SYNTHESIS AND LIQUID CRYSTALLINE PROPERTIES OF 4,4'-DISUBSTITUTED BIPHENYLS

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SYNTHESIS AND LIQUID CRYSTALLINE

PROPERTIES OF 4,4’-DISUBSTITUTED BIPHENYLS

D. Demus, L. Richter, C.-E. Rürup, H. Sackmann, H. Schubert

To cite this version:

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JOURNAL DE PHYSIQUE Colloque CI, supplknzent au no 3, Tome 36, Mars 1975, page C1-349

Classification Physics Abstracts

7.130

SYNTHESIS AND LIQUID CRYSTALLINE PROPERTIES

OF

4,Q-DISUBSTITUTED BIPHENYLS

(")

D. DEMUS, L. RICHTER, C.-E. RURUP, H. SACKMANN and H. SCHUBERT Sektion Chemie, Martin-Luther-Universitat Halle, Miihlpforte 1, German Democratic Republic

Rksumk. - On a synthetisk de nouvelles substances de type biphenyl non symktrique

R'WR'

o" Rl et R2 sont des groupements n-alkoxy, n-alkyl ou n-alkanoyl. On a Btabli une classification des phases A partir de mesures de miscibilite dans des systkmes binaires, d'observation des textures et d'ktudes comparatives de la variation des temperatures de transition d'une skrie d'homologues.

Les biphenyls 4-alkyIoxy-4'-n-alkanoyl ont des phases SE, SA, I. Les biphknyls 4-n-alkyl-4'-n-hexanoyl ont des phases SA, I et SB, SA, I tandis que les biphenyls 4-n-hexyIoxy-4'-n-hexyl ont un poly- morphisrne nouveau SE, SB, I.

Summary. -New substances of the type of unsymmetrical substituted biphenyls R1-R2 with Rl or R2 = n-alkyl, n-alkoxy and n-alkanoyl were synthezised.

MiscibiIity measurements in binary systems, texture observation and comparative studies of the trends of the transition temperatures in homologous series yield a classification of the phase types.

In the 4-n-alkyloxy-4'-n-alkanoylbiphenyls the smectic phase types A and E in the new variant SE, I and the variant SE, SA, I occur. The 4-n-alkyl-4'-n-hexanoylbiphenyls show the polymorphism SA,

I and SB, S.,, I. In the 4-11-hexyloxy-4'-n-hexylbiphenyl the new variant of polymorphism SE, SR, I exists.

1. Introduction.

-

4,4'-disubstituted biphenyls of different types are known and usually possess liquid crystalline properties [I, 21. Especially in the case of unsymmetrically substituted compounds with simple substituents low melting points are to be expected. Therefore we have synthesized disubstituted biphenyls of the following type :

with

R'

= n-alkyl

R2

= n-alkoxy R' = n-alkyl

R2

= n-alkanoyl

R'

= n-alkoxy

R2

= n-alkanoyl.

The polymorphism of these compounds was investigated and the type of the smectic phases was deter- mined by the miscibility criterion and texture observation [3].

2. Synthesis of materials.

-

The monoacylation of the biphenyl is a rather simple process ; the reduc-

(*) Paper no 21 in the series cc Relations of isomorphism

between liquid crystalline phases D.

tion to the corresponding 4-n-alkylbiphenyls is without any complication.

These hydrocarbons have been acylated in their 4'-position with high yields.

The combination of the n-alkoxy- and n-acyl- substituents is hard to achieve. The acylation of the n-alkoxy-biphenyl was performed under standard conditions with ether cleavage, other procedures of acylation having no success. We found the best method of synthesis to be the acylation of 4-methoxp-biphenyl in a special Friedel-Crafts reaction [4, 51, in which the ether cleavage occurs simultaneously and therefore yields the acylated 4-hydroxybiphenyls. These derivatives were converted into the corresponding ethers by n-alkyl-bromides, reduction with hydrazine yielding the 4-n-alkoxy-4'-n-alkyl-derivatives.

3. Polymorphism and transition temperatures.

-

The following tables show the transition temperatures of the new substances. The classification of the smectic modifications has been done according to the miscibility investigations described in section 4. The symbols used are : C =crystalline solid state ; S,, S,, S, =liquid crystalline states of the types smectic A, B, E resp. ;

I = isotropic liquid state. The temperatures are listed

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(21-350 D. DEMUS, L. RICHTER, C.-E. R ~ ~ R U P , H. SACKMANN A N D H. SCHUBERT

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PROPERTIES OF 4,4'-DISUBSTITUTED BIPHENYLS C1-351 4. The classification of the smectic phases. - 4.1 a) di-n-propyl p-terphenyl-4.4"-dicarboxylate, poly- MISCIBILITY. - In order to test the behaviour of morphism S,, S, 16, 71.

miscibility in binary systems the following substances b) n-decyl 4-[4-phenylbenzylideneamino]-cinnamate,

were used : polymorphism S,, S,, S, [8].

p p - -

50 mole '10

D l - n - p r o p y l - p - lerphenyl- 1-Athyloxy-1'- n- 1 , l " - d ~ c a r b o x y l a t e nonanoy l- b~phenyl

Di-n-prop y l S o mole 'I0 1 - n - ~ r o p ~ l o x ~ - C - n - p-lerpheny I-L,L5 proponoyl- b ~ p h e n y l dicarboxy l a t e FIG. 3. cl. p. t 1. 50 mole 'lo 0 1 - n - p r o p y l - p - terphe- L - n - B u t y l o x y - C - n - nyl-1,L'-d~carboxylote butanoyl

-

blphenyl

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c)4-[4-n-dodecyloxybenzylidene-amino]-azobenzene, melting or crystallisation is not exactly observable. In polymorphism S,, S, [9]. the diagrams this is indicated by lines which show the probable region of the start o f melting or crystallisa- The diagrams of state (temperature-concentration

tion. diagrams) have been investigated by means of micro-

scopic observation in polarized light with samples of According to the miscibility rule (uninterrupted miscibility shown in Fig. 1-6) the smectic phases of the known concentration. In the preparations the sub-

compounds I, 11,111, IV and V are classified as phases E stances were mounted between a glass slide and a cover

e l ; n and A.

311p.

In some cases the temperature of the beginning of the In the diagrams of the figure 7 and figure 8 the classification of the compounds VI and VII is shown.

D i - n - p r o p y l - p - 50 'mole% C-n-Decyloxy

-

1'- terpheny I - L.1'- ethanoyl- biphenyl dicorboxylate

s o l i d

L

_{5 0 m o l e %}

~ - ~ t h ~ l o x ~ - 1'-n- I - n - P r o p y l o x y - C ' - n - nonanoyl- biphenyl proponoyl

-

biphenyl

The diagram of figure 9 is more complicated. Accord- ing to the different variants of polymorphism of the compounds (S, or else S,, S,) the miscibility gap expected between the B- and E-phase regions can be

i

smectic E

I

5 0 k o 1 e '10

L - n -Propyloxy-C'-n- C - ~ t h ~ l o x ~ - C ' - n

-

propanoyl- biphenyl butonoyl- biphenyl

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PROPERTIES OF 4,4'-DISUBSTlTUTED BIPHENYLS Cl-353

observed. The appearence of an intermediate nematic phase is remarkable.

In figure 10 the polymorphism S,, S, of the compo-

nent VIII is demonstrated. In figure 1 I the classifica-

tion of the smectic high-temperature modification of the component 1X as a B-phase is to be seen. This is

also verified by figure 12 together with the classifica-

tion of the smectic low-temperature modification of the component IX as an E-phase.

4 . 2 POLYMORPHISM IN THE HOMOLOGOUS SERIES.

-

The classification of the phase types of the substances

I-VII by the investigation of miscibility is representa-

50mole % 1-n-Propyloxy - C - n - 1-[l - n - Dodecytoxy- p r o p a n o y l - blphenyl benzyl~dene-ammo] - azobenzenc FIG. 9. I I Somole%

1-n-Hex; loxy-C-n- I-11-n- Dodecyloxy- hexyl-biphenyl benzylidene-amino]

ozobenzene

-

5 0 mole '10

1 - n - O c t y l - 1 ' - n - 1 - [ L n - Dodecyloxy- hexanoyl

-

biphenyl benzylldene - a m ~ n $

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tive for the homologous series of the 4-n-alkoxy-4'-n- alkanoylbiphenyls with n = 2, n = 3, n = 4, n = 9 and n = 10 (table I).

With respect to the regular trends of the transition temperatures in all series of table I the classification of the smectic modifications as types SE and S, is justified.

The dependence of transition temperature on chain length of the alkanoyl residue in the homologous series of the 4-n-butyloxy-4'-n-alkanoylbiphenyl is given i n

figure 13.

i s o t r o p i c

; I F

s o l i d

The same trend of the transition temperatures can be observed with little variation in all homologous series of Table I.

The SA-1 and S,-SA transition temperatures decrease with increasing chain length, the latter more strongly. In members with long chains the transition SE-S,

cannot be observed since the temperatures of these transitions fall below the melting points. The first members of the series show only E-modifications. Therefore transitions from S, to 1 can be observed.

The polymorphism S,, SA found in substance

1X

should be representative for the other members of the homologous series of the 4-n-alkyl-4'-n-alkanoylbiphe-

nyls investigated so far (table TI).

Until now substance JX is the only investigated

example of the 4-n-alkoxy-4'-n-alkyl-biphenyls and shows the new variant of polymorphism S,, S, (Fig. I I ,

Fig. 12).

4 . 3 TEXTURES.

-

All investigated A-modifications yield the well-known fan-shaped textures. The stable textures of the E-modifications and of the B-modifications are mosaic-textures.

The smectic E- and B-modifications which have developed from the A-modifications mostly show para- morphic fan-shaped textures, sometimes with concen- tric arcs as described in references [3] and [7].

Because of the similarity or identity of the textures of the E- and B-phases the transition S,-S, must be carefully observed. Within the domains new orien- tations become observable.

The texture observations of the members of the homologous series not investigated by miscibility investigations confirm the classification deduced from transition-temperature trends in the above mentioned homologous series.

References

[l J GRAY. G. W., Molecular Structure and the Properties of Liquid Crystals (Academic Press, London-New York)

1962.

[2] DEMUS, D., DEMUS, H. and ZASCHKB, H., Flissige Kristalle in Tabellen. VEB Deutscher Verlag fiir Grundstoffindus- trie Leipzig, 1974.

[3] SACKMANN, H. and DEMUS, D., Mol. Cryst. Liqic. Crys!. 21

(1973) 239.

[4] RVRUP, C.-E., Dissertation Halle 1971.

[ 5 ] SCHUBERT, H. and DEHNE, H., Z . Chem. 12 (1972) 241.

161 DIELE, S., BRAND, P. and SACKMANN, H., Mol. Crysf. Liqu. Cryst. 17 (1972) 163.

[7] DEMUS, D., KOLZ, K.-H. and SACKMANN, H., Z. Phys. Chem.

(Leipzig) 252 (1973) 93.

[8] BIERING, A., DEMUS, D., GRAY, G. W. and SACKMANN, H., Mol. Cryst. Liqu. Cryst. 1974 (in press).