No abstract

In this paper, nitrogen-coordinated boroxines are exploited for the fabrication of self-healing and recyclable polymer composites with enhanced mechanical properties. The 3D polymer networks cross-linked with nitrogen-coordinated boroxines are first synthesized through the trimerization of ortho-aminomethyl-phenylboronic acid groups at the terminals of poly(propylene glycol) (PPG) chains, and subsequently, the mechanically robust polymer composites are fabricated by utilizing the complexation of nitrogen-coordinated boroxinecontaining PPG (N-boroxine-PPG) with poly(acrylic acid) (PAA) and hydrogenbonding interactions between them. The N-boroxine-PPG is soft with a tensile strength of 0.19 MPa, whereas the tensile strengths of N-boroxine-PPG/PAA composites can be tailored to range from 1.7 to 12.7 MPa by increasing the PAA contents in the polymer composites. It is revealed that the amine ligands can facilitate the formation and dissociation of nitrogencoordinated boroxines at room temperature. Moreover, the reversibility of nitrogen-coordinated boroxines and hydrogen-bonding interactions enable multiple cycles of healing and recycling of the damaged N-boroxine-PPG/PAA composites. The healed and recycled N-boroxine-PPG/PAA polymer composites regain most of their mechanical strength.

Strong supramolecular interactions, which induced tight packing and rigid molecules in crystals of cyano substituent oligo(para-phenylene vinylene) (CN-DPDSB), are the key factor for the high luminescence efficiency of its crystals; opposite to its isolated molecules in solution which have very low luminescence efficiency.

A series of highly efficient deep red to near-infrared (NIR) emissive organic crystals 1-3 based on the structurally simple 2'-hydroxychalcone derivatives were synthesized through a simple one-step condensation reaction. Crystal 1 displays the highest quantum yield (Φf) of 0.32 among the reported organic single crystals with an emission maximum (λem) over 710 nm. Comparison between the bright emissive crystals 1-3 and the nearly nonluminous compounds 4-7 clearly gives evidence that a subtle structure modification can arouse great property changes, which is instructive in designing new high-efficiency organic luminescent materials. Notably, crystals 1-3 exhibit amplified spontaneous emissions (ASE) with extremely low thresholds. Thus, organic deep red to NIR emissive crystals with very high Φf have been obtained and are found to display the first example of NIR fluorescent crystal ASE.

Human conversations naturally evolve around related concepts and scatter to multi-hop concepts. This paper presents a new conversation generation model, ConceptFlow, which leverages commonsense knowledge graphs to explicitly model conversation flows. By grounding conversations to the concept space, Con-ceptFlow represents the potential conversation flow as traverses in the concept space along commonsense relations. The traverse is guided by graph attentions in the concept graph, moving towards more meaningful directions in the concept space, in order to generate more semantic and informative responses. Experiments on Reddit conversations demonstrate ConceptFlow's effectiveness over previous knowledge-aware conversation models and GPT-2 based models while using 70% fewer parameters, confirming the advantage of explicit modeling conversation structures. All source codes of this work are available at https://github.com/ thunlp/ConceptFlow.