1,10-菲啰啉-四氰基乙烯配合物发光性质的研究
吕玉光, 石琦, 郭强, 宋姗姗, 秦宇珊, 王博, 杨立滨*
佳木斯大学药学院, 黑龙江 佳木斯 154007
摘要

基于探针在近年来得到发展, 制备光学性能更为良好的发光材料成为当前化学工作者的研究热点, 该工作预制备光学性能更为优良的新型发光材料, 以满足人们日常生活及医疗等方面的需求。 该工作以四氰基乙烯(TCNE)为第一配体, 以1,10-菲啰啉(phen)为第二配体, 通过分子间的电荷转移, 合成1,10-菲啰啉-四氰基乙烯的电荷转移络合物, 并对此反应机理进行初步探索。 运用紫外光谱法、 荧光光谱法和拉曼光谱法对配合物进行表征及发光性质的研究。 比较配合物和配体的紫外吸收峰发现, 配合物的吸收均源于配体1,10-菲啰啉的吸收, 说明TCNE与Phen形成了稳定的络合物。 同时分析荧光光谱, 发现配合物的发射峰与配体四氰基乙烯相似, 可认为配合物的荧光来自于配体的π—π*电子跃迁。 从拉曼图谱中可以看出, 在1 000~1 600 cm-1处配合物的拉曼强度比TCNE配体有明显的增强。 共振拉曼散射在1 000~1 600 cm-1处振动模式被强耦合, 由于分子间的电荷转移使得这些共振拉曼峰被强烈增强。 分析结果表明, 在一定条件下, 1,10-菲啰啉能与四氰基乙烯形成稳定的络合物, 且光学性能显著增强。 上述研究, 合成并研究了1,10-菲啰啉-四氰基乙烯荷移络合物的光学性质, 为设计、 合成荧光性能良好的配合物提供了实验依据, 并为探索和开发新的核酸探针做出了贡献。

关键词: 四氰基乙烯; 1; 10-菲啰啉; 荷移络合物; 荧光性能
中图分类号:O657.3 文献标志码:A
Studies on Luminescent Properties of TCNE-Phenanthroline Complex
LÜ Yu-guang, SHI Qi, GUO Qiang, SONG Shan-shan, QIN Yu-shan, WANG Bo, YANG Li-bin*
College of Pharmacy, Jiamusi University, Jiamusi 154007, China
*Corresponding author e-mail: ylb76@163.com
Abstract

Based on the development of probes in recent years, the preparation of luminescent materials with better optical properties has become a hotspot of current chemical workers. This work is intended to prepare a new type of luminescent material with better optical performance to meet people’s daily life and medical demands. The complex of tetracynoethylene-1,10-phenanthroline was formed with tetracynoethylene (TCNE) and 1,10-phenanthroline (Phen) under specific conditions and characterized by UV-Vis spectrometry, Fluorescence spectrometry and Raman scattering spectrometry. Then the reaction mechanism was explored preliminarily. The absorption peaks of complex was compared with the absorption peaks of ligands. It showed that the absorption of complexes was due to the absorption of ligand 1,10-phenanthroline, indicating that tetracynoethylene and 1,10-phenanthroline formed stable complexes. At the same time, the fluorescence spectra were analyzed. It was found that the emission peak of the complex was similar to that of the ligand tetracynoethylene, and the fluorescence of the complex was believed to be derived from the π—π* electron transition of the ligand. It can be seen from the Raman spectra that the Raman intensity of the complex at 1 000~1 600 cm-1 was significantly enhanced compared with the Raman intensity of tetracynoethylene ligand. The resonant Raman scattering was strongly coupled at 1 000~1 600 cm-1, and these resonant Raman peaks were strongly enhanced due to the charge transfer between molecules. The results suggested that the ligand tetracynoethylene had coordinated successfully with ligand 1,10-Phenanthroline and the fluorescence intensity was significantly improved. At the same time, the absorption of complex mainly came from the ligands absorption. In the above study, the 1,10-Phenanthroline-tetracyanoethylene charge transfer complex was synthesized for the first time and its optical properties were studied. This study provided an experimental basis for the design and synthesis of complexes with superior luminescent properties, promoting the progress of the career of the optics and contributed the exploration and development of new nucleic acid probes.

Keyword: Tetracyanoethylene (TCNE); 1; 10-Phenanthroline (Phen); Charge-transfer complex; Luminescence properties

Introduction

In recent years, many chemical workers have showed a strong interest in the research of fluorescent probe technology[1], which have made the complex luminescent material develop rapidly to a new stage. Fluorescent probe is a fast, convenient, high selectivity and high sensitivity detection means, with the fluorescent probe application gradually popularize, the requirements of the probe ligand also increased. Some of the original species have been unable to meet the needs in many applications. Therefore, it is necessary to find probe ligands with higher sensitivity and faster detection speed, making it better for optics applications.

Tetracyclopentylethylene (TCNE) is a highly planar π -electron acceptor that reacts with most of the electron-rich groups to form new charge transfer complexes[2]. The charge transfer complex is formed by charge transfer between an electron-rich material and an electron-deficient substance. These charge transfer complexes have excellent magnetic, electrical, optical and other properties[3]. With the continuous exploration of functional organic materials, TCNE as a stable strong electron acceptor, its application is expanding. In addition, 1, 10-Phenanthroline (1, 10-Phen) is a nitrogen-containing six-membered heterocyclic structure, and also has a π -conjugated system as well as rigidity, flatness[4], aromaticity, and strong coordination ability. 1, 10-Phen is prone to form a stable coordination compound. As a common ligand[5], 1, 10-Phen can enhance the stability and luminescence of complexes, and has wide application in optical properties[6, 7, 8, 9, 10].

Based on the above considerations, this study used TCNE as the main ligand, 1, 10-Phen as the auxiliary ligand, through the charge transfer between the two ligands[11] to form a complex, and systematically analyzed the fluorescence spectra, UV spectra, Raman spectra of the complex. The luminescent properties were studied as well.

1 Experimental
1.1 Instruments and reagents

Instrument: Fluorescence Spectrophotometer (970CRT, Shanghai Instrument Analysis Production Plant); UV-Vis spectrophotometer (UV/Vis-265); Raman Spectrum (Renishaw-1000, British Renishaw).

Reagents: 1, 10-Phen standard (China Pharmaceutical and Biological Products Institute, purity≥ 99.0%); TCNE standard (China Pharmaceutical and Biological Products Institute); reagents of were analytical purity; secondary distilled water.

1.2 Methods

1.2.1 Preparation of standard solution

1, 10-Phen standard solution: 10 mg of 1, 10-Phen standard was weighed accurately, then dissolved by a small amount of anhydrous ethanol, and equipped with a standard solution of 100 mg· L-1. It was diluted to the desired concentration when used.

TCNE standard solution: 64 mg TCNE standard was weighed accurately, and equipped with a standard solution of 5× 10-2 mol· L-1.

1.2.2 Determination of UV Spectra and Fluorescence Spectra

The appropriate amount of 1, 10-Phen standard solution was removed accurately to a colorimetric tube of 10 mL with the pipette, with 0.3 mL of TCNE solution and anhydrous ethanol to 10 mL added, and shake well. The yellow mixed solution was heated in a thermostatic water bath at 30 ℃ for 40 min and then cooled to room temperature. The sample was placed in an ultraviolet light cell and measured. And the blank test was conducted in the same way.

Similarly, the appropriate amount of sample was placed in the fluorescence cell and the fluorescence intensity of the charge transfer complex was measured.

1.2.3 Determination of Raman Spectroscopy

The carbon tetrachloride was used as the solvent, while the liquid was loaded into the OTA-LK-1 liquid sample cell using a 2 mL glass vial with a spectral range of 300 to 3 200 cm-1. The excitation source is an air-cooled argon ion laser (Spectra-Physics Model 163-C4260) with a excitation wavelength of 532.0 nm. The integration time of 30 s was 3 times, and the parallel detection was 3 times.

2 Results and discussion
2.1 UV spectrum

The UV/Vis absorption spectra of ligands a, c and complex b were determined using ethanol as solvent, and the results were showed in Fig.1.

Fig.1 UV absorbance spectra of TCNE (a), Phen (b) and 1, 10-Phen-TCNE (c)

It can be seen from the Fig.1 that the ligand a had an absorption peak at 250 nm due to the π — π * transition of C=C in the TCNE molecule and belonged to the K band. The complex c had two obvious absorption peaks at 233 and 264 nm, almost identical to that of ligand b. The absorption peaks of complex was compared with ligands, and it was found that the absorption of complex was due to the absorption of the ligand. The absorption peak at 233 nm in the complex was the result of π — π * transition from the aromatic ring of Phen. The absorption peak was the result of a n— π * transition by Phen’ s C=N double bond. It is further stated that the new stable complex was formed by the reaction between TCNE and Phen.

2.2 Fluorescence spectra

The fluorescence emission spectra of ligand a and complex b were recorded on a fluorescence spectrophotometer at room temperature, and the results were showed in Fig.2.

Fig.2 Fluorescence emission spectra of TCNE (a) and 1, 10-Phen-TCNE (b)

It can be seen from the Fig.2 that the ligand a had two emission peaks at 423 and 466 nm (λ ex=332 nm); the complex b had two emission peaks at 350 and 448 nm. It was found that the emission peak of the complex was similar to that of the ligand, and the fluorescence of the complex was believed to be derived from the π — π * electron transition of the ligand. The position of the peak of complex was significantly blue shift compared with that of the ligand, because of the coordination of the two ligands, which made the molecular energy level change.

2.3 Raman spectra

Fig.3 and Fig.4 showed the Raman spectra of the ligand TCNE and that of the complex at room temperature respectively. Carbon tetrachloride was used as the solvent. The spectral range was 300~3 200 cm-1. The liquid was loaded into the OTA-LK-1 liquid sample cell using a 2 mL glassinlet. The excitation wavelength was 532 nm. In the analysis process, it can be observed that the Raman peak of the complex (1 500 cm-1) was the strongest static Raman scattering spectrum, but the resonance Raman scattering spectrum of TCNE-1, 10-Phen (around 512 cm-1) was weaker and the Raman strength of the complex at 1 000~1 600 cm-1 was obviously enhanced. The resonant Raman scattering was strongly coupled at 1 000~1 600 cm-1, and these resonant Raman peaks were strongly enhanced due to the charge transfer between molecules.

Fig.3 Raman scattering spectrum of TCNE

Fig.4 Raman scattering spectrum of 1, 10-Phen-TCNE

2.4 Mechanism of Reaction

TCNE was an important strong electron acceptor which can form a charge transfer complex with a variety of types of electron donors. And the two nitrogen atoms on the 1, 10-phen had a pair of single electrons, which can be used as electron donors and formed a 1 to 1 nπ charge-transfer complex with TCNE, and the optimized structure were showed in Fig.5.

Fig.5 Molecular structure of TCNE, Phen and TCNE-Phen

3 Conclusion

In this work, TCNE and 1, 10-Phen were selected as ligands to synthesize 1, 10-Phen-TCNE charge transfer complex. The UV spectra, fluorescence spectra and Raman spectra of ligands and complexes were systematically analyzed. It was showed that the complex was successfully synthesized with 1, 10-Phen and TCNE in the anhydrous ethanol and carbon tetrachloride, and the optical properties were significantly enhanced. The above research provides a theoretical and experimental basis for the design and synthesis of functional materials with good luminous properties, which can promote the progress of optical industry. And Based on this a multi-functional composite fluorescent probe can be built, to explore and develop new nucleic acid probe.

Acknowledgments:

This work was a project supported by Department of scientific research project in Heilongjiang province (No.B201015), Scientific research project of Heilongjiang province education department (No.12541783). Support was also given by the Key Laboratory of Photochemistry, Institute of Chemistry, Chinese Academy of Sciences, and the Key Laboratory of Luminescence and Optical Information, Beijing Jiaotong University.

The authors have declared that no competing interests exist.

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