Synthesis and Photophysical Properties of Cycloplatinated(II) Complexes Bearing Isocyanide and Alkynyl Ligands

Cyclometalated platinum(II) complexes havegained increasing interest during the last yearsdue to their rich chemistry and uniqueluminescent properties, making them suitablefor light emitting diodes (OLEDs),photocatalysis, bioimaging or chemicalsensors. However, there are very scarceantecedents of heteroleptic cycloplatinated(II)compounds with isocyanide and alkynylligands.1To expand this research, we aimed to prepare anew family of luminescent cycloplatinatedcomplexes with 2-(2,4-difluorophenyl)pyridine(dfppy, a) and 4-(2-pyridyl)benzaldehyde(ppy-CHO, b) as cyclometalating ligands. Thealkynyl/tert-butyl isocyanide complexes[Pt(C^N)(CCR)(CNtBu)], bearing 4-ethynylanisole (2) and 2-ethynylthiophene (3)have obtained from the chloride derivatives[Pt(C^N)Cl(CNtBu)] (C^N = dfppy 1a, ppy-CHO 1b) using the Sonogashira protocol.These systems have been designed by takinginto account features that could make thesecomplexes interesting in biological studies.The complexes have been fully characterizedusing NMR spectroscopy together with X-raydiffraction. Their optical properties have beenstudied in detail and interpreted with the helpof TD-DFT calculations. The dfppy derivativesexhibit a mechanochromic behaviour, relatedto their strong tendency to form stackingstructures or aggregates by Pt···Pt and/or ···interactions

Study of cycloplatinated complexes with isocyanide ligands: isomerism, optical properties and mechanochromism

Platinum(II) cyclometalated derivatives have attracted a great interest dueto their rich photophysical properties, with interesting applications aschemical sensors, photocatalysts or in light emitting diodes (OLEDs). Thepresence of planar ligands in these complexes improves the luminescenceand the ability to form aggregates through the formation of Pt···Pt and/or··· interactions. In this context, there are very scarce examples ofheteroleptic complexes with isocyanide and alkynyl ligands.In this work, we present the synthesis and characterization of a group ofPt(II) compounds featuring 2-phenylpyridine and 2-phenylquinoline ascyclometalated ligands and 2,6-dimethylphenyl isocyanide as auxiliaryligand. The p-tolylacetylide complexes [Pt(C^N)(CCTol)(CNXyl)] (C^N =ppy 3, pq 4) have been obtained from the chloride derivatives[Pt(C^N)Cl(CNXyl)] (C^N = ppy 1, pq 2). The isomerism of thesecompounds in which the isocyanide ligand can be trans to the nitrogen or tothe carbon of the cyclometalated ligand has been determined by differenttechniques, as NMR and X-ray diffraction.The photophysical properties (absorption and emission) of all complexeshave been studied with the aid of theoretical calculations. Interestingly, thephenylpyridine derivatives exhibit mechanical stimuli responsive colour andluminescence changes correlated with the formation of different aggregateswith ··· and/or Pt···Pt interactions

New acyclic diaminocarbenes cycloplatinated(II) complexes: synthesis, photophysical properties and cytotoxic activity

Among all phosphorescent molecules, cyclometalated platinum(II) complexes have receivedconsiderable attention because of their photophysical properties and potential applications asdopants in OLEDs, LECs, photocatalysts or bioimaging. Another research of relevant interest istheir employment as anticancer drugs with a broader spectrum of action against differenttumours and fewer side effects than the well-known cisplatin. For that reason, the choice of thecyclometalated group and ancillary ligands play an important role not only in emissive behaviorbut also on the biological activity.1N-acyclic diaminocarbenes (ADCs) show several appealing characteristics; they display strongelectron-donating ability with structural flexibility and can be easily prepared. However, thereare only a few examples of ADC-platinum complexes used as perspective metal-based drugs inthe literature.2In this contribution, we describe a series of new luminescent ADC cycloplatinated(II) compoundsfeaturing 2-(2,4-difluorophenyl)pyridine (3) and 2-phenylquinoline (4) cyclometalated groups[Pt(C^N)Cl{C(NHXyl)(NHR)}] (R = Pr a, Benzyl b) obtained by nucleophilic addition of primarypropyl and benzyl amines, to the isocyanide ligand of the corresponding precursors[Pt(C^N)Cl(CNXyl)] (1, 2) recently reported by our group.3 Their optical properties haveexamined and interpreted with the aid of DFT/TD-DFT calculations and, finally, all newcompounds have been screened for their cytotoxic activity against various cancer cell lines

Shine bright or live long: substituent effects in [Cu(N^N)(P^P)]+-based light-emitting electrochemical cells where N^N is a 6-substituted 2,2'-bipyridine

We report [Cu(P^P)(N^N)][PF6] complexes with P^P = bis(2-(diphenylphosphino)phenyl)ether (POP) or 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene (xantphos) and N^N = 6-methyl-2,2′-bipyridine (Mebpy), 6-ethyl-2,2′-bipyridine (Etbpy), 6,6′-dimethyl-2,2′-bipyridine (Me2bpy) or 6-phenyl-2,2′-bipyridine (Phbpy). The crystal structures of [Cu(POP)(Phbpy)][PF6]·Et2O, [Cu(POP)(Etbpy)][PF6]·Et2O, [Cu(xantphos)(Me2bpy)][PF6], [Cu(xantphos)(Mebpy)][PF6]·CH2Cl2·0.4Et2O, [Cu(xantphos)(Etbpy)][PF6]·CH2Cl2·1.5H2O and [Cu(xantphos)(Phbpy)][PF6] are described; each copper(I) centre is distorted tetrahedral. In the crystallographically determined structures, the N^N domain in [Cu(xantphos)(Phbpy)]+ and [Cu(POP)(Phbpy)]+ is rotated ∼180° with respect to its orientation in [Cu(xantphos)(Mebpy)]+, [Cu(POP)(Etbpy)]+ and [Cu(xantphos)(Etbpy)]+; in each complex containing xantphos, the xanthene ‘bowl’ retains the same conformation in the solid-state structures. The two conformers resulting from the 180° rotation of the N^N ligand were optimized at the B3LYP-D3/(6-31G**+LANL2DZ) level and are close in energy for each complex. Variable temperature NMR spectroscopy evidences the presence of two conformers of [Cu(xantphos)(Phbpy)]+ in solution which are related by inversion of the xanthene unit. The complexes exhibit MLCT absorption bands in the range 378 to 388 nm, and excitation into each MLCT band leads to yellow emissions. Photoluminescence quantum yields (PLQYs) increase from solution to thin-film and powder; the highest PLQYs are observed for powdered [Cu(xantphos)(Mebpy)][PF6] (34%), [Cu(xantphos)(Etbpy)][PF6] (37%) and [Cu(xantphos)(Me2bpy)][PF6] (37%) with lifetimes of 9.6–11 μs. Density functional theory calculations predict that the emitting triplet (T1) involves an electron transfer from the Cu–P^P environment to the N^N ligand and therefore shows a 3MLCT character. T1 is calculated to be ∼0.20 eV lower in energy than the first singlet excited state (S1). The [Cu(P^P)(N^N)][PF6] ionic transition-metal (iTMC) complexes were tested in light-emitting electrochemical cells (LECs). Turn-on times are fast, and the LEC with [Cu(xantphos)(Me2bpy)][PF6] achieves a maximum efficacy of 3.0 cd A−1 (luminance = 145 cd m−2) with a lifetime of 1 h; on going to the [Cu(xantphos)(Mebpy)][PF6]-based LEC, the lifetime exceeds 15 h but at the expense of the efficacy (1.9 cd A−1). The lifetimes of LECs containing [Cu(xantphos)(Etbpy)][PF6] and [Cu(POP)(Etbpy)][PF6] exceed 40 and 80 h respectively

Highly stable and efficient light-emitting electrochemical cells based on cationic iridium complexes bearing arylazole ancillary ligands

A series of bis-cyclometalated iridium(III) complexes of general formula [Ir(ppy)2(N∧N)][PF6] (ppy− = 2-phenylpyridinate; N∧N = 2-(1H-imidazol-2-yl)pyridine (1), 2-(2-pyridyl)benzimidazole (2), 1-methyl-2-pyridin-2-yl- 1H-benzimidazole (3), 2-(4′-thiazolyl)benzimidazole (4), 1- methyl-2-(4′-thiazolyl)benzimidazole (5)) is reported, and their use as electroluminescent materials in light-emitting electrochemical cell (LEC) devices is investigated. [2][PF6] and [3][PF6] are orange emitters with intense unstructured emission around 590 nm in acetonitrile solution. [1][PF6], [4][PF6], and [5][PF6] are green weak emitters with structured emission bands peaking around 500 nm. The different photophysical properties are due to the effect that the chemical structure of the ancillary ligand has on the nature of the emitting triplet state. Whereas the benzimidazole unit stabilizes the LUMO and gives rise to a 3MLCT/3LLCT emitting triplet in [2][PF6] and [3][PF6], the presence of the thiazolyl ring produces the opposite effect in [4][PF6] and [5][PF6] and the emitting state has a predominant 3LC character. Complexes with 3MLCT/3LLCT emitting triplets give rise to LEC devices with luminance values 1 order higher than those of complexes with 3LC emitting states. Protecting the imidazole N−H bond with a methyl group, as in complexes [3][PF6] and [5][PF6], shows that the emissive properties become more stable. [3][PF6] leads to outstanding LECs with simultaneously high luminance (904 cd m−2), efficiency (9.15 cd A−1), and stability (lifetime over 2500 h).Spanish Ministry of Economy and Competitiveness (MINECO) of Spain (projects CTQ2014- 58812-C2-1-R, MAT2014-55200, CTQ2014-55583-R, CTQ2014-61914-EXP, CTQ2015-71955-REDT, CTQ2015- 70371-REDT, CTQ2015-71154-P, and Unidad de Excelencia Marıá de Maeztu MDM-2015-0538), European Feder funds (CTQ2015-71154-P), Obra Social “la Caixa” (OSLC-2012- 007), Junta de Castilla y León (BU033-U16), and Generalitat Valenciana (Prometeo2016/135

A Non-Viral Plasmid DNA Delivery System Consisting on a Lysine-Derived Cationic Lipid Mixed with a Fusogenic Lipid

The insertion of biocompatible amino acid moieties in non-viral gene nanocarriers is an attractive approach that has been recently gaining interest. In this work, a cationic lipid, consisting of a lysine-derived moiety linked to a C12 chain (LYCl) was combined with a common fusogenic helper lipid (DOPE) and evaluated as a potential vehicle to transfect two plasmid DNAs (encoding green fluorescent protein GFP and luciferase) into COS-7 cells. A multidisciplinary approach has been followed: (i) biophysical characterization based on zeta potential, gel electrophoresis, small-angle X-ray scattering (SAXS), and cryo-transmission electronic microscopy (cryo-TEM); (ii) biological studies by fluorescence assisted cell sorting (FACS), luminometry, and cytotoxicity experiments; and (iii) a computational study of the formation of lipid bilayers and their subsequent stabilization with DNA. The results indicate that LYCl/DOPE nanocarriers are capable of compacting the pDNAs and protecting them efficiently against DNase I degradation, by forming Lα lyotropic liquid crystal phases, with an average size of ~200 nm and low polydispersity that facilitate the cellular uptake process. The computational results confirmed that the LYCl/DOPE lipid bilayers are stable and also capable of stabilizing DNA fragments via lipoplex formation, with dimensions consistent with experimental values. The optimum formulations (found at 20% of LYCl content) were able to complete the transfection process efficiently and with high cell viabilities, even improving the outcomes of the positive control Lipo2000*

A gemini cationic lipid with histidine residues as a novel lipid-based gene nanocarrier: a biophysical and biochemical study

This work reports the synthesis of a novel gemini cationic lipid that incorporates two histidine-type head groups (C3(C16His)2). Mixed with a helper lipid 1,2-dioleoyl-sn-glycero3-phosphatidyl ethanol amine (DOPE), it was used to transfect three different types of plasmid DNA: one encoding the green fluorescence protein (pEGFP-C3), one encoding a luciferase (pCMV-Luc), and a therapeutic anti-tumoral agent encoding interleukin-12 (pCMV-IL12). Complementary biophysical experiments (zeta potential, gel electrophoresis, small-angle X-ray scattering (SAXS), and fluorescence anisotropy) and biological studies (FACS, luminometry, and cytotoxicity) of these C3(C16His)2/DOPE-pDNA lipoplexes provided vast insight into their outcomes as gene carriers. They were found to efficiently compact and protect pDNA against DNase I degradation by forming nanoaggregates of 120–290 nm in size, which were further characterized as very fluidic lamellar structures based in a sandwich-type phase, with alternating layers of mixed lipids and an aqueous monolayer where the pDNA and counterions are located. The optimum formulations of these nanoaggregates were able to transfect the pDNAs into COS-7 and HeLa cells with high cell viability, comparable or superior to that of the standard Lipo2000*. The vast amount of information collected from the in vitro studies points to this histidine-based lipid nanocarrier as a potentially interesting candidate for future in vivo studies investigating specific gene therapies