Synthesis and Properties of Novel Isothiocyanatotolane Liquid Crystals with Terminal Difluorovinyl Substitute†

doi:10.7503/cjcu20170031

Abstract

Abstract:

Four kinds of new isothiocyanate liquid crystals composed of tolane core and difluorovinyl terminal group(A1—A4) were synthesized via five step reactions based on 4-iodobenzaldehyde, and four ethyl analogues B1—B4 as comparison structures were also prepared. The structure characterizations of all related pro-ducts were performed using infrared spectrometer(IR), ¹H-nuclear magnetic resonance(¹H NMR) and mass spectrometer(MS). The mesomorphic properties were investigated by differential scanning calorimeter(DSC) and hot stage polarizing optical microscope(HS-POM). The birefringence values and rotational viscosity were extrapolated. The results showed that the target compounds A1, A2 and A3 exhibit wider nematic phase range(31—62 ℃). Replacement of ethyl chain by difluorovinyl as terminal group is enabled to not only enlarge the nematic phase temperature range but also increase birefringence(Δn=0.038—0.052) and reduce rotational viscosity. The high birefringence mixtures based new liquid crystals with terminal difluorovinyl substitute have wider nematic phase range, higher birefringence, lower rotational viscosity and larger figure-of-merit(FoM).

Key words: Difluorovinyl, Isothiocyanate, Nematic phase, Birefringence, Rotational viscosity

CLC Number:

O625

TrendMD:

LI Juanli, PENG Zenghui, LI Jian, HU Minggang, AN Zhongwei, ZHANG Lu. Synthesis and Properties of Novel Isothiocyanatotolane Liquid Crystals with Terminal Difluorovinyl Substitute^†[J]. Chem. J. Chinese Universities, 2017, 38(10): 1788.

Figures/Tables 11

Fig.1 Target compounds(A) and the comparison structures(B)

Scheme 1 Synthesis of target compounds A1—A4

Table 1 Yields, appearances, melting points and MS data of the intermediates and target compounds

Compd.	Yield(%)	Appearance	m. p./℃	MS, m/z(RI,%)
1	75	Colourless liquid		266.1(M⁺, 100), 139.1(24), 119.1(41), 99.1(10), 63.1(7)
2a	78	Brown solid	101.6—102.8	117.0(M⁺, 100), 89.0(25), 63.0(5)
2b	56	Brown liquid		134.9(M⁺, 100), 107.0(17), 88.0(6), 67.5(3)
2c	68	Brown solid	45.1—46.0	135.0(M⁺, 100), 107.0(24), 81.0(3), 67.6(3)
2d	55	Brown solid	65.0—67.2	153.0(M⁺, 100), 125.0(11), 106.0(12), 76.4(3), 62.0(1)
3a	67	Brown solid	105.5—108.7	255.1(M⁺, 100), 207.0(5), 176.0(2), 127.6(11)
3b	65	Brown solid	90.5—93.4	273.1(M⁺, 100), 225.0(7), 136.6(11)
3c	50	Brown solid	101.8—104.5	273.0(M⁺, 100), 225.0(5), 136.5(7)
3d	31	Brown solid	88.0—89.5	291.0(M⁺, 100), 271.0(2), 243(5), 145.5(7)
A1	92	White solid	73.4—73.9	297.7(M⁺,100), 265.8(24), 238.7(41), 189.6(23), 148.9(55), 119.4(27)
A2	67	White solid	96.3—97.7	315.6(M⁺,100), 283.8(26), 256.7(36), 207.6(18), 158.0(61), 128.5(30)
A3	79	White solid	92.2—93.2	314.9(M⁺,100), 283.0(8), 256.0(14), 207.0(6),157.6(19)
A4	68	White solid	120.3—120.7	333.6(M⁺,100), 301.8(27), 274.7(35), 167.0(61), 137.4(23)

Table 2 1H NMR and IR data of the intermediates and target compounds

Compd.	¹H NMR(CDCl₃, 500 MHz), δ	IR(KBr), $ν ˙$ /cm^-1
1	5.18—5.24(q, 1H), 7.05—7.09(d, 2H, J=8.5 Hz), 7.64—7.66(m, 2H)	3038, 2926, 2307, 1900, 1729, 1675, 1489, 1400, 1355, 1249, 1169, 1006, 940, 839, 801, 704
2a	2.95(s, 1H), 3.81(s, 2H), 6.59—6.60(m, 2H), 7.29—7.30(m, 2H)	3486, 3388, 3037, 2918, 2609, 2250, 2096, 1619, 1513, 1305, 1201, 1177, 1050, 939, 829, 672
2b	2.51(s, 1H), 3.88(s, 2H), 6.68(s, 1H), 7.10—7.13(m, 2H)	3476, 3382, 3296, 3225, 2926, 2664, 2186, 2104, 1628, 1515, 1439, 1365, 1246, 1187, 1122, 941, 874, 819, 598
2c	3.18(s, 1H), 3.94(s, 2H), 6.34—6.38(m, 2H), 7.22—7.26(q, 1H)	3482, 3389, 3268, 2103, 2609, 1626, 1509, 1331, 1117, 957, 849, 742
Compd.	¹H NMR(CDCl₃, 500 MHz), δ	IR(KBr), ν˙/cm^-1
2d	2.90(s, 1H), 3.83(s, 2H), 6.86—6.93(m, 2H)	3479, 3392, 3287, 3073, 2982, 2925, 2112, 1732, 1643, 1580, 1526, 1337, 1262, 1099, 959, 859, 800, 716, 691
3a	3.83(s, 2H), 5.24—5.30(q, 1H), 6.26—6.64(q, 2H), 7.27—7.29(d, 2H, J=8.5 Hz), 7.33—7.34(q, 2H), 7.44—7.46(d, 2H, J=8.5 Hz)	3471, 3377, 3091, 3034, 2209, 1617, 1597, 1517, 832, 725, 671, 528
3b	3.90(s, 2H), 5.24—5.30(q, 1H), 6.70—6.73(t, 1H), 7.12—7.18(m, 2H), 7.28—7.30(d, 2H, J=8.0 Hz), 7.44—7.46(d, 2H, J=8.5 Hz)	3450, 3367, 3046, 2205, 1630, 1570, 1520, 834, 767, 607, 536
3c	3.94(s, 2H), 5.24—5.30(q, 1H), 6.38—6.41(t, 2H), 7.28—7.36(m, 3H), 7.44—7.51(m, 2H)	3501, 3406, 3094, 3032, 2207, 1626, 1605, 1523, 838, 741, 675, 605
3d	3.88(s, 2H), 5.25—5.31(q, 1H), 6.98—7.05(m, 2H), 7.29—7.31(d, 2H, J=8.5 Hz ), 7.44—7.46(d, 2H, J=8.5 Hz)	3449, 3329, 3072, 3045, 2213, 1642, 1578, 1525, 840, 720, 617, 536
A1	5.26—5.32(q, 1H), 7.19—7.21(d, 2H, J=8.5 Hz), 7.31—7.33(d, 2H, J=8.5 Hz), 7.49(t, 4H, J=16 Hz)	3078, 3032, 2202(C≡≡C), 2109(NCS), 1608, 1518, 942, 840, 806, 620
A2	5.26—5.33(q, 1H), 7.15(t, 1H), 7.26—7.33(m, 4H), 7.47—7.49(d, 2H, J=8.5 Hz)	3090, 3036, 2209(C≡≡C), 2048(NCS), 1602, 1514, 937, 845, 779
A3	5.26—5.32(q, 1H), 6.96—7.02(m, 2H), 7.31—7.33(d, 2H, J=8.5 Hz), 7.46—7.51(m, 3H)	3072, 3032, 2217(C≡≡C), 2106(NCS), 1613, 1515, 938, 867, 852, 605
A4	5.27—5.33(q, 1H), 7.09—7.13(m, 2H), 7.32—7.34(d, 2H, J=8.0 Hz), 7.47—7.48(m, 2H, J=8.5 Hz)	3096, 3033, 2214(C≡≡C), 2050(NCS), 1620, 1515, 941, 849, 706, 624

Table 2 1H NMR and IR data of the intermediates and target compounds

Compd.	¹H NMR(CDCl₃, 500 MHz), δ	IR(KBr), $ν ˙$ /cm^-1
1	5.18—5.24(q, 1H), 7.05—7.09(d, 2H, J=8.5 Hz), 7.64—7.66(m, 2H)	3038, 2926, 2307, 1900, 1729, 1675, 1489, 1400, 1355, 1249, 1169, 1006, 940, 839, 801, 704
2a	2.95(s, 1H), 3.81(s, 2H), 6.59—6.60(m, 2H), 7.29—7.30(m, 2H)	3486, 3388, 3037, 2918, 2609, 2250, 2096, 1619, 1513, 1305, 1201, 1177, 1050, 939, 829, 672
2b	2.51(s, 1H), 3.88(s, 2H), 6.68(s, 1H), 7.10—7.13(m, 2H)	3476, 3382, 3296, 3225, 2926, 2664, 2186, 2104, 1628, 1515, 1439, 1365, 1246, 1187, 1122, 941, 874, 819, 598
2c	3.18(s, 1H), 3.94(s, 2H), 6.34—6.38(m, 2H), 7.22—7.26(q, 1H)	3482, 3389, 3268, 2103, 2609, 1626, 1509, 1331, 1117, 957, 849, 742
Compd.	¹H NMR(CDCl₃, 500 MHz), δ	IR(KBr), ν˙/cm^-1
2d	2.90(s, 1H), 3.83(s, 2H), 6.86—6.93(m, 2H)	3479, 3392, 3287, 3073, 2982, 2925, 2112, 1732, 1643, 1580, 1526, 1337, 1262, 1099, 959, 859, 800, 716, 691
3a	3.83(s, 2H), 5.24—5.30(q, 1H), 6.26—6.64(q, 2H), 7.27—7.29(d, 2H, J=8.5 Hz), 7.33—7.34(q, 2H), 7.44—7.46(d, 2H, J=8.5 Hz)	3471, 3377, 3091, 3034, 2209, 1617, 1597, 1517, 832, 725, 671, 528
3b	3.90(s, 2H), 5.24—5.30(q, 1H), 6.70—6.73(t, 1H), 7.12—7.18(m, 2H), 7.28—7.30(d, 2H, J=8.0 Hz), 7.44—7.46(d, 2H, J=8.5 Hz)	3450, 3367, 3046, 2205, 1630, 1570, 1520, 834, 767, 607, 536
3c	3.94(s, 2H), 5.24—5.30(q, 1H), 6.38—6.41(t, 2H), 7.28—7.36(m, 3H), 7.44—7.51(m, 2H)	3501, 3406, 3094, 3032, 2207, 1626, 1605, 1523, 838, 741, 675, 605
3d	3.88(s, 2H), 5.25—5.31(q, 1H), 6.98—7.05(m, 2H), 7.29—7.31(d, 2H, J=8.5 Hz ), 7.44—7.46(d, 2H, J=8.5 Hz)	3449, 3329, 3072, 3045, 2213, 1642, 1578, 1525, 840, 720, 617, 536
A1	5.26—5.32(q, 1H), 7.19—7.21(d, 2H, J=8.5 Hz), 7.31—7.33(d, 2H, J=8.5 Hz), 7.49(t, 4H, J=16 Hz)	3078, 3032, 2202(C≡≡C), 2109(NCS), 1608, 1518, 942, 840, 806, 620
A2	5.26—5.33(q, 1H), 7.15(t, 1H), 7.26—7.33(m, 4H), 7.47—7.49(d, 2H, J=8.5 Hz)	3090, 3036, 2209(C≡≡C), 2048(NCS), 1602, 1514, 937, 845, 779
A3	5.26—5.32(q, 1H), 6.96—7.02(m, 2H), 7.31—7.33(d, 2H, J=8.5 Hz), 7.46—7.51(m, 3H)	3072, 3032, 2217(C≡≡C), 2106(NCS), 1613, 1515, 938, 867, 852, 605
A4	5.27—5.33(q, 1H), 7.09—7.13(m, 2H), 7.32—7.34(d, 2H, J=8.0 Hz), 7.47—7.48(m, 2H, J=8.5 Hz)	3096, 3033, 2214(C≡≡C), 2050(NCS), 1620, 1515, 941, 849, 706, 624

Table 3 Effect of different substrates on the reaction

Substrate	n(Target product):n(Raw material)
4-[(3-Fluoro-4-isthiocyanatophenyl)ethynyl]benzaldehyde	0:100
4-Ethynylbenzadehyde	63:24
4-Bromobenzaldehyde	64:24
4-Iodobenzaldehyde	85:12

Table 4 Phase transition temperature and enthalpy change of compounds A1—A4 and B1—B4*

Compd.	Transition temperature/℃		Enthalpy change/(kJ·mol^-1)
	Heating process	Cooling process	Heating process		Cooling process
	Heating process	Cooling process	Melting enthalpy	Clearing enthalpy	Melting enthalpy	Clearing enthalpy
A1	Cr 73.39 N 135.29 I	I 134.00 N 68.64 Cr	25.11	0.49	-0.40	-12.10
A2	Cr 96.28 N 127.65 I	I 126.75 N 89.67 Cr	27.92	0.32	-0.42	-26.86
A3	Cr 92.21 N 132.64 I	I 110.69 N 84.33 Cr	26.62	0.38	-0.02	-19.80
A4	Cr 120.29 I	I 108.03 Cr	32.03		-27.35
B1	Cr 94.58 I	I 89.56 Cr	25.07		-15.37
B2	Cr 70.76 I	I 44.93 Cr	23.83		-16.21
B3	Cr 73.86 I	I 50.00 Cr	26.65		-25.21
B4	Cr 81.87 I	I 63.99 Cr	15.08		-16.87

Fig.2 POM images of compounds A2 and A3 during heating process(200×) Nematic schlieren texture of A2 at 102.1 ℃(A) and A3 at 100.5 ℃(B), respectively.

Fig.3 Effect of lateral fluorine substituent on the thermal properties of target compounds A1—A4

Table 5 Physical properties of the mixtures

Mixture or compd.	Δε	γ₁/(mPa·s)	Δn(589 nm)	Mixture or compd.	Δε	γ₁/(mPa·s)	Δn(589 nm)
P0	5.63	156.5	0.080	A1	5.23	1.83	0.483
A1+P0	5.61	125.3	0.1002	A2	9.63	4.40	0.478
A2+P0	5.83	130.9	0.0999	A3	6.03	4.46	0.474
A3+P0	5.65	131.0	0.0997	A4	10.83	2.25	0.442
A4+P0	5.89	126.6	0.0981	B1	16.83	5.43	0.442
B1+P0	6.19	132.3	0.0986	B2	21.23	5.12	0.428
B2+P0	6.41	131.9	0.0974	B3	10.03	2.33	0.436
B3+P0	5.85	126.8	0.0978	B4	26.23	4.97	0.390
B4+P0	6.66	131.7	0.0955

Table 6 Calculated and measured birefringence of the investigated compounds

Compd.	α_XX/a.u.	A_YY/a.u.	α_ZZ/a.u.	Δα/a.u.	$α ?$ /a.u.	Δn
A1	561.68	182.26	27.67	456.71	257.21	0.4707
B1	499.02	167.39	41.05	394.80	235.82	0.4606
A2	573.76	181.83	27.81	468.94	261.13	0.4552
B2	511.26	166.88	41.19	407.23	239.78	0.4439
A3	568.17	185.07	27.75	461.76	260.33	0.4483
B3	504.46	169.34	40.83	399.37	238.21	0.4354

Table 6 Calculated and measured birefringence of the investigated compounds

Compd.	α_XX/a.u.	A_YY/a.u.	α_ZZ/a.u.	Δα/a.u.	$α ?$ /a.u.	Δn
A1	561.68	182.26	27.67	456.71	257.21	0.4707
B1	499.02	167.39	41.05	394.80	235.82	0.4606
A2	573.76	181.83	27.81	468.94	261.13	0.4552
B2	511.26	166.88	41.19	407.23	239.78	0.4439
A3	568.17	185.07	27.75	461.76	260.33	0.4483
B3	504.46	169.34	40.83	399.37	238.21	0.4354

Table 7 Physical properties of the mixtures

Mixture	Composition	$T mp a$ /℃	$T b ni$ /℃	Δn(25 ℃, 589 nm)	γ₁/ $K c 11$ /(ms·m^-2)	FoM^d/(m²·s^-1)
Mix1-A	Host 1+8%A1+8%A2	-17.72	106.05	0.4179	11.71	14.9
Mix1-B	Host 1+8%B1+8%B2	-16.81	88.96	0.3935	13.07	11.8
Mix2-A	Host 2+6%A1+6%A2	<-40	81.66	0.3797	10.84	13.3
Mix2-B	Host 2+6%B1+6%B2	<-40	67.24	0.3559	11.26	11.2

Table 7 Physical properties of the mixtures

Mixture	Composition	$T mp a$ /℃	$T b ni$ /℃	Δn(25 ℃, 589 nm)	γ₁/ $K c 11$ /(ms·m^-2)	FoM^d/(m²·s^-1)
Mix1-A	Host 1+8%A1+8%A2	-17.72	106.05	0.4179	11.71	14.9
Mix1-B	Host 1+8%B1+8%B2	-16.81	88.96	0.3935	13.07	11.8
Mix2-A	Host 2+6%A1+6%A2	<-40	81.66	0.3797	10.84	13.3
Mix2-B	Host 2+6%B1+6%B2	<-40	67.24	0.3559	11.26	11.2

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