We herein report the reactivity and regioselectivity of 2-pyrenyl as a coupling unit in Scholl reactions.On the basis of the Scholl reactions of hexaarylbenzene substrates,we have found that pyrenyl units are preferab...We herein report the reactivity and regioselectivity of 2-pyrenyl as a coupling unit in Scholl reactions.On the basis of the Scholl reactions of hexaarylbenzene substrates,we have found that pyrenyl units are preferably oxidized over naphthyl and phenyl units under appropriate Scholl reaction conditions,allowing divergent synthesis through a highly controllable intramolecular coupling sequence.We find that the C1 and C3 positions of the 2-pyrenyl unit are the favorable sites for intramolecular coupling while C4 is not reactive to allow further coupling.The reactivity and regioselectivity pattern can be explained by the spin density distribution,which shows that carbon-carbon bonds preferably form at sites with higher positive spin density.Guided by these findings,we successfully synthesized a double helicene and a sextuple helicene through the controlled Scholl reactions of 2-pyrenyl units.展开更多
We study the collapsing and subsequent spontaneous twisting of a carbon nanotube by in situ transmission electron microscopy （TEM）. A custom-sized nanotube is first created in the microscope by selectively extractin...We study the collapsing and subsequent spontaneous twisting of a carbon nanotube by in situ transmission electron microscopy （TEM）. A custom-sized nanotube is first created in the microscope by selectively extracting shells from a parent multi-walled tube. The few-walled, large-diameter daughter nanotube is driven to collapse via mechanical stimulation, after which the ribbon-like collapsed tube spontaneously twists along its long axis. In situ diffraction experiments fully characterize the uncollapsed and collapsed tubes. The experimental observations and associated theoretical analysis indicate that the origin of the twisting is compressive strain.展开更多
基金supported by the University Grants Committee(Hong Kong)through a Research Matching Grant,Deutsche Forschungsgemeinschaft(DFG)through the research training group“Template-Designed Organic Electronics(TIDE)”(RTG 2591)the U.S.Department of Energy(DOE),Office of Science,Basic Energy Sciences(BES),Materials Sciences and Engineering Division under contract no.DE-AC02-05-CH11231(Nanomachine program KC1203)and contract no.DE-SC0023105.
文摘We herein report the reactivity and regioselectivity of 2-pyrenyl as a coupling unit in Scholl reactions.On the basis of the Scholl reactions of hexaarylbenzene substrates,we have found that pyrenyl units are preferably oxidized over naphthyl and phenyl units under appropriate Scholl reaction conditions,allowing divergent synthesis through a highly controllable intramolecular coupling sequence.We find that the C1 and C3 positions of the 2-pyrenyl unit are the favorable sites for intramolecular coupling while C4 is not reactive to allow further coupling.The reactivity and regioselectivity pattern can be explained by the spin density distribution,which shows that carbon-carbon bonds preferably form at sites with higher positive spin density.Guided by these findings,we successfully synthesized a double helicene and a sextuple helicene through the controlled Scholl reactions of 2-pyrenyl units.
文摘We study the collapsing and subsequent spontaneous twisting of a carbon nanotube by in situ transmission electron microscopy （TEM）. A custom-sized nanotube is first created in the microscope by selectively extracting shells from a parent multi-walled tube. The few-walled, large-diameter daughter nanotube is driven to collapse via mechanical stimulation, after which the ribbon-like collapsed tube spontaneously twists along its long axis. In situ diffraction experiments fully characterize the uncollapsed and collapsed tubes. The experimental observations and associated theoretical analysis indicate that the origin of the twisting is compressive strain.
