Influence of Ancillary Ligands on Photophysical Properties of Cyclometalated Organoplatinum(II) Complexes

Three series of cyclometalated organoplatinum(ii) complexes [Pt(p-MeC6H4)(bhq)(L)], in which bhq is benzo[h]quinolinate and L is PPh3 (1a), PPh2Me (1b), or PPhMe2 (1c); [Pt(p-XC6H4)(bhq)(PPh2Me)], in which X is H (2a), F (2b), Bu-t (2c), OMe (2d), or Me (2e = 1b); and [Pt(bhq)X(PPh2Me)], in which X is CF3CO2 (3a), Cl (3b), or I (3c) were synthesized and fully characterized using multinuclear (H-1 and P-31) NMR spectroscopy and elemental analysis. Typical complexes [Pt(p-MeC6H4)(bhq)(PPhMe2)], 1c, [Pt(p-MeC6H4)(bhq)(PPh2Me)], 2e, and [Pt(bhq)Cl(PPh2Me)], 3b, were further characterized by single crystal X-ray crystallography. The photophysical properties of all the complexes were studied and the influence of changing the ancillary ligands and substituents on their luminescence properties were investigated and the assignments were confirmed by TD-DFT calculations

Phosphorescent heterobimetallic complexes involving platinum(IV) and rhenium(VII) centers, connected by unsupported μ-oxido bridge

Heterobimetallic compounds [(CN)LMe2Pt(mu-O)ReO3] (CN = ppy, L = PPh3, 2a; CN = ppy, L = PMePh2, 2b; CN = bhq, L = PPh3, 2c; CN = bhq, L = PMePh2, 2d) containing a discrete unsupported Pt(IV)-O-Re(VII) bridge have been synthesized through a targeted synthesis route. The compounds have been prepared by a single-pot synthesis in which the Pt(IV) precursor [PtMe2I(CN)L] complexes are allowed to react easily with AgReO4 in which the iodide ligand of the starting Pt(IV) complex is replaced by an ReO4- anion. In these Pt-O-Re complexes, the Pt(IV) centers have an octahedral geometry, completed by a cyclometalated bidentate ligand (CN), two methyl groups and a phosphine ligand, while the Re(VII) centers have a tetrahedral geometry. Elemental analysis, single crystal X-ray diffraction analysis and multinuclear NMR spectroscopy are used to establish their identities. The new complexes exhibit phosphorescence emission in the solid and solution states at 298 and 77 K, which is an uncommon property of platinum complexes with an oxidation state of +4. According to DFT calculations, we found that this emission behavior in the new complexes originates from ligand centered (LC)-L-3 (CN) character with a slight amount of metal to ligand charge transfer ((MLCT)-M-3). The solid-state emission data of the corresponding cycloplatinated(IV) precursor complexes [PtMe2I(CN)L], 1a-1d, pointed out that the replacement of I- by an ReO4- anion helps enhancing the emission efficiency besides shifting the emission wavelengths

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)