Luminescent properties of a new Nd3+-doped complex with two different carboxylic acids and pyridine derivative
School of Mechanical Engineering, Jiangsu University
Institute of Laser Technology, Jiangsu University
School of Material Engineering, Jiangsu University
摘 要:
A new Nd3+-doped organic complex featuring two different perfluorinated carboxylic acids as the first ligand and pyridine derivative 2-amino-3-chloro-5- (trifluoromethyl) pyridine as the second ligand was designed and synthesized.Successful coordination between the ligands and central rare earth ions was confirmed by Fourier transform infrared spectroscopy (FT-IR) spectra, 1H nuclear magnetic resonance (1H NMR) spectra, and UV spectra, and the synthesized complex is inferred to be eight-coordinate structure.Solution of the complex dissolved in DMSO-d6 was prepared and then its fluorescence spectrum, UV–Vis–NIR absorption spectrum, and fluorescence decay curve were tested.The fluorescent lifetime is about 7 ls.Based on the above experimental research, Judd–Ofelt analysis was carried out, and the results indicate that appropriate coordination environment around Nd3?in this solution results in a high fluorescent quantum efficiency 2%and a large stimulated emission cross-section about 3.2 9 10-20cm2at 1, 064 nm.
收稿日期:25 September 2012
基金:supported by the Natural Science Foundation of Jiangsu Higher Education Institutions of China (No. 08KJD430009);Jiangsu University Senior Talent Starting Fund (No. 08JDG025);
Luminescent properties of a new Nd3+-doped complex with two different carboxylic acids and pyridine derivative
Yun-Xia Ye Li-Hua Wei Wei-Chen Mei Chen Yin-Qun Hua
School of Mechanical Engineering, Jiangsu University
Institute of Laser Technology, Jiangsu University
School of Material Engineering, Jiangsu University
Abstract:
A new Nd3+-doped organic complex featuring two different perfluorinated carboxylic acids as the first ligand and pyridine derivative 2-amino-3-chloro-5- (trifluoromethyl) pyridine as the second ligand was designed and synthesized. Successful coordination between the ligands and central rare earth ions was confirmed by Fourier transform infrared spectroscopy (FT-IR) spectra, 1H nuclear magnetic resonance (1H NMR) spectra, and UV spectra, and the synthesized complex is inferred to be eight-coordinate structure. Solution of the complex dissolved in DMSO-d6 was prepared and then its fluorescence spectrum, UV–Vis–NIR absorption spectrum, and fluorescence decay curve were tested. The fluorescent lifetime is about 7 ls. Based on the above experimental research, Judd–Ofelt analysis was carried out, and the results indicate that appropriate coordination environment around Nd3?in this solution results in a high fluorescent quantum efficiency 2 % and a large stimulated emission cross-section about 3.2 9 10-20cm2at 1, 064 nm.
Keyword:
Nd; Organic solution; Liquid laser; Quantum efficiency; Judd–Ofelt theory;
Author: Yun-Xia Ye e-mail: yeyunxia@ujs.edu.cn ;
Received: 25 September 2012
1 Introduction
Rare earth ions-doped fluorescent materials are widely researched and applied in laser systems, medical sensors, illumination, and so on.However, rare earth-containing organic luminescent materials were not developed well due to serious non-radiative deactivation by high energy vibration of surrounding coordination environment.So fluorescent quantum efficiency and lifetime of rare earth ions in organic system are both very low, especially for some near infrared ions, e.g., Nd3+and Er3+.For these ions, too small minimum energy gap between exciting states and lower levels can be very easily accepted by high vibration mode of O–H and C–H in organic system and cause non-radiative deactivation of excited states and fluorescence quench.So, researchers keep on working to find strategies for suppressing fluorescence quench and improving the fluorescent quantum efficiency of rare earth ions in organic systems.As far as I know, the influence of coordination environment on emission properties of rare earth ions in organic systems was thoroughly investigated by Hasegawa research group[1–5].Their work led to the most effective strategy to prevent luminescent ions from vibrational deactivation:detailedly designing the composition and structure of complex, and then realizing the coordination of rare earth ions with low-vibration ligands.In addition, the forbidden f–f transitions of rare earth ions in a symmetric environment cause low efficiency of absorbing exciting light, and also weaken the fluorescence.So, another effective approach to obtain stronger luminescence is forming an asymmetric surrounding around rare earth ions to increase transition probability of absorption and then enhance fluorescence intensity[4, 5].Under the guidance of these effective strategies, a number of lanthanide (III) -doped fluorescent complexes were synthesized and investigated[6–10].Until now, one of the most successful fluorescent complex structures is ternary complex, with some organic anions acting as the first ligands satisfying charge balance and neutral complex as second ligands to meet the requirements of high coordination number of rare earth ions.In this kind of structure, rare earth ions can be closely wrapped in a low-vibration coordination sphere so as to effectively reduce radiationless transitions.For this kind of complex, the carboxylic acid is commonly used as the first ligand through forming carboxylates[8, 11].And, some aromatic heterocyclic compounds, such as 2, 2-bipyridine and 1, 10-phenanthroline, can provide nitrogen atoms to coordinate with lanthanide ions and usually act as the second ligands[8, 12].
In the present study, we synthesized a new Nd3+-doped complex with two different perfluorinated carboxylic acids, pentafluoropropionic acid (C2F5COOH) , and 2, 3, 4, 5, 6-pentafluoro benzoic acid (C6F5COOH) , as the first ligand and2-amino-3-chloro-5- (trifluoromethyl) pyridine (C6H4Cl F3N2, abbreviation:tfpy) as the second ligand.Introducing two different acids into the most inner coordination sphere aims at: (1) forming a more asymmetric coordinating sphere around the luminescent ions to improve absorbing exciting light; (2) investigating the influence of the benzene ring in the pentafluoro benzoic acid on fluorescence.Choosing 2-amino-3-chloro-5- (trifluoromethyl) pyridine is because it has four hydrogen atoms, while there are eight hydrogen atoms in 2, 2-bipyridine (C10H8N2) and 1, 10-phenanthroline (C12H8N2) .The structure of the obtained complex was characterized by FT-IR spectra, 1H NMR spectra, and UV spectra.Solution of the complex dissolving in deuterated dimethyl sulfoxide (C2D6SO, DMSO-d6) , the best solvent for fluorescent rare earth-doped organic system ever reported in[4, 7, 13], was prepared and then its fluorescence spectrum, UV–Vis–NIR spectrum, and fluorescence decay curve were tested.Through Judd–Ofelt analysis, the coordination symmetry and fluorescent properties were investigated in detail.
2 Experimental
2.1 Materials and instruments
Pentafluoropropionic acid (98%) and 2, 3, 4, 5, 6-pentafluoro benzoic acid (99%) were purchased from Matrix Scientific Co.and 2-amino-3-chloro-5- (trifluoromethyl) pyridine (98%) from Tokyo Kasei Industry Co.Ltd.Na OH (99.99%) was obtained from Alfa Aesar, Nd Cl3.6H2O (99.9%) from Shanghai Di Yang Chemical Co.Ltd., deuterated dimethyl sulfoxide (DMSO-d6) from Acros Orcanics, and anhydrous ethanol (reagent grade) from Sinopharm Chemical Reagent Co.Ltd.Fourier transform infrared spectroscopy (FT-IR) spectra and UV spectra for characterizing the synthesized complex were obtained with Nexus 670 and UV-2450, respectively.The UV–Vis–NIR spectrum of Nd3+-doped solution was performed by UV2410.The1H NMR spectra were recorded on AVANCEII 400 MHz in DMSO-d6solvent.The fluorescence spectrum of the solution was obtained on Quanta Master TM40.For measuring fluorescent decay curves, the solution was excited with Q-switched double frequency Nd3+:YAG laser, DET210photoelectric tube as detector and TDS3054B as oscilloscope.
2.2 Preparation and characterization of complex
Pentafluoropropionic acid (0.63 ml, 6 mmol) , 2, 3, 4, 5, 6-pentafluoro benzoic acid (0.64 g, 3 mmol) , and Na OH (0.36 g, 9 mmol) were mixed in 15 ml anhydrous ethanol.The reaction mixture was stirred at 60°C for 4 h and then dried for 12 h under vacuum at 80°C.The obtained white solid powder and Nd Cl3.6H2O (1.08 g, 3 mmol) were added into 15 ml anhydrous ethanol again and reacted at60°C for 6 h under stirring.After this reaction, we obtained clarified solution through removing sodium chloride by filtration.Then 0.602 g (0.003 mol) 2-amino-3-chloro-5- (trifluoromethyl) pyridine was added into the solution and reacted at 60°C for 6 h under stirring.After reaction, the solution was dried for 48 h under vacuum at80°C to get final product complex Nd (C2F5COO) 2 (C6F5COO) tfpy.
The obtained complex was characterized by FT-IR, 1H NMR, and UV spectra.FT-IR spectra of free ligands and complex were obtained through KBr pellet pressing method to ascertain whether CF3CF2COOH, C6F5COOH, and tfpy were coordinated with central Nd3+as predicted.1H NMR spectra were also used to verify the successful coordination between tfpy and Nd3+.The solution of complex dissolving in DMSO-d6 was prepared with the concentration of 0.1 mol.L-1.
3 Results and discussion
3.1 Structure analysis
Fig.1 Infrared spectra of free ligands and complexes
Fig.2 UV spectra of free ligands and complex in ethanol
Fig.3 Chemical structure of complex
Table 1 Main absorption peaks in IR spectra of free ligands and complexes (cm-1) 下载原图
Table 1 Main absorption peaks in IR spectra of free ligands and complexes (cm-1)
Fig.4 UV–Vis–NIR absorption spectrum of Nd (C2F5COO) 2 (C6F5COO) tfpy in DMSO-d6 (0.1 mol.L-1)
Above all, we can infer that the synthesized complex is eight-coordinate structure with six Nd–O coordination bonds to carboxylic acids and two Nd–N coordinating bonds to tfpy.The chemical structure of the complex is shown in Fig.3.
3.2 Luminescence analysis
To evaluate the probability of non-radiative transition and quantum efficiency of Nd3+in solution, Judd–Ofelt[14, 15]theory (JO theory) was applied to analyze the radiative properties of rare earth ions-doped organic liquid material.The main results of JO theory are as follows:three intensity parameters
Fig.5 Emission spectrum of Nd (C2F5COO) 2 (C6F5COO) tfpy in DMSO-d6 (0.1 mol.L-1)
Fig.6 Fluorescence decay curves of Nd (C2F5COO) 2 (C6F5COO) tfpy in DMSO-d6 (0.1 mol.L-1)
Table 2 Emission quantum efficiencies, lifetimes, and stimulated emission cross-sections of Nd3+-doped organic media 下载原图
Table 2 Emission quantum efficiencies, lifetimes, and stimulated emission cross-sections of Nd3+-doped organic media
In the design and development of laser systems, the stimulated emission cross-section
4 Conclusion
In conclusion, a new Nd3+-doped complex was synthesized and the solution of new complex in DMSO-d6 was prepared.We chose two different perfluorinated carboxylic acids, C2F5COOH and C6F5COOH, as the first ligand and electrically neutral 2-amino-3-chloro-5- (trifluoromethyl) pyridine as the second ligand.The successful coordination between ligands and central Nd3+was verified through FT-IR, 1H NMR, and UV spectra.The complex is inferred to be eightcoordinate structure with six Nd–O and two Nd–N coordination bonds.Based on absorption spectrum, luminescence spectrum, and fluorescent decay curve, three intensity parameters
参考文献
[14] Judd BR.Optical absorption intensities of rare-earth ions.Phys Rev.1962;127 (3) :750.
[15] Ofelt GS.Intensities of crystal spectra of rare-earth ions.J Chem Phys.1962;37 (3) :511.