in the following , the present invention is illustrated . the phthalonitrile derivatives represented by the above described formula ( i ) of the present invention have a large negative dielectric anisotropy reaching about - 20 in case of fusing in a liquid crystal state . further , the novel phthalonitrile derivatives according to the present invention can be used as a mixture with known liquid crystals . as known liquid crystals , there are schiff type liquid crystal compounds such as methoxybenzylidene butylaniline or ethoxybenzylidenebutylaniline , etc ., ester type liquid crystal compounds such as p - methoxy - benzoic acid p &# 39 ;- pentylphenyl ester or trans - 4 - n - pentylcyclohexanecarboxylic acid p &# 39 ;- ethoxyphenyl ester , etc ., azoxybenzene type liquid crystal compounds such as p - methoxy - p &# 39 ;- butylazoxybenzene or p - methoxy - p &# 39 ;- ethylazoxybenzene , etc ., and oligo - 1 , 4 - phenylene type liquid crystal compounds such as 1 , 4 - bis ( trans - 4 - n - pentylcyclohexyl ) benzene or 4 -( trans - 4 - n - pentylcyclohexyl ) biphenyl , etc . as novel phthalonitrile derivatives represented by the formula ( i ), there are compounds represented by the following formulas ( ii ) and ( ii &# 39 ;). ## str8 ## ( wherein r 2 represents a hydrogen atom , an alkyl group having 1 to 9 carbon atoms , an alkoxy group having 1 to 9 carbon atoms , a halogen atom , ## str9 ## and r 3 represents an alkyl group having 1 to 9 carbon atoms or ## str10 ## ( wherein r 4 represents a hydrogen atom , an alkyl group having 1 to 9 carbon atoms or an alkoxy group having 1 to 9 carbon atoms )). ## str11 ## ( wherein r 2 &# 39 ; represents an alkyl group having 1 to 9 carbon atoms or an alkoxy group having 1 to 9 carbon atoms , and r 3 &# 39 ; represents an alkyl group having 1 to 9 carbon atoms or ## str12 ## ( wherein r 4 &# 39 ; represents an alkyl group having 1 to 9 carbon atoms or an alkoxy group having 1 to 9 carbon atoms )). in case that r 2 represents an alkyl group having 1 to 7 carbon atoms or an alkoxy group having 1 to 7 carbon atoms and r 3 represents an alkyl group having 1 to 7 carbon atoms , the compounds themselves are non - liquid crystal substances . however , when they are used as a liquid crystal composition , they show a low effect of increasing viscosity and produce a good result in various characteristics such as responce speed , etc . further , as novel phthalonitrile derivatives represented by the formula ( i ), there are compounds represented by the following formulas ( iii ) and ( iii &# 39 ;). ## str13 ## ( wherein r 5 represents a hydrogen atom , an alkyl group having 1 to 9 carbon atoms , an alkoxy group having 1 to 9 carbon atoms or ## str14 ## and r 6 represents an alkyl group having 1 to 9 carbon atoms , an alkoxy group having 1 to 9 carbon atoms , ## str15 ## ( wherein r 4 represents a halogen atom , a hydrogen atom , an alkyl group having 1 to 9 carbon atoms or an alkoxy group having 1 to 9 carbon atoms ), but r 6 does not represent an alkyl group having 1 to 9 carbon atoms or an alkoxy group having 1 to 9 carbon atoms in the case that r 5 represents an alkyl group having 1 to 9 carbon atoms ). ## str16 ## ( wherein r 5 &# 39 ; represents a hydrogen atom , an alkyl group having 1 to 9 carbon atoms or an alkoxy group having 1 to 9 carbon atoms , and r 6 &# 39 ; represents ## str17 ## ( wherein r 4 &# 34 ; represents a halogen atom , an alkyl group having 1 to 9 carbon atoms or an alkoxy group having 1 to 9 carbon atoms ). in case that r 5 represents an alkyl group having 1 to 7 carbon atoms and r 6 represents ## str18 ## ( wherein r 4 represents an alkyl group having 1 - 7 carbon atoms or an alkoxy group having 1 to 7 carbon atoms ), the compounds easily have a liquid crystal characteristic . when they are used as a liquid crystal composition , they have a wide range of liquid crystal temperature as compared with the case of using compounds in which r 6 represents an alkyl group or an alkoxy group , and they exhibit an excellent effect in responce characteristics . moreover , as novel phthalonitrile derivatives represented by the formula ( i ), there are compounds represented by the following formula ( iv ). ## str19 ## ( wherein r 7 represents an alkyl group having 1 to 9 carbon atoms , r 8 represents an alkyl group having 1 to 9 carbon atoms , an alkoxy group having 1 to 9 carbon atoms , ## str20 ## ( wherein r 4 represents a hydrogen atom , an alkyl group having 1 to 9 carbon atoms or an alkoxy group having 1 to 9 carbon atoms ), and p represents 0 or 1 ). these compounds are similarly useful as liquid crystal materials for guest - host type positive display . in case of using compounds wherein r 7 represents an alkyl group having 1 to 7 carbon atoms , p is 0 and r 8 represents ## str21 ## ( wherein r 4 represents an alkyl group having 1 to 7 carbon atoms or an alkoxy group having 1 to 7 carbon atoms ), it is possible to obtain a liquid crystal composition which shows a small temperature dependence of threshold voltage . these compounds represented by the formulas ( ii ), ( iii ) and ( iv ) can be used as a mixture with known liquid crystals as described in the case of the formula ( i ). the novel phthalonitrile derivatives represented by the formula ( i ) are synthesized by , for example , the following process for production . ## str22 ## a butadiene derivative represented by the formula ( v ) and fumaronitrile ( vi ) or dicyanoacetylene ( ix ) are subjected to cyclization reaction to produce a 1 , 2 , 3 , 6 - tetrahydrophthalonitrile derivative represented by the formula ( vi ) and a 3 , 6 - dihydrophthalonitrile derivative represented by the general formula ( vii ), respectively . the reaction is carried out in an absence of solvents or in a solvent such as benzene , toluene , xylene , chlorobenzene or dichlorobenzene , etc . at a reaction temperature of 10 °- 250 ° c . with adding , if necessary , a catalyst such as hydroquinone . the 1 , 2 , 3 , 6 - tetrahydrophthalonitrile derivative represented by the formula ( vi ) or the 3 , 6 - dihydrophthalonitrile derivative represented by the formula ( vii ) is oxidized by sulfur in an absence of solvents or in a solvent such as n , n - dimethylformamide or n - methylpyrrolidone , etc ., or brominated in a solvent such as acetic acid and , thereafter , carrying out dehydrobromination to produce a novel phthalonitrile derivative represented by the formula ( i ). hitherto , as phthalonitrile compounds having a negative dielectric constant , 3 - alkyloxy - 6 - cyclohexanecarboxy - phthalonitrile ( japanese patent application ( opi ) no . 102550 / 80 and 3 - alkyl - 6 - alkylcyclohexyl - phthalonitrile ( de no . 2 , 933 , 563 ) have been known . the phthalonitrile derivatives of the present invention are practically very useful , because the responce speed is greatly improved in case of using them for , for example , guest - host type liquid crystal display because of having a lower viscosity than the above described known compounds ( the former ), and they show a wide liquid crystal temperature range as compared with the above described known compounds ( the latter ). further , the phthalonitrile compounds of the present invention are useful as liquid crystal materials for tn liquid crystal display and , particularly , liquid crystal materials for carrying out high time split driving in addition to the above described materials for guest - host type liquid crystal display . for example , in order to carry out time split driving , it is important to have a good rising characteristic of luminance brightness in case of applying a voltage to the liquid crystal device . in order to increase a time split drive ratio ( number of scanning lines ), it is necessary to improve the rising characteristic . this rising characteristic is concerned with the dielectric parameter ( δε / ε ⊥) of the liquid crystal material , and a case having a lower value of δε / ε ⊥ is preferable ( japanese patent application ( opi ) no . 16087 / 82 ). in case of using the prior phthalonitrile compounds , it is difficult to reduce the value of δε / ε ⊥ to 2 or less . even if the value of δε / ε ⊥ can be reduced , it is not preferred , because the viscosity increases . on the contrary , when the value δε / ε ⊥ and the viscosity of liquid crystal materials for tn which are produced using the phthalonitrile compounds of the present invention are examined , it is understood that a composition having a value of δε / ε ⊥ of 1 . 5 or less can be obtained without changing the viscosity , and the time split drive ratio can be increased twice or more times as compared with the prior cases . in the following , the present invention is illustrated in greater detail with reference to examples , but it is not limited to examples unless it departs from the gist of the present invention . in the following examples , m . p . means a melting point and cl . p . means a phase transition point . 1 . 0 g of 1 , 4 - bis -( p - n - butoxyphenyl )- 1 , 3 - butadiene and 0 . 3 g of fumaronitrile were blended and subjected to reacting at 170 °- 180 ° c . in a nitrogen stream for 7 hours . after cooled , separation was carried out by column chromatography using silica gel as a carrier and chloroform as a separation solvent to obtain 1 . 1 g of a crude product of 3 , 6 - bis -( p - n - butoxyphenyl )- 1 , 2 , 3 , 6 - tetrahydrophthalonitrile . m + ( m / e )= 428 was shown in mass spectrum . 0 . 3 g of the resulted crude product and 0 . 05 g of sulfur were added to 20 ml of n - methylpyrrolidone , and the mixture was refluxed with heating for 2 hours . after cooled , n - methylpyrrolidone was distilled away under a reduced pressure , and the residue was purified by column chromatography using silica gel as a carrier and chloroform - n - hexane ( 2 : 1 ) as a separation solvent to obtain 0 . 07 g of 3 , 7 - bis -( p - n - butoxyphenyl ) phthalonitrile . m . p . was 179 . 5 ° c . 2 . 6 g of 1 -( p - methoxyphenyl )- 4 -( p &# 39 ;- n - heptyloxyphenyl )- 1 , 3 - butadiene and 0 . 73 g of dicyanoacetylene were blended and subjected to reacting in a sealed tube at 120 ° c . for 5 hours . after cooled , separation was carried out by column chromatography using silica gel as a carrier and chloroform as a separation solvent to obtain 2 . 5 g of a crude product of 3 -( p - methoxyphenyl )- 6 -( p &# 39 ;- n - heptyloxyphenyl )- 3 , 6 - dihydrophthalonitrile . m + ( m / e )= 426 was shown in mass spectrum . 2 . 0 g of the crude product and 1 . 2 g of sodium acetate were added to 20 ml of acetic acid , and 0 . 75 g of bromine was slowly added dropwise thereto with heating to 110 ° c . the reaction was carried out at this temperature for 2 hours . after cooled , water was added and extraction was carried out with chloroform . after chloroform was distilled away under a reduced pressure , the residue was purified by column chromatography using n - hexane ( 2 : 1 ) as a separation solvent to obtain 0 . 6 g of 3 -( p - methoxyphenyl )- 6 -( p &# 39 ;- n - heptyloxyphenyl ) phthalonitrile . it was a monotropic nematic liquid crystal having m . p . of 125 . 5 ° c . and cl . p . of 120 ° c . using 1 -( p - n - butoxyphenyl )- 4 -( p &# 39 ;- n - pentylphenyl )- 1 , 3 - butadiene and fumaronitrile , 3 -( p - n - butoxyphenyl )- 6 -( p &# 39 ;- n - pentylphenyl ) phthalonitrile was obtained by the same method as in example 1 . m . p . was 159 ° c . using 1 -( p - n - butoxyphenyl )- 4 - methyl - 1 , 3 - butadiene and fumaronitrile , 3 -( p - n - butoxyphenyl )- 6 - methylphthalonitrile was obtained by the same method as in example 1 . m . p . was 151 . 5 ° c . using 1 -( trans - 4 &# 39 ;- n - propylcyclohexyl )- 4 -( p - n - butoxyphenyl )- 1 , 3 - butadiene and fumaronitrile , 3 -( trans - 4 &# 39 ;- n - propylcyclohexyl )- 6 -( p - n - butoxyphenyl ) phthalonitrile was obtained by the same method as in example 1 . m . p . was 115 ° c . using 1 -( trans - 4 &# 39 ;- n - propylcyclohexyl )- 4 -( p - n - pentylphenyl )- 1 , 3 - butadiene and fumaronitrile , 3 -( trans - 4 &# 39 ;- n - propylcyclohexyl )- 6 -( p - n - pentylphenyl ) phthalonitrile was obtained by the same method as in example 1 . m . p . was 97 ° c . using 1 -( p - n - butoxyphenyl )- 6 -( p &# 39 ;-( trans - 4 &# 39 ;- n - pentylcyclohexyl ) phenyl )- 1 , 3 - butadiene and fumaronitrile , 3 -( p - n - butoxy )- 6 -( p &# 39 ;-( trans - 4 &# 39 ;- n - pentylcyclohexyl ) phenyl ) phthalonitrile was obtained by the same method as in example 1 . m . p . was 175 ° c . and cl . p . was 264 ° c . using 1 -( p - fluorophenyl )- 4 -( trans - 4 &# 39 ;- n - pentylcyclohexyl )- 1 , 3 - butadiene and fumaronitrile , 3 -( p - fluorophenyl )- 6 -( trans - 4 &# 39 ;- n - pentylcyclohexyl ) phthalonitrile was obtained by the same method as in example 1 . m . p . was 102 . 5 ° c . using 1 - cyclohexyl - 4 -( trans - 4 &# 39 ;- n - propylcyclohexyl )- 1 , 3 - butadiene and fumaronitrile , 3 - cyclohexyl - 6 -( trans - 4 &# 39 ;- n - propylcyclohexyl ) phthalonitrile was obtained by the same method as in example 1 . it was a monotropic nematic liquid crystal having m . p . of 102 . 5 ° c . and cl . p . of 92 ° c . using 1 -( p -( trans - 4 &# 39 ;- n - pentylcyclohexyl ) phenyl )- 4 -( trans - 4 &# 34 ;- n - pentylcyclohexyl )- 1 , 3 - butadiene and fumaronitrile , 3 -( p -( trans - 4 &# 39 ;- n - pentylcyclohexyl ) phenyl )- 6 -( trans - 4 &# 39 ;- n - pentylcyclohexyl ) phthalonitrile was obtained by the same method as in example 1 . using 1 -( p - n - propylphenyl )- 4 -( p &# 39 ;- n - pentylphenyl )- 1 , 3 - butadiene and fumaronitrile , 3 -( p - n - propylphenyl )- 6 -( p &# 39 ;- n - pentylphenyl ) phthalonitrile was obtained by the same method as in example 1 . using 1 -( trans - trans - 4 &# 39 ;- n - propylcyclohexylcyclohexyl )- 4 - methyl - 1 , 3 - butadiene and fumaronitrile , 3 -( trans - trans - 4 &# 39 ;- n - propylcyclohexylcyclohexyl )- 6 - methylphthalonitrile was obtained by the same method as in example 1 . using 1 -( p - 4 &# 39 ;- n - propyloxyphenyl ) phenyl )- 4 - methyl - 1 , 3 - butadiene and fumaronitrile , 3 -( p -( 4 &# 39 ;- n - propyloxyphenyl ) phenyl )- 6 - methylphthalonitrile was obtained by the same method as in example 1 . using 1 -( p -( 4 &# 39 ;- n - propylphenyl ) phenyl )- 4 - methyl - 1 , 3 - butadiene and fumaronitrile , 3 -( p -( 4 &# 39 ;- n - propylphenyl ) phenyl )- 6 - methylphthalonitrile was obtained by the same method as in example 1 . using 1 -( 4 &# 39 ;- n - propyl - 1 &# 39 ;- bicyclo ( 2 , 2 , 2 ) octyl )- 4 -( p - n - butoxyphenyl )- 1 , 3 - butadiene and fumaronitrile , 3 -( 4 &# 39 ;- n - propyl - 1 &# 39 ;- bicyclo ( 2 , 2 , 2 ) octyl )- 6 -( p - n - butoxyphenyl ) phthalonitrile was obtained by the same method as in example 1 . using 1 -( 4 &# 39 ;- n - propyl - 1 &# 39 ;- bicyclo ( 2 , 2 , 2 ) octyl )- 4 - n - pentyl - 1 , 3 - butadiene and fumaronitrile , 3 -( 4 &# 39 ;- n - propyl - 1 &# 39 ;- bicyclo ( 2 , 2 , 2 ) octyl )- 6 - n - pentylphthalonitrile was obtained by the same method as in example 1 . using 1 -( p -( 4 &# 39 ;- n - pentyl - 1 &# 39 ;- bicyclo ( 2 , 2 , 2 ) octyl ) phenyl )- 4 -( trans - 4 &# 39 ;- n - pentylcyclohexyl )- 1 , 3 - butadiene and fumaronitrile , 3 -( p -( 4 &# 39 ;- n - pentyl - 1 &# 39 ;- bicyclo ( 2 , 2 , 2 ) octyl ) phenyl )- 6 -( trans - 4 &# 39 ;- n - pentylcyclohexyl ) phthalonitrile was obtained by the same method as in example 1 . a mixture of 20 . 0 parts of trans - 4 - n - propylcyclohexanecarboxylic acid - p - n - pentyloxyphenyl ester , 20 . 0 parts of trans - 4 - pentylcyclohexanecarboxylic acid p - n - ethoxyphenyl ester , 30 . 0 parts of trans - 4 - n - pentylcyclohexanecarboxylic acid p - n - pentyloxyphenyl ester and 30 . 0 parts of p - methoxybenzoic acid p &# 39 ;- n - pentylphenyl ester had a nematic liquid crystal temperature range of - 6 °- 65 ° c . and δε of - 0 . 9 . a mixture prepared by blending 0 . 50 g of 3 -( p - methoxyphenyl )- 6 -( p &# 39 ;- n - heptyloxyphenyl ) phthalinitrile obtained in example 2 with 9 . 0 g of the above described mixture as a base solution crystal had a liquid crystal temperature range of - 5 °- 66 ° c . and δε of - 2 . 0 . 1 % by weight of the dye d - 16 produced by bdh co . as a guest was added to the resulted mixture as a host . when a guest - host effect was examined , the threshold voltage was 2 . 4 v and the saturation voltage was 2 . 9 . in case of measuring those of the base liquid crystal itself , they were 10 v or more , respectively . 3 -( p - n - butoxyphenyl )- 6 - methylphthalonitrile obtained in example 4 was used under the same condition as in example 19 instead of the compound obtained in example 2 . when the guest - host effect was examined , the threshold voltage was 2 . 3 v and the saturation voltage was 2 . 7 v . 3 - cyclohexyl - 6 -( trans - 4 &# 39 ;- n - propylcyclohexyl ) phthalonitrile obtained in example 9 was used under the same condition as in example 19 instead of the compound obtained in example 2 . when the guest - host effect was examined , the threshold voltage was 2 . 2 v and the saturation voltage was 2 . 6 v . viscosity of the compounds of the present invention and that of known phthalonitrile compounds were compared . namely , the viscosity of liquid crystal compositions obtained in examples 20 and 21 and that of liquid crystal compositions which were obtained by adding compounds shown in the following table 1 in such an amount that the threshold voltage became the same value , instead of phthalonitrile derivatives of the present invention were measured by the conventional method . the results are shown in table 1 . table 1______________________________________ vis - thres - cosity hold ( 20 ° no . phthalonitrile derivative voltage c .) ______________________________________1 compound in example 20 2 . 3 v 36 cp2 compound in example 21 2 . 2 v 38 cp ## str23 ## 2 . 6 v 42 cp 4 ## str24 ## 2 . 3 v 48 cp______________________________________ as be obvious from the above results , the compounds of the present invention have a characteristic of greatly improving the drawback of the prior known materials , that is , they have a low viscosity , namely , responce speed can be increased without changing other properties , as compared with the prior known materials . liquid crystal temperature range of compounds of the present invention and that of the known phthalonitrile compound were compared . namely , liquid crystal compositions were prepared by the same method as in example 19 , except that 0 . 5 parts of phthalonitrile compounds of the present invention obtained in examples 4 , 6 and 2 and the known compound ## str25 ## to 9 . 5 parts of the same base liquid crystal as in example 19 , respectively . the liquid temperature range of them are shown in table 2 . table 2______________________________________ liquid crystal temperatureno . composition range______________________________________1 . compound of example 4 0 - 58 ° c . ## str26 ## 2 . compound of example 6 - 5 - 65 ° c . ## str27 ## 3 . compound of example 2 - 5 - 66 ° c . ## str28 ## 4 . ## str29 ## 2 - 48 ° c . ______________________________________ as be obvious , a wider liquid crystal temperature range could be obtained by using the compound of the present invention . in a liquid crystal display device using a liquid crystal composition having a wide liquid crystal temperature range , a temperature range capable of displaying becomes wide . accordingly , it is obvious that the compounds of the present invention are superior to the above described known compound . while the invention has been described in detail and with reference to specific embodiments thereof , it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof .