Synthesis, Structures, and Photoluminescent Properties of Cyclometalated Platinum(II) Complexes bearing Upper-Rim Phosphinated Calix[4]arenes

Improvement of the Photophysical Performance of Platinum-Cyclometalated Complexes in Halogen-Bonded Adducts

Three groups of luminescent platinum complexes [Pt(C^N)(L)(Y)] [C^N=benzothienyl-pyridine (1), bezofuryl-pyridine (2), phenyl-pyridine (3); L/Y=DMSO/Cl (a), PPh₃ /Cl (b), PPh₃ /CN (c)] have been probed as halogen-bond (XB) acceptors towards iodofluorobenzenes (IC₆ F₅ and I₂ C₆ F₄ ). Compounds 1 a and 2 a (L/Y=DMSO/Cl) afford the adducts 1 a⋅⋅⋅I₂ C₆ F₄ and 2 a⋅⋅⋅I₂ C₆ F₄ , which feature I⋅⋅⋅S_btpy /I⋅⋅⋅π_btpy and I⋅⋅⋅O_DMSO /I⋅⋅⋅Cl short contacts, respectively. The phosphane-cyanide derivatives 1 c and 2 c (L/Y=PPh₃ /CN) co-crystallise with both IC₆ F₅ and I₂ C₆ F₄ . None of the phpy-based species 3 a-3 c participated in XB interactions. Although the native complexes are rather poor luminophores in the solid state (Φ_em =0.023-0.089), the adducts exhibit an up to 10-fold increase of the intensity with a minor alteration of the emission energy. The observed gain in the quantum efficiency is mainly attributed to the joint influence of non-covalent interactions (halogen/hydrogen bonding, π-π stacking), which govern the crystal-packing mode and diminish the radiationless pathways for the T₁ →S₀ transition by providing a rigid environment around the chromophore.

Benzothiazole-Based Cycloplatinated Chromophores: Synthetic, Optical, and Biological Studies

Cycloplatinated complexes based on 2-(4-substituted)benzothiazole ligands of type [Pt(R-PBT-κC,N)Cl(L)] (PBT=2-phenylbenzothiazole; R=Br (1), Me₂ N (2); L=dimethyl sulfoxide (DMSO; a), 1,3,5- triaza-7-phosphaadamantane (PTA; b), triphenylphosphine 3,3',3''-trisulfonate (TPPTS; c)) and [Pt(Br-PBT-κC)Cl(PTA)₂ ] (3) are presented. On the basis of the photophysical data and time-dependent (TD)-DFT calculations (1 a and 2 a), the low-lying transitions (absorption and emission) were associated with ligand-center (LC) charge transfer, with minor metal-to-ligand charge transfer (MLCT), and intraligand charge transfer (ILCT) [Me₂ N-PBT→PBT] excited states, respectively. Simultaneous fluorescence/phosphorescence bands were found in fluid solutions (and also in the solid state for 2 a), which become dominated by triplet emission bands in rigid media at 77 K. The effect of the concentration on emissive behavior of 2 a, b indicated the occurrence of aggregation-induced luminescence properties related to the occurrence of metal-metal and π⋅⋅⋅π interactions, which are more enhanced in 2 a because of the less bulky DMSO ligand. The behavior of 2 a toward para-toluenesulfonic acid (PTSA) in aerated acetonitrile and to hydrogen chloride gas in the solid state has been evaluated, thus showing a clear reversible change between the ¹ ILCT and ³ LC/³ MLCT states due to protonation of the NMe₂ group (theoretical calculations on 2 a-H⁺ ). Solid 2 a undergoes a surprising oxidation of the Pt^II center to Pt^IV with concomitant deoxygenation of DMSO, under prolonged reaction with hydrogen chloride gas to afford the Pt^IV /dimethyl sulfide complex (mer-[Pt(Me₂ N-PBT-κC,N)Cl₃ (SMe₂ )]; mer-4), which evolves in solution to fac-4, as confirmed by X-ray studies. Cytotoxic activity studies on A549 and HeLa cell lines indicated cytotoxic activity of 1 b and 2 a, b. In addition, fluorescent cell microscopy revealed cytoplasmic staining, more visible in perinuclear areas. Inhibition of tubulin polymerization by 1 b in both cells is presented as a preliminary mechanism of its cytotoxic action.

Luminescent cyclometallated platinum(ii) complexes: highly promising EGFR/DNA probes and dual-targeting anticancer agents

Cyclometallated platinum complexes bearing 4-anilinoquinazolines exhibit high potential as luminescent probes for EGFR/DNA in living cells and dual-targeting anticancer agents.

Dibenzothiophene-platinated complexes: probing the effect of ancillary ligands on the photophysical performance

Alteration of the ancillary mono- and bidentate ligands was used to influence the photoemission behaviour of a family of cyclometalated platinum complexes.

Singlet oxygen generation by cyclometalated complexes and applications

While cyclometalated complexes have been extensively studied for optoelectronic applications, these compounds also represent a relatively new class of photosensitizers for the production of singlet oxygen. Thus far, singlet oxygen generation from cyclometalated Ir and Pt complexes has been studied in detail. In this review, photophysical data for singlet oxygen generation from these complexes are presented, and the mechanism of (1) O2 generation is discussed, including evidence for singlet oxygen generation via an electron-transfer mechanism for some of cyclometalated Ir complexes. The period from the first report of singlet oxygen generation by a cyclometalated Ir complex in 2002 through August 2013 is covered in this review. This new class of singlet oxygen photosensitizers may prove to be rather versatile due to the ease of substitution of ancillary ligands without loss of activity. Several cyclometalated complexes have been tethered to zeolites, polystyrene, or quantum dots. Applications for photooxygenation of organic molecules, including "traditional" singlet oxygen reactions (ene reaction, [4 + 2] and [2 + 2] cycloadditions) as well as oxidative coupling of amines are presented. Potential biomedical applications are also reviewed.

Efficient singlet oxygen generation by luminescent 2-(2′-thienyl)pyridyl cyclometalated platinum(II) complexes and their calixarene derivatives

Luminescent cyclometalated platinum(II) complexes, namely [Pt(Thpy)(PPh3)X]n+ (HThpy = 2-(2′-thienyl)pyridine; X = Cl− (1), n = 0; X = CH3CN (2), pyridine (3), n = 1) and [Pt(Thpy)(HThpy)Y]n+ (Y = Cl− (4), n = 0; Y = pyridine (5), n = 1), exhibit structured emission with peak maximum at ∼556 and 598 nm in degassed acetonitrile and with emission quantum yield and lifetime of up to 0.38 and 26 μs, respectively. These complexes are efficient photosensitizers of singlet oxygen with yields up to >90%. Complex 5 exhibited photocytotoxicity towards cancer cells and fluorescence microscopic images of cells incubated with 5 reveal substantial uptake at the nucleus and mitochondria.