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Towards More Effective, Reversible pH Control by Visible Light Alone: a Thioindigo Photoswitch Undergoing a Strong pKa Modulation by Isomer Specific Hydrogen Bonding
摘要： We have synthesized and characterized a thioindigo photoswitch featuring phenolic residues forming an intramolecular H bond exclusively in the cis isomer. In acetone water mixtures, wavelength dependent photostationary states their extremes of up to 95 % and down to 11 % cis isomers at ca. 580 and 480 nm, respectively. Within a few hours, room temperature thermal isomerization is negligible in neutral and mildly acidic solutions. Protic media decrease trans→cis but increase cis→trans quantum yields. In CD3OD solution, in which light of any wavelength absorbed triggers the latter process almost exclusively, 19F NMR titration provides pKa values of 7.2 (trans) and 5.0 (cis; both rescaled to water) corresponding to a change in dissociation constant of 2.2 orders of magnitude. Future derivatives featuring solubility and reversible photochromism in plain water may provide pH modulation of similar amplitude in a range adjustable by the choice of phenolic substituents.
关键词： thioindigo,acidity,kinetics,hydrogen bonds,photochromism
更新于2025-09-23 15:21:01
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Photo-electrochemical Behavior of Silver Nanoparticles inside Mesoporous Titania: Plasmon induced charge separation effect
摘要： The self-assembly block copolymer method was used to synthesize mesoporous titania films and silver nanoparticles (NPs) were grown inside the films. Such silver NPs-titania films are known for their multicolor photochromic properties, due to a photo-oxidation reaction of silver in the presence of titania under light excitation which is attributed to a plasmon induced charge separation (PICS). Here, the photo-electrochemical properties of these composite films have been investigated at different light wavelengths and chemical environment in order to characterize the light-induced redox reactivity modifications. Cyclic voltammetry (CV) study shows that the Ag+ electro-reduction peak potential varies depending on the light irradiation, which determines the state of the silver nanoparticles complexed or not by titania.
关键词： cyclic voltammetry,Silver nanoparticles,photochromism,plasmon,mesoporous titania
更新于2025-09-19 17:15:36
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Synthesis, crystal structure and photochromic property of a phenethyl viologen bismuth(III) chloride
摘要： Viologen bismuthate halides generally show photochromic properties. In the present work, phenylethyl alcohol was introduced into chloro bismuthates in the hope to prepare photochromic crystalline materials and finally a photochromic inorganic-organic hybrid, (PeV)3(Bi2Cl9)2 (1), based on (PeV2+ = phenethylviologen = N,N′-diphenethyl-4,4′-bipyridinium), has been obtained, whose microstructure contains a discrete dimer [Bi2Cl9]3– counterion identified by single crystal X-ray diffraction. More importantly, 1 exhibits a typical photochromic behavior, which can be mainly attributed to the reversible inter-conversion between the monocation viologen radical [PeV]+? and the viologen dication [PeV]2+.
关键词： π–π Interactions,Inorganic-organic hybrids,Photochromism,Phenethyl viologens
更新于2025-09-19 17:15:36
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Light-wavelength-based Quantitative Control of Dihydrofolate Reductase Activity Using Photochromic Isostere of Inhibitor
摘要： Photopharmacology has attracted research attention as a new tool to achieve the optical control of biomolecules following the methods of caged compounds and optogenetics. We have developed an efficient photopharmacological inhibitor, azoMTX, for Escherichia coli dihydrofolate reductase (eDHFR) by replacing some atoms of the original ligand, methotrexate, to obtain the photoisomerization property. This fine molecular design enabled the quick structural conversion between the active 'bent' Z-isomer and the inactive 'extended' E-isomer of azoMTX, and this property afforded quantitative control of the enzyme activity, depending on the wavelength of irradiated light. The real-time photoreversible control of enzyme activity was also achieved.
关键词： methotrexate,photochromism,enzymes,azobenzene,photopharmacology
更新于2025-09-19 17:15:36
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Rewritable Optical Patterns in Light Responsive Ultra High Molecular Weight Polyethylene
摘要： Spiropyran is used as a photochromic dye to create colored patterns in highly drawn ultra high molecular weight polyethylene (UHMW PE) films. The dye is incorporated in highly crystalline, drawn UHMW PE tapes and fibers and isomerizes to its merocyanine state upon UV light irradiation, resulting in a color change from transparent to purple. The isomerization from merocyanine to spiropyran to erase the color can be simply induced using heat or a green LED light. The combination of the use of a mask and the reversibility of the isomerization results in colored patterns which can be written, erased and re-written using UV light and heat or green LED light.
关键词： Polymer fibers,ultra high molecular weight polyethylene,photochromism,light responsive materials,rewritable optical materials,spiropyran
更新于2025-09-19 17:15:36
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Rational Molecular Design for Controlling Photochromism Involving Thermally-Activated Valence Isomerization of Phenoxyl-Imidazolyl Radical Complexes
摘要： We report a strategy to control the reversible photoinduced valence isomerization between a biradical and a quinoidal form based on a photochromic phenoxyl-imidazolyl radical complex (PIC) framework. The thermal equilibrium of the valence isomerization is biased toward the biradical form by substituting the π-conjugated substituents and the electron-donating groups, while the equilibrium is biased toward the quinoidal form by twisting the substituting group at the 2-position of the imidazole ring. The precise control of the reversible photoinduced valence isomerizations is especially important for fundamental spin chemistry. Moreover, because biradicals have several fascinating properties such as initiators for polymerizations, broad absorption in visible and near infrared regions, and large two-photon absorption cross section, light- and time-gated open-shell characteristics would stimulate to develop further photofunctional materials utilizing biradicals.
关键词： open shell,Photochromism,biradical,quinoid,photofunctional
更新于2025-09-19 17:15:36
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Thiophenylazobenzene - an alternative photoisomerization controlled by lone pair???π interaction
摘要： Azoheteroarene photoswitches have attracted attention due to their unique properties. We present here the stationary photochromism and the ultrafast photoisomerization mechanism of thiophenylazobenzene (TphAB) – an alternative sulfur-based azoheteroarene design. TphAB demonstrates impressive fatigue resistance and photoisomerization efficiency, and shows favorably separated (E)- and (Z)-isomer absorption bands, allowing for highly selective photoconversion. The (Z)-isomer of TphAB adopts an unusual orthogonal geometry where the plane of the thiophene is perfectly perpendicular to that of the benzene. This geometry is stabilized by a rare lone pair???π interaction between the S-atom and the benzene. The photoisomerization of TphAB occurs on the sub-ps to ps timescale and is governed by the lone pair???π interaction. Therefore, the adoption and disruption of the orthogonal geometry requires significant movement along the inversion reaction coordinates (CNN and NNC angles). Our results establish TphAB as an excellent photoswitch with versatile properties that expand the application possibilities of AB derivatives.
关键词： time-resolved spectroscopy,photochromism,photoswitch,thiophenylazobenzene,isomerization mechanism
更新于2025-09-19 17:13:59
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Positional Isomerism Controlled Electronic and Photochromic Properties of Naphthalene Diimide-Based Chlorozincate Hybrids
摘要： Two organic-inorganic hybrids, [3-H2DPNDI][ZnCl4]·0.5H2O (1) and [4-H2DPNDI][ZnCl4]·0.5H2O (2) (3-H2DPNDI2+ = protonated N, N-di(3-pyridyl)-1,4,5,8-naphthalene diimide, 4-H2DPNDI2+ = protonated N, N-di(4-pyridyl)-1,4,5,8-naphthalene diimide), have been designed and prepared. Compounds 1 and 2 are constructed from typical [ZnCl4]2- inorganic clusters and positional isomeric organic cations of [H2DPNDI]2+, which are assembled into different 3-D supramolecular networks via different anion-π interactions and hydrogen-bonding interactions. Photochromism of 1 and non-photochromism of 2 are attributable to the usage of positional isomers, which lead to the different spatial stack of [ZnCl4]2- donors and [H2DPNDI]2+ acceptors, suggesting delicate modulating effect of the distinct interfacial contacts on the intermolecular charge transfer/electron transfer and consequently photoresponsive behaviors.
关键词： organic-inorganic hybrids,positional isomerism,anion-π interactions,chlorozincate,photochromism,naphthalene diimide
更新于2025-09-16 10:30:52
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Photoinduced Reversible Modulation of Fluorescence of CdSe/ZnS Quantum Dots in Solutions with Diarylethenes
摘要： Steady-state absorption and fluorescence spectra, fluorescence decay kinetics of CdSe/ZnS quantum dots (QD) with photochromic diarylethenes (DAE) in toluene have been studied. Two kinds of QDs emitting at 525 and 600 nm were investigated and DAE were selected to ensure good overlap of their photoinduced absorption band with QDs emission spectra. It has been found that photochromic molecules form complexes with QD which results in partial fluorescence quenching. A reversible modulation of QDs emission intensity which correlates with magnitude of transient photoinduced absorption band of the diarylethenes during photochromic transformations has been demonstrated.
关键词： Photochromism,Nanophotoswitches,Quantum dots,Diarylethenes
更新于2025-09-12 10:27:22
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Thiophenylazobenzene – an alternative photoisomerization controlled by lone pair???π interaction
摘要： Azoheteroarene photoswitches have attracted attention due to their unique properties. We present here the stationary photochromism and the ultrafast photoisomerization mechanism of thiophenylazobenzene (TphAB) – an alternative sulfur-based azoheteroarene design. TphAB demonstrates impressive fatigue resistance and photoisomerization efficiency, and shows favorably separated (E)- and (Z)-isomer absorption bands, allowing for highly selective photoconversion. The (Z)-isomer of TphAB adopts an unusual orthogonal geometry where the plane of the thiophene is perfectly perpendicular to that of the benzene. This geometry is stabilized by a rare lone pair???π interaction between the S-atom and the benzene. The photoisomerization of TphAB occurs on the sub-ps to ps timescale and is governed by the lone pair???π interaction. Therefore, the adoption and disruption of the orthogonal geometry requires significant movement along the inversion reaction coordinates (CNN and NNC angles). Our results establish TphAB as an excellent photoswitch with versatile properties that expand the application possibilities of AB derivatives.
关键词： photochromism,time-resolved spectroscopy,thiophenylazobenzene,isomerization mechanism,photoswitch
更新于2025-09-11 14:15:04