Synthesis,Characterization And Electronic Transmission Behavior Of Molecular Wires Bridged By Benzo-Crown Ether

Molecular wires are one of the most researching hotspots currently.As a bridge between molecular devices and external,molecular wires plays an important role in energy and information transfering.Metal organic molecule wires,which formed by transition metal(electroactive center)complexes and conjugated organic bridged ligand,had been widely used in molecular electronics because of their rich ligand structure and good electrochemical properties.The electronic transmission behaviors of this kind of molecular wires are associated with the metal central,bridged ligands,molecular configuration as well as the medium etc.Phenyl acetylene compounds have stable chemical structure and special electrical properties,so that they are one of the most researched and reported molecular wires.Meanwhile,crown ether can selectively combine and dissociate with metal cation,and the combining ability varies with the ionic radius.When the metal cations were introduced to the space of crown ether,electronic transmission performance of the molecular wires which constructed by phenylethynyl and crown ether would be changed.This paper systematically investigated the effects of different metal cations on electronic transmission performance of the benzo-crown ether double metal organic molecular wires(both ends of the ruthenium metal complex),single metal organic molecular wires(one end of the ruthenium metal complex,the other end is mercapto)and pure organic molecular wires(both ends of the mercapto).Detailed contents are as follows:1.In order to study the influences of alkali-metal cations(Li+?Na+?K+)and alkaline-earth metal cation(Ba2+)on the electrochemical performance of benzo-crown ether double ruthenium metal molecular wires,the benzo-crown ether double ruthenium complex(2-d)were synthesized and confirmed by 1H NMR?13C NMR?31P NMR?UV-Vis spectroscopy and X-ray single crystal diffraction.We studied the electrochemical properties of this double ruthenium complex by voltammetry technology and in-situ electrochemical spectroscopy(UV-Vis-NIR-IR)technique.The results showed that:(1)This kind of bimetallic complexes have continuous two-step single electron redox process,and the interaction(?E)between the dinuclear metal would be varied with the radius and effective charge of cation,electrolyte as well as solvent;(2)When used the CH2Cl2 as the solvent and Bu4NB(C6F5)4 as the electrolyte,the metal cations(Li+?Na+?K+)can combined with double ruthenium mixed valence complexes,the lithium ion can stabilize the mixed valence complexes and the stability of mixed valence complex was decreased with the increase of metel ionic radius.2.In order to study the impacts of alkali-metal cation(Li+\Na+?K+)on the electronic transfer capacity of benzo-crown ether single ruthenium metal molecular wires which anchored on the surface of gold electrode,the benzo-crown ether single ruthenium complex(3-d)with the anchor dihydrobenzo[b]thiophene(BT)were synthesized and confirmed by 1H NMR?13C NMR?31P NMR?UV-Vis spectroscopy.We studied the electrochemical properties of this single ruthenium compexes by cyclic voltammetry technology when were introduced different metal cations.It indicated that molecular coverage(?)and electron transfer rate constant(kapp)of self-assembled monolayers on the gold electrode was decreased when metal ions were introduced to the molecular wires,and the values of kapp were increased with the increase of the cationic radius.3.In order to study the effects of alkali-metal cations(Li+?Na+?K+?Rb+)and alkaline-earth metal cations(Ca2+?Ba2+)on the electronic transmission behavior of benzo-crown ether organic molecular wires,the benzo-crown ether compounds(4-d)with the anchor BT groups were synthesized and confirmed by1H NMR?13C NMR?MS?UV-Vis spectroscopy and X-ray single crystal diffraction.Scanning tunneling microscopy break junction(STM-BJ)techniques were employed to investigate single-molecule conductance characteristics of benzo-crown ether organic compounds when were introduced different metal cations.The results showed that:(1)The values of single molecular conductance were increased when the cations were introduced(except Rb+)to molecular wires,and it was increased with the increase of the effective ionic charge.The reason is likely that the HOMO orbitals are more closer to the Fermi energy of gold electrode as well as the gaps between HOMO and LUMO are decreased when the metal cations were introduced;(2)Surprisingly,the molecular conductance has an unusual change when K+ or Ba2+ were introduced.The reason is likely that sandwich complexes were formed between the cations and the molecular wires and then the molecular conductance was increased.In conclusion,we systematically studied the effects of alkali-metal cations(Li+?Na+?K+)and alkaline-earth metal cations(Ca2+?Ba+)on the electronic transmission performance of crown ether molecular wires,it is of great reference value to control the electronic transmission behaviors of crown ether molecular wires by introducing different metal cations.