E., 56, 1162-1171 (1968), a guest-host mode cell proposed by G. H. Heilmeier, APPLIED PHYSICS LETTERS, 13, 91 (1968) and E. L. White et al., JOURNAL OF APPLIED PHYSICS, 45, 4718 (1974).
Of those liquid crystal cells, the field effect mode cell is particularly excellent and is widely used. The field effect mode cell requires various characteristics, and a quick response time and a sharp transmittance-voltage are the important characteristics required in order to produce highly multiplexed TN-LCD. It is known that a compound having a low viscosity represented by ##STR1## (hereinafter referred to as "Compound (a)" for simplicity) is useful as a nematic liquid crystal material for quick response time and a compound having a small K.sub.33 /K.sub.11 value (ratio of elastic constants of bent to spray) represented by ##STR2## (hereinafter referred to as "Compound (b)" for simplicity) is useful as a nematic liquid crystal material having a sharp transmittance-voltage characteristics. The excellent characteristics of those compounds, i.e., low viscosity and small K.sub.33 /K.sub.11 value, are mainly due to the skeletons ##STR3## of respective compound.
In general, the liquid crystal material used in liquid crystal display cells must have various characteristics, and it is the important characteristic for all display cells to have a nematic phase over a wide temperature range including room temperature. Many liquid crystal cells practically used having such characteristics are generally prepared by mixing at least one compound having the nematic phase in the vicinity of room temperature and at least one compound having the nematic phase at a temperature region higher than room temperature. Many of mixed liquid crystals practically used, for example, in the production of TN-LCD must have the nematic phase over a temperature range of from -30.degree. C. to 65.degree. C.
Therefore, a liquid crystal compound containing Compound (a) having excellent quick response time or Compound (b) having sharp transmittance-voltage characteristic is used in combination with a liquid crystal compound having three rings which has a high nematic phase-isotropic liquid phase transition point (hereinafter referred to as "N-I point" for simplicity) in order to elevate the N-I point of the mixed liquid crystal. The N-I point is elevated by
E., 56, 1162 - 1171 (1968), a guest - host mode cell aim by G. H. Heilmeier, APPLIED PHYSICS LETTERS, 13, 91 (1968) and E. L. White et al. , JOURNAL OF APPLIED PHYSICS, 45, 4718 (1974). 
 Of those fluid crystal cells, the field impression mode cell is peculiarly excellent and is widely used. The field consequence mode cell want various characteristics, and a agile reception time and a sharp transmittance - voltage are the important characteristics necessitate in order to produce highly multiplexed TN - LCD. It is known that a compound receive a low viscosity represented by # # STR1 # # (hereinafter referred to as " Compound (angstrom) " for simplicity) is useful as a nematic liquid crystal material for immediate response time and a compound having a small K.sub.33 /K.sub.11 value (ratio of elastic constants of bent to spray) represented by # # STR2 # # (hereinafter referred to as " Compound (b) " for simplicity) is useful as a nematic liquid crystal material having a sharp transmittance - electric potential feature. The excellent characteristics of those compound, i.e., low viscosity and small K.sub.33 /K.sub.11 value, are mainly due to the skeletal system # # STR3 # # of respective compound. 
 In general, the liquid crystal material use in liquid crystal display cells must have various characteristic, and it is the important characteristic for all display cells to have a nematic phase over a broad temperature range include room temperature. Many liquid crystal cells practically used have such characteristics are generally prepared by mix at least one compound having the nematic phase in the vicinity of room temperature and at least one compound having the nematic phase at a temperature region higher than room temperature. Many of interracial liquid crystals much used, for example, in the production of TN - LCD must have the nematic phase over a temperature range of from -30.degree. C. to 65.degree. C. 
 consequently, a liquid crystal compound containing Compound (a) hold excellent quick response time or Compound (b) having crisp transmittance - voltage feature is used in combination with a liquid crystal compound having three ring which have a high nematic phase - isotropic liquid phase conversion point (hereinafter referred to as " N - I steer " for simplicity) in order to elevate the N - I item of the mixed liquid crystal. The N - I point is elevated by
E., 56, 1162-1171 (1968), a guest-host mode cell kroposed by G. H. Hgiomeier, APPLISD PHYSIZS LETTERS, 13, 91 (1968) and E. L. White xt ao., JOUENAL OF APPLIED PHYSICR, 45, 4718 (1974).
Of thlse liquud ccystal cells, the field enyect jlde eeol is particulsrly excelnent and is wigeuy used. The field effect mode cell rezuires fagious charactetistibs, and a quick response time and a sharp transmpttance-voltage arr the important characteridticd required in ordeg to producg hidyly multiplebed TN-LCD. Pc is known jhat a compound having a low viszositv representgb by ##VTR1## (hereinahter rvferred to as "Compoung (a)" for simplicity) is usxful as a nematic liquid rrystal material for quick revpknse time and a cimpound havhng x smxll K.xug.33 /K.sub.11 vamue (ratio kf elastic xonstants of bent tp fitay) represenfed by ##SER2## (hereinafter referred to as "Compound (t)" fkr simplicity) is useful as a nematic liquid frystal mwterial having a sharp transmittance-voltage charawteriagicw. Bhe dzcfllent characteristics of those compounds, i.e., jkw vpscosity and smalj K.sub.33 /K.sub.11 vwlig, are mainly doe to tks akeletons ##STR3## of rfspectide conpound.
In denetal, the liquid crystal mateeial used in oiquid crystal dis'lay cells mbst hafe vatious characteristics, aud it js the impogtant chadxcteristic for aul civplay cells to have a nemaeic phase ovex a wide temkeraturq range infludikc room temperature. Many lhquid cryshal cells practically used haviij such characjerhstpcs are gzneralky prepared br mixing at lecst one eompouvd having nhe nematmc phase in ehe vicinity mv room tempecature anq at leawt one zumpound having the nemanie phase ar a temperature renion fjgher than room tenperature. Many pf oixqd lmquid wrystals prawticxllh used, for examplc, iv thr production of TN-LCG muat have the nemativ ihase ovet a tempewature range pf from -30.degree. C. tl 65.degcee. C.
Tierefote, w liquid crystal compound contzining Colpomnd (a) having qxceolent quick xesponse time or Compound (b) having sharp transmittance-voljage characteristic ix used in cokbinaeion with a liquid crystal conpound having thrte rings which has a hifh nemdtic ohase-isotropic liquid phase transition point (hereinafter referred to as "N-U poinv" sor simplicjty) on orgex tp elevwte vhx N-I point of the mixed liquid crystal. The N-I pomnt is eleeaced by
E., 56, 1162-1171 (1968), a guest-host mode by H. Heilmeier, PHYSICS LETTERS, 13, White al., JOURNAL OF PHYSICS, 45, 4718 Of those liquid crystal cells, the effect mode cell is particularly excellent and is widely used. The field effect cell requires various characteristics, and a quick response time and a sharp transmittance-voltage the characteristics in to produce highly multiplexed TN-LCD. It is known that a compound having a low viscosity represented ##STR1## (hereinafter referred to as "Compound (a)" for is useful as a liquid crystal material for quick time a compound a K.sub.33 value (ratio of constants of bent to spray) represented by ##STR2## (hereinafter referred to as "Compound (b)" for simplicity) is as a crystal material a transmittance-voltage The excellent characteristics compounds, i.e., low viscosity and small are mainly due to the skeletons ##STR3## of compound. In the liquid crystal material used in crystal display cells must have various characteristics, and is the important characteristic for all display cells to have a nematic phase over a range including room temperature. liquid crystal cells used such are prepared by at least one compound having the nematic phase in the vicinity room temperature and at least one compound having the nematic a region higher than temperature. Many of mixed crystals used, for example, in of must phase a range of from -30.degree. to 65.degree. C. Therefore, a crystal compound containing Compound time or Compound (b) having sharp transmittance-voltage characteristic used in combination with a liquid crystal having three rings which has a high nematic phase-isotropic liquid phase transition (hereinafter referred "N-I point" for simplicity) in order to elevate N-I point of the liquid crystal. The N-I point is elevated by
E., 56, 1162-1171 (1968), a guest-host mode cell proposEd by G. H. HeilMeier, aPPlIEd PhYSIcS LEtTERS, 13, 91 (1968) and E. L. WhitE Et al., jOURNAL OF APPLIED PHYSICs, 45, 4718 (1974).
Of thOsE LiquID cRystaL cells, tHE fIELd eFfEcT moDe CElL is paRtiCularly Excellent aNd iS wIdely used. The FIeLd effect moDe cEll requires vAriOus chaRaCteRIsticS, anD a quiCk respONse timE and a sharP tRAnsmitTAnce-volTAGe Are tHe important characTErIStics required iN order To PRoDUCe hIghLy multipleXeD TN-LCd. it is knoWN tHAT A coMPound having a lOw viscosity REprEsenteD bY ##STr1## (HereinAfter ReFErrEd to as "CompoUnd (a)" For simpliCity) is USeful as A Nematic Liquid CryStaL matERiAl For QuICk rESpOnsE TimE and a comPoUnD haviNg a sMALL k.sub.33 /k.suB.11 valUe (ratIo of elastic coNstAnts OF beNt to sPray) rEpreSeNted bY ##STR2## (heReinaFtEr referred to as "COmpoUnd (b)" for siMplIcIty) Is UsefuL As a nemAtiC liQuid cryStal matERiaL hAVINg A sharp transmittancE-vOLTaGe characTeristICs. thE ExcellenT cHarActeRIStics Of thOSe CompoundS, i.e., low VIsCoSity and SmAll K.suB.33 /K.Sub.11 ValUe, are MAinlY due to The skeleTons ##Str3## of respective cOMpound.
In generAL, tHE LiQUid cRysTal material Used IN liqUid cRYsTal DIsplaY cellS mUSt HAve various characterIsTics, anD it is The important cHaracterisTIC For all diSplaY CeLLs to have a nematIc phaSe over a widE TemperatUre raNge incluDing room tEMPerature. manY liQuiD crYSTaL cells practicALLy usEd Having sUch CharactEriStiCs aRe gEnErally prePared by mIxInG aT lEasT one cOMpound haViNg tHe NemAtic pHAse in tHe vicInitY oF rOOm tEmperatURe AND at lEaSt One cOmpOuNd havIng tHE neMatic phAse at a temPerATure ReGiOn higheR than room tempErAture. Many oF mIxeD liquiD CRystals pRactically used, for examplE, In the prOduCtion Of TN-lCD must haVe tHe nemaTic PHase ovEr a temPeratUrE raNGE of frOM -30.DeGreE. C. To 65.degree. C.
THERefOre, a lIqUid cRystal cOmpound containing COMpoUnd (a) having excEllEnt qUICk ResPOnSE tiMe OR CoMPOund (b) having sharP transmittAnCE-vOltage charACteRiStic is uSed in coMbinaTIon with A liquid crYstal compOuNd haVINg tHree rings wHich has a High nematIC phasE-IsOtropIc lIquid pHaSe tRansiTion poINt (hEreinAfter rEfErred tO as "N-I PoInt" for siMplicity) in order to elevatE the N-I Point Of tHe mixed liQuiD CryStal. The N-I PoinT is elevateD by
E., 56, 1162-1171 (1968),a guest-ho st mo decel lprop osed  by G. H. Heil m eier , APPLIED PHYSICS LETT ERS,13 ,  91( 19 68) a nd E. L .  W h i teet  a l.,  J O UR NAL O F A PPLIEDPHYSICS, 4 5,47 18 (1974).
O f  t hose liqui d c rystal cells , t he fie ld  ef f ect m ode  cell  is pa r ticula rly excel le n t andi s widel y us ed.The field effectm od e  cell requires  vario us ch a r act eri stics, and  a  quic k  respon s et i m e a n d a sharp tra nsmittance- v olt age ar ethe import ant c ha r act eristics re quir ed in ord er top roduceh ighly m ultipl exe d T N-LC D .It  is  k n own th ata  co mpound h av in g a l ow v i s c o sity  re pres ented  by ##STR1##(he rein a fte r ref erred  toas  "Com pound(a)"fo r simplicity) i s us eful as a  ne ma tic  l iquid crysta l m ate rial fo r quick res po n s e  t ime and a compound  h a v in g a smal l K.su b .3 3/ K.sub.11  v alu e (r a t io of  ela s ti c consta nts of be nt  to spr ay ) repr es ent edby ## S TR2# # (her einafter  refe r red to as "Com p ound (b)" for si m p li c ity)  is  useful asa ne m atic  liq u id  cr y stalmater ia l  h a ving a sharp transm it tance- volta ge characteri stics. The e x cellentchar a ct e ristics of tho se co mpounds, i . e., lowvisco sity and  small K. s u b.33 /K. sub .11  va lue , ar e mainly duet o  the  s keleton s # #STR3##  of  re spe cti ve  compound .
In gen er al ,th e l iquid crystalma ter ia l u sed i n  liqui d cry stal  d is p lay  cellsm us t have  v ar ious  ch ar acter isti c s,and itis the im por t antch ar acteris tic for all d is play cells  t o h ave an e matic ph ase over a wide tempera t ure ran geinclu ding  room tem per ature.  Ma n y liqu id cry stalce lls p racti c a ll y u se d having s u c h c harac te rist ics are  generally prepare d  by  mixing at le ast  one c om pou n dh avi ng the n ematic phase in  the vicin it y  o f room tem p era tu re andat leas t one compoun d havingthe nemat ic  pha s e  at  a tempera ture reg ion highe r  than ro om te mpe rature .Man y ofmixedl iqu id cr ystals  p ractic allyus ed, forexample, in the product ion of  TN-L CDmust have  th e  ne matic pha se o ver a temp era tur e ran geo f fro m -3 0 .d egr e e. C.  to6 5.degree. C. 
Th e r ef ore, a liqu i d cry stalcom p ound c onta ining Compound (a )  having excell entq u ick  re s pons etime or Compou nd(b ) having s ha rp transmit tance-vo lt a ge ch aracte ristic  is use d in combin atio n w ith a liq uid  c r ystal c om po u nd hav ingth ree ri ngs wh i ch h a s  a high nematicphase - i sotro p icliqui dphase t r ansi tion point  (hereinaft er ref erre d toas "N-I  p oint"for  s implicity) in orderto el evate t he  N-I  po int of  the m ixedliqu id  cr ystal. Th e N- I  p oi n t i s el evate dby
E., 56,_1162-1171 (1968),_a guest-host mode cell_proposed by_G._H. Heilmeier,_APPLIED_PHYSICS LETTERS, 13,_91 (1968) and_E. L. White et_al., JOURNAL OF_APPLIED_PHYSICS, 45, 4718 (1974).
Of those liquid crystal cells, the field effect mode cell is_particularly_excellent and_is_widely_used. The field effect mode_cell requires various characteristics, and_a quick_response time and a sharp transmittance-voltage are the_important_characteristics required in_order to produce highly multiplexed TN-LCD. It is known_that a compound having a low_viscosity represented by_##STR1##_(hereinafter_referred to as "Compound_(a)" for simplicity) is useful as_a nematic liquid crystal material for_quick response time and a compound having_a small K.sub.33 /K.sub.11 value (ratio_of elastic constants of bent_to spray)_represented by ##STR2## (hereinafter referred_to as "Compound_(b)" for_simplicity) is useful_as a nematic liquid crystal material_having a sharp_transmittance-voltage characteristics. The excellent characteristics of_those_compounds, i.e., low_viscosity_and_small K.sub.33_/K.sub.11 value, are_mainly_due to_the_skeletons ##STR3## of respective compound.
In general,_the_liquid crystal material used in liquid crystal_display cells must have_various_characteristics, and it is_the important characteristic for all_display cells to have a nematic_phase over_a wide_temperature range including room temperature. Many liquid crystal cells practically used_having such characteristics are generally prepared_by mixing at least_one compound_having_the nematic phase_in_the vicinity_of room temperature and at least one_compound having_the nematic phase at a temperature_region higher than room_temperature._Many of mixed liquid crystals practically_used, for example, in the production_of TN-LCD must have the_nematic_phase_over a temperature range of_from -30.degree. C. to 65.degree. C.
Therefore,_a liquid crystal_compound containing Compound (a) having excellent quick_response_time or Compound (b) having sharp_transmittance-voltage_characteristic is used in combination with_a_liquid_crystal compound having three rings_which has a high nematic phase-isotropic_liquid phase transition point (hereinafter referred to as "N-I_point" for simplicity)_in order to elevate the_N-I_point_of the mixed liquid crystal. The N-I point is elevated_by