Luminescent mononuclear and dinuclear cycloplatinated (II) complexes comprising azide and phosphine ancillary ligands

A new series of cycloplatinated (II) complexes with general formulas of [Pt (bhq)(N-3)(P)] [bhq = deprotonated 7,8-benzo[h]quinoline, P = triphenyl phosphine (PPh3) and methyldiphenyl phosphine], [Pt (bhq)(PP)]N-3 [PP = 1,1-bis (diphenylphosphino)methane (dppm) and 1,2-bis (diphenylphosphino)ethane] and [Pt-2(bhq)(2)(mu-PP)(N-3)(2)] [PP = dppm and 1,2-bis (diphenylphosphino)acetylene] is reported in this investigation. A combination of azide (N-3(-)) and phosphine (monodentate and bidentate) was used as ancillary ligands to study their influences on the chromophoric cyclometalated ligand. All complexes were characterized by nuclear magnetic resonance spectroscopy. To confirm the presence of the N-3(-) ligand directly connected to the platinum center, complex [Pt (bhq)(N-3)(PPh3)] was further characterized by single-crystal X-ray crystallography. The photophysical properties of the new products were studied by UV-Vis spectroscopy in CH2Cl2 and photoluminescence spectroscopy in solid state (298 or 77 K) and in solution (77 K). Using density functional theory calculations, it was proved that, in addition to intraligand charge-transfer (ILCT) and metal-to-ligand charge-transfer (MLCT) transitions, the L ' LCT (L ' = N-3, L = CN) electronic transition has a remarkable contribution in low energy bands of the absorption spectra (for complexes [Pt (bhq)(N-3)(P)] and [Pt-2(bhq)(2)(mu-PP)(N-3)(2)]). It is indicative of the determining role of the N-3(-) ligand in electronic transitions of these complexes, specifically in the low energy region. In this regard, the photoluminescence studies indicated that the emissions in such complexes originate from a mixed (ILCT)-I-3/(MLCT)-M-3 (intramolecular) and also from aggregations (intermolecular)