Multicolor Fluorescence Writing Based on Host–Guest Interactions and Force‐Induced Fluorescence‐Color Memory

A new strategy is reported for multicolor fluorescence writing on thin solid films with mechanical forces. This concept is illustrated by the use of a green‐fluorescent pentiptycene derivative 1 , which forms variably colored fluorescent exciplexes: a change from yellow to red was observed with anilines, and fluorescence quenching (a change to black) occurred in the presence of benzoquinone. Mechanical forces, such as grinding and shearing, induced a crystalline‐to‐amorphous phase transition in both the pristine and guest‐adsorbed solids that led to a change in the fluorescence color (mechanofluorochromism) and a memory of the resulting color. Fluorescence drawings of five or more colors were created on glass or paper and could be readily erased by exposure to air and dichloromethane fumes. The structural and mechanistic aspects of the observations are also discussed.     

Why do flavylium salts show so various colors in solution?: Effect of concentration and water on the flavylium’s color changes

When synthesized flavylium salts (FVs) were allowed to stand in an acetonitrile–water mixture, the color of the solutions changed from yellow to red via green. This color change in FV solution has been studied by observing the change in UV–VIS absorption spectra. In particular, change in the color from green to red depends on the concentration of FV and an amount of water. The solution color, however, changed from red to green on dehydration of the solution. It is concluded that water molecules are responsible for the change in solution color from green to red and the change is due to dimerization and/or aggregation of FVs.     

Preparation, structure, and unique redox properties of mono-, bis-, and Tris(diarylmethylene)-1,3,5-trithianes and related compounds

A series of 1,3,5-trithianes 1-3 having diarylmethylene units were designed as novel electron donors giving highly colored cationic species upon oxidation. They were prepared along with the dithiane and dithiazine derivatives 4-6 by the reactions of lithiated heterocycles with diaryl ketones followed by dehydration. Voltammetric analyses indicate that a large structural change and/or transannular bonding are induced during their electrochemical oxidation. Mono(diarylmethylene) derivative 1a exhibits electrochromism with vivid change in color from faintly yellow to deep blue with concomitant rotation around the exocyclic bond. Both of the strongly colored salts obtained upon oxidation of 2,4-bis- and 2,4,6-tris(diarylmethylene)-1,3,5-trithianes (2aa and 3) consist of the dications with a 1,2,4-trithiane ring, suggesting the easy skeletal rearrangement of the transannular dications with a trithiabicylo[3.1.0]hexane ring. Upon reduction of these salts were obtained bright yellow 12 and 13, respectively, with high electron-donating properties due to the tetraarylbutadiene-type conjugation, thus giving another class of electrochromic compounds.     

Thermochromism in polydiacetylene solutions

A novel planar ? nonplanar visual thermochromic conformational transition of polydiacetylene molecules in poor solvents is reported. The conformational transition is associated with both a color change (blue or red ? yellow) and a change in the state; the yellow solution (liquid) transforms to a blue or red gel (solid). The color transition occurs within a narrow range of temperature and has a large associated hysteresis. The enthalpy of the conformational transition is 29 kJ/mole of repeat unit. Fourier-transform infrared studies show that molecules acquire a planar conformation in red or blue gels by formation of intramolecular H bonds between the adjacent substituent groups. Virtually all H bonds break (a nonplanar conformation) when the gels turn into yellow solutions.     

A new class of platinum (II) vapochromic salts

Luminescent chloride and hexaflurophosphate salts of Pt(Me2bzimpy)Cl+ (Me2bzimpy = 2,6-bis(1-methylbenzimidazol-2-yl)pyridine) are reported. As solids, both compounds are vapochromic, undergoing pronounced and reversible changes of color and emission in the presence of volatile organic compounds. The chloride salt responds to vapors of methanol, chloroform, ethanol, and acetonitrile, undergoing a distinct change in color from yellow to red within seconds. The PF6- salt responded selectively to acetonitrile vapor, changing from yellow to violet while sorbing 1.0 +/- 0.1 equiv. For either salt, leaving vapor-exposed samples in air for several days or heating for several minutes restored the original color. UV-visible absorption spectra and solid-state room temperature and 77 K emission spectra are reported, and the accumulated data are consistent with a decrease in Pt...Pt separation accompanying vapor sorption.     

Remarkable ESIPT induced NIR emission by a selective colorimetric dibenzimidazolo diimine sensor for acetate

A new dibenzimidazolo diimine sensor (DDS) has been designed and synthesized for selective detection of acetate ion. Significant naked eye recognized color change of DDS solution from light yellow to pink upon addition of only acetate ion is accompanied with near infra red (NIR) emission exploiting excited state intramolecular proton transfer (ESIPT).     

BODIPY based colorimetric fluorescent probe for selective thiophenol detection: theoretical and experimental studies

A BODIPY-based selective thiophenol probe capable of discriminating aliphatic thiols is reported. The fluorescence off-on effect upon reaction with thiol is elucidated with theoretical calculations. The sensing of thiophenol is associated with a color change from red to yellow and 63-fold enhancement in green fluorescence. Application of the probe for selective thiophenol detection is demonstrated by live cell imaging.     

Multicolor saccharide-sensing chips based on boronic acid-containing thin films showing stepwise release and binding of dyes

A novel saccharide sensor that shows a distinct color change resembling a "traffic signal" was developed. By copolymerizing a boronic acid monomer and an amine monomer on a glass plate, a boronic acid-containing thin film was obtained. After adsorbing anionic blue and yellow dyes, the thin film was immersed in aqueous saccharide solutions containing a cationic red dye. As saccharide concentration increased, the thin film changed its color from green to red via yellow. Origin of the distinct color change was attributed to a stepwise release and binding of dyes.     

Comparative Studies on the Quick Recognition of Melamine Using Unmodified Gold Nanoparticles and p‐Nitrobenzenesulfonic Grafted Silver Nanoparticles

Both unmodified gold nanoparticles (AuNPs) and p‐nitrobenzenesulfonic (p‐NBS) grafted silver nanoparticles (AgNPs) were prepared by chemical synthesis, respectively. They could be used for visual detection via the interaction with the twelve amide compounds including melamine. These color changes could be seen with the naked eye directly and monitored by ultraviolet visible (UV‐Vis) absorbance spectra. The recognition mechanism for both nanoparticles was comparatively investigated by the addition of glutathione (GSH) in the presence of melamine, respectively. The triple hydrogen bonding recognition and the attractive van der Waals interactions between melamine (0.5 mg/L) and AuNPs were responsible for the color change during its aggregation (red‐to‐purple or blue), whilst the electron donor‐acceptor interaction between melamine (0.2 mg/L) and p‐NBS modified on the surface of AgNPs resulted in the color changes (yellow‐to‐grey or dark green).     

Modulation of color changing paths for flavylium salts by solvent and concentration

The modulations of the color changing paths for flavylium salt (2-phenylbenzopyrilium, abbreviated as FV) by solvent and their concentrations have been studied by observing changes in the UV-Vis absorption spectra. The feature of the spectral changes varies with the solvent and solution FV concentration. The color of the solutions in ethanol at high concentration changed from yellow to red via green. It has been proposed that the yellow, green, and red species of FV are a monomer, a monomer with charge-transfer character, and a dimer and/or aggregate of FV, respectively. The spectral changes showed different behaviors in different solvents. In ethanol solution with a low concentration, a chalcone was generated by nucleophilic addition. The PM3 calculation revealed a new reaction path where the green FV is converted to a chalcone in propylene glycol. The color changing paths for FVs were able to be modulated in different solvents and by their concentration change. The previous proposed scheme well explained the experimental results in various solvents.     

Tunable multicolor pattern and stop-band shift based on inverse opal hydrogel heterostructure

The inverse opal hydrogel heterostructure (polyacrylamide (PAAm) (left side)-polyacrylic acid (PAA)/PAAm interpenetrating polymer network (IPN) (right side) is created by colloidal crystal templating. The two parts, PAAm and IPN, appear different structural colors due to the varied lattice constants and solvent response behaviors. The IPN part keeps red color and PAAm part shows different colors when the composition of the mixed solvent (ethanol and water) and crosslinking degree are changed. For example, as the ethanol content in the mixed solvents increases from 0% to 70%, the PAAm part color changes from red, yellow, green to blue when the PAAm crosslinking degree is 5 mol% or 1 mol%. Meanwhile, a large blue shift of about 200 nm can be realized covering almost the entire wavelength of visible light due to the decreased lattice spacing induced by the PAAm shrinkage. Thus, multi two-color patterns can be realized by changing the color of PAAm and the color of IPN remain red as background for contrast. Moreover, the IPN part can change from red to green by reducing the PAAm infiltration time in IPN part, which can realize the change from two-color pattern to one-color pattern at green region.     

Solid-state thermochromism and phase transitions of charge transfer 1,3-diamino-4,6-dinitrobenzene dyes

The lower 1,3-bis(hydroxyalkylamino) homologues of the strong intramolecular X-type charge transfer (CT) system 1,3-diamino-4,6-dinitrobenzene (DADNB) exhibit reversible color change in the solid state from yellow at room temperature (RT) to orange and red at high temperature (HT). To investigate the structural prerequisites for occurrence of this phenomenon, we prepared 10 new derivatives of DADNB where the hydroxyalkyl arms at the amino groups were replaced with substituents having different electronic and steric profiles. Two of the new materials exhibit sharp and reversible thermochromic change in the solid state: when heated, the bis(aminoethyl) derivative (DADNB-1) undergoes color change from orange-red to brown, while one of the three polymorphs of the bisphenyl product (DADNB-2) changes its color from red to yellow. The physicochemical analysis and the crystal structures of seven of these compounds, one of which is trimorphic, confirmed that both phenomena are due to solid-solid phase transitions. The brown high-temperature phase of DADNB-1 presents the first example where the absorption is shifted beyond the red region. Form C of DADNB-2 is the first material of this group that exhibits "negative" thermochromism, where the high-temperature phase absorbs at lower wavelength than the low-temperature one. The results demonstrate the potentials of these simple and easily accessible organic molecular materials for thermal switching of the optical properties by utility of intermolecular interactions to modulate the intramolecular CT.     

Colorimetric and bare-eye detection of alkaline earth metal ions based on the aggregation of silver nanoparticles functionalized with thioglycolic acid

We describe a simple and rapid method for colorimetric and bare-eye detection of the alkaline earth metal ions Mg(II), Ca(II), Sr(II) and Ba(II) based on the use of silver nanoparticles (AgNPs) functionalized with thioglycolic acid (TGA). The TGA ligand was self-assembled onto the AgNPs to form a probe that undergoes a color change from yellow to orange or red on exposure to the alkaline earth ions. It is presumed that the color change is a result of the aggregation of the AgNPs caused by the interaction of the bivalent ions with the carboxy groups on the AgNPs. The color change can be used for bare-eye and colorimetric determination of the alkaline earth metal ions, for example to rapidly determine water hardness.

Single chemosensor for highly selective colorimetric and fluorometric dual sensing of Cu(II) as well as ‘NIRF’ to acetate ion

A novel fluorescent probe for the copper(II) ion in mixed aqueous media, based on fluorescence quenching mechanism with noticeable color change from light to dark yellow, was designed and synthesized. It also exhibited high selectivity for acetate in acetonitrile over other common anions in the near infrared region (NIR) accompanied with exciting color changes from light yellow to pink. Hence sensor 1 ascertains its dual chemosensing ability toward Cu(II) and acetate ions as evidenced by competitive experiments.     

Core-substituted naphthalene bisimides: new fluorophors with tunable emission wavelength for FRET studies

Highly colored and photoluminescent naphthalene bisimide dyes have been synthesized from 2,6-dichloronaphthalene bisanhydride 1 by means of a stepwise nucleophilic displacement of the two chlorine atoms by alkoxides and/or alkyl amines. The alkoxy-substituted derivatives are yellow dyes with green emission and low photoluminescence quantum yields, whereas the amine-substituted derivatives exhibit a color range from red to blue with strong photoluminescence up to 76%. Structure-property relationships for this class of two-dimensional chromophores were evaluated based on a single-crystal X-ray analysis for dye 5a, the observed solvatochromism, and quantum-chemical calculations. Owing to the simple tuning of the absorption properties over the whole visible range by the respective substituents, the pronounced brilliancy, and the intense photoluminescence, this class of dyes is considered to be highly suited for numerous applications such as fluorescent labeling of biomacromolecules and light-harvesting in supramolecular assemblies. As an important step towards such applications efficient FRET (fluorescence resonance energy transfer) has been demonstrated for a covalently tethered bichromophoric compound that contains a red and a blue naphthalene bisimide dye.     

12-钼磷酸与聚乙烯醇固容体的光致变色及其稳定性

以ESR,XPS,IR和UV-vis等手段,研究12-钼磷酸与聚乙烯醇黄色固容体的光致变色及其稳定性。由测试结果得知,该固容体的光致变蓝色是因其在紫外光照射下的光化学反应产物多价钼(VI,V,IV)配合物呈蓝色,而另一种产物带部分羰基的聚乙烯醇为无色所致。随着它们的生成,后者产物因具有螺旋状结构能与前者产物发生包合作用,从而提高光致变色的稳定性。     

A highly selective and colorimetric naked-eye chemosensor for Cu2+

A sample and practical colorimetric naked-eye chemosensor 3-nitro-4-ethylenediamido-nitrobenzene (2) for metal cations was designed and synthesized. It displays high selectivity and sensitivity for Cu2+ by the UV absorption which appeared a new peak at 525 nm and color change from yellow to red by naked-eye in CH3OH/H2O pH 7.6.     

A qualitative and quantitative color reaction for pyridoxal with sulfuric acid

The carbonyl-phenol-acid reaction system yields color reactions with phenols, carbonyl compounds (aldehydes and ketones), and inorganic acids. 'I'o test for one of the components of this reaction system, the remaining two components constitute the specific reagents.The four related compounds, pyridoxine, pyridoxamine, pyridoxal, and pyridoxic acid each possess a phenolic hydroxyl. Pyridoxal possesses an aldehyde group in addition to the phenolic hydroxyl. Pyridoxal yields an intense yellow color on treatment with concentrated sulfuric acid. Pyridoxine, pyridoxamine and pyridoxic acid prove not to be chromogenic on treatment with concentrated sulfuric acid. Pyridoxal can therefore be differentiated by means of the sulfuric acid reaction from the other three compounds related to vitamin B₆.The colored product obtained by the interaction of pyridoxa1 and concentrated sulfuric acid yields a characteristic absorption spectrum and follows the Beer-Lambert law in the concentrations of pyridoxal tested (l0—100 μg).