the following description is of the best - contemplated mode of carrying out the invention . this description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense . the scope of the invention is best determined by reference to the appended claims . the invention provides a liquid crystal compound as shown in formula 1 . r is h , f , cl , linear or branched c 1 - 10 alkyl group , linear or branched c 1 - 10 alkenyl group , c 1 - 10 ether group , c 1 - 10 alkoxyl group , linear or branched c 1 - 10 fluorinated alkyl group , linear or branched c 1 - 10 fluorinated alkenyl group , or c 1 - 10 fluorinated ether group . each of a , b , and c , being the same or different , is a six member ring such as satured cyclohexyl group , unsatured cyclohexenyl group , or aromatic benzene ring . the carbon of the cyclohexyl group can be replaced by oxygen such as tetrahydropyranyl group or dioxanyl group . the carbon of the cyclohexenyl group can be replaced by oxygen such as dioxinyl group . the carbon of the phenyl group can be replaced by nitrogen such as pyridinyl group , pyridazinyl group , or pyrimidinyl group . each of l 1 , l 2 , l 3 , l 4 , and l 5 , being the same or different , is h or f . z is — c (═ o ) o —, — oc (═ o )—, — ch 2 o —, — och 2 —, — cf 2 o —, — ocf 2 —, — ch 2 ch 2 —, — cf 2 cf 2 —, — c ≡ c —, or — ch ═ ch —. y is cf 3 , cf 2 h , or cfh 2 . m , n is independently selected from an integer of 0 - 2 , and 1 ≦ m + n ≦ 3 . for achieving a linear structure , the substituents of the a , b , c rings in the liquid crystal compound are para substituted . for example , r and b ring are para substituted on the a ring . the described liquid crystal compound includes two ring structures as shown in formulae 2 - 5 or three ring structures as shown in formulae 6 - 9 . the liquid crystal compound of the invention can be used alone or accompanied with other liquid crystal compounds such as commercially available products . in one embodiment , the other liquid crystal compounds are shown as formulae 10 - 12 . in formula 10 , each of r and r ′, being the same or different , is h , f , linear or branched c 1 - 10 alkyl group , linear or branched c 1 - 10 alkenyl group , or c 1 - 10 ether group . each of a , b , and c , being the same or different , is a six member ring such as satured cyclohexyl group , unsatured cyclohexenyl group , or aromatic benzene ring . the carbon of the cyclohexyl group can be replaced by oxygen such as tetrahydropyranyl group or dioxinyl group . the carbon of the cyclohexenyl group can be replaced by oxygen such as dioxinyl group . the carbon of the phenyl group can be replaced by nitrogen such as pyridinyl group , pyridazinyl group , or pyrimidinyl group . each of l 1 and l 2 , being the same or different , is h , f , or cl . z is — c (═ o ) o —, — oc (═ o )—, — ch 2 o —, — och 2 —, — cf 2 o —, — ocf 2 —, — ch 2 ch 2 —, — cf 2 cf 2 —, — c ≡ c —, or — ch ═ ch —. m , n is independently selected from an integer of 0 - 2 , and 1 ≦ m + n ≦ 3 . in formula 11 , r is h , f , linear or branched c 1 - 10 alkyl group , linear or branched c 1 - 10 alkenyl group , or c 1 - 10 ether group . each of a , b , and c , being the same or different , is a six member ring such as satured cyclohexyl group , unsatured cyclohexenyl group , or aromatic benzene ring . the carbon of the cyclohexyl group can be replaced by oxygen such as tetrahydropyranyl group or dioxinyl group . the carbon of the cyclohexenyl group can be replaced by oxygen such as dioxinyl group . the carbon of the phenyl group can be replaced by nitrogen such as pyridinyl group , pyridazinyl group , or pyrimidinyl group . each of l 1 l 2 , l 3 , and l 4 , being the same or different , is h or f . z is — c (═ o ) o —, — oc (═ o )—, — ch 2 o —, — och 2 —, — cf 2 o —, — ocf 2 —, — ch 2 ch 2 —, — cf 2 cf 2 —, — c ≡ c —, or — ch ═ ch —. m , n is independently selected from an integer of 0 - 2 , and 0 ≦ m + n ≦ 2 . in formula 12 , r is h , f , linear or branched c 1 - 10 alkyl group , linear or branched c 1 - 10 alkenyl group , or c 1 - 10 ether group . each of a , b , and c , being the same or different , is a six member ring such as satured cyclohexyl group , unsatured cyclohexenyl group , or aromatic benzene ring . the carbon of the cyclohexyl group can be replaced by oxygen such as tetrahydropyranyl group or dioxinyl group . the carbon of the cyclohexenyl group can be replaced by oxygen such as dioxinyl group . the carbon of the phenyl group can be replaced by nitrogen such as pyridinyl group , pyridazinyl group , or pyrimidinyl group . l is h or f . z is — c (═ o ) o —; — oc (═ o )—, — ch 2 o —, — och 2 —, — cf 2 o —, — ocf 2 —, — ch 2 ch 2 —, — cf 2 cf 2 —, — c ≡ c —, or — ch ═ ch —. m , n is independently selected from an integer of 0 - 2 , and 0 ≦ m + n ≦ 2 . while various structures are applied with the core part in the general formula 1 described above , they make the compounds develop excellent characteristics . among them , some further examples are shown in following general formulae 13 to 30 are preferred . the definition of groups r and y , rings a , b , and c , are same as above . because the liquid crystal compound of the invention and the commercially available liquid crystal compound have similar structures , the combination thereof may prevent problems such as low miscibility or un - dissolvable solids . in addition , the liquid crystal compound of the invention has wide nematic liquid crystal temperature range , low viscosity , low driving voltage , and short response time , such that the liquid crystal compound is suitable for transmission , reflection , or transflection lcd and to be driven by tn , ips , or va mode . accordingly , the liquid crystal compound of the invention may efficiently improve the lcd panel performance . fig1 shows a cross section of an lcd in one embodiment of the invention . the lcd 100 includes a top substrate 101 and a bottom substrate 103 and a liquid layer 105 disposed therebetween . in one embodiment , one of the substrates is a color filter substrate and another substrate is an array substrate . in one embodiment , one of the substrates is an array on color filter substrate ( aoc ) or color filter on array substrate ( coa ), and another substrate is a transparent substrate such as glass or plastic . the liquid crystal layer 105 includes the liquid crystal compound of the invention , thereby reducing the response time . fig2 is a diagram of an optoelectronic device 200 in an embodiment of the invention . referring to fig2 , the lcd panel 100 of the aforementioned embodiments is applied in the optoelectronic device 200 and connected to an electric device 203 such as a control device , operator device , process device , input device , memory device , driving device , illumination device , protection device , or other functional device , or combinations thereof . the electronic apparatus can be a mobile product such as a cell phone , video camera , camera , laptop computer , video game console , watch , music player , e - mail transceiver , digital photo - frame , electronic map navigation , and the like . the electronic apparatus can be visual - audio products ( such as media players and the like ), a monitor , a television , a billboard ( such as indoor / outdoor ), a projector , or others . the raw materials , solvents , or silica gel for chromatography were commercially available from fine chemical supply , such as affa ( lancaster ), tcl , aldrich , acros , merck , and the likes . the synthesis of the liquid crystal compound is described as below , a series of compounds were completed by 2 - 5 reactions . the compound properties such as electricity were analyzed by bruker advance drx - 400 nmr , lc vision lcas ( i ), autronic - melchers gmbh dms 803 , abbe refractometer , ta q10 thermal differential , scanning , calorimetry ( dsc ), olympus mx40 polarized optical microscope , or other related instruments . commercially available starting material was charged in a reaction bottle , added dried tetrahydrofuran ( hereinafter thf ) as solvent , added n - butyl lithium in dry - ice bath (− 78 ° c . ), and stirred at low temperature for 30 minutes . the mixture was then dropwise added trifluoromethyl acetate ( cf 3 co 2 et ), retained in low temperature for 15 minutes , slowly warmed up to room temperature , and reacted at room temperature for 4 hours . the reaction was quenched by adding satured nacl solution at room temperature , and then extracted by ethyl ether . the organic layer of the extraction was dried by anhydrous mgso 4 and concentrated to form crude . the crude was purified by recrystallization with hexane to form intermediate . methyltriphenylphosphonium bromide , dried thf , and potassium t - butoxide were sequentially charged in another reaction bottle in ice bath and stirred for half hour to be evenly mixed . the mixture were added the described intermediate in ice bath and reacted for 1 hour . after removing the ice bath , the reaction was reacted at room temperature for another 2 hours . the reaction was quenched by satured nacl solution , and then extracted by hexane . the organic layer of the extraction was dried and concentrated to form crude . the crude was purified by chromatography , with a few silica gel and hexane as eluent , to form compounds 1 - 4 . the described reaction was shown as formula 13 , and the total yield was about 45 - 60 %. measured by dsc , the phase transfer point in heating was 16 . 5 ° c . for compound 1 , 9 . 2 ° c . for compound 2 , 54 . 6 ° c . for compound 3 , and 44 . 7 ° c . and 47 . 8 ° c . for compound 4 , respectively . the compound 4 had apparent liquid crystal phase and compounds 1 - 3 showed a phase , transfer point while cooling , meaning compounds 1 - 4 were all liquid crystal materials . the 1 h nmr spectrum ( 400 mhz , cdcl 3 ) of compound 1 : δ 0 . 89 - 1 . 47 ( m , 12h ), 1 . 91 ( m , 4h ), 2 . 50 ( tt , j = 12 . 0 , 3 . 2 hz , 1h ), 5 . 75 ( d , j = 1 . 0 hz ), 5 . 91 ( d , j = 1 . 0 hz , 1h ), 7 . 22 ( d , j = 8 . 0 hz , 2h ), 7 . 38 ( d , j = 8 . 0 hz , 2h ). the 1 h nmr spectrum ( 400 mhz , cdcl 3 ) of compound 2 : δ 0 . 86 - 1 . 43 ( m , 16h ), 1 . 89 ( m , 4h ), 2 . 50 ( tt , j = 12 . 0 , 4 . 0 hz , 1h ), 5 . 75 ( d , j = 1 . 0 hz ), 5 . 91 ( d , j = 1 . 0 hz , 1h ), 7 . 22 ( d , j = 8 . 0 hz , 2h ), 7 . 38 ( d , j = 8 . 0 hz , 2h ). the 1 h nmr spectrum ( 400 mhz , cdcl 3 ) of compound 3 : δ 0 . 91 ( m , 3h ), 1 . 37 ( m , 4h ), 1 . 65 ( m , 2h ), 2 . 67 ( t , j = 7 . 6 hz , 2h ), 5 . 84 ( d , j = 1 . 4 hz , 1h ), 5 . 98 ( d , j = 1 . 4 hz , 1h ), 7 . 27 ( d , j = 8 . 0 hz , 2h ), 7 . 53 - 7 . 62 ( m , 4h ), 7 . 63 ( d , j = 8 . 0 hz , 2h ). the 1 h nmr spectrum ( 400 mhz , cdcl 3 ) of compound 4 : δ 0 . 87 ( t , j = 7 . 2 hz , 3h ), 1 . 29 - 1 . 35 ( m , 8h ), 1 . 66 ( m , 2h ), 2 . 64 ( t , j = 7 . 6 hz , 2h ), 5 . 82 ( d , j = 1 . 2 hz , 1h ), 5 . 97 ( d , j = 1 . 2 hz , 1h ), 7 . 26 ( d , j = 6 . 4 hz , 2h ), 7 . 51 - 7 . 53 ( m , 4h ), 7 . 60 ( d , j = 6 . 4 hz , 2h ). 1 - butyl - 4 - ethynyl benzene , 1 - bromo - 4 - iodobenzene , sodium carbonate , tetrakis -( triphenyl phosphine ) palladium , 1 , 2 - dimethoxyethane ( hereinafter dme ), and deionized water were sequentially charged in a reaction bottle . the mixture was heated to 70 ° c . and reacted under nitrogen for 8 hours . the resulting material was filtered by celite to remove solid , extracted by satured nacl solution and hexane . the organic layer of the extraction was dried and concentrated to form crude . the crude was purified by chromatography , with a few silica gel and hexane as eluent , to form intermediate . the intermediate was processed as the reaction as described in example 3 to form compound 5 . the described reaction is shown in formula 14 . the compound 5 had a melting point of 26 . 1 ° c . the 1 h nmr spectrum ( 400 mhz , cdcl 3 ) of compound 5 : δ 0 . 94 ( t , j = 7 . 2 hz , 3h ), 1 . 26 - 1 . 39 ( m , 2h ), 1 . 56 - 1 . 65 ( m , 2h ), 2 . 63 ( t , j = 7 . 6 hz , 2h ), 5 . 83 ( s , 1h ), 5 . 99 ( s , 1h ), 7 . 18 ( d , j = 8 . 0 hz , 2h ), 7 . 44 - 7 . 47 ( m , 4h ), 7 . 54 ( d , j = 8 . 4 hz , 2h ). commercially available starting material was dissolved in dried thf , added mg ( piece ) and slightly heated to start the reaction , then stirred for 30 minutes . the reaction was then set in ice bath to add trimethyl borate , and then stirred at room temperature for 2 hours . the reaction was terminated by 6n hcl , and then stirred at room temperature for 4 hours . the resulting material was extracted by satured nacl solution and a great amount of ethyl ether . the organic layer of the extraction was concentrated to form crude , and the crude was purified by recrystallization ( ether / hexane ) to form boranic acid intermediate . the boranic acid intermediate was then processed as the reaction described in example 2 to form bromide intermediate . the bromide intermediate was then processed as the reaction described in example 1 to form compound 6 . the described reaction is shown in formula 15 . the compound 6 had a melting point of 150 . 2 ° c . the 1 h nmr spectrum ( 400 mhz , cdcl 3 ) of compound 6 : δ 0 . 91 ( m , 3h ), 0 . 94 - 1 . 16 ( m , 2h ), 1 . 27 - 1 . 33 ( m , 8h ), 1 . 46 - 1 . 56 ( m , 3h ), 1 . 89 - 1 . 96 ( m , 4h ), 2 . 53 ( tt , j = 12 . 0 , 4 . 0 hz , 1h ), 5 . 84 ( s , 1h ), 5 . 98 ( s , 1h ), 7 . 31 ( d , j = 8 . 0 hz , 2h ), 7 . 53 - 7 . 54 ( m , 4h ), 7 . 62 ( d , j = 8 . 0 hz , 2h ). lithium aluminum hydride ( lah ) was charged in a reaction bottle , added a few dried thf as solvent , and stirred in ice bath for 5 minutes to be evenly mixed . the commercially available staring material dissolved in thf was dropwise added to the mixture in ice bath , and the ice bath was then removed . when the temperature of the reaction bottle reached room temperature , the reaction was slightly heated to reflux and reacted in reflux for another 4 hours and then cooled to room temperature . the reaction was terminated by concentrated hcl and extracted by satured nacl solution and ethyl ether . the organic layer of the extraction was dried by anhydrous mgso 4 and concentrated to form crude . the crude was added to hbr solution ( 48 %), refluxed for 24 hours , and extracted by satured nacl solution and ethyl ether . the organic layer of the extraction was dried by anhydrous mgso 4 , concentrated , and purified by chromatography to form pure bromide intermediate . the eluent of the chromatography was ethyl acetate / hexane ( 1 / 8 ). the bromide intermediate was dissolved in dimethyl foramide ( hereinafter dmf ), added 4 - bromophenol and potassium carbonate , heated to 60 ° c . and stirred for 12 hours to complete the reaction . the resulting material was extracted by water and hexane , the organic layer of the extraction was dried and concentrated to form crude . the crude was then purified by recrystallization with hexane , and the purified crude was processed as the reaction described in example 1 to form compound 7 . the described reaction is shown in formula 16 . compound 7 had two phase transfer points ( 76 . 1 ° c . and 111 . 9 ° c .) in heating . in addition , the liquid phase of the compound 7 was determined by polarized optical microscope . the 1 h nmr spectrum ( 400 mhz , cdcl 3 ) of compound 7 : δ 0 . 86 - 1 . 31 ( m , 21h ), 1 . 74 - 1 . 77 ( m , 6h ), 2 . 02 ( m , 2h ), 3 . 75 ( d , j = 9 . 6 hz , 2h ), 5 . 68 ( d , j = 1 . 0 hz , 1h ), 5 . 85 ( d , j = 1 . 0 hz , 1h ), 6 . 88 ( d , j = 8 . 6 hz , 2h ), 7 . 37 ( d , j = 8 . 6 hz , 2h ). the bromide intermediate was formed by different starting material accompanying a similar reaction as described in example 4 . the bromide intermediate and a great amount of triphenylphosphine ( pph 3 ) were charged in a reaction bottle , heated to 80 ° c . and reacted for 10 hour to obtain a white solid . the white solid was washed by hexane to remove un - reacted pph 3 , and reacted with bromobenzaldehyde to process a wittig reaction to form an intermediate with an alkylene bridge . the intermediate with an alkylene bridge was purified by chromatography with hexane as eluent , and then processed a hydrogenation for transferring alkylene bridge to alky bridge . the hydrogenated intermediate was processed as the reaction described in example 1 to form compound 8 and 9 . the described reaction is shown in formula 17 . compound 8 had a melting point of 134 . 2 ° c ., and compound 9 had a melting point of 91 . 7 ° c . the 1 h nmr spectrum ( 400 mhz , cdcl 3 ) of compound 8 : δ 0 . 86 - 1 . 31 ( m , 17h ), 1 . 51 - 1 . 53 ( m , 2h ), 1 . 72 - 1 . 85 ( m , 8h ), 2 . 6 - 2 . 67 ( m , 2h ), 3 . 16 ( m , 2h ), 5 . 77 ( d , j = 1 . 2 hz , 1h ), 5 . 93 ( d , j = 1 . 2 hz , 1h ), 7 . 19 ( d , j = 8 . 0 hz , 2h ), 7 . 39 ( d , j = 8 . 0 hz , 2h ). the 1 h nmr spectrum ( 400 mhz , cdcl 3 ) of compound 9 : δ 0 . 88 - 0 . 93 ( m , 3h ), 1 . 04 - 1 . 07 ( m , 2h ), 1 . 25 - 1 . 47 ( m , 7h ), 1 . 89 ( m , 4h ), 2 . 46 ( tt , j = 12 . 0 , 4 . 0 hz , 1h ), 2 . 93 ( m , 4h ), 5 . 77 ( s , 1h ), 5 . 94 ( s , 1h ), 7 . 24 ( d , j = 8 . 0 hz , 2h ), 7 . 40 ( d , j = 8 . 0 hz , 2h ). trifluorobronic acid was selected as starting material to process reaction described in example 2 to form bromide intermediate . the bromide intermediate was processed as the reaction described in example 1 to form compound 10 . the described reaction is shown in formula 18 . the 1 h nmr spectrum ( 400 mhz , cdcl 3 ) of compound 10 : δ 5 . 85 ( d , j = 1 . 4 hz , 1h ), 6 . 02 ( d , j = 1 . 4 hz , 1h ), 7 . 21 ( m , 2h ), 7 . 54 ( m , 4h ). commercially available liquid crystal compound were mixed in different ratios to form a liquid crystal combination . the structure and the weight ratio of the liquid crystal compounds were tabulated as in table 1 . the described liquid crystal combination had a dielectric anisotropy ( δ ∈) of 9 . 48 , a rotational viscosity ( γ 1 ) of 285 mpas , and a clear point temperature of 94 . 7 ° c . the compounds 1 and 2 and intermediate 1a were mixed with the liquid crystal combination , and the properties thereof were tabulated as in table 2 . as shown in table 2 , both compounds 1 and 2 reduced the rotational viscosity of the liquid crystal combination , thereby reducing the response time . on the other hand , the intermediate 1a enhanced the rotational viscosity of the liquid crystal combination and increased the response time . while the invention has been described by way of example and in terms of preferred embodiment , it is to be understood that the invention is not limited thereto . to the contrary , it is intended to cover various modifications and similar arrangements ( as would be apparent to those skilled in the art ). therefore , the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements .