Synthesis and photophysical and magnetic studies of ternary lanthanide(III) complexes of naphthyl chromophore functionalized imidazo[4,5-f][1,10] phenanthroline and dibenzoylmethane

The luminescent ternary lanthanide(III) complexes [Ln(DBM)(3)(L1)] and [Ln(DBM)(3)(L2)] (Ln = Eu and Tb) of dibenzoylmethane (DBM) and 2-(2-naphthyl)-1H-imidazo[4,5-f][1,10] phenanthroline (L1) and 2-(2-hydroxy- 1-naphthyl)-1H-imidazo[4,5-f][1,10] phenanthroline (L2) are reported in this work. The naphthyl chromophore functionalized imidazophenanthroline ligands L1 and L2 are structurally characterized by using single crystal X-ray diffraction: (L1), a = 14.933(4) angstrom, b = 7.4965(13) angstrom, c = 15.999(4) angstrom, alpha = gamma = 90 degrees, beta = 102.670(7)degrees, V = 1747.4(6) angstrom(3), Z = 4, monoclinic, P2(1)/c and (L2), a = 7.8555(11) angstrom, b = 26.216(4) angstrom, c = 10.0748(17) angstrom, alpha = gamma = 90 degrees, beta = 96.799(7)degrees, V = 2060.2(6) angstrom(3), Z = 4, monoclinic, P2(1)/n. A photophysical study reveals that the ligands L1 and L2 sensitize europium(III) emission. The complexes [Eu(DBM)(3)(L1)] and [Eu(DBM)(3)(L2)] exhibit the characteristic emission of the Eu(III) ion at 298 and 77 K. The terbium(III) complexes [Tb(DBM)(3)(L1)] and [Tb(DBM)(3)(L2)] exhibit only ligand centred fluorescence at room temperature, while metal centred emission is observed at 77 K. The non-luminescence of the Tb(III) center at room temperature is due to the proximity of the triplet states of the ligands to the D-5(4) level of the Tb(III) ion. DC magnetic susceptibility studies have been conducted on the Tb(III) complexes in a 1 T field over the temperature range 20-300 K. The complexes display room temperature (300 K)(chi M)T values of 9.69 and 10.21 cm(3) mol(-1) K, respectively. A gradual decrease in the T-chi M values is observed on reducing the temperature and reached the value of 7.80 and 6.60 cm(3) mol(-1) K, respectively, at 20 K. The decrease in the T-chi M values as the temperature is lowered could be attributed to the depopulation of the Zeeman split crystal field levels.