Synthesis and Characterization of Iridium(III) Complexes with Substituted Phenylimidazo(4,5-f)1,10-phenanthroline Ancillary Ligands and Their Application in LEC Devices

In this work, we report on the synthesis and characterization of six new iridium(III) complexes of the type [Ir(C^N)2(N^N)]+ using 2-phenylpyridine (C1-3) and its fluorinated derivative (C4-6) as cyclometalating ligands (C^N) and R-phenylimidazo(4,5-f)1,10-phenanthroline (R = H, CH3, F) as the ancillary ligand (N^N). These luminescent complexes have been fully characterized through optical and electrochemical studies. In solution, the C4-6 series exhibits quantum yields (Ф) twice as high as the C1-3 series, exceeding 60% in dichloromethane and where 3MLCT/3LLCT and 3LC emissions participate in the phenomenon. These complexes were employed in the active layer of light-emitting electrochemical cells (LECs). Device performance of maximum luminance values of up to 21.7 Lx at 14.7 V were observed for the C2 complex and long lifetimes for the C1-3 series. These values are counterintuitive to the quantum yields observed in solution. Thus, we established that the rigidity of the system and the structure of the solid matrix dramatically affect the electronic properties of the complex. This research contributes to understanding the effects of the modifications in the ancillary and cyclometalating ligands, the photophysics of the complexes, and their performance in LEC devices.

Air- and Water-Stable Heteroleptic Copper (I) Complexes Bearing Bis(indazol-1-yl)methane Ligands: Synthesis, Characterisation, and Computational Studies

A series of four novel heteroleptic Cu(I) complexes, bearing bis(1H-indazol-1-yl)methane analogues as N,N ligands and DPEPhos as the P,P ligand, were synthesised in high yields under mild conditions and characterised by spectroscopic and spectrometric techniques. In addition, the position of the carboxymethyl substituent in the complexes and its effect on the electrochemical and photophysical behaviour was evaluated. As expected, the homoleptic copper (I) complexes with the N,N ligands showed air instability. In contrast, the obtained heteroleptic complexes were air- and water-stable in solid and solution. All complexes displayed green-yellow luminescence in CH2Cl2 at room temperature due to ligand-centred (LC) phosphorescence in the case of the Cu(I) complex with an unsubstituted N,N ligand and metal-to-ligand charge transfer (MLCT) phosphorescence for the carboxymethyl-substituted complexes. Interestingly, proper substitution of the bis(1H-indazol-1-yl)methane ligand enabled the achievement of a remarkable luminescent yield (2.5%) in solution, showcasing the great potential of this novel class of copper(I) complexes for potential applications in luminescent devices and/or photocatalysis.

Theoretical Approach for the Luminescent Properties of Ir(III) Complexes to Produce Red-Green-Blue LEC Devices

With an appropriate mixture of cyclometalating and ancillary ligands, based on simple structures (commercial or easily synthesized), it has been possible to design a family of eight new Ir(III) complexes (1A, 1B, 2B, 2C, 3B, 3C, 3D and 3E) useful as luminescent materials in LEC devices. These complexes involved the use of phenylpyridines or fluorophenylpyridines as cyclometalating ligands and bipyridine or phenanthroline-type structures as ancillary ligands. The emitting properties have been evaluated from a theoretical approach through Density Functional Theory and Time-Dependent Density Functional Theory calculations, determining geometric parameters, frontier orbital energies, absorption and emission energies, injection and transport parameters of holes and electrons, and parameters associated with the radiative and non-radiative decays. With these complexes it was possible to obtain a wide range of emission colours, from deep red to blue (701-440 nm). Considering all the calculated parameters between all the complexes, it was identified that 1B was the best red, 2B was the best green, and 3D was the best blue emitter. Thus, with the mixture of these complexes, a dual host-guest system with 3D-1B and an RGB (red-green-blue) system with 3D-2B-1B are proposed, to produce white LECs.

Effective Treatment against ESBL-Producing Klebsiella pneumoniae through Synergism of the Photodynamic Activity of Re (I) Compounds with Beta-Lactams

BACKGROUND

Extended-spectrum beta-lactamase (ESBL) and carbapenemase (KPC+) producing Klebsiella pneumoniae are multidrug-resistant bacteria (MDR) with the highest risk to human health. The significant reduction of new antibiotics development can be overcome by complementing with alternative therapies, such as antimicrobial photodynamic therapy (aPDI). Through photosensitizer (PS) compounds, aPDI produces local oxidative stress-activated by light (photooxidative stress), nonspecifically killing bacteria.

METHODOLOGY

Bimetallic Re(I)-based compounds, PSRe-µL1 and PSRe-µL2, were tested in aPDI and compared with a Ru(II)-based PS positive control. The ability of PSRe-µL1 and PSRe-µL2 to inhibit K. pneumoniae was evaluated under a photon flux of 17 µW/cm2. In addition, an improved aPDI effect with imipenem on KPC+ bacteria and a synergistic effect with cefotaxime on ESBL producers of a collection of 118 clinical isolates of K. pneumoniae was determined. Furthermore, trypan blue exclusion assays determined the PS cytotoxicity on mammalian cells.

RESULTS

At a minimum dose of 4 µg/mL, both the PSRe-µL1 and PSRe-µL2 significantly inhibited in 3log10 (>99.9%) the bacterial growth and showed a lethality of 60 and 30 min of light exposure, respectively. Furthermore, they were active on clinical isolates of K. pneumoniae at 3-6 log10. Additionally, a remarkably increased effectiveness of aPDI was observed over KPC+ bacteria when mixed with imipenem, and a synergistic effect from 3 to 6log10 over ESBL producers of K. pneumoniae clinic isolates when mixed with cefotaxime was determined for both PSs. Furthermore, the compounds show no dark toxicity and low light-dependent toxicity in vitro to mammalian HEp-2 and HEK293 cells.

CONCLUSION

Compounds PSRe-µL1 and PSRe-µL2 produce an effective and synergistic aPDI effect on KPC+, ESBL, and clinical isolates of K. pneumoniae and have low cytotoxicity in mammalian cells.

Effective Photodynamic Therapy with Ir(III) for Virulent Clinical Isolates of Extended-Spectrum Beta-Lactamase Klebsiella pneumoniae

Background: The extended-spectrum beta-lactamase (ESBL) Klebsiella pneumoniae is one of the leading causes of health-associated infections (HAIs), whose antibiotic treatments have been severely reduced. Moreover, HAI bacteria may harbor pathogenic factors such as siderophores, enzymes, or capsules, which increase the virulence of these strains. Thus, new therapies, such as antimicrobial photodynamic inactivation (aPDI), are needed. Method: A collection of 118 clinical isolates of K. pneumoniae was characterized by susceptibility and virulence through the determination of the minimum inhibitory concentration (MIC) of amikacin (Amk), cefotaxime (Cfx), ceftazidime (Cfz), imipenem (Imp), meropenem (Mer), and piperacillin–tazobactam (Pip–Taz); and, by PCR, the frequency of the virulence genes K2, magA, rmpA, entB, ybtS, and allS. Susceptibility to innate immunity, such as human serum, macrophages, and polymorphonuclear cells, was tested. All the strains were tested for sensitivity to the photosensitizer PSIR-3 (4 µg/mL) in a 17 µW/cm² for 30 min aPDI. Results: A significantly higher frequency of virulence genes in ESBL than non-ESBL bacteria was observed. The isolates of the genotype K2+, ybtS+, and allS+ display enhanced virulence, since they showed higher resistance to human serum, as well as to phagocytosis. All strains are susceptible to the aPDI with PSIR-3 decreasing viability in 3log10. The combined treatment with Cfx improved the aPDI to 6log10 for the ESBL strains. The combined treatment is synergistic, as it showed a fractional inhibitory concentration (FIC) index value of 0.15. Conclusions: The aPDI effectively inhibits clinical isolates of K. pneumoniae, including the riskier strains of ESBL-producing bacteria and the K2+, ybtS+, and allS+ genotype. The aPDI with PSIR-3 is synergistic with Cfx.

The mode of action of the PSIR-3 photosensitizer in the photodynamic inactivation of Klebsiella pneumoniae is by the production of type II ROS which activate RpoE-regulated extracytoplasmic factors

BACKGROUND

Due to increased bacterial multi-drug resistance (MDR), there is an antibiotic depletion to treat infectious diseases. Consequently, other promising options have emerged, such as the antimicrobial photodynamic inactivation therapy (aPDI) based on photosensitizer (PS) compounds to produce light-activated local oxidative stress (photooxidative stress). However, there are scarce studies regarding the mode of action of PS compounds to induce photooxidative stress on pathogenic γ-proteobacteria such as MDR-Klebsiella pneumoniae.

METHODOLOGY

The mode of action exerted by the cationic Ir(III)-based PS (PSIR-3) to inhibit the growth of K. pneumoniae was analyzed. RT-qPCR determined the transcriptional response induced by PSIR-3 on bacteria treated with aPDI. The expression levels of genes associated with a bacterial oxidative response, such as oxyR and sodA, and the extracytoplasmic, regulators rpoE and hfq were determined. Also, were determined the transcriptional response of the extracytoplasmic factors mrkD, acrB, magA, and rmpA.

RESULTS

At 17 μW/cm² photon flux and 4 μg/mL of the PSIR-3 compound, the K. pneumoniae growth was inhibited in 3 log₁₀. Compared with untreated bacteria, the transcriptional response induced by PSIR-3 occurs via the extracytoplasmic sigma factor rpoE and hfq. In contrast, no participation in the oxyR pathway or induction of the sodA gene was observed. This response was accompanied by the upregulation of the extracytoplasmic virulence factors mrkD, magA, and rmpA.

CONCLUSIONS

PDI aPDI produced by PSIR-3 kills K. pneumoniae and may induce damage to the bacterial envelope. The bacterium tries to avoid this injury by activation of extracytoplasmic factors mediated through the rpoE regulon.

Novel iridium complexes with N-heterocyclic dicarbene ligands in light-driven water oxidation catalysis: photon management, ligand effect and catalyst evolution

Iridium complexes [IrClCp*diNHC]PF6, with N-heterocyclic dicarbene (diNHC) and pentamethylcyclopentadienyl (Cp*) ligands, have been investigated in light driven water oxidation catalysis within the Ru(bpy)32+/S2O82- cycle (bpy = 2,2'-bipyridine). In particular, the effect of different diNHC ligands was evaluated by employing the complex 1a (diNHC = 1,1'-dimethyl-3,3'-ethylenediimidazol-2,2'-diylidene) and the novel and structurally characterised 2 (diNHC = 1,1'-dimethyl-3,3'-ethylene-5,5'-dibromodiimidazol-2,2'-diylidene) and 3 (diNHC = 1,1'-dimethyl-3,3'-ethylene-dibenzimidazol-2,2'-diylidene). The presented results include: (i) a photon management analysis of the 1a/Ru(bpy)32+/S2O82- system, revealing two regimes of O2 evolution rate, being dependent on the light intensity at low photon flux, where the system reaches an overall quantum yield up to 0.17 ± 0.01 (quantum efficiency 34 ± 2%), while being independent of light intensity at high photon flux thus indicating a change of limiting step; (ii) a trend of O2 evolution activity that follows the order 1a > 2 > 3 both under low and high photon flux conditions, with the reactivity that is favoured by the electron donating nature of the diNHC ligand, quantified on the basis of the carbene carbon chemical shift; (iii) an analogous trend also in the bimolecular rate constants of electron transfer kET from the iridium species to photogenerated Ru(bpy)33+, with kET values in the range 4.2-6.1 × 104 M-1 s-1, thus implying a significant reorganisation energy to the iridium sphere; (iv) the evolution of 1a, as the most active Ir species in the series, to mononuclear iridium species with lower molecular weight and originating from oxidative transformation of the organic ligand scaffold, as proven by converging UV-Vis, MALDI-MS and 1H-NMR evidences. These results can be used for the further design and engineering of novel catalysts.

Heteroleptic Cu(i) complexes bearing methoxycarbonyl-imidoylindazole and POP ligands – an experimental and theoretical study of their photophysical properties

Substitutions in the ligand play a key role in the photophysical properties of new Cu(i) complexes.