Synthesis and spectroscopic characterization of organometallic chromophores for photoluminescent materials: cyclopalladated complexes

A homologous series of isostructural and isoelectronic palladium acetylacetonato complexes containing different cyclometalated ligands HL (HL=2-phenylpyridine H(PhPy), benzo[h]quinoline H(BhQ), 9-diethylamino-benzo[a]phenoxazin-5-one H(NR), azobenzene H(Azo), 5-[(4′-methyl)-phenylazo]-8-methoxyquinoline H(QAzo), 2-benzoylpyridine H(BKPy), phenyl-2-pyridylketone-2,4-dinitrophenylhydrazone, H(BHPy)) has been prepared. The photophysical characterization of the newly synthesized products shows that many of them are luminescent in solution at room temperature. The best performances are exhibited by the H(NR) derivative (Φem=0.23, λem=660, in dichloromethane solution), which improves the emission features displayed by the unmetalated ligand (Φem=0.13, λem=602, in dichloromethane solution). H(NR) is a well known laser dye commonly named nile red and to the best of our knowledge [(NR)Pd(acac)] is the first example reported up to now of its incorporation in a transition metal complex. Interestingly, the results of the present investigation prove that “[(NR)Pd]” can be an useful building block for the preparation of luminescent organometallic complexes.