Monoanionic C^N^N Luminophores and Monodentate C-Donor Co-Ligands for Phosphorescent Pt(II) Complexes: A Case Study Involving Their Photophysics and Cytotoxicity

Abstract

A family of Pt­(II) complexes bearing monoanionic C^N^N ligands as luminophoric units as well as a set of monodentate ligands derived from allenylidene and carbene species were synthesized and characterized in terms of structure and photophysical properties. In addition, we present the extraordinary molecular structure of a phosphorescent complex carrying an allenylidene ligand. Depending on the co-ligand, an effect can be observed in the photoluminescence lifetimes and quantum yields as well as in the radiative and radiation less deactivation rate constants. Their correlation with the substitution pattern was analyzed by comparing the photoluminescence in fluid solution at room temperature and in frozen glassy matrices at 77 K. Moreover, in order to gain a deeper understanding of the electronic states responsible for the optical properties, density functional theory calculations were performed. Finally, the cytotoxicity of the complexes was evaluated in vitro, showing that the cationic complexes exhibit strong effects at low micromolar concentrations. The calculated half-maximum effective concentrations (EC50 values) were 4 times lower in comparison to the established antitumor agent oxaliplatin. In contrast, the neutral species are less toxic, rendering them as potential bioimaging agents.

Luminescent Anionic Cyclometalated Organoplatinum (II) Complexes with Terminal and Bridging Cyanide Ligand: Structural and Photophysical Properties

“…The emissions in glassy solutions do not reveal any systematic dependence on the solvent (Figure S19 for 6 and 9 ). These emissions are typical of metal-perturbed C^N 3 (π → π*) excited states and, accordingly, the energy peak maximum is subtly red-shifted on going from dfppy to ppy and to bzq derivatives (MeOH, 77 K: 456 6 ; 474 5 ; 477 nm 4 and 458 3 ; 478 2 ; 479 nm 1 ), in line with the more delocalized bzq target ligand and the presence of electron-acceptor fluorine atoms in the phenyl ring. ,,,, According to DFT calculations, , these emissions are ascribed to 3 LC with 3 MLCT character. For the bzq complexes, the lifetimes are extremely longer than those measured for the ppy and dfppy (MeOH 77 K, 323.2 1 ; 289.9 μs 4 ).…”

“…These emissions are typical of metal-perturbed C^N 3 (π → π*) excited states and, accordingly, the energy peak maximum is subtly red-shifted on going from dfppy to ppy and to bzq derivatives (MeOH, 77 K: 456 6; 474 5; 477 nm 4 and 458 3; 478 2; 479 nm 1), in line with the more delocalized bzq target ligand and the presence of electron-acceptor fluorine atoms in the phenyl ring. 31,43,57,76,77 According to DFT calculations, 78,79 these emissions are ascribed to 3 LC with 3 MLCT character.…”

Site-specific covalent metalation of DNA oligonucleotides with phosphorescent platinum(ii) complexes

“…S20-S24 †). [29][30][31] The photoluminescence lifetimes are summarized in Table 4. They are in the order of ms and conrm that phosphorescent oligonucleotides were obtained.…”

“…These species show robust phosphorescence, with an emission wavelength essentially independent of the identity of the monodentate ligand. [29][30][31] While their green phosphorescence (lifetimes and intensities) is quenched by triplet dioxygen ( 3 O 2 ), their dimers and higher aggregates appear with a red-shied yet oxygen-insensitive luminescence portraying excimeric character supported by metal-metal interactions (i.e., coupling between d z 2 -orbitals protruding out of the coordination plane). The site-specic incorporation of a Pt(II) complex into DNA is complicated by the high affinity of Pt(II) for purine N7 positions, as is well-known from the mode of action of the antitumor drug cisplatin.…”

Phosphorescent Pt(ii) complexes bearing cyclometalated difluorophenylpyridinate and diphosphine building blocks

“…Cycloplatinated(II) complexes are one of the most intriguing classes of luminescent compounds that have advanced rapidly in recent decades. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] Due to their astonishing luminescence properties, they have been utilized in different research areas such as bioimaging, [18][19][20][21] LEDs (light-emitting diodes), [22][23][24][25] chemosensing, 26,27 photocatalysts, 28,29 dye sensitized solar cells, 30 and photo-switches. 31,32 To a great extent, the luminescence properties of such complexes depend on the cyclometalated ligand.…”