基于密度泛函理论的对二甲苯分子电子光谱的外场效应研究

引用本文

张倩, 杜建宾, 冯志芳, 张亚如, 唐延林. 基于密度泛函理论的对二甲苯分子电子光谱的外场效应研究[J]. 光谱学与光谱分析, 2019,39(8): 2337-2340.
ZHANG Qian, DU Jian-bin, FENG Zhi-fang, ZHANG Ya-ru, TANG Yan-lin. Investigation of External Electric Field Effect on Ultraviolet-Visible Spectra of Para-Xylene Molecule by Density Functional Theory[J]. Spectroscopy and Spectral Analysis, 2019,39(8): 2337-2340.
Doi:10.3964/j.issn.1000-0593(2019)08-2337-04 复制到剪切板

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基于密度泛函理论的对二甲苯分子电子光谱的外场效应研究

张倩¹, 杜建宾^1,^2,^*, 冯志芳³, 张亚如¹, 唐延林⁴

1. 廊坊师范学院物理与电子信息学院, 河北廊坊 065000

2. 天津大学精密仪器与光电子工程学院, 天津 300072

3. 廊坊师范学院数学与信息科学学院, 河北廊坊 065000

4. 贵州大学物理学院, 贵州贵阳 550025

*通讯联系人 e-mail: dujianbinfzf@sina.com

作者简介: 张倩, 女, 1985年生, 廊坊师范学院物理与电子信息学院讲师 e-mail: 514520923@qq.com

收稿日期: 2018-10-16 接受日期: 2019-02-10

基金: 河北省教育厅青年基金项目(QN2015219); 廊坊市科技项目(2017011008); 廊坊师范学院自然基金项目(LSZQ201105)资助

摘要

对二甲苯(PX)是化工领域一种非常重要的原料, 被广泛地用于香料、医药、油墨和农药等的生产, 因此研究PX分子的电子光谱和外场效应, 对于它的检测和降解具有十分重要的意义。为研究外电场作用下, PX分子的紫外-可见(UV-Vis)光谱的变化, 采用密度泛函理论(density functional theory, DFT)B3LYP方法在6-311++G(d, p)基组水平上, 优化了不同外电场(0~0.025 a.u., 0~1.285 6×10¹⁰ V·m^-1)作用下PX分子的基态几何构型, 在此基础上利用含时密度泛函理论(TDDFT)计算了PX分子的UV-Vis吸收光谱, 最后对PX分子紫外吸收峰和摩尔吸收系数受外电场作用的的影响规律进行了研究。结果表明: 有波长为189 nm、摩尔吸收系数为35 580 L·mol^-1·cm^-1的强吸收峰, 处于 E₁带, 它是环状共轭的三个乙烯键的苯型体系中的π→π^*电子跃迁产生的; 与苯分子相比, 吸收峰出现11 nm的红移: 由于两个甲基和苯环形成p-π共轭, 苯环的大π键变弱, 故PX分子的紫外吸收峰出现红移; 当增加了外电场后, 最低未占据轨道(LUMO)向外电场的反方向偏移, 导致苯环上的电子密度减小, 大π键变弱, π→π^*跃迁需要的能量降低, 电子跃迁产生的波长增大, 吸收峰出现显著红移, 当外电场增大到0.020 a.u.时, 红移已经非常明显; 外电场的引入, 导致苯环上的电子密度减小, 大π键变弱, π→π^*跃迁的电子数减少, 摩尔吸收系数降低, 随着外电场的增强, 摩尔吸收系数降低明显, 尤其在外电场增强到0.020a.u.后, 摩尔吸收系数降低非常显著。这些工作为PX的检测和降解方法研究提供了一定的理论依据, 也对其他有机污染物的检测方法和降解机理的研究有启示作用。

关键词: 对二甲苯; 外电场; 紫外-可见光谱; 密度泛函理论

中图分类号:O561.3 文献标志码:A

Investigation of External Electric Field Effect on Ultraviolet-Visible Spectra of Para-Xylene Molecule by Density Functional Theory

ZHANG Qian¹, DU Jian-bin^1,^2,^*, FENG Zhi-fang³, ZHANG Ya-ru¹, TANG Yan-lin⁴

1. College of Physics and Electrical Information, Langfang Normal University, Langfang 065000, China

2. College of Precision Instrument and Optoelectronics Engineering, Tianjin University, Tianjin 300072, China

3. College of Mathematics and Information, Langfang Normal University, Langfang 065000, China

4. College of Physics, Guizhou University, Guiyang 550025, China

*Corresponding author

Abstract

Para-xylene(PX) is an important raw material in chemical industry. In order to study the change of ultraviolet-visible(UV-Vis) spectra of PX under external electrical field, the density functional theory (DFT) has been employed to calculate geometrical parameters of the ground state of PX molecule under different external electric fields ( from 0 to 0.025 a.u.) in this paper. On this basis, the UV-Vis absorption spectra of PX molecule were calculated by employing the time-dependent density functional theory (TDDFT). At last, by employing the TDDFT in the same fundamental group, we studied wavelength and the molar absorption coefficient of the first twenty-six excited states of PX molecule under different external electric fields. The results show that the most absorption of UV-Vis absorption spectra appears in the E₁ belt of benzene electronic transition from π to π^*; the ultraviolet absorption peaks of excited states of PX are proved to appear observably red shift and the molar absorption coefficient sharply decreases with the increase of the field intensity.

Keyword: Para-xylene; External electric field; Ultraviolet-visible spectra; Density functional theory

文章图片

引言

对二甲苯(para-xylene, PX)作为聚酯行业的重要原料, 主要用于制造精对二苯甲酸或精对二苯甲酸二甲酯, 进而生产聚酯^[1], 还可用作溶剂以及合成纤维、材料等行业^[2]。长期接触对二甲苯, 会导致肝、肾损伤, 严重时会危及生命。张冰洁等研究了PX对人类肝细胞的毒性效应^[3], 刘洋等对微孔活性炭对PX的吸附和脱附性能进行了研究^[4], 林华等探讨了外电场对PX结构和光谱特性的影响^[5], 但对于PX在外电场下的电子光谱的深入研究目前还未见报道。本文采用含时密度泛函理论(time-dependent density functional theory, TDDFT)^{[6, 7, 8]}对不同外电场下PX分子的紫外-可见(ultraviolet-visible, UV-Vis)光谱的变化进行了研究, 这为以PX为原料合成的有机污染物的降解和检测方法研究提供了理论依据。

1 理论和计算方法

分子体系的哈密顿量H当有外电场时加入由两项组成^[9], 即无电场时的哈密顿量H₀和外电场与分子体系相互作用的哈密顿量H_int

$H = H_{0} + H_{int} (1)$

H_int在偶极近似下可以表示为

$H_{int} = - μF (2)$

其中μ 为分子的电偶极矩。

PX分子的结构如图1所示, 在沿x轴方向上加上一系列强度为0~0.025 a.u.(0~1.285 6× 10¹⁰ V· m^-1)的外电场, 即在Gaussian程序的哈密顿量中添加$H_{int}$^[10-11], 然后利用TDDFT来精确计算分子前26个激发态的波长和摩尔吸收系数在外电场作用下产生的变化。全部计算在Gaussian09软件包中完成。

	Figure Option View Download New Window
	图1 PX分子结构示意图Fig.1 Optimized molecular structure of PX

2 PX分子的激发态波长以及外电场对激发态波长和摩尔吸收系数的影响

2.1 PX的激发态波长

在分子基态几何结构优化的基础上, 采用含时密度泛函理论(time-dependent density functional theory, TDDFT)方法计算了PX分子的UV-Vis吸收光谱, 如图2所示, 有一个波长为189 nm、摩尔吸收系数为35 580 L· mol^-1· cm^-1的强吸收峰, 处于E₁带, 它是环状共轭的三个乙烯键的苯型体系中的π → π ^*电子跃迁产生的。在NIST Chemistry WebBook(国际标准与技术学会化学电子数据库)中给出了苯分子165~205 nm波长范围的UV-Vis吸收光谱, 其最强吸收峰出现在波长178 nm处。 PX是苯分子对位的两个H被两个甲基取代所形成, 这两个给电子基团和苯环形成p-π 共轭, 苯环的大π 键变弱, 分子的紫外吸收峰出现红移, 与理论的计算结果是一致, 说明理论计算的PX分子UV-Vis吸收光谱是可信的。

	Figure Option View Download New Window
	图2 无外电场时PX分子的UV-Vis吸收光谱Fig.2 UV-Vis absorption spectra of PX without external electric fields

2.2 外电场对激发态波长和摩尔吸收系数的影响

在PX分子基态优化的基础上, 采用TDDFT方法研究了0~0.025 a.u.的外电场对分子激发态波长λ 和摩尔吸收系数的产生影响, 如图3所示, 可以看出, 当外电场较弱时, 吸收峰的波长变化不明显, 但随着外电场的增强, 吸收峰出现显著红移, 当外电场增大到0.020 a.u.时, 红移已经非常明显, 这是由于无外电场时, 分子中的电子轨道主要分布在苯环上(如图4所示), 当增加了外电场后, LUMO轨道向外电场的反方向偏移, 导致苯环上的电子密度减小, 大π 键变弱, π → π ^*跃迁需要的能量降低, 电子跃迁产生的波长增大, 因此出现吸收峰红移。当外电场增大到0.020 a.u.时, LUMO偏移更加明显, 出现了电子密度为0的区域, 因此吸收峰也出现了显著红移。

	Figure Option View Download New Window
	图3 PX分子在不同外电场作用下的UV-Vis吸收光谱Fig.3 UV-Vis absorption spectra of PX under different external electric fields

	Figure Option View Download New Window
	图4 不同外电场下PX激发态的分子前线轨道 HOMO: 最高占据轨道; LUMO: 最低未占据轨道Fig.4 Excited state frontier orbital diagram of PX molecular under different external electric fields HOMO: Highest occupied molecular orbital; LUMO: Lowest unoccupied molecular orbital

随着外电场的增强, 吸收峰的红移, 摩尔吸收系数降低明显, 尤其在外电场增强到0.020 a.u.后, 摩尔吸收系数降低已经非常显著, 这是由于外电场作用使电子云的整体偏移, 使得LUMO偏离苯环, 苯环上的电子云密度变小(如图4所示), π → π ^*跃迁的电子个数减少, 从而摩尔吸收系数降低。

3 结论

基于密度泛函理论研究了不同外电场对PX分子的激发态波长和摩尔吸收系数的影响。结果表明, 无外电场时, 分子最强吸收峰的波长为189 nm, 由环状共轭的三个乙烯键的苯型体系中的π → π ^*电子跃迁所产生; 随着外电场的增强, 分子的紫外吸收峰明显红移, 摩尔吸收系数显著下降。综上分析可见, 在外电场的作用下, 分子的UV-Vis吸收光谱变化显著。与塑化剂类分子的外场效应对比, 苯环上连有长支链的有机物对外电场的变化更加敏感^[7]。这些工作对PX的检测和降解方法研究提供了一定的理论依据, 也对其他有机污染物的检测方法和降解机理的研究有启示作用。

参考文献

文献列表

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[2]	LIU Jun-xia, CHEN Jing-run, WANG Jun-feng, et al(刘俊霞, 陈景润, 王军峰, 等). Industrial Catalysis(工业催化), 2017, 25(4): 12. [本文引用:1]
[3]	ZHANG Bing-jie, LIU Qian, ZHOU Qun-fang, et al(张冰洁, 刘倩, 周群芳, 等). Acta Scien. Circum. (环境科学学报), 2018, 38(4): 1682. [本文引用:1]
[4]	LIU Yang, BAI Jin-feng, LI Bin, et al(刘洋, 白金锋, 李彬, 等). Coal Conversion(煤炭转化), 2017, 40(1): 53. [本文引用:1]
[5]	LIN Hua, LIU Yu-zhu, HE Jun-bo, et al(林华, 刘玉柱, 何君博, 等). Chin. J. Atom. Mol. Phys. (原子与分子物理学报), 2018, 35(3): 407. [本文引用:1]
[6]	Liu X G, Xu Z C, Cole J M. J. Phys. Chem. C, 2013, 117(32): 16584. [本文引用:1]
[7]	DU Jian-bin, WU De-qi, TANG Yan-lin, et al(杜建宾, 武德起, 唐延林, 等). Acta Phys. Sin. (物理学报), 2015, 64(7): 073101. [本文引用:2]
[8]	DU Jian-bin, FENG Zhi-fang, HAN Li-jun, et al(杜建宾, 冯志芳, 韩丽君, 等). Acta Phys. Sin. (物理学报), 2018, 67(22): 223101. [本文引用:1]
[9]	Wu D L, Tan B, Wan H J, et al. Chin. Phys. B, 2013, 22(12): 123101. [本文引用:1]
[10]	XIE An-dong, XIE Jing, ZHOU Ling-ling, et al(谢安东, 谢晶, 周玲玲, 等). Chin. J. Atom. Mol. Phys. (原子与分子物理学报), 2016, 33(6): 989. [本文引用:2]
[11]	DU Jian-bin, TANG Yan-lin, LONG Zheng-wen(杜建宾, 唐延林, 隆正文). Acta Phys. Sin. (物理学报), 2012, 61(15): 153101. [本文引用:2]

2017

0.0

... 引言对二甲苯(para-xylene, PX)作为聚酯行业的重要原料, 主要用于制造精对二苯甲酸或精对二苯甲酸二甲酯, 进而生产聚酯^[1], 还可用作溶剂以及合成纤维、材料等行业^[2] ...

2017

0.0

2018

0.0

... 张冰洁等研究了PX对人类肝细胞的毒性效应^[3], 刘洋等对微孔活性炭对PX的吸附和脱附性能进行了研究^[4], 林华等探讨了外电场对PX结构和光谱特性的影响^[5], 但对于PX在外电场下的电子光谱的深入研究目前还未见报道 ...

2017

0.0

2018

0.0

2013

0.0

... 本文采用含时密度泛函理论(time-dependent density functional theory, TDDFT)^[6,7,8]对不同外电场下PX分子的紫外-可见(ultraviolet-visible, UV-Vis)光谱的变化进行了研究, 这为以PX为原料合成的有机污染物的降解和检测方法研究提供了理论依据 ...

2015

0.0

Jian-bin

, WU

De-qi

, TANG

Yan-lin

, et al(杜建宾, 武德起, 唐延林, 等). Acta Phys. Sin. (物理学报), 2015, 64(7): 073101.

Dibutyl phthalate (DBP) is the main component of the plasticizers. In order to study the influence of an external electrical field on the molecular structure and spectra of DBP, the method B3LYP of the density functional theory (DFT) at 6-311++G(d, p) level has been used in this paper to calculate its geometrical parameters and infrared (IR) spectra, in the ground state of DBP molecule under different external electric fields (from 0 to 0.020 a.u.). On this basis, the UV-Vis absorption spectra of DBP are studied using the time-dependent density functional theory (TDDFT) in the same fundamental groups and compared with the ultraviolet(UV) absorption peak of the molecules measured by UNICO ultraviolet and visible spectrophotometer. The rule of variation of wavelength and oscillator strength of the first twenty-six excited states of a DBP molecule under the influence of the external electric fields are studied. Results show that the molecular geometric parameter is strongly dependent on the external field intensity, and the dipole moment of DBP is proved to be sharply increased, and the total energy first decreases with the increases of the external field intensity; the significant negative (“red”) and positive (“blue”) frequency shifts are observed, i.e., vibrational Stark effect (VSE) is shown obviously; the ultraviolet absorption peaks of the excited states of DBP show an observable red shift, and the oscillator strength decreases sharply with increasing field intensity.

1. College of Physics and Electrical Information, Langfang Normal University, Langfang 065000, China; 2. Institute of Microelectronics, Chinese Academy of Sciences, Beijing 100029, China; 3. Department of Physics, Guizhou University, Guiyang 550025, China

邻苯二甲酸二丁酯(dibutyl phthalate, DBP)是增塑剂的主要成分之一.为研究外电场对环境毒物增塑剂类化合物的分子结构和光谱产生的影响, 本文采用密度泛函(density functional theory, DFT) B3LYP方法在6-311++G(d, p)基组水平上优化了不同静电场(0–0.020 a.u.)作用下DBP分子的基态几何结构, 在此基础上利用同样的方法计算了DBP分子的电偶极矩、分子总能量和红外(infrared, IR)光谱, 最后利用含时密度泛函(time-dependent density functional theory, TDDFT)在同一基组下研究了不同外电场对DBP分子紫外-可见(UV-Vis)吸收光谱产生的影响, 并与实验测得的光谱图进行了比较.结果表明, 在外电场的作用下, 分子结构变化剧烈, 电偶极矩增大, 分子总能量减小, 红外光谱吸收峰出现红移或蓝移, 分子的摩尔吸收系数重新分配, 振动斯塔克效应(vibrational stark effect, VSE)明显; 随着外电场的增强, 分子UV-Vis光谱的吸收峰红移显著, 振子强度剧烈下降.

... 与塑化剂类分子的外场效应对比, 苯环上连有长支链的有机物对外电场的变化更加敏感^[7] ...

2018

0.0

Jian-bin

, FENG

Zhi-fang

, HAN

Li-jun

, et al(杜建宾, 冯志芳, 韩丽君, 等). Acta Phys. Sin. (物理学报), 2018, 67(22): 223101.

Various environmental poisons have caused damage to human production and life, and dioxin has seriously harmed human health. The C 12 H 4 Cl 4 O 2 (2, 3, 7, 8-tetrachlorodibenzo- p -dioxin, TCDD) is currently the most toxic compound. In order to study the influence of external electrical field on molecular structure and spectrum, herein the density functional theory (DFT) at a B3LYP/6-31+g (d,p) level is employed to calculate the geometrical parameters of the ground state of TCDD molecule under external electric fields ranging from 0 to 0.025 a.u. (0-1.2856×10 10 V/m). Based on the optimized structure, time-dependent DFT at the same level as the above is adopted to calculate the absorption wavelengths and the molar absorption coefficients for the first twenty-six excited states of TCDD molecule under external electric fields. The results show that the most absorption band located at 221 nm with a molar absorption coefficient of 54064 L·mol -1 ·cm -1 in the UV-Vis absorption spectrum appears in the E belt, which originates from the benzene electronic transition from π to π * . In addition, a shoulder peak at 296 nm appears in the B belt, which is the characteristic absorption of aromatic compounds' electron transition from π to π * . Compared with the data in the literature, the wavelength of the shoulder is blue-shifted only 9 nm. The molecular geometry parameters are strongly dependent on the external field intensity, and the total energy decreases with external field intensity increasing. With the enhancement of external electric field, the electrons in the molecule have an overall transfer, which makes the big bond of benzene ring weakened, the energy of the transition decreases, and the wavelength of the transition increases, that is, the absorption peak is red-shifted. When the external electric field increases to 0.02 a.u., the electron cloud migration phenomenon of occupied and transition orbits of TCDD molecule are obvious, and the absorption peak red shift phenomenon is also very significant. With the enhancement of external electric field, the overall transfer of electrons in the molecule also reduces the density of the benzene rings and the surrounding electron cloud, reduces the number of electrons in the transition from π to π * , and also reduces the molar absorption coefficient. When the external electric field is enhanced to 0.02 a.u., the molar absorption coefficient decreases significantly. This work provides a theoretical basis for studying the TCDD detection and degradation method, and also has implications for other environmental pollutants detection methods and degradation mechanisms.

1. College of Physics and Electrical Information, Langfang Normal University, Langfang 065000, China; 2. College of Mathematics and Information Science, Langfang Normal University, Langfang 065000, China; 3. College of Physics, Guizhou University, Guiyang 550025, China; 4. College of Information Engineering, Henan Mechanical and Electrical Vocational College, Zhengzhou 451191, China

各种环境毒物危害着人类的生产生活,二噁英更是严重危害人类的健康.C 12 H 4 Cl 4 O 2 （2,3,7,8-tetrachlorodibenzo-p-dioxin,TCDD）是二噁英中毒性最强的化合物,也是目前已知毒性最强的污染物.为研究TCDD外场效应,采用密度泛函理论方法优化了不同静电场0–0.025 a.u.（0–1.2856×10 10 V/m）作用下TCDD分子的基态几何结构,得到了分子总能量；在此基础上,采用含时密度泛函理论方法对TCDD分子的紫外-可见（UV-Vis）吸收光谱在不同外电场下的变化进行了研究.结果表明：分子几何构型与电场大小呈现强烈的依赖关系,分子总能量随着外电场的增强而减小；伴随着外电场的增强,分子激发态的摩尔吸收系数逐渐减小,UV-Vis吸收峰显著红移.

2013

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... 1 理论和计算方法分子体系的哈密顿量H当有外电场时加入由两项组成^[9], 即无电场时的哈密顿量H₀和外电场与分子体系相互作用的哈密顿量H_int ...

2016

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2012

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Jian-bin

, TANG

Yan-lin

, LONG

Zheng-wen

(杜建宾, 唐延林, 隆正文). Acta Phys. Sin. (物理学报), 2012, 61(15): 153101.

In order to study the influence of external electrical field on molecular structure, chemical bond and electronic spectrum of environmental poison chlorophenol, the method B3LYP of the density functional theory (DFT) at 6-311++G(d, p) level is used to calculate geometrical parameters, dipole moments and total energies of the ground state of pentachlorophenol molecule under different external electric fields (from 0 to 0.025 a.u.) in this article. On this basis, the UV absorption spectra of pentachlorophenol (PCP) are studied using the time-dependent density functional theory (TDDFT) in the same fundamental group and compared with the ultraviolet absorption peak of phenol given in the literature. Finally, the rules of external electric field influencing wavelengths and oscillator strengths of the first ten excited states of a PCP molecule are studied. The results show that molecular geometry is strongly dependent on the field intensity, the molecular dipole moment is proved to be first decreasing, then increasing and the total energy first increasing then decreasing with the increase of the field intensity. Compared with the ultraviolet absorption peak of phenol, that of PCP is red-shifted. The oscillator strength of excited state of PCP is proved to be decreasing, and the ultraviolet absorption peak is also red-shifted with the increase of the field intensity.

Laboratory for Photoelectic Technology and Application, Guizhou University, Department of Phisics, Guizhou University, Guiyang 550025, China

为研究外电场对环境毒物氯酚类化合物的分子结构、化学键和电子光谱产生的影响, 本文采用密度泛函(DFT)B3LYP方法在6-311++G(d,p)基组水平上优化并计算了不同外电场(0—0.025 a.u.) 作用下五氯酚分子的基态几何结构、电偶极矩和分子总能量, 在此基础上利用含时密度泛函(TDDFT)在同一基组下研究了五氯酚(pentachlorophenol, PCP)的紫外吸收光谱, 并与文献中给出的苯酚的紫外吸收峰的波长进行了比较, 最后对PCP分子的前10个激发态的波长和振子强度受外电场作用的的影响规律进行了研究. 结果表明, 分子几何构型与电场大小呈现强烈的依赖关系, 分子偶极矩随着外电场的增强先减小后增加, 而分子总能量随着外电场的增强先增加后减小; PCP的紫外吸收峰相对苯酚出现了红移, 其激发态的振子强度随着电场的增强而减小、紫外吸收峰也出现红移.