Reversible color modulation of luminescent conjugated polymers based on a chemical redox mechanism and applications in rewritable paper and multiple information encryption.

Reversible color modulation plays a key role in the field of information recording and encryption, but for the common colorful conjugated polymer materials, currently a convenient method to achieve their reversible color modulation is still lacking. Herein, six luminescent conjugated polymers P1 to P6 were successfully designed and synthesized, all of which could realize reversible color modulation through a similar reversible chemical redox behavior accompanied by reversible color and fluorescence changes. The same absorption spectral changes as those under electrochemical redox conditions strongly confirmed that these polymers underwent reversible redox reactions in the Fe3+ and H2O system, which happened spontaneously according to the theoretical analysis of the reaction thermodynamics. Based on the reversible color modulation in the Fe3+ and H2O system, polymers P1, P2 and P3, with different colors (yellow, orange and red) and fluorescence emissions, were successfully applied as rewritable paper with multi-color and multi-fluorescence printing as well as long-term recording capabilities. Meanwhile, polymers P1, P4, P5 and P6, which showed similar green fluorescence and yellow color but different oxidation potentials, were also introduced to accomplish multiple encryption and decryption of information, based on the step-by-step selective oxidation of the four polymers by adjusting the concentration of Fe3+.

Multicolour Fluorescence Based on Excitation-Dependent Electron Transfer Processes in o-Carborane Dyads.

Organic materials with excitation wavelength-dependent (Ex-de) emission are highly attractive for anticounterfeiting, optoelectronics and bioassay applications; however, the realization of Ex-de fluorescence, independent of aggregation states, remains a challenge. We herein report a photoinduced electron transfer (PeT) strategy to design Ex-de fluorescence materials by manipulating the relaxation pathways of multiple excited states. As expected, the o-carborane dyad presents a clear Ex-de fluorescence colour in the aggregated states, resulting from the tunable relative intensity of the dual-fluorescence spectra. Taking TP[1]B as an example, the amorphous powders emitted bright blue-violet, white and yellow colours under 390 nm, 365 nm and 254 nm UV illumination, respectively. Importantly, multicolour, flexible and transparent films as well as an anticounterfeiting application using this o-carborane dyad are demonstrated.

Red to Near-Infrared Mechanochromism from Metal-free Polycrystals: Noncovalent Conformational Locks Facilitating Wide-Range Redshift.

Piezochromic organic materials that present a large difference in fluorescence wavelength in the near-infrared region have important potential applications; however, few such metal-free luminophores have been reported. In this study, we design and prepare π-conjugated electron acceptors whose planar conformation can be locked by the noncovalent interactions. The planar fused-ring geometry can narrow the optical band gap, enhance the molecular stability and rigidity, as well as increase the radiative rate. As expected, the polymorphs Re-phase and Ni-phase emit the high-brightness fluorescence with wavelength maxima (λem,max ) at 615 and 727 nm, respectively. Upon full grinding, the λem,max of Re-phase is bathochromically shifted to 775 nm. The ground powder of Re-phase becomes metastable as a consequence of noncovalent conformational locking and that the red to near-infrared (large colour difference) mechanochromism arises from the high degree of conformational coplanarity. This strategy is both conceptually and synthetically simple and offers a promising approach to the development of organic piezochromic materials with wide-range redshift and excellent penetrability.

Emission enhancement and high sensitivity of a π-conjugated dye towards pressure: the synergistic effect of supramolecular interactions and H-aggregation.

Piezoresponsive fluorescent (PRF) materials are highly promising for applications in deformation, flaw detection and haptic sensing. However, traditional PRF materials generally suffer from low sensitivity and fluorescence quenching processes. This study involved the preparation of H-aggregated dyes with weak supramolecular interactions, which showed enhanced emission under a low pressure.

Palladium-catalyzed allylation of aminophenol with alkynes to construct C-N bonds.

A method for the allylic alkylation of aminophenol with alkynes was developed using a palladium-catalysed allylation reaction with 100% atom economy. A series of structurally diverse N-allylic substituted allylamines were synthesized in good yields with high chemo-, regio-, and stereoselectivities under mild conditions.

Photo-irradiated E/Z isomerization reaction of star-shaped isomers containing two cyanostilbene arms with charge transfer excited states.

The E/Z isomerization reaction of the multi-cyanostilbene molecule is still not clear. Herein, we have designed and synthesized three star-shaped molecular isomers with a triphenylamine core linked to two cyanostilbene groups with E/Z isomerization, Z,Z-TPDCF, Z,E-TPDCF and E,E-TPDCF, possessing three different isomeric molecular configurations, to investigate the specific E/Z isomerization reaction of the cyanostilbene groups in the two molecular arms. The in situ UV, 1H NMR and HPLC spectra under UV-irradiation clearly showed that the E/Z isomerization reactions of both E,E-TPDCF and Z,Z-TPDCF firstly turned them into Z,E-TPDCF, and the Z,E-TPDCF was almost simultaneously turned into more E,E-TPDCF and less Z,Z-TPDCF due to the calculated lowest unoccupied molecular orbitals of Z,E-TPDCF on the cyanostilbene arm with the Z-configuration. In general, Z,E-TPDCF exhibited a relatively better configurational stability than Z,Z-TPDCF or E,E-TPDCF under the photo-irradiation conditions. Further research demonstrated that all three isomers exhibited excellent aggregation-induced emission (AIE) properties.

Ratiometric Piezochromism of Electrospun Polymer Films: Intermolecular Interactions for Enhanced Sensitivity and Color Difference.

Many piezochromic luminescent (PCL) dyes are known for their fluorescent switching capacity in the powdered phase, but they are usually difficult to utilize practically owing to poor mechanical properties. Herein, a nanofiber film fabricated through an electrospinning process is doped with PCL dye. The electrospun film not only reveals the mechanics of macromolecular materials, but also achieves precise, gradient pressure recognition (ratiometric PCL behavior). The PCL sensitivity and color difference of the dye in a crystalline state are calculated to be 15.7 nm GPa-1 and 149 nm, respectively. The sensitivity of an electrospun film containing 0.1 % (w/w) dye decreased to 3.6 nm GPa-1 . Moreover, the individual effects of molecular conformation and intermolecular interaction on the PCL properties have been clearly distinguished through in situ high-pressure experiments. Intermolecular interactions play a more significant role in PCL color difference and sensitivity. The film fabricated through an electrospinning process contributes to understanding of the working mechanism and real applications of piezochromic materials.

Highly Twisted Isomers of Triphenylacrylonitrile Derivatives with High Emission Efficiency and Mechanochromic Behavior.

Two novel triphenylacrylonitrile derivatives (TPAN-C2 and TPAN-C3) with highly twisted conformations have been successfully prepared by Suzuki coupling reaction. Both of them show mechanochromic (MC) fluorescent behaviour and exhibit remarkable fluorescence redshifts from sky-blue to light green upon fully grinding them. Interestingly, the ground powders recover their original states upon heating at 100 °C for 1 min or fuming with solvents vapour. Such intriguing MC properties of TPAN-C2 and TPAN-C3 are attributed to their phase transitions between crystalline and amorphous states, which are confirmed by powder X-ray diffraction (XRD) data. Moreover, the behaviour of both TPAN-C2 and TPAN-C3 indicates that the aggregation-induced emission (AIE) gives rise to rather high fluorescence quantum efficiencies (Φf ) of 0.78 and 0.97, respectively. The influences of stacking mode and molecular conformation on MC properties and the high Φf of TPAN-C2 and TPAN-C3 are discussed.

Proton-bound complex mediating retro-Michael-type fragmentation of protonated 3-substituted oxindoles in the Orbitrap high-energy collisional dissociation cell.

RATIONALE: Oxindole derivatives are valuable building blocks for indole chemistry. Systematically exploring the fragmentation behavior of the protonated 3-pyrazole-substituted oxindoles by kinetic methods combined with density functional theory (DFT) calculations is useful for further understanding their basic properties, and might provide some insights into their reactivity trends in synthesis and metabolism. METHODS: All high-resolution high-energy collision-induced dissociation tandem mass spectrometry (CID-MS/MS) experiments were carried out using electrospray ionization hybrid Quadrupole-Orbitrap mass spectrometry in positive ion mode. Theoretical calculations were carried out by the DFT method at the B3LYP level with the 6-311G (d, p) basis set in the Gaussian 03 package of programs. RESULTS: In the fragmentation of protonated 3-pyrazole-substituted oxindoles, the characterized protonated 3-(3-methyl-5-oxo-1H-pyrazol-4(5H)-ylidene)indolin-2-one derivatives and the protonated 5-methylpyrazolone were observed, which were proposed from the cleavage of the C(ß)-C(γ) bond in a retro-Michael reaction. With the kinetic plot, a linear correlation was established between the intensities of this two competitive product ions and the difference in proton affinities of the corresponding neutral molecules, which demonstrated that the retro-Michael reaction was mediated by a proton-bound complex. CONCLUSIONS: Using the kinetic method combined with theoretical calculations, a proton-bound complex mediating retro-Michael reaction was proposed for the fragmentation of protonated 3-pyrazole-substituted oxindoles in the high-energy collisional dissociation tandem mass spectrometry for the first time, which provided potential evidence to further understand their intrinsic bioactivities.

Synthesis of novel chiral tridentate Schiff-base ligands and their applications in catalytic asymmetric Henry reaction.

A series of chiral tridentate Schiff-bases were prepared and used as ligands in the catalytic asymmetric Henry reaction. Under the optimal conditions, a variety of arylaldehydes were smoothly converted into corresponding adducts with high yields (up to 98%) and excellent enantioselectivities (up to 97% ee).

Gold-catalyzed cascade reaction of hydroxy enynes for the synthesis of oxanorbornenes and naphthalene derivatives.

An efficient and selective gold-catalyzed cascade reaction for the synthesis of oxanorbornenes and naphthalene derivatives from easily prepared hydroxy enynes has been developed. Divergent products could be obtained from the same substrates by different gold catalytic systems.

Hiyama cross-coupling of arenediazonium salts under mild reaction conditions.

Palladium acetate [Pd(OAc)(2)]-catalyzed Hiyama cross-coupling of arenediazonium salts with organosilanes was found to generate biaryl products in high yields in alcoholic solutions. The simple and efficient protocol does not require any bases, ligands, or air/moisture. The transformation can tolerate either electron-donating or electron-withdrawing functional groups. Theoretical studies show that the transmetalation is the rate-limiting step for the cross-coupling reaction and both acetate and tetrafluoroborate anions may be involved in the direct reaction with the silicon atom.

Mass spectrometry analysis of terpene lactones in Ginkgo biloba.

Terpene lactones are a family of compounds with unique chemical structures, first recognised in an extract of Ginkgo biloba. The discovery of terpene lactone derivatives has recently been reported in more and more plant extracts and even food products. In this study, mass spectrometric characteristics of the standard terpene lactones in Ginkgo biloba were comprehensively studied using both an ion trap and a quadrupole time-of-flight (QTOF) mass spectrometer. The mass spectral fragmentation data from both techniques was compared to obtain the mass spectrometric fragmentation pathways of the terpene lactones with high confidence. The data obtained will facilitate the analysis and identification of terpene lactones in future plant research via the fragmentation knowledge reported here.

Pd-catalyzed synthesis of beta-biarylacryl ferrocenes via Suzuki cross-coupling.

Some novel beta-biarylacryl ferrocene derivatives were synthesized via Pd-catalytic Suzuki cross-coupling reactions of beta-(2-bromophenyl)acrylferrocene and arylboronic acids. The structures were determined with elemental analyses, IR spectra, and (1)H-NMR spectra.