Spectral and photophysical properties of mono and dinuclear Pt(II) and Pd(II) complexes: An unusual emission behaviour

Eight mononuclear complexes of the formula [M(N-N)(DHB)] and two binuclear complexes of the formula [M-2(BPY)(2)(THB)] {where M = Pd(II) or Pt(II), N-N = 2,2'-bipyridine (BPY), 2,2'-biquinoline (BIQ), 4,7-diphenyl-1,10-plienanthroline (DPP), 1, 10-phenanthroline (PHEN); DHB = dianion of 3,4-dihydroxybenzaldehyde and THB = tetraanion of 3,3',4,4'-tetrahydroxy benzaldazine} were prepared and their electrochemical, spectral and photophysical properties were examined. These complexes were characterized by chemical analysis, IR and proton NMR spectroscopy. A detailed study on the absorption spectroscopy of these complexes was made. These complexes were found to show a low-energy solvatochromic ligand-to-ligand charge-transfer (LLCT) band. The electronic energies of these bands have been analyzed and compared with electrochemical data. Emission behaviour of the complexes of the series, [Pt(N-N)(DHB)], [Pt(N-N)(DHBA)] {where DHBA is the dianion of 3,4-dihydroxybenzoic acid} and [Pt-2(BPY)(2)(THB)] was also investigated. These platinum complexes were found to emit from a low-energy state at low temperature and a high-energy state at room temperature. Photophysics of these complexes is also discussed. (C) 2004 Elsevier Ltd. All rights reserved.