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Abstract

Nematic liquid crystal materials designed for optics, microwave communication tuning, etc. need high response speed, which is related to the rotational viscosity and the birefringent index of the liquid crystal. In order to achieve a wide tuning range of phase modulation, the nematic liquid crystals often employ large π-electron conjugated systems and large polar groups to enhance the birefringence and dielectric anisotropy of the liquid crystal molecule, which, however, increases the viscosity of the liquid crystal material, deteriorating the response speed of the microwave device. Herein, we explore the viscosity of the nematic liquid crystal from the perspective of liquid crystal compound structure by testing the viscosity of our designed and synthesized forty-two different nematic liquid crystals by using a rotating rheometer at 25 ℃. To the best of our knowledge, the BPNN-QSAR quantitative structure-activity model between nematic liquid crystal molecular structure and viscosity is established for the first time. The correlation coefficient between the predicted value and the experimental value is q ²= 0.607 > 0.5, indicating that the model can be used to predict the viscosity performances of liquid crystal compounds. Besides, the molecular structure descriptors affecting the viscosity properties are explored. Based on the practical application and this model, seven liquid crystal molecules of two series with large birefringent index are designed and tested. The viscosity predicted by the BPNN model is smaller than that of the molecules of the same type and matches with the measured viscosity.

Keywords:

nematic liquid crystal/
viscosity/
molecular structure/
quantitative structure-activity relationship

Authors and contacts

Corresponding author:Wang Ting-Ting,1125364902@qq.com

Funds:Project supported by the National Equipment Development Department Pre-research Fund (Grant No. 61409230701).

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序号	化合物	分子结构	分子量/(g·mol^–1)	混晶黏度η/ (mPa·s^–1)	相变温度T/℃
1	3CC2		236.25	19.647	Cr –8.3 N 93.0 Iso
2	3CC4		264.28	20.983	Cr –10.9 N 66.8 Iso
3	5CPF		248.19	23.914	Liquid
4	3CPO1		232.18	21.619	Cr 32.0 Iso
5	5PP1		238.17	22.624	Cr 48.0 Iso
6	3GPS		271.08	24.313	Cr 45.0 Iso
7	2CPUS		357.14	23.961	Cr 50.0 N 175.0 Iso
8	5CPUS		399.18	24.874	Cr 50.5 N 196.3 Iso
9	3PGUF		344.12	24.694	Cr 62.5 Iso
10	5PGUF		372.15	25.021	Cr 56.4 Iso
11	5PGUS		411.13	26.486	Cr 57.4 N 159.2 Iso
12	5CPGUF		454.23	25.983	Cr 62.23 S 70 N 215 Iso
13	5CPGUS		493.21	26.400	Cr 71.53 N 234.15 Iso
14	5PGUOCF3		438.14	26.242	Cr 47.4 N 69.3 Iso
15	5CPGUOCF3		520.22	26.558	Cr 58.10 S 82.6 N 230.35 Iso
16	4PGPUF		434.17	24.884	Cr 96.8 SmC 111.9 SmA 214.6 N 231.4 Iso
17	5PP(2)GIP4		478.30	26.865	Cr 53.55 S 72.65 N 109.84 Iso
18	3PUQUF		428.10	25.191	Cr 47.2 Iso
19	3PGUQUF		522.12	26.205	Cr 88 N 135 Iso
20	3CEPC3		370.29	21.039	Cr 116.7 N 205.9 Iso
21	2CEPPN		333.17	21.072	Cr 89.0 N 245.6 Iso
22	3CPEP3		364.24	22.042	Cr 100.7 N 202.9 Iso
23	3CPEGN		365.18	23.498	Cr 107.1 N 214.4 Iso
24	2PEPN		251.09	20.946	Cr 77.6 N 80.9 Iso
25	3PEPN		265.11	22.869	Cr 108.1 N 113.5 Iso 51.9 N
26	4PEPN		279.13	24.478	Cr 71.3 N 74.2 Iso
27	3PTGS		295.08	22.476	Cr 55.22 S 69.37 Iso
28	5PTGS		323.11	23.248	Cr 50.59 N 90.59 Iso
29	7PTGS		351.15	24.016	Cr 41.98 N 45.06 Iso
30	5PTPO2		292.18	21.512	Cr 65.6 N 95.3 Iso 88.3 N
31	5PTUS		341.1	22.577	Cr 43.99 Iso
32	5CPTUS		423.18	22.974	Cr 62 N 228 Iso
33	5PPTUS		417.14	23.809	Cr 55.0 S 119.0 N 208.5 Iso
34	4PUTGS		421.11	22.559	Cr 93 Iso
35	2PTPP3		360.17	22.768	Cr 73.5 N 186 Iso
36	3PTPP2		360.17	22.583	Cr 73 N 189 Iso
37	3PTPP4		388.20	23.682	Cr 66.1 S 88.0 N 169.5 Iso
38	4PTPP3		388.29	23.445	Cr 38.5 S 60.0 N 174.0 Iso
39	4PTGTP4		444.21	26.201	Cr 78 N 180 Iso
40	4PTGTP5		458.22	26.918	Cr 72.12 N 172.81 Iso
41	5PP(1)PUF		444.21	25.014	Cr 76.9 N 127.6 Iso
42	5PPI(1)PUF		444.21	24.608	Cr 77.4 N 134 Iso
43	5CB		249.15	25.010	Cr 24 N 35.3 Iso
注: Cr, 各向异性晶体相; S, 近晶相; N, 向列相; Iso, 各向同性; SmA, SmA相态; SmC, SmC相态.

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网络结构	R²	R²(cross-validated)	q²
12-4-1	0.9238	0.5089	0.6070

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No.	Compounds	η/(mPa·s)	$ {{\mathrm{VM}}}_{{\mathrm{expt}}} $	$ {{\mathrm{VM}}}_{{\mathrm{pred}}} $	$ \Delta {\mathrm{VM}} $	δ
1*	3CC2	19.647	1.293	1.319	0.026	0.020
2	3CC4	20.983	1.322	1.318	0.004	0.003
3	5CPF	23.914	1.379	1.376	0.002	0.002
4	3CPO1	21.619	1.335	1.336	0.001	0.001
5	5PP1	22.624	1.355	1.357	0.002	0.001
6	3GPS	24.313	1.386	1.363	0.023	0.017
7*	2CPUS	23.961	1.380	1.378	0.002	0.001
8	5CPUS	24.874	1.396	1.401	0.006	0.004
9	3PGUF	24.694	1.393	1.396	0.004	0.002
10*	5PGUF	25.021	1.398	1.405	0.006	0.004
11	5PGUS	26.486	1.423	1.425	0.002	0.001
12	5CPGUF	25.983	1.415	1.414	0.000	0.001
13	5CPGUS	26.400	1.422	1.418	0.004	0.003
14	5PGUOCF3	26.242	1.419	1.417	0.002	0.001
15	5CPGUOCF3	26.558	1.424	1.424	–0.001	0.000
16	4PGPUF	24.884	1.396	1.410	0.014	0.010
17	5PP(2)GIP4	26.865	1.429	1.426	0.003	0.002
18	3PUQUF	25.191	1.401	1.411	0.010	0.007
19	3PGUQUF	26.205	1.418	1.411	0.007	0.005
20	3CEPC3	21.039	1.323	1.326	0.003	0.002
21	2CEPPN	21.072	1.324	1.320	0.003	0.003
22	3CPEP3	22.042	1.343	1.344	0.001	0.001
23	3CPEGN	23.498	1.371	1.365	0.006	0.004
24	2PEPN	20.946	1.321	1.341	0.020	0.015
25*	3PEPN	22.869	1.359	1.353	0.006	0.004
26	4PEPN	24.478	1.389	1.365	0.024	0.017
27	3PTGS	22.476	1.352	1.347	0.005	0.004
28*	5PTGS	23.248	1.366	1.372	0.006	0.004
29	7PTGS	24.916	1.396	1.401	0.004	0.004
30	5PTPO2	21.512	1.333	1.337	0.004	0.003
31	5PTUS	22.577	1.354	1.364	0.011	0.007
32	5CPTUS	22.974	1.361	1.367	0.006	0.004
33*	5PPTUS	23.809	1.377	1.427	0.050	0.036
34	4PUTGS	22.559	1.353	1.364	0.011	0.008
35	2PTPP3	22.768	1.357	1.353	0.004	0.003
36	3PTPP2	22.583	1.354	1.345	0.009	0.007
37*	3PTPP4	23.682	1.374	1.374	-0.001	0.001
38	4PTPP3	23.445	1.370	1.366	0.004	0.003
39*	4PTGTP4	26.201	1.418	1.398	0.020	0.014
40	4PTGTP5	26.918	1.430	1.427	-0.003	0.002
41	5PP(1)PUF	25.014	1.398	1.412	0.014	0.010
42	5PPI(1)PUF	24.608	1.391	1.406	0.015	0.011
注: *为测试组数据.

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描述符	结构信息	敏感度
ES-Count-aasC	代表具有两个芳香键和一个单键的碳的电拓扑状态 (Electrotopological State, Estate)和电子结构信息	0.999735
Dipole-X	指示静电场中分子的强度和取向行为的3D电子描述符	0.947414
Num-RotatableBonds	可旋转键, 定义为既不在环中又不在末端的重原子之间的单键, 即连接到仅与氢相连的重原子. 作为一种特殊情况, 酰胺C—N键是不可旋转的	0.814023
Shadow-Xlength	阴影X长度, 表征分子形状的一组几何描述符, 代表分子在x维度上的长度	0.307771
ES-Sum-sssCH	计算具有三个单键的CH的电拓扑状态(Estate)总和	0.208536
JX	Balaban指数	0.118169
ES-Count-tsC	代表具有一个三键的碳的电拓扑状态(Estate)计数	–0.707114
ES-Count-ssCH₂	代表具有两个单键的CH₂的电拓扑状态(Estate)计数	–0.671564
Wiener	维纳指数, 代表分子中所有重原子对之间存在的化学键的总和	–0.653192
ES-Sum-sF	计算F原子的电拓扑状态(Estate)	–0.400111
ES-Count-sF	F原子的电拓扑状态(Estate)计数	–0.400111
ALogP	使用Ghose和Crippen发表的基于原子的方法计算辛醇-水分配系(LogP)	–0.128786
注: ES-Sum-xxx: 某原子电子结构和拓扑结构计算总和; ES-Count-xxx: 某种类型的原子在分子中出现的数目; -xxx中s, 单键; d, 双键; t, 三键; a, 芳香键^[38,39].

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Vol. 73, Issue 6 - 2024-03-20

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