Function by Switching: Heterodiazocines

Synthesis and the effect of alkyl chain length on photochromic properties of diarylethene derivatives

摘要： A new class of photochromic diarylethenes bearing pyrrole and thiophene units with different length of alkyl chains at 2-position of thiophene rings have been synthesized. Their characteristics, including photochromism and fatigue resistance were investigated systematically, and each diarylethene derivative showed good photochromic properties whether in solution or in PMMA films. The alkyl group moiety was connected directly to the central cyclopentene ring as a heteroaryl unit and availably participated in photoisomerization reaction. And some properties, for example, the conversion ratio in the photostationary state(PSS) and the absorption coefficient of the ring-closed isomers in acetonitrile were significantly affected by the alkyl chain length. The results revealed that substituents of alkyl chain played an important role in the photoisomerization process of diarylethenes.

Synthesis and photochromic properties of azobenzene-derived glycomacrolactones Chaoqi Lin,[a] Stéphane Maisonneuve,[a] Cyril Theulier,[a] and Juan Xie*[a]

摘要： Reversible photocontrol of glycosides and glycoconjugates structures is a very attractive approach to modulate, in a spatiotemporal way, the various properties and biological activities of carbohydrates. We have synthesized three new azobenzene-derived glycomacrolactones from thioglycopyranosides. The synthesized cyclic glycoazobenzenes can be reversibly photoisomerized between E and Z isomers with high fatigue resistance. 1H NMR study shows that E→Z isomerization of glycomacrocycles induces large conformational change of the macrocyclic structures, without changing sugar 4C1 chair conformation. The Z-glycoazobenzenes can be thermally converted back to the E-isomers. Interestingly, these 16 to 17-membered Z-glycomacrolactones display higher thermal stability than the reported macrocyclic azobenzenes, with the half-life varied from 37 to 72 days. The excellent photoswitching property and bi-stability of the synthesized glycoazobenenes open a new opportunity for the convergent synthesis of diastereomers of glycomacrocycles. Furthermore, chiroptical properties have been observed for both E and Z glycomacrolactones. The geometry of different isomers of macrocycles has been optimized with DFT calculations. Theoretical CD spectra obtained by TD-DFT suggest that the E and Z glycomacrocycles adopt preferentially (P) helical structure for the azobenzene moiety.

Photochromic properties in silver-doped titania nanoparticles

摘要： The Ag-doped TiO2 nanoparticles were synthesized at room temperature using a solution of titanium isopropoxide and silver nitrate as precursors. The inclusion of Ag in the nanocrystalline TiO2 lattice was systematically analyzed both from a morphological and a structural point of view. Raman spectroscopy, electron microscopy, electronic diffraction and x-rays allow us to testify that the dopant Ag does not modify the nanocrystalline anatase tetragonal structure of the nanoparticles, but causes a small distortion of the structure. UV–vis spectroscopy allowed to analyze the optical properties of the obtained nanoparticles. Kubelka Munk’s model allowed the interpretation of diffuse reflectance spectra. We have obtained a very different system from the hetero-system Ag-TiO2 described in the literature, but it shows an interesting photochromic behaviour. Ag-doped TiO2 nanoparticles darken and whiten under UV light and visible light, respectively, in a very fast way. A simple kinetic model has been used to process experimental data and describe the observed photochromic process and to determine the darkening and whitening constants.

A photochromic benzothiadiazole-diarylethene with tuneable on-off fluorescence modulation

摘要： Organic molecules with photoswitchable emission properties are of interest in the optical devices field. We present herein in-solution studies for two dimethoxy-DTE-fluorophore-conjugates with carboxylic acid anchor group attachable to semiconductor surfaces (DTE-BODIPY and BTD-DTE). Both conjugates show almost quantitative reversible photoisomerization between open (OF) and closed form (CF). With excitation of the fluorophores, both conjugates emit fluorescence with highly solvent dependent OFs (BTD-DTE > DTE-BODIPY) and minor solvent dependent CFs. In the polar solvent MeCN for BTD-DTE a TICT state is clearly observed, which will be located in the twisted conjugated structure of the benzoic acid-BTD-fluorophore-methoxy thiophene unit. BTD-DTE shows positive solvatofluorochromism with decrease of fluorescence quantum yields by increasing Δf verified in Lippert-Mataga plots. This leads to solvent dependent on-off/off-on (CF-OF) emission modulation by FRET with well-separated emission bands for BTD-DTE.

Light driven PVDF fibers based on photochromic nanosilica@naphthopyran fabricated by wet spinning

摘要： Photoresponsive polyvinylidene fluoride (PVDF) fibers doped with naphthopyran-functionalized silica nanoparticles (SiO2@NPT) were successfully prepared by dry–jet wet spinning. The incorporated photochromic nanomaterials, SiO2@S1 and SiO2@S2, were previously prepared by covalent post-grafting of the silylated NPTs – 2H-naphtho[1,2-b]pyran derivatives, S1 and S2 – onto nano-sized SiO2 (15 ± 3 nm). The morphological and chemical characterization of the resulting doped fibers PVDF@SiO2@S1 and PVDF@SiO2@S2 was evaluated by scanning electron microscopy with energy dispersive spectroscopy and Fourier transform infrared spectroscopy-attenuated total reflectance (FTIR-ATR). Both PVDF@SiO2@S1 and PVDF@SiO2@S2 fibers presented average diameters of 133 ± 8 μm and 98 ± 7 μm, respectively, and a porous outer surface. The presence of the SiO2@NPT within the fibers was confirmed through the observation of dense clusters embedded within the polymeric matrix. Furthermore, the FTIR-ATR spectra of the fibers revealed that the PVDF matrix was composed of α and β crystalline and amorphous phases. The PVDF@SiO2@S1 and PVDF@SiO2@S2 fibers showed photoresponsive properties under UV and sunlight irradiation, exhibiting fast coloration kinetics and good optical contrast (ΔE*ab = 7.2 and 15.1, respectively), and changing from a pale orange and an off-white color to a more intense yellow-orange and purple coloration, respectively, in less than 1 min. Moreover, they showed an initial fast bleaching, losing half of their color in less than 30 min (t1/2 = 28 and 20 min for PVDF@SiO2@S1 and PVDF@SiO2@S2 fibers, respectively), but displaying a residual coloration that took 1 and 2 h to return to the initial uncolored state (t3/4 = 95 and 49 min, respectively). The PVDF@SiO2@S2 fibers presented the best photochromic performance.

2 <i>H</i> -Naphthopyran-Based Three-State Systems: From Solution Studies to Photoresponsive Organic/Inorganic Hybrid Materials

摘要： Densely packed self-assembled monolayers with photoresponsive naphthopyrans attached to COOH headgroups on Si(111) were studied at the solid/inert-gas interface. We demonstrate that 2H-naphtho[1,2-b]pyrans are suitable three-state photochromic systems for solution and surface studies. Switching between three states on the surface was realized using UV light, thermal relaxation and visible light as trigger and release elements as analyzed by ATR-FTIR. Compared to solution studies, surface polarity and environmental effects, especially steric hindrance, contribute to state formation by stabilization of photoisomers, acceleration and deceleration of photochemical processes, and slowed down of thermal fading.

Multi-modulated photochromic behavior of a D-A type dithienylethene

摘要： The development of multiresponsive photochromic materials is of increasing interest for their potential application in the complicated chemical and biological environment. Here, a novel D-A type dithienylethene derivative NDM, in which dimethylamino group acted as both electron donor (D) and recognition moiety for H+, and the dicyanovinyl group functioned as electron acceptor (A) and responsed to cyanide anion, has been designed and synthesized. And its structure was confirmed by 1H NMR, 13C NMR and HRMS (ESI). As expected, dithienylethene NDM exhibited distinctive multi-modulated photochromic properties by solvent, acid and cyanide anion stimulation. Moreover, NDM can be acted as a potential fluorescent turn-on pH-sensor and colorimetric sensor for CN- in biological field.

Synthesis and photochromic properties of some N-phthalimide azo-azomethine dyes. A DFT quantum mechanical calculations on imine-enamine tautomerism and trans-cis photoisomerization

摘要： This paper presents synthesis, photophysical characterization and quantum mechanical calculations of some N-phthalimide azo-azomethine dyes. The dyes were synthesized via azo coupling reaction between 2,4-substituted aromatic anilines and salicylic aldehyde followed by condensation reactions between azo dyes and N-aminophtalimide. Quantum chemical calculations to optimise the molecular geometry and to determine the electron densities of the trans (E) imine ? enamine and the cis (Z) imine ? enamine isomers and their vibrational frequencies have been computed by using DFT at B3LYP/6–31 + G(d,p) level of theory in vacuo. The effect of the used DMF solvent on the molecular structure and bond energies has been determined by using the IEFPCM model. Thermodynamic parameters such as total electronic energy E(RB3LYP), enthalpy H298 (sum of electronic and thermal enthalpies), free Gibbs energy G298 (sum of electronic and thermal free Gibbs energies) and dipole moment μ were computed in order to estimate the ΔE, Δμ, ΔH, ΔG and ΔS values. The NBO analysis was performed in order to understand the intramolecular charge transfer and the energy of resonance stabilization. After molecular geometry optimization, the electronic spectra were obtained by TD-DFT calculations at the above mentioned basis set using the IEFPCM model of DMF as a solvent. The solvatochromic effect of the dyes in four solvents with different polarity has been studied by UV–VIS spectroscopy and compared with the theoretically predicted. The coincidence between measured and calculated spectra is satisfactory. The dynamic photoisomerization experiments were performed in DMF under irradiation with UV light at λ = 365 nm (mostly E → Z) and with VIS light at λ = 400–800 nm (mostly Z → E). The spectra were recorded in the spectral region from 300 to 800 nm at identical sample concentrations of the three dyes and illumination times in order to investigate the photodynamical E → Z → E conversion of the\N_N\chromophore group of the dyes as well as the imine ? enamine tautomerization.

Understanding the Microscopic Behavior of Binary Mixtures of Ionic Liquids Through Various Spectroscopic Techniques

摘要： In recent times it has been shown that certain binary mixture of pure ionic liquids having appropriate chemical composition can behave like a new chemical entity. However, current knowledge about the microscopic behavior of these interesting systems is rather limited. The present study is undertaken with an objective to understand the microscopic behavior in terms of intermolecular interaction, structure and dynamics of these systems. In the present study, few (IL+IL) mixtures are chosen with a common cation and a variation of anion. The investigations are also carried out by taking individual pure ILs so that the difference in behavior between pure IL and (IL+IL) mixtures are understood. Initially the systems have been investigated by studying the thermophysical properties of the concerned mixtures. Synergistic effect between combining pure ILs through photochromism has also been studied. These mixtures have been investigated further through steady state and time resolved fluorescence spectroscopy, electron paramagnetic resonance (EPR), nuclear magnetic resonance (NMR) and fluorescence correlation spectroscopy (FCS). Interestingly, time-resolved fluorescence data also pointed out that (IL+IL) mixtures are not only spatially heterogeneous but they are dynamically heterogeneous too. EPR measurements have suggested that the micro-polarity (ET(30)) of (IL+IL) mixture is close to aliphatic polyalcohol. Measurements of translational diffusion coefficients of the diffusing species through NMR and FCS studies have provided idea about the nano-structural organization within (IL+IL) binary mixtures. The analysis of data essentially reveals that the mixtures of ILs that are used in the current study do not behave like a non-ideal solution. The behavior of the IL mixtures is observed to be more like quasi-ideal type.