(2)
(1) where Z is an alkyl (CnH2n +1), alkoxy (CnH2n + 1O), alkylphenyl group ( C n H 2n + 1 Ph ) or alkyl cyclohexyl (CnH 2n + 1C6H10– ), A is a single bond or –CH2CH2– group and one of the lateral substituents X1, X2 or X3 is F, Cl or CH3 group.
University of Technology, Institute of Chemistry, Warsaw, Poland rdabrowski@.pl ′w, Poland of Physics, Jagiellonian University, Krako of Optics/CREOL, University of Central Florida, Orlando, USA
1,88 1 1,82 2
ቤተ መጻሕፍቲ ባይዱ
1,76
3 4
F Cl Cl
Cr 103.2 (N 93.6) Iso Cr 96.7 (N 89.9) Iso Cr 55.4 Iso Cr 81.6 (N 31)** Iso Cr 75.2 Iso
1,7
18
12 TN–1 – T,°C
6
0
Fig. 1. Temperature dependent extraordinary refractive index of the alkyl and alkoxy NCS tolanes studied. 1 – 4OTOLCl0, 2 – 5TOLCl0, 3 – 5TOLF0, 4 – 4OTOLF0. 1,62
ÓÄÊ
ÆÈÄÊÎÊÐÈÑÒÀËËÈ×ÅÑÊÈÅ ÌÀÒÅÐÈÀËÛ Ñ ÁÎËÜØÈÌ ÄÂÓËÓ×ÅÏÐÅËÎÌËÅÍÈÅÌ
2005 ã. À. Ñïàäëî; Ð. Äàáðîâñêè; Äæ. Äçÿäóæåê; Ñ. Óðáàí; Å. Ñêèáüîð; Ñ. Ãàóçà; Ñ. Ò. Âó
The mesogenic, optical and dielectric properties of the new mixtures of nematic liquid crystals with high birefringence on the base of isothiocyanatotolanes have been investigated and examples of multicomponent mixtures with low viscosity and optical anisotropy ∆n ≈ 0.4 are presented.
Èññëåäîâàíû ìåçîãåííûå, îïòè÷åñêèå è äèýëåêòðè÷åñêèå ñâîéñòâà ñìåñåé íåìàòè÷åñêèõ æèäêèõ êðèñòàëëîâ ñ áîëüøèì äâóëó÷åïðåëîìëåíèåì íà îñíîâå èçîòèîöèàíîòîëàíîâ è ïðèâåäåíû ïðèìåðû ìíîãîêîìïîíåíòíûõ ñìåñåé ñ ìàëîé âÿçêîñòüþ è îïòè÷åñêîé àíèçîòðîïèåé ∆n ≈ 0,4. Êîäû OCIS: Ïîñòóïèëà â ðåäàêöèþ 14.12.2004.
“Îïòè÷åñêèé æóðíàë”, òîì 72, ¹ 9, 2005
Z C 2H 5 C 3H 7 C 4H 9 C5H11 C7H15 C 2H 5O C 4H 9O C5H11 C 4H 9O C5H11O
** **
X3 F
Mesophase, °C Cr 71.3 Iso Cr 73.9 Iso Cr1 38.4 Cr2 40.50 (N 17.6) Iso Cr 49 (N 40.6) Iso Cr 41.7 (N 44.4) Iso
Introduction High birefringence nematic liquid crystals are used to build quickly operating displays as well as being used for steering laser beams, colour filters, broad band reflectors, polymer dispersed liquid crystals and in holography [1]. The birefringence, dielectric anisotropy, viscosity and phase transition temperatures are the most important properties of liquid crystalline materials (LCs) deciding on their quality and practical applications. The usefulness of LCs well describe parameter called Figure-of-Merit – FoM = K11∆n2/γ (where: K11 – the splay elastic constant, ∆n – birefringence, γ – rotational viscosity) [2, 3]. Isothiocyanatotolanes, among liquid crystal structure, should exhibit high birefringence, moderate viscosity and good thermal, chemical and photochemical stability [4, 5]. Recently we have been investigating some high birefringence LC isothiocyanatotolane derivatives with the following common formula (1):
10
Mesomorphic properties of novel isothiocyanatotolanes The phase transition temperatures and heat fusion of enthalpies of prepared compounds were measured using a differential scanning calorimeter (SETARAM 141) at 2 K/min temperature scanning rate. The
Ordinary index
X1 = X2 = H; A is single bond. Virtual transition estimated from clearing point of solutions ** in 6CHBT.
2 1 3 4
1,59 1,56 1,53
investigated compounds, and their phase transition and enthalpies are given below in Table 1. The 4′-alkyl-4-isothiocyanatotolanes with short alkyl chain does not exhibit mesomorphic properties. The monotropic nematic phase is observed for longer alkyl chains. The butyl and heptyl members have low melting point and melting enthalpy (see Table 1), so may be used as base components of mixtures. The fluorosubstituted 4′-alkoxy-4-isothiocyanatotolanes listed in Table 1 are monotropic nematics, but their melting point and enthalpy are rather high. Chlorosubstituted two ring isothiocyanatotolanes are listed also in Table 1. The isothiocyanatotolanes with alkyl chain have lower melting point than alkoxy analogues. A virtual nematic phase maybe estimated in the case of the butoxy derivative. Stability of nematic phase was estimated from point of solution in 6 CHBT. The birefringence of novel isothiocyanatotolanes The optical anisotropy and refractive indices of the alkyl and alkoxy fluoro- and chloro-substituted tolanes were measured by the refractometric method [8]. Optical indices and birefringence of the presented compounds were calculated from the measurements of the 20 wt. % solutions in 6CHBT. Results are plotted in Figs. 1–3. Experimental points are joined for more convinient seeing. Table 2 shows the extrapolated birefringence and optical indices of some isothiocyanatotolanes (at temperatures 20 °C below the nematic-isotropic transition). Alkyl derivative have both higher refractive indices and birefringence than the alkoxy derivatives analogous. Chloro-derivatives show much higher value of the or“Îïòè÷åñêèé æóðíàë”, òîì 72, ¹ 9, 2005