| Molecular spintronics is a new research field.Advances in molecular spintronics with multiple spin relaxation channels are highly desirable for fabricating miniaturized data storage devices and logic gates.Scanning tunneling microscopy(STM)has been demonstrated to be a powerful tool for studying the interactions between the unpaired molecular spins and the conduction band electrons of the substrate.The spin properties of single molecule can be characterized through the signal of Kondo effect and modulated by STM.The Kondo effect arouses from the exchange and coupling between the unpaired electron of paramagnetic molecules and the conduction electrons of the metal substrate.It is usually manifested as a peak or dip near the Fermi level at low temperature.Recent studies have shown that metal complexes of porphyrins and their analogues efficiently couple their delocalized unpaired?-electrons with the conduction band electrons of the metal substrate.Consequently,they have been studied for molecular spintronics applications.As a representative porphyrin branch,corrole can be viewed as a ring-contracted porphyrinoid containing direct pyrrole–pyrrole linkages and with the trianionic characteristics of the macrocyclic ligand.Non-innocent ligands are widespread among metallocorroles,especially among coinage metal corroles.Previous studies have shown that copper corroles are non-innocent,while gold corroles are innocent,depending on the metal(92-2–corrole(?)orbital interactions.However,describing silver corroles as innocent or non-innocent is challenging.Previously,we reported a planar triplet ground-state Cu(II)tetrabenzocorrole with four fused benzene rings on the corrole ligand.Kondo resonance signals can be observed in the ligand of tetrabenzo-fused copper corroles.However,the research on benzo-fused metallo corroles is limited by the difficulties during the synthesis of free-base benzo-fused corroles.Therefore,it is necessary to design and synthesize free-base benzo-fused corroles and their corresponding non-copper metallo complexes,so as to investigate the influences of the number of benzene rings on the corroleporbital and(9-pinteraction of centered metal ions as well as their spintronics properties.1.Synthesis and characterization of free-base dibenzo-fused corroleIn this work,we first synthesized 2,2'-bicyclo[2.2.2]octadiene-fused(BCOD)pyrrole and 1,9-bibenzoyl-5-phenyldipyrromethane,followed by the condensation reaction to form 2,17-dibicyclo[2.2.2]octadiene-fused corrole.Finally,2,17-dibenzo-fused corrole,the first case of free-base benzo-fused corrole was obtained through the retro-Diels–Alder from the precursor with the extrusion of ethylene molecules.Characterization of the 2,17-dibenzo-fused corrole showed a red shift of 26 nm in the ultraviolet spectrum compared with 5,10,15-triphenylcorrole,indicating that the introduction of the benzene rings enhanced the aromaticity of the ligand.On the other hand,the fluorescence intensity and quantum yield of 2,17-dibenzo-fused corrole decreased significantly.In conclusion,this novel synthesis of benzo-fused free-base corrole provides a new routine for other benzo-fused metallo corroles except copper.2.Synthesis,characterization and spintronics of dibenzo-fused silver corroleA facile method for the quantitative preparation of silver dibenzo-fused corrole(Ag-1)is described.The electronic structure of Ag-1 can still be described as a close-shell Ag(III)state.Notably,Ag-1 adopts an unprecedented domed geometry,with up-and down-orientations,when adsorbed on Ag(111)surface.Sharp Kondo resonances near Fermi level,both at the corrole ligand and the silver center,were observed by cryogenic STM,with relatively high Kondo temperature(172 K),providing the first direct spectroscopic evidence for a non-innocent Ag(II)–corrole·2-species.Benzene ring fusion and molecule–substrate interactions play pivotal roles in enhancing Ag(4(92-2)-corrole(?)orbital interactions,thereby stabilizing the open-shell singlet Ag(II)–corrole·2-on Ag(111)surface.This strategy provides a new pathway for the design of multichannel molecular spintronics devices for data storage and logic gates.3.Synthesis and characterization of benzo-fused copper and gold corrolesIn this work,we successfully synthesized 2,17-dibenzo-fused copper corrole(Cu-1)and 2,17-dibenzo-fused gold corrole(Au-1),followed with the characterization of their properties.Comparison with the properties of Cu-Dibenzo(Cu-1),Cu TPC and Cu-Tetrabenzo,we found that the introduction of benzene rings can effectively affect the electronic state of copper corroles,and the influences are related to the number of benzene rings.Cu-1 is an intermediate between Cu TPC and Cu-Tetrabenzo,and its ground state is open-shell singlet copper(II)corrole radical.The difference between Au-1 and Cu-1 shows that the influence of(9-?interaction on the innocent property of the metallo corroles can also be studied by adjusting the energy of the(9 orbital.In conclusion,we can adjust the(9-?interaction by changing the energy of centered metal ions'(9 orbital or the ligands'?orbital.This method provides a theoretical basis for the development of new molecular materials in the field of molecular spintronics for the miniaturization of data storage devices and has a good application prospect. |
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