Assembly and Photophysics of Ternary Luminescent Lanthanide Molecular Complex Systems

Transcription

1 Journal of the Chinese Chemical Society, 2004, 51, Assembly and Photophysics of Ternary Luminescent Lanthanide Molecular Complex Systems B. Yan* ( ) and Q. Y. Xie ( ) Department of Chemistry, Tongji University, Shanghai , P. R. China In this paper, according to the molecular fragment principle, a series of eight ternary luminescent lanthanide complex systems were assembled, and whose compositions were determined with elemental analysis and infrared spectrum: Ln(MA) 3 (L) H 2 O, where Ln = Sm, Eu, Tb, Dy; HMA = -methylacrylic acid; L = 1,10-phenanthroline (phen), 2,2 -bipyridine (bipy). The photophysical properties of these functional molecular systems were studied with ultraviolet-visible absorption spectrum, and fluorescence excitation and emission spectrum. It was found that the heterocylic compounds (phen and bipy) act as the main energy donor and luminescence sensitizer for their suitable energy match and effective energy transfer to the emission energy level of Ln 3+ ions. MMA ligand was only used as the terminal structural ligand to influence the luminescence. Especially terbium complex systems show the strongest luminescence for the optimum energy match and transfer between phen (bipy) and Tb 3+ ion. Keywords: Molecular assembly; Ternary lanthanide complex systems; Photophysical properties. INTRODUCTION The photophysical properties of lanthanide coordination compounds with organic ligands have been the hot subject of much interest because these functional complex systems have potential applications such as being the active center of luminescent materials 1-3 or the structural and functional probe for the chemical and biological macromolecule systems. 4-6 A variety of research has been reported on the energy transfer mechanism and luminescence of lanthanide complexes with -diketones, aromatic carboxylic acid, and heterocyclic compounds, which have good energy matches and are suitable for the luminescence of lanthanide ions We also have studied the energy match and intramolecular energy transfer mechanism of lanthanide complexes with aromatic carboxylic acids and 1,10-phenanthroline in detail In this context, according to the molecular fragments principle, using heterocycle compounds (1,10-phenanthroline and 2,2 -bipyridine) as the energy donor and luminescence sensitizer for lanthanide ions and -methylacrylic acid molecules as the terminal structural ligands, a series of eight ternary lanthanide (Eu 3+,Tb 3+,Sm 3+,Dy 3+ ) complexes systems were assembled. Their corresponding photophysical properties were studied in detail. EXPERIMENTAL SECTION Synthesis of Lanthanide Complexes Lanthanide oxides (Eu 2 O 3,Tb 4 O 7,Sm 2 O 3,Dy 2 O 3 ) were converted to their nitrate by treating with concentrated nitric acid. The ternary lanthanide complexes were prepared by homogeneous precipitation. Ethanol solutions of lanthanide nitrate were added very slowly to the ethanol solution of methylacrylic acid, whose ph value was adjusted to 6.5 with sodium hydroxide. After one hour, 1,10-phenanthroline or 2,2 -bipyridine was added to the above solution with the molar ratio of HMA, phen (bipy) to Ln 3+ equal to 3:1:1. After continued stirring for 8 hours, the light purple solution was filtered off and the filtrate was allowed to stand at room temperature; after one week, the microcrystal samples were finally obtained. Physical Measurement Elemental analysis (C, H, N) was carried out by an Elementar Cario EL elemental analyzer. Infrared spectroscopy on KBr pellets was performed on a Nicolet Nexus 912 AO446 model spectrophotometer in the range of cm -1. Ultraviolet absorption spectrum was measured with an Agilent 8453 spectrophotometer. Luminescence (excitation * Corresponding author. Tel: ; fax: ; byan@tongji.edu.cn

2 698 J. Chin. Chem. Soc., Vol. 51, No. 4, 2004 Yan and Xie and emission) spectrum was determined with a Perkin-Elmer LS-55 spectrophotometer whose excitation and emission slits were 10 nm and 5 nm, respectively. RESULTS AND DISCUSSION On the basis of elemental analysis, the compositions of these complex systems were obtained with the formula of Ln(MA) 3 (L) H 2 O, and the detailed data are shown in Table 1, where HMA = -methylacrylic acid, L = 1,10-phenanthroline (phen), 2,2 -bipyridine (bipy). The IR spectra of these molecular systems show similar features. For example, in the IR spectra of the Ln(MA) 3- (phen) H 2 O system, the characteristic absorption bands of C=O and C-O belonging to the free ligands (HMA, 1697 and 1645 cm -1 ) disappear, while the characteristic absorption peaks of the carboxylic group COO - appear (1535, 1548 cm -1 for Vs(COO-) and 1431, 1444 cm -1 for Vas(COO-), respectively), suggesting that the oxygen atoms of -methylacrylic acid s conbonyl group are coordinated with Tb 3+. The vibration frequency of 1652 cm -1 belonging to the phenyl ring of 1,10-phenanthroline becomes weaker than that of free phen. The out-of-plane bending vibrations of the hydrogen atom on the phenyl ring of phen shifts from 867, 744 cm -1 of free ligand to a lower frequency of 854, 737 cm -1, indicating that phen participates in the coordination with lanthanide ions. Besides this, there exist some apparent bands at about 3450 cm -1 and 1613 cm -1, respectively, which are attributed to the vibration stretching band and in-plane bending band of H 2 O molecules. The absorption bands corresponding to the inplane swing vibration of coordinated H 2 O molecules have not been observed in the range of cm -1, which verifies the a water molecule has not coordinated to a lanthanide ion and belongs to a crystal a water molecule. 15 Ln(MA) 3 (bipy) H 2 O complex systems show similar features. Table 2 shows the detailed data for the main absorption bands and assignments. Fig. 1 shows the typical ultraviolet absorption spectrum for Tb(MA) 3 (phen) H 2 O (A) and Tb(MA) 3 (bipy) H 2 O (B), respectively. The ultraviolet absorption spectrum for Tb(MA) 3 (phen) H 2 O shows a strong absorption band at 264 nm, and the ultraviolet absorption spectrum for Tb(MA) 3- (bipy) H 2 O exhibits a strong absorption peak at 281 nm, both of which are attributed to be characteristic absorptions of phen and bipy, respectively. This indicates that the heterocylic ligands (phen and bipy) are the main energy donor and luminescence sensitizer for the Tb 3+ ion. Other ultraviolet ab- Table 1. The compositions of lanthanide complexes by elemental analysis Complex systems wi (found)/% wi (calc.)/% C H N RE C H N RE Eu(MA) 3 (phen) H 2 O Tb(MA) 3 (phen) H 2 O Sm(MA) 3 (phen) H 2 O Dy(MA) 3 (phen) H 2 O Eu(MA) 3 (bipy) H 2 O Tb(MA) 3 (bipy) H 2 O Sm(MA) 3 (bipy) H 2 O Dy(MA) 3 (bipy) H 2 O Table 2. The I.R. spectra and band assignments of the lanthanide complexes Complex systems v S,COO- (cm -1 ) V as,coo- (cm -1 ) v S,C-O-NN (cm -1 ) V H2O (cm -1 ) Eu(MA) 3 (phen) H 2 O , 1613 Tb(MA) 3 (phen) H 2 O , 1613 Sm(MA) 3 (phen) H 2 O , 1613 Dy(MA) 3 (phen) H 2 O , 1613 Eu(MA) 3 (bipy) H 2 O , 1607 Tb(MA) 3 (bipy) H 2 O , 1607 Sm(MA) 3 (bipy) H 2 O , 1607 Dy(MA) 3 (bipy) H 2 O , 1607

3 Assembly and Photophysics of Lanthanide Complexes J. Chin. Chem. Soc., Vol. 51, No. 4, sorption spectra show a similar feature. The excitation spectra of these complex systems show that they have no effective absorption in the long wavelength ultraviolet region of nm. Fig. 2 gives the excitation spectrum of Eu(MA) 3 (phen) H 2 O. The effective energy absorption mainly exists in the narrow ultraviolet region of nm, which consists of about five main peaks, i.e. 204 nm, 224 nm, 243 nm, 256 nm, 271 nm, respectively. We further measured the corresponding emission spectra by selective excitation with five different excitation wavelengths; they show similar emission positions except for different luminescent intensities. This indicates that the five excitation bands belong to the effective characteristic absorption of phen and bipy ligands for the luminescence of the Eu 3+ ion. The excitation spectrum of Tb(MA) 3 (bipy) H 2 O exhibits similar bands (as shown in Fig. 3); there exist four bands with maximum wavelengths at 223 nm, 243 nm, 258 nm and 271 nm, respectively. Figs give the selected emission spectra of these complex systems. For Eu(MA) 3 (phen) H 2 O complex (Fig. 4), the emission spectrum shows four emission peaks under the excitation of 242 nm: nm, nm, nm and nm, corresponding to the characteristic emission 5 D 0 7 F j transitions (j = 1, 2, 3, 4) of the Eu 3+ ion. Among the red luminescence intensity of 5 D 0 7 F 2 transition is the strongest, and the emission intensity of 5 D 0 7 F 1 transition be- Fig. 1. Ultraviolet absorption spectra of Tb(MA) 3 - (phen) H 2 O (A), Tb(MA) 3 (bipy) H 2 O (B) complexes. Fig. 3. Excitation spectrum of Tb(MA) 3 (bipy) H 2 O complex ( em = 544 nm). Fig. 2. Excitation spectrum of Tb(MA) 3 (phen) H 2 O complex ( em = 543 nm). Fig. 4. Emission spectrum of Eu(MA) 3 (phen) H 2 O complex ( ex = 242 nm).

4 700 J. Chin. Chem. Soc., Vol. 51, No. 4, 2004 Yan and Xie comes stronger for the covering of the 5 D 0 7 F 0 transition. Eu(MA) 3 (bipy) H 2 O complex shows a similar feature (Fig. 5). For Tb(MA) 3 (phen) H 2 O complex (Fig. 6), the emission spectrum shows four emission peaks under the excitation of 223 nm: nm, nm, nm and nm, respectively, attributed to the characteristic emission 5 D 4 7 F j (j = 6, 5, 4, 3) transition of Tb 3+ ion. Among the 5 D 4 7 F 5 transition exhibits the strongest green emission, and 5 D 4 7 F 6 transition shows the second strongest blue emission. Tb(MA) 3- (bipy) H 2 O complex shows a similar spectrum (Fig. 7). For Sm(MA) 3 (phen) H 2 O complex (Fig. 8), it shows four apparent emission bands under the excitation of 241 nm and the maximum emission wavelengths are at nm, nm, nm and nm, respectively. This corresponded to the characteristic emission 4 G 5/2 6 H j (j = 5/2, 7/2, 9/2, 11/2) transitions of Sm 3+ ion. The emission corresponding to the 4 G 5/2 6 H j transition shows a red shift, while the emission to 4 G 5/2 6 H j transition shows a blue shift, which may be due to the hydrogen bonding interaction in the complex systems. For Dy(MA) 3 (phen) H 2 O complex (Fig. 9), the luminescence spectra show two apparent emission peaks under the excitation of 238 nm: one is at nm, the other is at nm, which corresponds with be the characteristic emission 4 F 9/2 6 H j (j = 15/2, 13/2) transition of Dy 3+ ion. Dy(MA) 3- (bipy) H 2 O complex exhibits a similar emission (Fig. 10). Comparing the luminescence intensities of these com- Fig. 5. Emission spectrum of Eu(MA) 3 (bipy) H 2 O Fig. 7. Emission spectrum of Tb(MA) 3 (bipy) H 2 O Fig. 6. Emission spectrum of Tb(MA) 3 (phen) H 2 O complex ( ex = 223 nm). Fig. 8. Emission spectrum of Sm(MA) 3 (phen) H 2 O

5 Assembly and Photophysics of Lanthanide Complexes J. Chin. Chem. Soc., Vol. 51, No. 4, CONCLUSION A series of lanthanide (Eu, Tb, Sm, Dy)- -methylacrylic acid (HMA)-L(phen, bipy) ternary complex systems have been synthesized and characterized. The photophysical properties of these complexes have been studied with ultraviolet spectra, and excitation and emission spectra. In these complex systems, the heterocycle ligands (phen, bipy) act as the main energy donors and sensitize the luminescence of lanthanide ions. -Methylacrylic acid only behaves as a terminal structural ligand to influence the energy transfer process and luminescence. Among these systems, ternary terbium complex systems exhibit the strongest luminescence. Fig. 9. Emission spectrum of Dy(MA) 3 (phen) H 2 O complex ( ex = 238 nm). ACKNOWLEDGEMENTS This work was supported by the Science Fund of Tongji University for Talents and the National Natural Science Foundation of China. Received June 26, REFERENCES Fig. 10. Emission spectrum of Dy(MA) 3 (bipy) H 2 O plex systems, it can be found that ternary terbium complex systems show the strongest luminescence among the lanthanide complex systems. The ternary europium and dysprosium complex systems show weaker luminescence than terbium ones but stronger than samarium ones. This indicates that the triplet state energy of phen and bipy are more suitable for the luminescence of terbium ion than europium and dysprosium ions. Because of the existence of internal energy level ( 6 F 11/2, 6 F 9/2,..., 6 H 11/2 etc) between the first excited state 4 G 5/2 and ground state 6 H 9/2 of Sm 3+, the non-radiative energy transfer process takes place easily to lose the excited energy of the phen (or bipy) ligand. So Sm 3+ complex systems exhibit the weakest luminescence. 1. Yan, B.; Zhang, H. J.; Wang, S. B.; Ni, J. Z. Mater. Chem. Phys. 1997, 52, Yan, B.; Zhang, H. J.; Wang, S. B.; Ni, J. Z. Mater. Res. Bull. 1998, 33, Jin, T.; Tsutsumi, S.; Deguchi, Y.; Machida, K. I.; Adachi, G. Y. J. Alloys. Compds. 1997, 252, Meares, C. F.; Wensel, T. G. Acc. Chem. Res. 1984, 17, Ci, Y. X.; Li, Y. Z.; Chang, W. B. Anal. Chim. Acta 1991, 248, Scott, L. K.; Horrocks, W. D. J. Bioinorg. Chem. 1992, 46, Yang, Y. S.; Gong, M. L.; Li, Y. Y.; Lei, H. Y.; Wu, S. L. J. Alloys. Compds. 1994, 207/208, Lawandy, M. A.; Pan, L.; Huang, X. Y.; Li, J.; Yuen, T.; Lin, C. J. Mater. Res. Soc. Symp. Proc. 2001, 658, GG Wan, Y. H.; Jin, L. P.; Wang, K. Z. J. Mol. Struct. 2003, 649, Feng, C. J.; Luo, Q. H.; Duan, C. Y. J. Chem. Soc. Dalton. Trans. 1998, Yan, B.; Zhang, H. J.; Wang, S. B.; Ni, J. Z. J. Photochem. Photobiol. A. Chem. 1998, 116, 209.

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