•We synthesized a ratiometric pH probe base on dicyanomethylene-4H-chromene..•We firstly reported pyrrolidine had a dual roles in this Knoevenagel condensation.•This probe showed high selectivity and sensitivity for pH variation (pH=2.44–6.00).•The probe was stable in the studied solvent within one month at room temperature.We report here a ratiometric pH probe (Z)−2-(2-(2-(4-hydroxyphenyl)−2-(pyrrolidin-1-yl)vinyl) −4H-chromen-4-ylidene)-malononitrile over the pH range of 2.44–6.00. It was synthesized by Knoevenagel Reaction from dicyanomethylene-4H-chromene and pyrrolidine. This is the first example of pyrrolidine as a part of the product structure in Knoevenagel condensation. High selectivity and sensitivity for pH variation were observed with significant fluorescent ratiometric responses and a remarkable Stokes shift (about 138 nm). The probe was stable in the studied solvent and no obvious fluorescence changes were detected in acidic media within one month at room temperature.Download high-res image (151KB)Download full-size image

We studied and compared the photophysical and aggregation-induced emission properties of three isomers: trans-1,2-di(9-anthryl)ethylene (DAE), trans-1-(9-anthryl)-2-(9-phenanthryl)ethylene (APE), and trans-1,2-di(9-phenanthryl)ethylene (DPE). Both DAE and APE molecules have a twisted conformation due to intramolecular H···H steric hindrance. By contrast, this kind of steric hindrance drastically decreases in DPE molecule. From DAE, APE, to DPE, there are a blue shift in the optical spectra and a marked increase in the fluorescence efficiency. Mainly due to the restriction of intramolecular rotation, DAE displays an aggregation-induced emission behavior. However, the fluorescence efficiency of APE decreases from solution to solid state. Different from DAE and APE, DPE is a dual-state highly-efficient chromophore. The fluorescence efficiencies of its solution and the as-prepared powder (DPE-α) are 60% and 81%, respectively. J-aggregate was observed in the crystal structure of DPE-α, which correlates with its high emission efficiency. Interestingly, a new metastable polymorph of DPE was unexpectedly obtained by a solvent-antisolvent rapid precipitation. This new polymorph displays vapour- and temperature-induced crystal-to-crystal phase transition and fluorochromism.Download high-res image (142KB)Download full-size image

Three (9-anthryl)vinylstyrylbenzene (ASB) position isomers were synthesized and compared. Substitution position affects temperature-induced polymorphism, crystal packing and crystallization-induced emission (CIE) properties. Different from 1,2-ASB and 1,4-ASB, 1,3-ASB undergoes a crystal-to-crystal phase transition upon heating. The crystal structure of a new phase (1,3-ASB-β) was successfully solved. Thus, the solid emission of 1,3-ASB could be tuned by polymorphism. In contrast, the solid emission of 1,4-ASB is controlled by its crystallinity. In the crystal structures of 1,2-ASB and 1,3-ASB-β, the adjacent interacting anthryls are inclined to adopt an edge-to-face configuration with C–H⋯π interactions. In contrast, the adjacent anthracene rings in the 1,4-ASB crystals are parallel to each other with π⋯π interactions. Furthermore, multiple intermolecular interaction modes such as C–H⋯π and H⋯H interactions coexist in the crystal structure of 1,4-ASB, which collectively results in a closer packing. Interestingly, 1,4-ASB displays CIE behaviour. In contrast, the emission of the other two isomers is quenched in the solid state. The effect of substitution position on the photophysical properties is systematically studied.

Despite the lack of typical electron donor and acceptor in the molecule structure, a pure aromatic hydrocarbon, trans,trans-1-(9-anthryl)vinyl-4-(1-pyrenyl)vinylbenzene (trans,trans-1,4-AVPVB), shows unusual fluorescence solvatochromism with emission shift over 80 nm. In addition, it displays an aggregation-induced emission (AIE) activity. For comparison, other three isomers, trans,trans-1,2-AVPVB, trans,trans-1,3-AVPVB, and trans,cis-1,4-AVPVB, were also synthesized. The effects of substitution position and vinylene bond geometry on solvatochromism, temperature-induced phase transition and AIE activity were systematically studied. Different from the other isomers, the as-prepared sample of trans,trans-1,2-AVPVB shows an endothermic peak and an exothermic peak before the melting point in the DSC curve. They correspond to a solid-to-gas transition and a solid-to-solid transition, respectively. Theoretical calculation indicates that the fluorescence solvatochromism may be related to the conformational change from the ground to the excited states. The solvatochromic degree is determined by conjugative effect. Trans,trans-1,2-AVPVB and trans,cis-1,4-AVPVB display moderate fluorescence solvatochromism. In contrast, the solvatochromic effect of trans,trans-1,3-AVPVB is weak due to meta-substitution. However, the conjugation interruption by meta-substitution is beneficial for solution emission, and trans,trans-1,3-AVPVB emits most efficiently in solution. Similar to trans,trans-1,4-AVPVB, trans,trans-1,2-AVPVB, and trans,cis-1,4-AVPVB also display an AIE behavior.

A new colorimetric and on–off fluorescence sensor based on diketopyrrolopyrrole (DPP) was synthesized for detection of fluoride anion. The sensor displayed a rapid responsivity and high selectivity and sensitivity towards F− over other anions, and it also exhibited a very low detection limit of 4.07 × 10−8 M. The signaling process was confirmed by UV-vis, fluorescence measurements as well as 1H and 19F NMR spectroscopy. The experimental results revealed that the formation of anionic species from deprotonation of the hydrazone N–H moiety by fluoride ion was responsible for the spectral changes. Density function theory calculations were conducted to rationalize the optical response of the sensor.

A series of diketopyrrolopyrrole (DPP) derivatives DPPPHs based on phenylhydrazone group were designed and synthesized. The presence of nitro moiety at ortho-position of phenylhydrazone in o-NO2-DPPPH and o,p-di-NO2-DPPPH significantly altered the electronic properties through intramolecular hydrogen bonding. Among these receptors, p-NO2-DPPPH showed excellent selectivity toward fluoride anions in both UV–vis and fluorescence channels in DMSO solution. Experimental results, 1H NMR and 19F NMR revealed that the formation of anionic species from deprotonation of the hydrazone N–H moiety by fluoride ion was responsible for the spectral changes. Density function theory calculations were conducted to rationalize the optical response of sensors. Especially, the spectral responses of sensors could be switched back and forth alternatively by adding F− and HSO4− anions in DMSO solution.

The different combinations of five benzene rings and two C═C double bonds yield four isomers: 4,4″-bistyryl-p-terphenyl (BSTP), 4-styryl-4′-[2-(p-biphenyl)vinyl]biphenyl (SBVB), 1-styryl-4-[2-(p-terphenyl)vinyl]benzene (STVB), and 1,4-bis[2-(p-biphenyl)vinyl]benzene (BBVB). The position variations of two C═C double bonds affect aggregate microstructures, as well as thermal and optoelectronic properties. Except BBVB, the other three isomers all have a phase transition upon heating. X-ray diffraction and optical absorption analyses reveal that the molecules of four isomers all take an H-aggregation in the crystalline solid. However, the microstructures are different for orientation disorder exists in STVB crystals. Both the absorption and emission spectra of these four isomers display a bathochromic shift when the position interval between two double bonds ranges from three, two, to one benzene rings. The CH2Cl2 solutions of these four isomers are highly emissive with quantum yields ranging from 83% to 96%. Intriguingly, though the molecules crystallize into an H aggregation, the quantum yields of polycrystalline samples are also extraordinarily high, from 73% to 94%. All the isomers display moderate hole-transport ability. Different-oriented grains coexist in the vacuum-deposited films, which play different roles in the carrier transport.

Three [(9-anthryl)vinyl][(9-phenanthryl)vinyl]benzene (APB) position isomers were synthesized and compared. The molecular configuration exhibits an extraordinary ability to affect polymorphism probability, unexpected solvatochromism, and aggregation-induced emission property. With the substitution changing from para-, ortho-, to meta-position, the polymorph number changes from 1, 2, to 3. Both 1,2-APB and 1,3-APB display a temperature-induced crystal-to-crystal phase transition. Furthermore, a pair of concomitant conformational polymorphs were obtained for 1,3-APB. Crystal structure analyses reveal that the steric hindrance between the two substituents leads to different molecular conformation and packing pattern. The unexpected solvatochromism is attributed to the strong electron-withdrawing ability of anthracene against phenanthrene, which produces permanent dipole moment. The solvatochromic degree is determined by the conjugative effect that varies with substitution position. 1,4-APB displays the most remarkable solvatochromic effect. Furthermore, it shows a totally different emission decay dynamics from 1,2-APB and 1,3-APB in polar solvents. Interestingly, the solution fluorescence quantum yields of these three isomers all increase with increased solvent polarity, displaying a negative solvatokinetic effect. Both 1,2-APB and 1,4-APB display an aggregation-induced emission enhancement. Although 1,3-APB is quenched in the solid state, it emits most efficiently among these three isomers either in solution or in solid state. The effect of the medium environment on the radiative process plays a vital role in determining their different aggregation-induced emission behaviors.

In order to explore new furan-based functional materials, investigate the effect of the degree of branching on their optoelectronic properties and search for three-dimensional organic semiconductors from planar π-conjugated molecules, the compounds 1,4-bis[2-(benzofuran-2-yl)vinyl]benzene (2BFVB) with a linear shape, 1,3,5-tris[2-(benzofuran-2-yl)vinyl]benzene (3BFVB) with a star shape and 1,2,4,5-tetra[2-(benzofuran-2-yl)vinyl]benzene (4BFVB) with a cruciform shape were synthesized and compared. 2BFVB adopts a two-dimensional herringbone packing motif and there are two kinds of molecular conformation. The crystal packing of 3BFVB is more sensitive to the crystallization conditions. Two single-crystal phases and one thin-film phase were found. 3BFVB (β-phase) molecules pack into a three-dimensional cofacial herringbone structure. 4BFVB forms an inter-inserted two-dimensional hexagonal packing structure. The molecular shape and aggregate packing exert remarkable effects on the optoelectronic properties. The quantum yield of 2BFVB is very high both in the solution (74%) and in the crystalline solid (76%) states. The high solid emission efficiency of 2BFVB is possibly related to the two molecular conformations in the herringbone-arranged H-aggregates. Both 2BFVB and 3BFVB display hole-transport abilities. The performance of 3BFVB amorphous film is nearly equal to that of its crystalline film, which would be helpful in simplifying device fabrication. This study shows that the substitution degree exerts drastic effects on solubility, polymorphism, crystal packing and optoelectronic properties.

The variation in the substitution position exerts a much more distinct influence on the solution optical properties of four NAB isomers, which leads to totally different emission behaviors.

Yttria-stabilized zirconia powders were prepared by the sol–gel method coupled with supercritical CO2 fluid-drying technology, using ZrOCl2·8H2O as the precursor, urea as the precipitant, and yttria as the stabilizer. The particles were characterized by X-ray diffraction, TEM and BET. The Co3O4/ZrO2(Y2O3) catalysts were prepared by the impregnation method. The content of cobalt was varied from 5 to 12 wt%. The prepared catalysts were calcined at 200–500 °C and the pretreating temperature was varied from 200–400 °C. The performance of CO catalytic oxidation was tested and the catalyst with 8% Co loading, calcined at 200 °C, and with a pretreating temperature of 300 °C, showed the highest catalytic activity. The temperature for 95% CO conversion was as low as 113 °C; and, the catalyst showed both good cycling stability and excellent long-term stability.

In order to explore new furan-based functional materials, investigate the effect of the degree of branching on their optoelectronic properties and search for three-dimensional organic semiconductors from planar π-conjugated molecules, the compounds 1,4-bis[2-(benzofuran-2-yl)vinyl]benzene (2BFVB) with a linear shape, 1,3,5-tris[2-(benzofuran-2-yl)vinyl]benzene (3BFVB) with a star shape and 1,2,4,5-tetra[2-(benzofuran-2-yl)vinyl]benzene (4BFVB) with a cruciform shape were synthesized and compared. 2BFVB adopts a two-dimensional herringbone packing motif and there are two kinds of molecular conformation. The crystal packing of 3BFVB is more sensitive to the crystallization conditions. Two single-crystal phases and one thin-film phase were found. 3BFVB (β-phase) molecules pack into a three-dimensional cofacial herringbone structure. 4BFVB forms an inter-inserted two-dimensional hexagonal packing structure. The molecular shape and aggregate packing exert remarkable effects on the optoelectronic properties. The quantum yield of 2BFVB is very high both in the solution (74%) and in the crystalline solid (76%) states. The high solid emission efficiency of 2BFVB is possibly related to the two molecular conformations in the herringbone-arranged H-aggregates. Both 2BFVB and 3BFVB display hole-transport abilities. The performance of 3BFVB amorphous film is nearly equal to that of its crystalline film, which would be helpful in simplifying device fabrication. This study shows that the substitution degree exerts drastic effects on solubility, polymorphism, crystal packing and optoelectronic properties.