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Over the last several years， since the discovery of air and water stable ionic liquids （ILs） by Wilkes in 1992 ［49］， they have been widely promoted as more reliable class of “ green solvents” compare with organic carbonates， attribute to their unique properties， such as thermal stability， high electrical conductivity， high polarity ［50］， and negligible vapor pressures［51］， coupled with a wide liquid range． Thus， ILs are recently fascinating considerable attention for application in numerous fields， though they were described almost a century ago．
ILs are a class of designable organic compounds which display two characteristic structures： firstly， they consist only of ions which are poorly． coordinated． Secondly， they are liquids below 100 ℃ ［52］， if the ILs are liquid at room temperature， they are called room temperature ionic liquids（RTILs） ［53］． Combining organic cations with suitable anions allows to tailoring the appropriate physical， chemical and biological properties for ILs，while some even possess unexpected functions resulting from synergetic collaboration between the two components． Hence， the attractive flexibility or‘tunability’ in the design has driven phenomenal interest in ILs’ synthesis ［54］． The unique structure and performance of ILs as a platform not only offers additional breaks to modify these ionic materials’ physical properties （e．g． melting point， density， polarity， viscosity， hydrophobicity ／ hydrophilicity， solubility） for specific applications， but also offers other gorgeous chemical features such as fundamental ionic conductivity， tremendous thermal，chemical， and electrochemical stability ［55］．
By either a physical combination of ILs or chemical modification （ covalent functionalization or ion exchange metathesis process of the ionic constituents， specific functional groups can be easily incorporated into the ILs skeleton）， a number of IL-containing composite materials and functional ILs have been effectively realized and applied in the enormous area．
First of all， nowadays notable efforts for ILs have been made focusing on the design of safer and more environmental kindly solvents ［56］， due to conventional organic solvents are often toxic， flammable and volatile． Compared with the volatile organic compounds， ILs display excellent dissolution performance for organic， inorganic， and polymer materials， and their immeasurable vapor pressure ［57］ and non-flammability properties provide them the ability to avoid atmospheric pollution because there would be no loss of solvent through evaporation． The thermal decomposition temperatures higher than 300℃ could enhance their recycling efficiency ［58］． Accordingly， ILs can be applied to replacing traditional volatile organic solvents for a host of practices linked to green chemistry and clean technology such as organic reactions［59］， extraction， catalysis， and separation processes ［55］．
Secondly， ILs have a very broad range of viscosities， which may vary between 20 and 40，000 cp as are compared with the viscosities of typical organic solvents which are in a range of 0. 2 and 100 cp． For ILs， only minor change of structure may result in a significant change in viscosity． Thus， ILs are discovered extensive use as engineering fluids or as innovative lubricating systems ［50］． IL-based materials could straightforwardly be operated under extreme conditions such as high or low temperature and high vacuum or pressure， owing to their significant thermal stability in a quite wide liquid phase temperature range from 200 to 300 ℃ ， with designable excellent mechanical，chemical， and electrochemical stability．
Thirdly， the special designable structures and functional properties not only retain the key features of the original materials but also possess the characteristics of ILs． It is thought that the ionic nature of ILs， which the molecular materials lack， can offer these materials with intrinsic ion conductivity as well as a substantial ionic skeleton for producing progressive materials． At the meantime， ILs exhibit perfect electrochemical stability in a wide electrochemical window of 2 ～ 5 V ［60］． Thus， ILs， especially RTILs， would be an excellent candidate for prospective applications as encouraging electrolyte bases or additives in lithium secondary batteries and other energy related applications， such as fuel cells， supercapacitors ［61］， and dye sensitized solar cells ［62］［63］．
Since many factors can affect their conductivity， such as viscosity， density， ion size， anionic charge delocalization， aggregations and ionic motions， ILs are expected as key materials which might give a solution to the safety problems of batteries due to their non-flammable property． However，the selectivity of carrier ion transport is one of the problems when ILs are applied to batteries． Since ILs do not include electroactive species， it is necessary to add salts or acids before their use． The mobility of electroactive ions shows great effects on the electrical power of the batteries as lithium cation does on lithium-ion batteries， while the introduction of ethylene oxide chains attached to the methyl pyrrolidine， butyl imidazolium ring or diethylsulfide may lead to lower glass transition temperature， and also improve ionic conductivity ［41］．
In these applications， ILs are constantly discussed as beneficial and high potential building blocks for innovative advanced functional materials． The resulting ILs are expected to offer many more advantages over the traditional molecular materials．
The wide range of possible cation and anion combinations allows for a large variety of tunable interactions and applications ［64］． Generally studied ILs are consist of bulky， N-containing organic cations in combination with anions， alternating from the inorganic ions to more various organic species．Simple deviations in the cation and anion groupings or the nature of the moieties attached to each ion allows the properties of ILs to be tailored for specific applications．
The cation and its structure can positively influence the physical properties as well as interact via dipolar， ð-ð， and n-ð interactions with dissolved molecules． However， its range of effects has not been studied as extensively．［65］ Generally， the commonly used cations include alkyl imidazolium ［RR’Im］ ＋ ， alkyl pyridinium ［RPy］ ＋ ， tetraalkylammonium ［NR 4 ］ ＋ ， tetra alkyl phosphonium ［PR 4 ］ ＋ and others ［62］：
Most widely used anions consist of chloride Cl－， bromide Br－， iodide I－， hexafluorophosphate ［ PF 6 ］－， tetrafluoroborate ［ BF 4 ］－， nitrate［NO 3 ］－， methanesulfonate （mesylate） ［CH 3 SO 3 ］－， trifluoromethane sulfonate （triflate） ［CF 3 SO 3 ］－， bis- （ trifluoromethane sulfonyl） amide ［CF 3 SO 2 ）2 N］－or abbreviated from here on as ［TFSI］－， dicyanamide ［DCA］－，and others ［62］．
As a new family of ILs， DILs are consist of the anion and the doubly charged cation which is composed of two singly charged cations as head groups linked by a variable length of alkyl or oligo ethylene glycol chain as a rigid or flexible spacer． Thus， the DILs matrix created offers the opportunity to investigate （a） the influence of cation and anion variation， （b） the influence of the chain length．
Recently， the number of DILs described in the literature is growing rapidly． Anderson et al． presented the synthesis and characterisation of a variety of DILs containing alkane spacers ［65］． Kubisa and Biedron investigated DILs obtained by the functionalization of PEG with triphenylphosphine ［66］．Ohno and co-workers have shown that dicationic PEG-based molten salts are bearing imidazolium cations as ion conducting materials ［67 ］． Dicationic and polycationic ILs linked by alkyl chains display extraordinarily higher chemical and thermal stability than their mono-cationic analogs published by Armstrong and coworkers ［65］． It has also been presented that the acute toxicity of DILs is in several cases below the levels detected for those monocationic and that the use of head groups connected via polyethylene glycol could be identified as structural elements reducing the toxicity ［50］．
Based on the literature， DILs possess distinctive features in critical micelle concentration ［57］， such as a wider liquid range and higher thermal stability， better behavior as electrolytes characteristics， and higher thermal stabilities than mono-cationic ILs and other traditional solvents ［68］． As we know， ILs should have the capability to dissolve more Li salt to have a higher Li ＋ conductivity， if ILs are intended to be applied in Li batteries． Thus， by incorporating a PEO oligomer into the DILs structure， the conductivity could be enhanced primarily by improving cation transport in the PEO segment， although the viscosity of DILs does not decrease ［69］ due to the weak interaction of ethylene oxide segment compared to the alkyl chain ［70］．
Until now most of the researchers have focused on mono cationic type ILs， although the number of DILs described in the literature is increasing［62］． For DILs， the relationship studies between their structure and physicochemical characteristics and molecular structures are， as yet， still relatively rare ［71］． Therefore， it is urgent and necessary to explore other new DILs structures to gain further understanding and extend the applications of DILs as electrolyte components．
Although many ILs have been reported， most are not suitable for electrochemical applications because of poor conductivity （＜1 mS） and／ or high viscosity （＞ 100 cP） at room temperature， also due to a poor electrochemical window． However， the combination of a fluorinated cation with an anion such as TFSI or DCA has resulted in ILs that display non-volatility， non-flammability ［72］， relatively wide electrochemical windows and also low viscosities and high conductivities that are favorable for electrochemical applications ［73］．
Among the tools available to synthetic chemists to tune ILs properties，selective fluorination is among the most productive， having been extensively developed and explored since the introduction of diversely located fluoro substituents including terminal chain， linking arm or core position which provides an excellent opportunity for investigating the relationship between structures and properties and for modifying and optimizing the physical ／ chemical properties of compounds ［74］．
Meanwhile， although many FRTILs have also been synthesized and shown to display excellent modified properties due to the existence of fluoro substituents， investigations involving this kind of RTILs bearing fluoro substituents have been reported only rarely． In this work， we have described the design and syntheses of twelve novel unsymmetrical mono cationic based FRTILs with side chains． Their properties and potential applications as solvents，electrolytes， high ion transport materials and templates have also been extensively developed．