SYNTHESIS, ABSORPTION-SPECTRA, AND LUMINESCENCE PROPERTIES OF PLATINUM(II) COMPLEXES WITH AMINOQUINOLINE AND AMINOACRIDINE LIGANDS

The synthesis, characterization, absorption spectra, and luminescence properties of three new platinum(II) complexes are reported. The complexes are [Pt(C6H5)2(CO)(5-AQ)] (1), [Pt(C6H5)2(CO)(9-AA)] (2), and [Pt(C6H5)2(5-AQ)2] (3) (5-AQ = 5-aminoquinoline; 9-AA = 9-aminoacridine). For the sake of comparison, the same properties of the 5-AQ and 9-AA free ligands have been studied. The absorption spectra of the complexes exhibit moderately intense bands (epsilon in the range 10(3)-10(4) M-1 cm-1) with maxima in the region 370-450 nm, which are assigned to pi-pi* transitions centered in the N-heterocyclic ligands. The "Pt(C6H5)2(CO)" and "Pt(C6H5)2" moieties can be regarded as electron-withdrawing substituents of the aromatic ligands in that they substantially affect the energy of the bands by decreasing the pi-pi* transition energies. All the complexes emit strongly both in fluid solution at room temperature (e.g., PHI = 0.037 for 2 in dichloromethane) and in a rigid matrix at 77 K. The emission bands are solvent dependent, with the emission energy decreasing on increasing solvent polarity, and the luminescence lifetimes are in the nanosecond range; the luminescence properties indicate that emission occurs from singlet pi-pi* excited states centered in the N-heterocyclic aromatic ligands. Because of the nature of the heterocyclic amino-substituted ligands, and of the absorption and luminescence properties, these and similar complexes hold promise of being good luminescent probes for biological applications.