4
This work has been digitalized and published in 2013 by Verlag Zeitschrift für Naturforschung in cooperation with the Max Planck Society for the Advancement of Science under a Creative Commons Attribution 4.0 International License. Dieses Werk wurde im Jahr 2013 vom Verlag Zeitschrift für Naturforschung in Zusammenarbeit mit der Max-Planck-Gesellschaft zur Förderung der Wissenschaften e.V. digitalisiert und unter folgender Lizenz veröffentlicht: Creative Commons Namensnennung 4.0 Lizenz. Nematic Liquid Crystals with High Positive Dielectric Anisotropy M a g e d A . Osman* Brown Boveri Research Center, Chemistry Group, CH-5405 Baden-Dättwil, Switzerland Z. Naturforsch. 34b, 1092-1095 (1979); received March 23, 1979 Liquid Crystals, Nematic Phases, High Positive Dielectric Anisotropy, Alkylamino-cyano-biphenyls, Alkylamino-cyano-phenylbenzoates Alkylamino- and formyl alkylamino-cyano Schiff's base, biphenyl and phenylbenzoate liquid crystals were synthesized. The mesomorphic behaviour of these compounds is described. The introduction of the formyl group in the higher homologues lead to the disappearance of the mesophase. The alkylamino and formylalkylamino substituents are strong electron donating groups and lead to nematic phases with remarkably high positive dielectric anisotropy. Interest in electrooptical displays based on the twisted nematic effect [1] has lead to a growing demand for nematic liquid crystals with positive dielectric anisotropy. Non-polar or almost non-polar nematic compounds of the type 1 were found to possess a very small positive dielectric anisotropy (As = 0.05-0.5) [5-7], X =-CH= N- |21 , - C 0 0 - 131,—N=N— |4| 1 Nematic phases of the Schiff's base and phenyl- benzoate type with larger A a were synthesized by A. Boiler [8, 9] through replacement of one of the alkyl groups by the cyano group which possess a larger dipole moment (—4 D). The remaining alkyl group on the other end of the molecule, which has a dipole moment of -f- 0.3 D , was not changed. Recently, G. Gray [10] and R. Eidenschink [11] prepared analogous nematic phases of the biphenyl and phenyl cyclohexane types. All these compounds have A e values from 8 to 20 [12-14] which allow an operating voltage of 3 volts for a twisted nematic display. Since the threshold voltage and, correspond- ingly, the operating voltage is proportional to \J11A e, it is clear that new nematic liquid crystals with larger dielectric anisotropics are required if the operating voltage is to be substantially reduced. This can be achieved by replacing the remaining alkyl group with an electron donating substituent having a stronger dipole moment along the molecu- lar axis. The first attempt along this line was made by introducing the dimethylamino group (-(-1.6 D) * Reprint requests to Dr. M. A. Osman. 0340-5087/79/0800-1092/$ 01.00/0 at the other end of the benzyliden-aminobenzo- nitrile molecule, but this gave an isotropic com- pound melting at 183 °C [15]. The disappearance of the liquid crystalline properties is probably due to the high melting point of this compound and to the bulkiness of the dimethylamino group which lowers its clearing point. The aim of this work is to introduce the less bulky monoalkylamino group in molecules of type 1 and to study the effect of this substitution on their mesomorphic behaviour and on the magni- tude of the dielectric anisotropy. Results and Discussion N-(4-Methylaminobenzylidene)-4'-aminobenzo- nitrile (2) was prepared by condensing 4-methyl- aminobenzaldehyde with 4-aminobenzonitrile in bulk [16]. CH3 HN-^)-cho+H2 N-<Q>-CN-^CH3 HN-Q>-CH-N^Q>-CN z The aldehyde was prepared by the Vilsmeier re- action [17]. 2"c> ~HjC :N CN H0 ~ H 3 CHN <> CHO Compound 2 melted at 163.1 °C and showed a monotropic nematic phase clearing at 138.0 °C. This confirmed that the disappearance of the meso- phase in the dimethylamino derivative was caused by the bulkiness of this group. However, the melting point of compound 2 is too high for practical applications and for conveniently measuring the dielectric anisotropy. The higher homologues of alkylaminobenzaldehyde and their Schiff's bases were therefore prepared in an attempt to lower the melting point. It seemed also of interest to in-

Nematic Liquid Crystals with High Positive Dielectric Anisotropyzfn.mpdl.mpg.de/data/Reihe_B/34/ZNB-1979-34b-1092.pdfNematic Liquid Crystals with High Positive Dielectric Anisotropy

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  • This work has been digitalized and published in 2013 by Verlag Zeitschrift für Naturforschung in cooperation with the Max Planck Society for the Advancement of Science under a Creative Commons Attribution4.0 International License.

    Dieses Werk wurde im Jahr 2013 vom Verlag Zeitschrift für Naturforschungin Zusammenarbeit mit der Max-Planck-Gesellschaft zur Förderung derWissenschaften e.V. digitalisiert und unter folgender Lizenz veröffentlicht:Creative Commons Namensnennung 4.0 Lizenz.

    Nematic Liquid Crystals with High Positive Dielectric Anisotropy

    M a g e d A . O s m a n *

    B r o w n Boveri Research Center, Chemistry Group, CH-5405 Baden-Dättwil , Switzerland

    Z. Naturforsch. 34b, 1092-1095 (1979); received March 23, 1979

    Liquid Crystals, Nematic Phases, High Positive Dielectric Anisotropy,

    Alkylamino-cyano-b iphenyls , Alkylamino-cyano-phenylbenzoates Alky lamino- and formyl a lkylamino-cyano Schif f 's base, biphenyl and phenylbenzoate

    l iquid crystals were synthesized. The mesomorphic behaviour o f these compounds is described. The introduction of the formyl group in the higher homologues lead to the disappearance o f the mesophase. The alkylamino and formylalkylamino substituents are strong electron donating groups and lead to nematic phases with remarkably high posit ive dielectric anisotropy.

    I n t e r e s t i n e l e c t r o o p t i c a l d i s p l a y s b a s e d o n t h e

    t w i s t e d n e m a t i c e f f e c t [1] h a s l e a d t o a g r o w i n g

    d e m a n d f o r n e m a t i c l i q u i d c r y s t a l s w i t h p o s i t i v e

    d i e l e c t r i c a n i s o t r o p y . N o n - p o l a r o r a l m o s t n o n - p o l a r

    n e m a t i c c o m p o u n d s o f t h e t y p e 1 w e r e f o u n d t o

    p o s s e s s a v e r y s m a l l p o s i t i v e d i e l e c t r i c a n i s o t r o p y

    (As = 0 . 0 5 - 0 . 5 ) [ 5 - 7 ] ,

    X =-CH= N - |21 , - C 0 0 - 131,—N=N— |4|

    1

    N e m a t i c p h a s e s o f t h e S c h i f f ' s b a s e a n d p h e n y l -

    b e n z o a t e t y p e w i t h l a r g e r A a w e r e s y n t h e s i z e d b y A . B o i l e r [8, 9] t h r o u g h r e p l a c e m e n t o f o n e o f t h e

    a l k y l g r o u p s b y t h e c y a n o g r o u p w h i c h p o s s e s s a

    l a r g e r d i p o l e m o m e n t ( — 4 D ) . T h e r e m a i n i n g a l k y l

    g r o u p o n t h e o t h e r e n d o f t h e m o l e c u l e , w h i c h h a s a

    d i p o l e m o m e n t o f -f- 0.3 D , w a s n o t c h a n g e d .

    R e c e n t l y , G . G r a y [10] a n d R . E i d e n s c h i n k [ 1 1 ]

    p r e p a r e d a n a l o g o u s n e m a t i c p h a s e s o f t h e b i p h e n y l

    a n d p h e n y l c y c l o h e x a n e t y p e s . A l l t h e s e c o m p o u n d s

    h a v e A e v a l u e s f r o m 8 t o 20 [ 1 2 - 1 4 ] w h i c h a l l o w a n o p e r a t i n g v o l t a g e o f 3 v o l t s f o r a t w i s t e d n e m a t i c

    d i s p l a y . S i n c e t h e t h r e s h o l d v o l t a g e a n d , c o r r e s p o n d -

    i n g l y , t h e o p e r a t i n g v o l t a g e is p r o p o r t i o n a l t o

    \J11A e, i t is c l e a r t h a t n e w n e m a t i c l i q u i d c r y s t a l s w i t h l a r g e r d i e l e c t r i c a n i s o t r o p i c s a r e r e q u i r e d i f t h e

    o p e r a t i n g v o l t a g e is t o b e s u b s t a n t i a l l y r e d u c e d .

    T h i s c a n b e a c h i e v e d b y r e p l a c i n g t h e r e m a i n i n g

    a l k y l g r o u p w i t h a n e l e c t r o n d o n a t i n g s u b s t i t u e n t

    h a v i n g a s t r o n g e r d i p o l e m o m e n t a l o n g t h e m o l e c u -

    l a r a x i s . T h e f i rs t a t t e m p t a l o n g t h i s l i n e w a s m a d e

    b y i n t r o d u c i n g t h e d i m e t h y l a m i n o g r o u p ( - ( - 1 . 6 D )

    * Reprint requests to Dr . M. A . Osman. 0340-5087/79/0800-1092/$ 01.00/0

    a t t h e o t h e r e n d o f t h e b e n z y l i d e n - a m i n o b e n z o -

    n i t r i l e m o l e c u l e , b u t t h i s g a v e a n i s o t r o p i c c o m -

    p o u n d m e l t i n g a t 183 °C [15] . T h e d i s a p p e a r a n c e o f

    t h e l i q u i d c r y s t a l l i n e p r o p e r t i e s is p r o b a b l y d u e t o

    t h e h i g h m e l t i n g p o i n t o f t h i s c o m p o u n d a n d t o t h e

    b u l k i n e s s o f t h e d i m e t h y l a m i n o g r o u p w h i c h l o w e r s

    i t s c l e a r i n g p o i n t . T h e a i m o f t h i s w o r k is t o i n t r o d u c e

    t h e less b u l k y m o n o a l k y l a m i n o g r o u p i n m o l e c u l e s

    o f t y p e 1 a n d t o s t u d y t h e e f f e c t o f t h i s s u b s t i t u t i o n

    o n t h e i r m e s o m o r p h i c b e h a v i o u r a n d o n t h e m a g n i -

    t u d e o f t h e d i e l e c t r i c a n i s o t r o p y .

    Results and Discussion

    N - ( 4 - M e t h y l a m i n o b e n z y l i d e n e ) - 4 ' - a m i n o b e n z o -

    n i t r i l e (2) w a s p r e p a r e d b y c o n d e n s i n g 4 - m e t h y l -

    a m i n o b e n z a l d e h y d e w i t h 4 - a m i n o b e n z o n i t r i l e i n

    b u l k [16].

    CH3HN-̂ )-cho+H2N--CN-̂ CH3HN-Q>-CH-N^Q>-CN

    z

    T h e a l d e h y d e w a s p r e p a r e d b y t h e V i l s m e i e r re-

    a c t i o n [17] .

    2"c> ~ H j C : N C N H 0 ~ H 3 C H N < > CHO

    C o m p o u n d 2 m e l t e d a t 1 6 3 . 1 °C a n d s h o w e d a

    m o n o t r o p i c n e m a t i c p h a s e c l e a r i n g a t 138.0 °C.

    T h i s c o n f i r m e d t h a t t h e d i s a p p e a r a n c e o f t h e m e s o -

    p h a s e i n t h e d i m e t h y l a m i n o d e r i v a t i v e w a s c a u s e d

    b y t h e b u l k i n e s s o f t h i s g r o u p . H o w e v e r , t h e m e l t i n g

    p o i n t o f c o m p o u n d 2 is t o o h i g h f o r p r a c t i c a l

    a p p l i c a t i o n s a n d f o r c o n v e n i e n t l y m e a s u r i n g t h e

    d i e l e c t r i c a n i s o t r o p y . T h e h i g h e r h o m o l o g u e s o f

    a l k y l a m i n o b e n z a l d e h y d e a n d t h e i r S c h i f f ' s b a s e s

    w e r e t h e r e f o r e p r e p a r e d in a n a t t e m p t t o l o w e r t h e

    m e l t i n g p o i n t . I t s e e m e d a l s o o f i n t e r e s t t o in-

  • M. A. Osman • Nematic Liquid Crystals 1093

    * > - ® - C H - N - © - C N

    X R TM [°C] Tc [°C] Gernerai C [ % ] H [ % ] N [ % ] formula calcd found calcd found calcd found

    H CH3 163.2 138.0 C15H13N3 76.57 76.46 5.57 5.61 17.86 17.68 H C2H5 154.6 129.1 C16H15N3 77.08 77.02 6.06 6.04 16.86 16.86 H C3H7 151.7 — C17H17N3 77.53 77.51 6.51 6.55 15.91 15.96 H C4H9 129.6 — Ci8HI9N3 77.94 77.76 6.91 6.88 15.15 15.06 H C6H13 97.8 78.6 CsoHagNg 78.65 78.78 7.59 7.72 13.76 13.73 H C8H17 95.8 78.1 C22H27N3 79.24 79.36 8.16 8.28 12.60 12.45 CHO CH3 159.1 134.8 C16H13N3O 72.98 72.83 4.98 5.10 15.96 15.92 CHO C2H5 132.3 — C17H15N3O 73.63 73.49 5.45 5.55 15.15 15.00 CHO C4H9 81.2 — C19H19N3O 74.73 74.55 6.27 6.32 13.76 13.60

    v e s t i g a t e t h e e f f e c t o f i n t r o d u c i n g t h e f o r m y l g r o u p

    i n t h e a l k y l a m i n o S c h i f ' s b a s e s .

    T h e m e l t i n g a n d c l e a r i n g p o i n t s o f t h e S c h i f f ' s

    b a s e s a r e g i v e n i n T a b l e I .

    A s i t w a s e x p e c t e d t h e m e l t i n g p o i n t s f e l l r a p i d l y

    f r o m 1 6 3 . 1 °C t o 9 7 . 8 °C w i t h g r o w i n g c h a i n l e n g t h

    u p t o CÖ- H o w e v e r , e x t e n s i o n o f t h e a l k y l c h a i n t o C 8 d i d n o t m a r k e d l y l o w e r t h e m e l t i n g p o i n t .

    U n f o r t u n a t e l y t h e c l e a r i n g p o i n t s s u f f e r e d a s i m i l a r

    d e c r e a s e s o t h a t a l l t h e s y n t h e s i z e d a l k y l a m i n o

    S c h i f f ' s b a s e s s h o w e d o n l y m o n o t r o p i c n e m a t i c

    p h a s e s . T h e n e m a t i c t o i s o t r o p i c t r a n s i t i o n t e m -

    p e r a t u r e s i n t h i s s e r i e s a r e m u c h h i g h e r t h a n t h o s e

    o f t h e c o r r e s p o n d i n g a l k y l d e r i v a t i v e s [9]. T h e

    i n t r o d u c t i o n o f t h e f o r m y l g r o u p i n c o m p o u n d 2 d i d

    n o t h a v e a s i g n i f i c a n t e f f e c t o n e i t h e r i t s m e l t i n g

    p o i n t o r o n i t s c l e a r i n g p o i n t . H o w e v e r , i t d i d c a u s e

    a r e m a r k a b l e d e c r e a s e o f t h e m e l t i n g p o i n t s as w e l l

    a s o f t h e c l e a r i n g p o i n t s o f t h e h i g h e r h o m o l o g u e s s o

    t h a t t h e m e s o m o r p h i c p r o p e r t i e s d i s a p p e a r e d i n

    t h e s e c o m p o u n d s . T h e n e m a t i c p h a s e i n t h i s ser ies

    w a s o n l y m o n o t r o p i c a n d t h e m e a s u r e m e n t s o f t h e

    d i e l e c t r i c a n i s o t r o p y i n t h e s u p e r c o o l e d s t a t e w a s

    p r a c t i c a l l y i m p o s s i b l e .

    T h e c h e m i c a l l y m o r e s t a b l e 4 - a l k y l a m i n o - 4 ' -

    c y a n o b i p h e n y l s w e r e p r e p a r e d a c c o r d i n g t o t h e

    f o l l o w i n g s c h e m e :

    jsn/HCl

    T h e 4 - b r o m o - 4 ' - n i t r o b i p h e n y l w h i c h w a s o b t a i n e d

    b y b r o m i n a t i n g 4 - n i t r o b i p h e n y l [18], w a s f i rs t

    c o n v e r t e d t o t h e n i t r i l e d e r i v a t i v e [19] . T h e 4 - c y a n o -

    4 ' - n i t r o b i p h e n y l w a s t h e n r e d u c e d b y S n / H C l [20]

    t o t h e a m i n o d e r i v a t i v e a n d a l k y l a t e d w i t h t h e

    c o r r e s p o n d i n g a l k y l i o d i d e i n t h e n o r m a l w a y . T h e

    r e s u l t i n g m o n o a n d d i a l k y l d e r i v a t i v e s w e r e chro-

    m a t o g r a p h i c a l l y s e p a r a t e d .

    T h e m e l t i n g a n d c l e a r i n g p o i n t s o f t h e a l k y l a m i n o -

    a n d a l k y l f o r m y l a m i n o - c y a n o b i p h e n y l s a r e g i v e n i n

    T a b l e I I . A l l t h e m e m b e r s o f t h i s s e r i e s s h o w

    n e m a t i c p h a s e s w h i c h a r e t h e r m o d y n a m i c a l l y m o r e

    s t a b l e t h a n t h e c o r r e s p o n d i n g a l k y l d e r i v a t i v e s [10]

    ( F i g . 1). T h e f i rs t t h r e e m e m b e r s s h o w e d a n u n u s u a l

    s h a r p d e c r e a s e i n b o t h t h e m e l t i n g a n d t h e c l e a r i n g

    p o i n t s w i t h g r o w i n g a l k y l c h a i n l e n g t h a n d a r e

    m o n o t r o p i c l i q u i d c r y s t a l l i n e . T h e n e m a t i c - i s o t r o p i c

    t r a n s i t i o n s o f t h e h i g h e r h o m o l o g u e s f o l l o w t h e

    u s u a l a l t e r n a t i n g o d d - e v e n e f f e c t w i t h a d e c r e a s i n g

    t e n d e n c y . T h e m e l t i n g p o i n t s h o w e d a s i m i l a r a l t e r -

    n a t i o n b u t w i t h a h i g h e r a m p l i t u d e s o t h a t t h e

    p e n t y l , o c t y l a n d n o n y l d e r i v a t i v e s h a d e n a n t i o -

    t r o p i c n e m a t i c p h a s e s . T h e s h a r p d e c r e a s e i n t h e

    c l e a r i n g p o i n t s o f t h e f i rs t t h r e e m e m b e r s o f t h e

    ser ies c o u l d b e e x p l a i n e d o n t h e b a s i s o f h y d r o g e n

    b o n d s w h i c h m a y s t e r i c a l l y h i n d e r t h e f r e e r o t a t i o n

    o f t h e a l k y l c h a i n . I n t r o d u c i n g t h e f o r m y l g r o u p i n

    t h e s e c o m p o u n d s a l s o c a u s e d a m a r k e d d e p r e s s i o n

    i n b o t h m e l t i n g a n d c l e a r i n g t e m p e r a t u r e s . T h e

    n e m a t i c p h a s e c o u l d o n l y b e o b s e r v e d i n t h e m e t h y l

    f o r m y l a m i n o d e r i v a t i v e . T h i s is p r o b a b l y b e c a u s e

    t h e f o r m y l g r o u p s t e r i c a l l y f o r c e s t h e a l k y l g r o u p

    o u t o f t h e p l a n e o f t h e m o l e c u l e t h u s d e c r e a s i n g i t s

    g e o m e t r i c a l a n i s o t r o p y .

    T h e d i e l e c t r i c a n i s o t r o p i e s o f t h e p e n t y l a n d o c t y l

    d e r i v a t i v e s w e r e m e a s u r e d a t a r e d u c e d t e m p e r a t u r e

    o f 0.96 ( T a b l e I I I ) . I t c a n b e s e e n f r o m T a b l e I I I

    t h a t 4 - c y a n o - 4 ' - 7 i - p e n t y l a m i n o b i p h e n y l p o s s e s s a

    d i e l e c t r i c a n i s o t r o p y w h i c h is t w o a n d a h a l f t i m e s

    l a r g e r t h a n 4 - c y a n o - 4 ' - 7 i - h e x y l b i p h e n y l a t t h e s a m e

    r e d u c e d t e m p e r a t u r e .

  • 1094 M. A . Osman • Nemat ic L iquid Crystals

    Table I I .

    X R T M [°C] TC [°C] General C [ % ] H [ % ] N [ % ] formula calcd found calcd found calcd f o u n d

    H CH 3 199.2 180.0 C14H12N2 80.74 80.76 5.81 5.91 13.45 13.31 H C2H5 180.4 139.9 C15H14N2 81.05 81.08 6.35 6.40 12.60 12.51 H C3H7 106.4 100.2 C16H16N2 81.32 81.27 6.83 6.82 11.86 11.84 H C4H9 113.6 101.7 CI7HIGN2 81.56 81.47 7.25 7.27 11.19 11.12 H C5H11 86.3 90.7 C i 8H 2 ON 2 81.78 81.71 7.63 7.64 10.60 10.62 H C6H13 105.3 93.8 C19H22N2 81.97 81.98 7.97 7.93 10.06 10.00 H C7H15 92.2 89.0 C2oH2 4N2 82.14 82.26 8.27 8.32 9.58 9.55 H C8H17 81.4 91.8 C21H26N2 82.31 82.29 8.55 8.57 9.14 9.10 H C9H19 83.9 89.8 C22H28N2 82.45 82.60 8.81 8.85 8.74 8.77 C H O CH 3 127.0 84.4 C15H12N2O 76.25 76.27 5.12 5.24 11.86 11.92 C H O C2H5 106.2 — C I 6 H I 4 N 2 0 76.78 76.77 5.64 5.73 11.19 11.25 C H O C9H19 50.9 — C23H28N2O 79.27 79.24 8.10 8.14 8.04 8.04

    190

    Tc

    t °C

    150

    100

    7 5

    50

    "I 1 1 1 1 1 1 T

    CnH2n + 1 N H - 0 - 0 - C N

    \ J 1 I I 1 I I I

    n+1

    - • C n H 2 n + 1 ^ Q - 0 - C N

    Fig. 1. Clearing points o f alkyl- and a lkylamino-cyano-biphenyls.

    Table I I I .

    1 el Ae

    4 -n -Pentylamino - 4 ' - cy anobipheny 1 4 -n -Octy lamino-4 ' - cyanobiphenyl 4 -n -Hexy l -4 ' - cyanob ipheny l

    36.8 30.7 17.4

    9.8 8.1 6.6

    27.0 22.6 10.8*

    4 - w - H e x y l - 4 ' - c y a n o p h e n y l - b e n z o a t e h a s a A e o f

    2 1 . 7 c o m p a r e d t o 10.8 f o r 4 - c y a n o - 4 ' - n - h e x y l b i -

    p h e n y l a t t h e s a m e r e d u c e d t e m p e r a t u r e . T h i s

    i n c r e a s e is c a u s e d b y t h e d i p o l a r c o n t r i b u t i o n o f t h e

    c a r b o x y l g r o u p . I t is t h e r e f o r e t o b e e x p e c t e d t h a t

    t h e a l k y l a m i n o - c y a n o p h e n y l b e n z o a t e s w i l l p o s s e s s

    m u c h h i g h e r d i e l e c t r i c a n i s o t r o p i e s . T h e s e c o m -

    p o u n d s w e r e s y n t h e s i z e d a s f o l l o w s :

    0ZN-OC0CI + H0-©>-CN 0j,N-(Q-C0-CN

    Zn CH.COOH

    * B D H .

    T h e 4 - n i t r o - 4 ' - c y a n o p h e n y l b e n z o a t e , o b t a i n e d b y

    e s t e r i f i c a t i o n o f 4 - n i t r o b e n z o y l c h l o r i d e i n p y r i d i n e

    i n t h e u s u a l w a y , w a s first r e d u c e d t o t h e c o r -

    r e s p o n d i n g a m i n o e s t e r [20]. T h e a l k y l a m i n o e s t e r s

    w e r e t h e n o b t a i n e d b y r e d u c t i v e a l k y l a t i o n o f t h e

    a m i n e a c c o r d i n g t o t h e m e t h o d d e s c r i b e d b y A .

    S u r r e y [21] ,

    T h e t r a n s i t i o n t e m p e r a t u r e s o f t h e s e c o m p o u n d s

    a r e g i v e n i n T a b l e I V . A l l t h e s y n t h e s i z e d p r o d u c t s

    s h o w e d t h e r m o d y n a m i c a l l y m o r e s t a b l e n e m a t i c

    p h a s e s t h a n t h e c o r r e s p o n d i n g a l k y l d e r i v a t i v e s a n d

    n o s e m a t i c p h a s e s c o u l d be o b s e r v e d ( F i g . 2). A s

    i n t h e b i p h e n y l ser ies , t h e first t h r e e m e m b e r s

    s h o w e d a n u n u s u a l s h a r p d e c r e a s e o f t h e c l e a r i n g

    p o i n t s w i t h g r o w i n g a l k y l c h a i n l e n g t h . F r o m C3

    u p w a r d s t h e t r a n s i t i o n t e m p e r a t u r e s a l t e r n a t e d i n

    t h e u s u a l w a y a n d r e m a i n e d b e t w e e n 89 °C a n d

    84 °C w h i c h is a b o u t 10 °C l o w e r t h a n t h e cor-

    r e s p o n d i n g b i p h e n y l d e r i v a t i v e s . T h i s b e h a v i o u r is

    i n c o n t r a s t t o t h e a l k y l d e r i v a t i v e s w h e r e t h e e s t e r s

    p o s s e s s h i g h e r c l e a r i n g p o i n t s . T h e m e l t i n g t e m -

  • M. A. Osman • Nematic Liquid Crystals 1095

    Table IV. W

    X R T m [ °C ] T c [ °C] General C [ % ] H [ % ] N [ % ] formula calcd found calcd found calcd found

    H CH3 184.9 145.9 CI5H12N202 71.41 71.25 4.80 4.79 11.11 11.04 H C2H5 171.5 127.1 C16H14N2O2 72.16 72.16 5.30 5.31 10.52 10.43 H C3H7 169.0 84.9 C17H16N2O2 72.84 72.79 5.75 5.79 9.99 9.83 H C4H9 141.3 89.1 C18H18N2O2 73.45 73.35 6.16 6.16 9.52 9.37 H C5H11 108.4 77.3 C19H20N2O2 74.00 73.96 6.59 6.59 9.09 9.10 H C6H13 117.7 84.5 C20H22N2O2 74.50 74.45 6.88 6.91 8.69 8.67 H C7H15 117.3 81.2 C2IH24N202 74.97 74.96 7.19 7.22 8.33 8.34 H C8H17 118.5 82.0 C22H26N202 75.40 75.50 7.48 7.53 7.99 8.01 CHO CH3 173.2 116.2 C16H12N2O3 68.56 68.69 4.32 4.46 10.00 10.02 CHO C2H5 109.4 — C17H14N2O3 69.37 69.34 4.80 4.79 9.52 9.51 CHO C5H11 43.5 — C20H20N2O3 71.41 71.43 5.99 6.03 8.33 8.45 CHO C6H13 52.2 — C21H22N2O3 71.98 71.86 6.33 6.35 8.00 8.07

    1 5 0 TC

    t

    100

    3 0 0 1 2 3 4 5 6 7 8 9 Fig. 2. Clearing points of alkyl- and alkylamino-cyano-phenylbenzoates.

    [1] M. Schadt and W. Helfrich, Appl. Phys. Lett. 18, 127 (1971).

    [2] M. A. Osman, Z. Naturforsch. 31b, 801 (1976). [3] R. Steinsträsser, Z. Naturforsch. 27b, 774 (1972). [4] J. van der Veen, W. H. de Jeu, A. H. Grobben,

    and J. Boven, Mol. Cryst. Liq. Cryst.17,291(1972). [5] R. T. Klingbiel, D. J. Genova, T. R. Criswell, and

    J. P. van Meter, J. Am. Chem. Soc. 96 (25), 7651 (1974).

    [6] W. H. de Jeu and Th. W. Lathouwers, Mol. Cryst. Liq. Cryst. 26, 225 (1974).

    [7] W. H. de Jeu and Th. Lathouwers, Z. Natur-forsch. 29a, 909 (1974).

    [8] A. Boller and H. Scherrer, German patent disclosure 2306739 (1973).

    [9] A. Boller and H. Scherrer, German patent disclosure 2306738 (1973).

    [10] G. W. Gray, K. J. Harison, J. A. Nash, J. Constant, D. S. Hulme, J. Kirton, and E. P. Raynes, Liquid Crystals and Ordered Fluids, vol. 2, 617 (1974).

    p e r a t u r e s o f t h e s e p r o d u c t s w e r e g e n e r a l l y h i g h e r

    t h a n t h e c o r r e s p o n d i n g b i p h e n y l s so t h a t t h e

    n e m a t i c p h a s e s w e r e o n l y m o n o t r o p i c . T h e d i e l e c t r i c

    a n i s o t r o p i c s c o u l d t h e r e f o r e n o t be m e a s u r e d . T h e s e

    a l k y l a m i n o b e n z o a t e s a r e e s t i m a t e d t o possess a A e o f m o r e t h a n 40. T h e i n t r o d u c t i o n o f t h e f o r m y l

    g r o u p in t h i s t y p e o f c o m p o u n d h a d t h e s a m e e f f e c t

    a s in t h e S c h i f f ' s b a s e s a n d t h e b i p h e n y l s .

    Experimental A l l s u b s t a n c e s w e r e i n v e s t i g a t e d b y p o l a r i z i n g

    m i c r o s c o p y a n d b y d i f f e r e n t i a l s c a n n i n g c a l o r i m e t r y ( D S C ) . T h e m i c r o s c o p i c o b s e r v a t i o n s w e r e m a d e u n d e r a L e i t z O r t h o p l a n m i c r o s c o p e u s i n g a M e t t l e r F P 52 h o t - s t a g e . T h e t r a n s i t i o n t e m p e r a t u r e s w e r e d e t e r m i n e d w i t h a n a c c u r a c y o f ± 0.1 °C. T h e p u r i t y o f t h e p r o d u c t s w a s > 9 9 . 7 % as d e t e r m i n e d b y G L C .

    T h e a u t h o r is g r a t e f u l t o D r . J . N e h r i n g f o r m e a s u r i n g t h e d i e l e c t r i c a n i s o t r o p y .

    [11] R. Eidenschink, D. Erdmann, T. Krause, and L. Pohl, Angew. Chem. 89, 103 (1977).

    [12] L. Pohl, R. Eidenschink, G. Krause, and D. Erd-mann, Phys. Lett. 60 A, 421 (1977).

    [13] A. Boller, M. Cereghetti, M. Schadt, and H. Scherrer, Mol. Cryst. Liq. Cryst. 42, 215 (1977).

    [14] P. G. Cummins, D. A. Dunmur, and D. A. Laidler, Mol. Cryst. Liq. Cryst. 30, 109 (1975).

    [15] J. A. Castellano, J. E. Goldmacher, L. A. Barton, and J. S. Kane, J. Org. Chem. 33, 3501 (1968).

    [16] M. A. Osman, German patent disclosure 2443618 (1976).

    [17] Houben-Weyl VII/1, 30 (1954). [18] R. Le Fevre and E. Turner, J. Chem. Soc. 1926,

    2041. [19] G. W. Gray and A. Mosley, J. Chem. Soc. Perkin

    Trans. 2, 97 (1976). [20] A. J. Hill and M. V. Cox, J. Am. Chem. Soc. 48,

    3218 (1926). [21] A. R. Surrey and H. F. Hammer, J. Am. Chem.

    Soc. 66, 2127 (1944).

    • - A / - -i i i i i f

    n + 1 o

    CnH2n+1-O-C-0Hn)-CN

    -

    J I I I I I I I