Rizhe Jin

Ultrasound-promoted chiral fluorescent organogel

In this paper, we have described a chiral binaphthyl-based fluorescent organogel. Very interestingly, similar to sonocrystallisation of organics, ultrasound can promote the gelation while it cannot occur spontaneously at relatively high temperature or low concentration. The fluorescence enhancement of the gel obtained via ultrasound irradiation is observed. In solution there exist rapid dynamic equilibria between (S)-1 oligomers. The association interactions both between gelator molecules and between solvent and gelator molecules could together effect the helical growth of distorted (S)-1nanocrystals. The dihedral angle between the two naphthyl rings of the 1,1′-binaphthyl unit in (S)-1 will increase upon gelation. It has been assumed that ultrasound can play an important role in gelation with a high energy barrier. Sonication-induced gelation is a rapid crystallisation behavior yielding fiber-like aggregates in a metastable system.

Sulfonated polyimides containing 1,2,4-triazole groups for proton exchange membranes

A series of sulfonated polyimide copolymers as novel proton exchange materials were synthesized by the polycondensation of 1,4,5,8-naphthalene-tetracarboxylic dianhydride (NTDA), sulfonated diamine based on pyridine group and diamine containing N-phenyl-1,2,4-triazole moiety. Flexible, transparent and tough membranes with high thermal stability and good mechanical properties were obtained. They exhibited good stability in boiling water and Fenton’s reagent at 80 °C. More interestingly, a nonlinear relationship between proton conductivities of the resulting membranes and the degree of sulfonation (DS) was observed. The membrane with 50% DS exhibited the maximum proton conductivity, which was due to the combinational contributions of sulfonic acid and N-pheny-1,2,4-triazole groups. Thus, the N-phenyl-1,2,4-triazole moiety in this study not only can depress water absorption but also increase proton conductivity, especially at low DS.

Synthesis of 3,3′‐Di(2‐Pyridyl)‐1,1′‐Bi‐2‐Naphthol Derivatives

Abstract A new kind of (S)‐3,3′‐dipyridyl BINOLs (3a–d) with C 2‐symmetry were synthesized in 79–84% yields by Suzuki coupling of the diboronic acid dipinacol ester (S)‐1 containing a (S)‐binaphthyl group with bromopyridine derivatives (2a–d) followed by hydrolysis.

In situ iodoalkane-reduction of graphene oxide in a polymer matrix: an easy and effective approach for the fabrication of conductive composites

In situ chemical reduction (ISCR) of graphene oxide (GO) dispersed in a polymer matrix has been regarded as an effective path to fabricate electrically conductive graphene/polymer composites due to the combination of perfect dispersion of GO in a polymer matrix and high electrical conductivity of graphene. However, there are only very limited number of reducing agents that can be applied to the ISCR process for the fabrication of graphene/polymer composites. Herein, we report a highly efficient reducing agent, 1,2-diiodoethane, which can be used in the preparation of graphene (IGO)/polyimide (PI) composites via the ISCR process. The results showed that the electrical conductivity of IGO/PI composites with 2.5 wt% of IGO was 2.22 S m−1, nearly seven orders of magnitudes higher than that of GO/PI without the addition of 1,2-diiodoethane. Moreover, the tensile strength and modulus of IGO/PI composites were increased by about 43% and 52% as compared with that of the pure PI, respectively. Furthermore, 1,2-diiodoethane and its decomposition products would not remain in the composites. The ISCR-based methodology can be extended to many other polymer composites and thus paves the way for easy and effective fabrication of conductive polymer composites.

An Optically Active Polymer for Broad-Spectrum Enantiomeric Recognition of Chiral Acids

Recognition of enantiomers of chiral acids by anion-π or lone pair-π interactions has not yet been investigated but is a significant and attractive challenge. This study reports an optically active polymer-based supramolecular system with capabilities of discriminating enantiomers of various chiral acids. The polymer featuring alternate π-acidic naphthalenediimides (NDIs) and methyl l-phenylalaninates in the backbone exhibits an unprecedented slow self-assembly process that is susceptible to perturbation by various chiral acids. Thus, the combination of anion-π or lone pair-π interactions and sensitivity of the polymeric self-assembly process to external chiral species endows the system with recognition capabilities. This is the first time that anion-π or lone pair-π interactions have been applied in the recognition of enantiomers of various chiral acids with a single system. The results shed light on new strategies for material design by integrating π-acidic aromatic systems and chiral building blocks to afford relevant advanced functions.

Ni-Catalyzed cross coupling of aryl grignard reagents with aryl halides in a nonpolar solvent and an efficient synthesis of biaryls under neat conditions

This study details Ni-catalyzed cross coupling of aryl Grignard reagents with aryl halides in toluene, a nonpolar solvent with a high boiling point. The reaction was applied for the synthesis of various biaryls in good yields without the introduction of a large steric ligand. The Kumada-Tamao-Corriu(KTC) reaction in toluene was then successfully modified to proceed under neat conditions for the efficient syntheses of symmetrical biaryls, particularly in large-scale preparations. Unactivated aryl chlorides show higher reactivity than aryl bromides, particularly under neat conditions. Mechanistic investigations suggest a radical procedure for the catalytic cycle, and the origin of the radical intermediates being aryl halides.

Synthesis and properties of fluorescence poly(benzoxazole–imide)s containing naphthalene

Novel aromatic poly(benzoxazole–imide)s containing naphthalene were prepared from synthesized 1,4-di(5-aminobenzoxazol-2-yl)naphthalene and commercial dianhydrides by conventional two-step polymerization. The polymers showed high levels of tensile strength of up to 294 MPa and modulus of up to 6.5 GPa. The glass transition temperatures of the polymers were observed between 267°C and 345°C. The 5% weight loss temperatures of the polymers were tested in the range of 517–562°C in nitrogen atmosphere. The excellent properties of polymers were attributed to their rigid-rod-like molecular structure. The polymers emitted different fluorescence with maximum emission wavelengths in the range of 470–560 nm. Increasing the dianhydride electron affinity, the emission spectra peak value of polyimides (PIs) except PI6 increased gradually, but the fluorescent intensity of the PIs decreased. The 1,4-bis(3,4-dicarboxyphenoxy)benzene dianhydride-derived PI film exhibit highly fluorescent characteristics; however, the PI film from pyromellitic dianhydride was nonfluorescent.

Preparation and Properties of Imidazole-containing Polyimide/Silica Hybrid Films

Imidazole-containing polyimide/silica(PI/SiO2) hybrid films were prepared from 3,3′,4,4′-biphenyltetra-carboxylic dianhydride(BPDA) and 2,2′-di(p-aminophenyl)-5,5′-bibenzimidazole in N,N-dimethylacetamide(DMAc) by sol-gel method and thermal imidization. The hybrid film with high silica mass fraction up to 40% was transparent. Scanning electron microscope(SEM) and transmission electron microscope(TEM) results of the film indicate a homogeneous dispersion of silica nanoparticles in the polyimide matrix. One hybrid film PI/SiO2 with 15% SiO2 exhibits better mechanical properties with a tensile strength of 222 MPa, an elongation at break of 12%, and a tensile modulus of 5.66 GPa. The reinforced mechanism on mechanical properties was also studied.

Efficient Synthesis of 6‐[(R)‐1,1′‐Binaphthyl‐6‐]‐ 2,2′‐Bipyridine Derivatives

Abstract Chiral 6‐[(R)‐2,2′‐dimethoxyl‐1,1′‐binaphthyl‐6‐]‐2,2′‐bipyridine derivatives (3a–c, 5a, b) were synthesized from (R)‐6‐acetyl‐2,2′‐dimethoxyl‐1,1′‐binaphthalene by the Kröhnke method in one pot. Furthermore, 6‐aryl‐6′‐[(R)‐2,2′‐dimethoxyl‐1,1′‐binaphthyl‐6‐]‐2,2′‐bipyridines (6a–d) were obtained from 5b by Suzuki coupling in 86–90% yield.

Sequence‐Dependent Self‐Assembly of Chiral Polyimides

Sequence-defined chiral polyimides comprising identical asymmetric diamine monomers arranged in different directions along the main chain were designed and prepared. These new sequence-defined polymers exhibit sequence-dependent self-assembly behaviors and responses to ibuprofen enantiomers, as revealed by their chiroptical spectra and gelation properties. For the first time, the self-assembly of polymers and their interactions with guest molecules have been successfully controlled by means of the directional arrangement of the monomers in their polymer backbones.