Luminescence properties of heterodinuclear Pt–Eu complexes from unusual nonadentate ligands

The synthesis of ligand L(1), based on the tetramethyl ester of [4'-ethynyl-(6,6''-bis(aminomethyl))-2,2':6',2''-terpyridine]tetrakisacetate, and its acidic form L(2), are described. Using a Cu-assisted coupling reaction, L(1) was connected to the Pt atom of a [(tpy)Pt] precursor (tpy = 2,2':6',2''-terpyridine) to afford the [(tpy)PtL(1)](BF(4)) metallosynthon, from which a hydrolysis reaction gave Na(3)[(tpy)PtL(2)]. The photophysical properties of the metallosynthons were studied by means of absorption and steady state emission spectroscopic techniques in various solvents, which revealed a dramatic impact of the solvent polarity. DFT and TDDFT calculations (B3LYP) were used to investigate the absorption and emission properties of the [(tpy)PtL(1)](+) system both in vacuo and in different solvents. Spectrophotometric titrations of [(tpy)PtL(1)](+) with EuCl(3) x 6 H(2)O in acetonitrile revealed the formation of complicated mixtures of complexes with different [(tpyPt(1))(x)Eu(y)] stoichiometries, all of which display the typical Eu(III) centred luminescence upon excitation into the Pt centred (1)MLCT absorption band. The energy transfer from the Pt subunit of [(tpy)PtL(2)](3-) to Eu(III) is inefficient in polar solvents, but it is restored in a TFA-CH(2)Cl(2) mixture, together with the observation of a new emission band at 684 nm, likely arising from a charge transfer process involving reduction of Eu(III).