by the bisazo polymers is discussed in terms of extent of chiral conformation assumed by the macromolecules as a consequence of dipole-dipole interactions between the bisazoaromatic chromophores.The photoinduction of birefringence has been assessed on thin films of the investigated copolymers in order to evaluate their behaviour as materials for optical data storage. The results are interpreted in terms of copolymer composition and conformational stiffness of the bisazoaromatic chromophoric co-units, which are responsible for the optical response rates, and are compared to those of the similar derivatives containing only one azo bond. The observed enhanced thermal properties and the temporal stability appear of interest for a potential use of these materials in nano technologies for all-optical data manipulation and in optoelectronics.     

Nanostructured tungsten oxide as photochromic material for smart devices,energy conversion,and environmental remediation

The reversible photochromic response of tungsten oxide (WO₃) holds promise for solar-related applications as it is capable of photo charging during illumination (color-switching) and spontaneous discharging post-illumination (self-bleaching). Advances in WO₃-based nanostructures synthesis via micro/nanofabrication techniques have created remarkable potential application opportunities. Smart windows represent a typical energy-saving technology; ultraviolet indicators can sense radiation safety limits, and the around-the-clock photocatalysts can be used for pollutant degradation and bacterial disinfection applications. These materials, their distinct properties, and the effects of their application must be comprehensively understood prior to commercialization. In this work, we first summarize the affiliation between the crystallographic properties-optical features-photochromic behavior of WO₃. Several photochromic models and kinetic equations are then presented, accompanied by the related characterization techniques and evaluation methods. The factors affecting photochromic efficiency (e.g., light absorption, surface reaction, and carrier migration) are delineated to clarify the advantages of the specific nanostructured WO₃ and the most efficient available strategies for constructing WO₃-based nanomaterials. The theory, technique, and performance associated with chromogenic applications in smart devices, energy conversion, and environmental remediation are deliberated in detail. Finally, we outline the challenges and emerging trends in this area calling for further innovation to fill various gaps.     

Structural, optical and photoelectric properties of ZnO:In and Mg x Zn1 −x O nanofilms prepared by sol-gel method

The photochromic sol-gel hybrid materials containing cyanoazobenzene chromophores were described. These materials were obtained by copolycondensation of the functionalized triethoxysilane and tetraethoxysilane precursor. They were deposited on glass substrates via spin coating and casting techniques to provide thin transparent films. The UV-vis spectroscopy showed reversibility of the trans-cis photoisomerization of the chromophoric fragments. The reversible change of refractive index of the films on illumination with white light was determined by ellipsometry. The difference of real part of the refractive index of the sample was in the range 0.0053–0.0075. Formation of diffraction grating was achieved by two beam coupling arrangement using a 532 nm laser. The diffraction efficiency for the first order diffraction was in the range of 2–3.5%. The kinetics of photochromic grating recording and erasing was described by biexponential function approach.     

Monitoring surface reactions optically in a self-assembled monolayer with a photochromic core

Photochromic aldehyde-substituted spiropyran molecules were incorporated in a self-assembled monolayer structure and the rate of imine formation was determined by the shift in absorbance for the photomerocyanine upon UV irradiation.     

Combined Optical/MCD/ODMR investigations of photochromism in doubly-doped Bi 12 GeO 20

Electron paramagnetic resonance is detected optically via the change of magnetic circular dichroism under microwaves at 35 v GHz. The technique is applied to Bi 12 GeO 20 samples co-doped with vanadium and a second transition metal (Cr, Mn, Co, Cu). The optical and magnetic properties of several paramagnetic defects (V Ge 4+ and Cr Ge 4+ ) are directly correlated. The basic photochromic processes occuring in samples doped with V, Mn, and Mn+V are explained. The V Ge 4+/5+ level is positioned roughly 2.2 v eV above the valence band.     

Preparation of photochromic polymers by stereospecific copolymerization of trans-4-(2-methacryloxyethyloxy)azobenzene and (−)-menthyl methacrylate

The synthesis is reported of a new photochromic monomer, trans-4-(2-methacryloxyethyloxy) azobenzene (MEAB), where the azobenzene chromophore is separated from the ester group by an ethylenoxy spacer arm. Comparative experiments show that trans-4-methacryloxyazobenzene (MAB), having the azobenzene group directly attached to the ester functionality, does not homopolymerize or copolymerize with (?)-menthyl methacrylate (MnMA) in the presence of different anionic initiators, whereas isotactic homopolymers and copolymers of MEAB can be obtained: the microstructure is described with reference to analogous atactic macromolecules.