Photophysical properties of lanthanide coordination polymers dependent on metal complex ligands (Hokkaido Univ.) YAMAMOTO, Masanori; NAKANISHI, Takayuki; KITAGAWA, Yuichi; SEKI, Tomohiro; ITO, Hajime; FUSHIMI, Koji; HASEGAWA, Yasuchika

[Introduction] Lanthanoid (Ln) complexes with monochromatic 4f-4f luminescence (narrow FWHM) are promising materials for application such as EL devices and molecular sensors [1-2]. In particular, three-dimensional Ln coordination polymers (3DLnCPs) composed of Ln complexes and bridged ligands are expected to open-up a new field of photo-functional materials. In the previous study, 3DLnCPs with dicarboxylic acid or bipyridine as a bridged ligands have been reported[3]. We here focused on transition-metal complexes with various coordination structures as bridged ligands. Combination of lanthanide complex (luminescent block) and the transition-metal complex with characteristic coordination structure (bridged block) promotes conformation of remarkable three-dimensional structures of 3DLnCPs (Fig. 1). We selected Pd(II), Zn(II), and Al(III) complexes as a bridged block. In this presentation, preparations and photophysical properties of 3DLnCPs with transition-metal complexes as bridged ligands are demonstrated. [Experimental] Phosphine oxide containing pyridyl groups was prepared by the reaction of bromo-pyridine with diphenylphosphine. Transition-metal complexes were synthesized by the chelation of the phosphine oxide with metal chloride (palladium chloride, zinc chloride, or aluminum chloride) in methanol. The 3DLnCPs with transition-metal complexes as bridged ligands are obtained by the reaction of synthesized transition-metal complexes with Eu(hfa)3(H2O)2 (hfa: hexafluoroacetylacetone) in organic solvent (Fig. 2). Identification of compounds were conducted 1H NMR, mass spectrometry, and elemental analyses.

Fig. 1 Image of 3DLnCPs with transition-metal complexes

1P027

[Results and Discussion] Single crystal X-ray structure analysis of 3DLnCPs with Pd(II) complex (Eu-Pd) confirmed formation of coordination polymers composed of bridged blocks (transition-metal complex) and luminescent blocks (Eu(III) complex) (Fig. 3). The Eu-Pd shows one-dimensional polymer structure without molecular interactions such as CH-π or CH-F interactions. We consider that Eu-Zn and Eu-Al might have formed three-dimensional polymer structures because Zn(II) and Al(III) complexes typically form five and six coordination structures, respectively. The emission spectra of Eu-Pd, Eu-Zn and Eu-Al excited at 465 nm are shown in Fig. 4. We observed various shapes of electronic dipole transition band with characteristic stark splitting at around 610 nm. The quantum yield of Eu-Pd is much smaller than those of Eu-Zn and Eu-Al. The lower emission quantum yield of Eu-Pd is due to large non-radiative rate constant based on the energy transfer from emitting level of Eu (5D0) to triplet state of Pd complex. In this presentation, we also explain the radiative rate constants of Eu-Pd, Eu-Zn, and Eu-Al 3DLnCPs. [1] K. Miyata, Y. Konno, T. Nakanishi, A. Kobayashi, M. Kato, K. Fushimi and Y. Hasegawa,

Angew. Chem. Int. Ed., 2013, 52, 6413-6416. [2] M. Varlan, B. A. Blight, and S. Wang, Chem. Commun., 2012, 48, 12059-12061. [3] H. Zhang, L. Zhou, J. Wei, Z. Li, P. Lin, and S. Du, J. Mater. Chem., 2012, 22, 21210-21217.

Fig. 2 Synthetic scheme of Eu(III) coordination polymers

Fig. 4 Emission spectra of Eu-Pd, Eu-Zn and Eu-Al.

Fig. 3 Crystal structure of Eu-Pd