Dimedone and Phenylazo Dimedone Chelates of Europium as Emitters in Polymers Susannah Seth, 1 K. K. Aravindakshan 2 1 P.G and Research Department of Chemistry, Malabar Christian College, Kozhikode 673001, Kerala, India 2 Department of Chemistry, University of Calicut, 673635 Kerala, India Received 9 January 2010; accepted 10 November 2010 DOI 10.1002/app.33741 Published online 23 February 2011 in Wiley Online Library (wileyonlinelibrary.com). ABSTRACT: Transparent polymers when incorporated with strongly fluorescent europium chelates were found to be responding to excitation with UV radiation. In this work, two novel europium chelates have been synthesized using the b-diketones dimedone and phenylazo dimedone along with 1,10-phenanthroline. These chelates were characterized by elemental analyses, magnetic susceptibility measurements, UV, IR, and ESI mass spectral techniques. The chelates syn- thesized with metal : b-diketone : 1,10-phenanthroline ratio 1 : 3 : 1 were incorporated into polymer matrices. Four poly- mers, polyethylene vinyl acetate or acetate (EVA), polystyrene (PS), poly methyl methacryalate (PMMA), and polyethylene glycol (PEG) were used for the studies. All these, except the liquid oligomer PEG were cast into thin films. PEG was used as such for the studies. The photoluminescence spectra of the plain polymers were found to be having peaks very close to the absorption peaks of the polymers doped with europium chelate. This observation can be used in optical devices. Thermal analyses like TG/DTG/DTA of the polymer films were conducted to ascertain the thermal stability of the material. The SEM analyses of the films indicated a smooth surface with uniform distribution of the doped chelate. V C 2011 Wiley Periodicals, Inc. J Appl Polym Sci 121: 696–701, 2011 Key words: dyes; films; photophysics; europium chelates; SEM INTRODUCTION Polymers and glasses were found 1,2 to accommodate organic and inorganic molecules into their matrices without affecting the photophysical properties of the guest compounds. A polymer when excited can transfer its energy to the neighboring chromophore non-radiatively if its emission band overlaps the absorption band of the acceptor. The distance between the donor and acceptor must also be less than 10 nm. This property of the chelate-polymer system is exploited in this work, where polymer do- nor transfers energy to the embedded europium which in turn emits radiation at  613 nm. The ligand of the chelate is excited to higher energy state by the ultraviolet light. Next, by intersystem cross- ing, energy is transferred to the triplet state and from there to the excited state of the lanthanide ion. In the case of europium, the excited state is 5 D. Therefore, when the metal returns to the ground state 7 F, fluorescence is emitted. 3 Lanthanide che- lates stay at excited state for about 10 5 times longer than other fluorophores and hence significantly enhance sensitivity and also dramatically reduce back ground fluorescence. These chelates have wider stokes shift (about 200–300 nm) than other fluoro- phores and have sharp emission peaks, which are independent of the structure of the ligand and are stable upto 7 years. Lanthanides also possess the unique property of emission, which is independent of the matrix into which they are embedded. While synthesizing lanthanide chelates for optical applica- tions, one part of the ligand is usually designed to bind strongly and shield, (Fig. 1) the lanthanide ion against quenching. b-diketones, cryptands, calixar- enes, cyclodextrins, crown ethers, etc, are used for the purpose. In addition to such molecules, organic chromophores like N-heterocycles are also used to complex with the lanthanide ions. These light har- vesting moieties enhance absorption cross section of Ln 3þ absorption bands which are otherwise narrow (Dk <1 nm) and weak (e < 1M 1 cm 1 ) and serve as antennae molecules to transfer energy toward the central metal ion. 4 Pyridines, bipyridine, 1,10-phe- nanthroline, etc., are some examples for antennae molecules. This work is focused on complexes of eu- ropium in which b-diketones act as shielding ligand and 1, 10-phenanthroline act as antenna ligand. The luminescence phenomenon in the visible region is not disturbed by vibrational CAH overtone absorp- tions of the matrix. Moreover, for the same reason, polymers have their low loss windows in the spec- tral region  600 nm, which is also one of the stand- ard wavelengths 5 in optical telecommunications. Therefore, europium, one of the strongest emitters Correspondence to: S. Seth (susannahseth@yahoo.co.in). Journal of Applied Polymer Science, Vol. 121, 696–701 (2011) V C 2011 Wiley Periodicals, Inc.