查看更多>>摘要：Design and construction of suitable pore microenvir-onments for selective catalytic reactions of small guest molecules is a major goal for chemists.Herein,we report control of competitive E-Z photoisomeri-zation and photodimerization within porous metal-organic frameworks(MOFs)by fine-tuning the pore microenvironments using different dicarboxylate lin-kers.MOFs with small pores((E)-XMOF,and(E)-XMOF1')favor the photoinduced E-Z isomerization of one encapsulated diaryl alkene substrate while those with large pores(((E)-X)2MOF2)prefer the photodi-merization of two encapsulated alkene substrates.Both reactions show broad functional group compat-ibility and proceed stereospecifically in good yields under mild conditions.High local concentration of diaryl alkene ligands and their preorientation within pores facilitate stereoselective dimerization.This pore engineering strategy is applicable to control and create pore microenvironemnts for other photo-induced organic reactions within porous MOFs.
查看更多>>摘要：One major remaining challenge in polymer chemistry is the development of efficient chemical recycling strategies to fully retrieve starting materials.Polyte-trahydrofuran(PTHF)is widely used,but its stable ether bonds make it difficult to chemically reuse after disposal.Here,we propose a"polymer A → polymer B"strategy for one-step quantitative upcycling of PTHF to polyesters.The route undergoes a cascade pro-cess:PTHF is depolymerized to give tetrahydrofuran(THF)that then alternately copolymerizes with cyclic anhydrides in situ,thereby pushing the chemical equilibrium of"PTHF ⇄ THF"to the right.The proto-col demonstrates facile features:the use of common and metal-free Brønsted/Lewis acid as catalyst,a favorable reaction temperature of 100 ℃,and no use of solvents.This method also accommodates 18 cyclic anhydrides to give a library of polyesters with alternating sequences,tunable thermal proper-ties,and high-fidelity carboxyl terminals.This is an unprecedented strategy for chemical recycling of waste polyether.
查看更多>>摘要：Stimuli-responsive materials ho-d great potential for the development of smart materials due to their specifically tailored characteristics. However, it is challenging to un-derstand internal molecular dynamics when the macro-scopic mechanics of materials change in response to specific applled stimuli. Herein, we present the biological composite fibers of which mechanical properties can be reversibly controlled on demand by photothermal effect of an alternating near-infrared light irradiation.In stark contrast to the weakening of the mechanica-properties of conventional materials by heating, the mechanical perfor-mance of the obtained fibers are significantly enhanced,showing an increase of Young's modulus by a factor of four. The outstanding photothermal-mechanical behavior relies on the evolution of hydrogen bonds within the system. We envision that this type of fiber material will inspire a new strategy for the construction of smart devices.
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