Efficient microwave synthesis of luminescent europium(III) complexes with polypyridine and the study of electrospectrochemistry

Abstract

We have developed an efficient synthetic method of photosensitive Eu(III)–polypyridine complexes, assisted with microwave irradiation. We succeeded in obtaining pure complexes in a shorter time with a 70% or more yield by reflux synthesis in ethyleneglycol under microwave irradiation and report their physicochemical properties. The results of the absorption spectra of the complexes in ethyleneglycol solution are obtained. All the Eu(III) complexes exhibit a very strong spectral absorption at 397 and 664 nm. These bands are attributed to intraligand π → π* transition and n → π* charge transfer transition. A general feature in the spectra of Eu(III) ion is a shift of absorption bands toward lower energy on complex formation. “Nephelauxetic effect; β”. We calculated the values of β, b 1/2 (measure of covalent), and δ% (Sinha's parameter) of Eu(III)–polypyridine complexes. The values of b 1/2 was in the ligand order: (pyre) > (tpy) > (bpyca)>(biq), (dmbpy) > (bpy). The fluorescent intensity of Eu(III) complex with bpyca ligand was strong enhanced by about 7.56 times when compared with that of Eu(III) ion, and for strong Eu(III) complex with tpy ligand it was enhanced by about 30 times. The dominant fluorescent transition of intramolecular energy transfer (IMET) process takes place from chelate absorption band state in Eu(III)–polypyridine to the J manifold of 7F, which is a spin forbidden type and the role of the triplet state is enormously important. The formula of Nicolson–Shain was used for the analysis of an electrode reaction parameter. From the analytic results of C– V, the transfer coefficient ( α), the diffusion coefficient ( D, cm 2/s), the standard rate constants, k 0 f (cm/s) of the electrode reaction for Eu(III) complexes with polypyridine were obtained. And the formation constants ( K f) were also discussed.