The Role of Substituents on Functionalized 1,10-Phenanthroline in Controlling the Emission Properties of Cationic Iridium(III) Complexes of Interest for Electroluminescent Devices

Tunability of triplet excited states and photophysical behaviour of bis-cyclometalated iridium(III) complexes with imidazo[4,5-f][1,10]phenanthroline

This is a comprehensive study of the photophysical behaviour of heteroleptic iridium(III) complexes with imidazo[4,5-f][1,10]phenanthroline (imphen) as an ancillary ligand, represented by the general formula [Ir(N∩C)2(imphen)]PF6. As cyclometalating ligands, 2-phenylpyridine (Hppy), 2-phenylquinoline (Hpquin), 2-phenylbenzothiazole (Hpbztz), and 2-(2-pyridyl)benzothiophene (pybzthH) were used. The impact of structural modifications of cyclometalating ligands was widely explored by a combination of steady-state and time-resolved optical techniques accompanied by theoretical calculations. We evidenced that the cyclometalating ligands induce essential changes in the nature of the emissive excited state and the emission characteristics of [Ir(N∩C)2(imphen)]PF6. While the complex [Ir(ppy)2(imphen)]PF6 (1) is a typical 3MLLCT emitter, the lowest triplet states of [Ir(pquin)2(imphen)]PF6 (2), [Ir(pbztz)2(imphen)]PF6 (3) and [Ir(pybzth)2(imphen)]PF6 (4) have a predominant 3LCN∩C character. The phosphorescence colour of the investigated Ir(III) complexes changes from greenish-yellow to red, their quantum yields vary from 56 to 2%, and their triplet excited-state lifetimes fall in the 743-3840 ns range. The highest photoluminescence quantum yield was revealed for 2 in CH2Cl2, while complex 3 in MeCN shows the most pronounced increase in the lifetime. Both complexes 2 and 3 show an increased efficiency of singlet oxygen generation. The herein discussed structure-property relationships are of high significance for controlling photoinduced processes in heteroleptic iridium(III) complexes with the imphen-based ancillary ligand, and making further progress in effectively tuning the emission energies, quantum yields and excited-state lifetimes of these systems by structural modifications of cyclometalating ligands, especially the π-conjugation, the position of the N-donor and the presence of sulfur heteroatoms.

Experimental and theoretical studies of pH-responsive iridium(III) complexes of azole and N-heterocyclic carbene ligands

A series of nine luminescent iridium(III) complexes with pH-responsive imidazole and benzimidazole ligands have been prepared and characterized. The first series of complexes were of the form [Ir(ppy)2(N^N)]+ or [Ir(ppy)2(C^N)]+ (where ppy is 2-phenylpyridine and N^N is 2-(2-pyridyl)imidazole or 2-(2-pyridyl)benzimidazole and C^N represents a pyridyl-triazolylidene-based N-heterocyclic carbene ligand). For these complexes, the benzimidazole group was either unsubstituted or substituted with electron-withdrawing (Cl) or electron-donating (Me) groups. The second series of complexes were of the form [Ir(phbim)2(N^N)]+ or [Ir(phbim)2(C^N)]+ (where phbim is 2-phenylbenzimidazole and N^N is either 2,2'-bipyridine or 1,10-phenanthroline and C^N is either a pyridyl-imidazolylidene or pyridyl-triazolylidene N-heterocyclic carbene ligand). UV-visible and photoluminescence pH titration studies showed that changing the protonation state of these complexes results in significant changes in the photoluminescence emission properties. The pKa values of prepared complexes were estimated from the spectroscopic pH titration data and these values show that the nature of the pH-sensitive ligands (either main or ancillary ligands) resulted in a significant capacity to modulate the pKa values for these compounds with values ranging from 5.19-11.22. Theoretical investigations into the nature of the electronic transitions for the different protonation states of compounds were performed and the results were consistent with the experimental results.

Mechanism of photocatalytic CO2 reduction to HCO2H by a robust multifunctional iridium complex

The tetradentate PNNP-type IrIII complex Mes-IrPCY2 ([Cl-IrIII-H]+) is reported to be an efficient catalyst for the reduction of CO2 to formate with excellent selectivity under visible light irradiation. Density functional calculations have been carried out to elucidate the mechanism and the origin of selectivity in the present work. Calculations suggest that the double-reduced complex 1-H (1[IrI-H]0) demonstrates higher activity than the single-reduced complex 2-H (2[IrIII(L˙-)-H]+), possibly owing to the higher hydride donor ability of the former compared to the latter; thus 1-H functions as the active species in the overall CO2 reduction reaction. In the HCOO- formation pathway, the hydride of 1-H performs a nucleophilic attack on CO2via an outer-sphere fashion to generate species 1-OCHO (1[IrI-OCHO]0), which then releases HCOO- to produce an IrI intermediate. A subsequent protonation and chloride coordination of the Ir center leads to the regeneration of catalyst 1[Cl-IrIII-H]+. For the CO production, a nucleophilic attack on CO2 takes place by the Ir atom of 1-Hvia an inner-sphere manner to afford complex O2C-3-H (1[O2C-IrIII-H]0), followed by a two-proton-one-electron reduction to furnish the OC-2-H complex (2[OC-IrIII(L˙-)-H]+) after liberating a H2O. Ultimately, CO is released to form 2-H. The stronger nucleophilicity as well as smaller steric hindrance of the hydride than the Ir atom of the active species 1-H (1[IrI-H]0) is found to account for the favoring of formate formation over CO formation. Meanwhile, the CO2 reduction reaction is calculated to be preferred over the hydrogen evolution reaction, and this is consistent with the experimental product distributions.

Synthesis and comparison study of electrochemiluminescence from mononuclear and corresponding heterodinuclear Ir-Ru complexes via an amide bond as a bridge

A mononuclear iridium-based complex with a primary amine group (named Ir-NH₂), a mononuclear ruthenium-based complex with a butanoic acid group (named Ru-COOH) and the corresponding heterodinuclear complex containing an iridium and ruthenium center via an amide bond bridge (named Ir-Ru) were designed and successfully synthesized in this study. The photophysical and electrochemical properties and ECL performances of these three metal complexes under various experimental conditions were well characterized. For the first time, the insights from this comprehensive comparison study indicate that the two metal-based subunits with comparable luminescent properties are significant in the design of bimetallic-based multicolor luminophores at the molecular level, which helps us to further understand the emission performances of bimetallic complexes and to rationally design more efficient corresponding organometallic luminophores with multicolor emission for wide applications in the future.

Highly Efficient Ir(III)-Coumarin Photo-Redox Catalyst for Synergetic Multi-Mode Cancer Photo-Therapy

Four photo-catalysts of the general formula [Ir(CO6/ppy)₂ (L)]Cl where CO6=coumarin 6 (Ir1-Ir3), ppy=2-phenylpyridine (Ir4), L=4'-(3,5-di-tert-butylphenyl)-2,2' : 6',2''-terpyridine (Ir1), 4'-(3,5-bis(trifluoromethyl)phenyl)-2,2' : 6',2''-terpyridine (Ir2 and Ir4), and 4-([2,2' : 6',2''-terpyridin]-4'-yl)-N,N-dimethylaniline (Ir3) were synthesized and characterized. These photostable photo-catalysts (Ir1-Ir3) showed strong visible light absorption between 400-550 nm. Upon light irradiation (465 and 525 nm), Ir1-Ir3 generated singlet oxygen and induced rapidly photo-catalytic oxidation of cellular coenzymes NAD(P)H. Ir1-Ir3 showed time-dependent cellular uptake with excellent intracellular retention efficiency. Upon green light irradiation (525 nm), Ir2 provided a much higher photo-index (PI=793) than the clinically used photosensitizer, 5-aminolevulinicacid (5-ALA, PI>30) against HeLa cancer cells. The observed necro-apoptotic anticancer activity of Ir2 was due to the Ir2 triggered photo-induced intracellular redox imbalance (by NAD(P)H oxidation and ROS generation) and change in the mitochondrial membrane potential. Remarkably, Ir2 showed in vivo photo-induced catalytic anticancer activity in mouse models.

Harnessing Bismuth Coordination Chemistry to Achieve Bright, Long-Lived Organic Phosphorescence

A new bismuth(III)-organic compound, Hphen[Bi₂(HPDC)₂(PDC)₂(NO₃)]·4H₂O (Bi-1; PDC = 2,6-pyridinedicarboxylate and phen = 1,10-phenanthroline), was synthesized, and the structure was determined by single-crystal X-ray diffraction. The compound was found to display bright-blue-green phosphorescence in the solid state under UV irradiation, with a luminescent lifetime of 1.776 ms at room temperature. The room temperature and low-temperature (77 K) emission spectra exhibited the vibronic structure characteristic of Hphen phosphorescence. Time-dependent density functional theory studies showed that the excitation pathway arises from an energy transfer from the dimeric structural unit to Hphen, with participation from a nine-coordinate Bi center. The triplet state of Hphen is believed to be stabilized via supramolecular interactions, which, when coupled with the heavy-atom effect induced by Bi, leads to the observed long-lived luminescence. The compound displayed a solid-state quantum yield of over 27%. To the best of our knowledge, this is the first such compound to exhibit phenanthrolinium phosphorescence with such long-lived, room temperature lifetimes in the solid state. To further elucidate the energy-transfer mechanism, Ln³⁺ (Ln = Eu, Tb, Sm) ions were successfully doped into the parent compound, and the resulting materials exhibited dual emission from Hphen and Ln, promoting tunability of the emission color.

Memristors Based on an Iridium(III) Complex Containing Viologen for Advanced Synaptic Bionics

Memristors with nonvolatile memory properties are expected to open the era of neuromorphic computing. However, it remains a huge challenge to develop memristors with high uniformity, high stability, and low power consumption for advanced synaptic bionics. Herein, an electroactive iridium(III) complex Ir-vio was designed and synthesized by incorporating a viologen moiety into its N^∧N ligand. Complex Ir-vio showed multiple redox states and high sensitivity to an electrical stimulus. Importantly, two-terminal memristors with Ag/Ir-vio/W structure were successfully fabricated by the solution-processable method, which exhibited multilevel storage characteristics with a low switching threshold voltage of 0.5 V and high ON1/ON2/ON3/OFF current ratio of 10⁵/10³/10²/1 at a low reading bias of 0.05 V. Moreover, the memristors can mimic synaptic plasticity, indicating that they can act as artificial synapses to construct brain-inspired neural networks. The memristive mechanisms can be ascribed to the interconversion among different charge-transfer and redox states under various electrical stimulus. To the best of our knowledge, this work is the first experimental demonstration of memristors based on iridium(III) complexes, opening a new era for the development of synaptic bionic devices based on organometallic compounds.

Building C(sp3 ) Molecular Complexity on 2,2'-Bipyridine and 1,10-Phenanthroline in Rhenium Tricarbonyl Complexes

The reactions of [Re(N-N)(CO)₃ (PMe₃ )]OTf (N-N=2,2'-bipyridine, bipy; 1,10-phenanthroline, phen) compounds with tBuLi and with LiHBEt₃ have been explored. Addition to the N-N chelate took place with different site-selectivity depending on both chelate and nucleophile. Thus, with tBuLi, an unprecedented addition to C5 of bipy, a regiochemistry not accessible for free bipy, was obtained, whereas coordinated phen underwent tBuLi addition to C2 and C4. Remarkably, when LiHBEt₃ reacted with [Re(bipy)(CO)₃ (PMe₃ )]OTf, hydride addition to the 4 and 6 positions of bipy triggered an intermolecular cyclodimerization of two dearomatized pyridyl rings. In contrast, hydride addition to the phen analog resulted in partial reduction of one pyridine ring. The resulting neutral Re^I products showed a varied reactivity with HOTf and with MeOTf to yield cationic complexes. These strategies rendered access to Re^I complexes containing bipy- and phen-derived chelates with several C(sp³ ) centers.

A computational study on second-order nonlinear optical properties based on bis-cyclometalated Ir(iii) complexes: redox and substituent effects

A series of neutral Ir(iii) complexes that possess cyclometalated ligands (C^N) and different ancillary ligands, N-heterocyclic carbene (NHC) and their ionic complexes 1+/−–5+/− have been investigated using density functional theory.

Transition metals induce control of enhanced NLO properties of functionalized organometallic complexes under laser modulations

The molecular engineering of organometallic complexes has recently attracted renewed interest on account of their potential technological applications for optoelectronics in general and optical data storage. The transition metal which induces control of enhanced nonlinear optical properties of functionalized organometallic complexes versus not only the intensity but also the polarization of the incident laser beam is original and important for all optical switching. This makes organometallic complexes valuable and suitable candidates for nonlinear optical applications. In the present work, we report the synthesis and full characterization of four organometallic complexes consisting of N, N-dibutylamine and azobenzene fragments but differ by auxiliary alkynyl ligands or metal cations. Thus, a ferrocenyl derivative 1 and three ruthenium complexes 2-4 have been prepared. The nonlinear optical properties of the four new azo-based ruthenium and iron organometallic complexes in the solid state, using polymethylmethacrylate as matrix, have been thoroughly studied. This concept is extended to computing the HOMO and LUMO energy levels of the considered complexes, dipole moment, first and second order hyperpolarizabilities using the 6-31 + G(d,p) + LANL2DZ mixed basis set. The second and third nonlinear optical properties of the resulting polymer composites were obtained by measuring SHG and THG response by means of the Maker fringe technique using a laser generating at 1,064 nm with a 30 ps pulse duration. The values of the second and third order NLO susceptibilities of the four organometallic complexes were found to be higher than the common references used. Theoretical calculation shows that the large first and second order hyperpolarizablities are caused by strong intramolecular charge transfer between the transition metal parts and the ligands though a conjugated transmitter. These results indicate that the present organometallic complexes are valuable candidates for optoelectronic and photonic applications.

A Porous Aromatic Framework Functionalized with Luminescent Iridium(III) Organometallic Complexes for Turn-On Sensing of 99TcO4. ACS APPLIED MATERIALS & INTERFACES 2020;12:15288-15297. [PMID: 32131587 DOI: 10.1021/acsami.0c01929]

Contamination of ⁹⁹TcO₄^-, a problematic radioactive anion in the nuclear fuel cycle, in groundwater has been observed in a series of legacy nuclear sites, representing a notable radiation hazard and environmental concern. The development of convenient, rapid, and sensitive detection methods is therefore critical for radioactivity control and remediation tasks. Traditional detection methods suffer from clear demerits of either the presence of large interference from coexisting radioactive species (e.g., radioactivity counting methods) or the requirement of extensive instrumentation and analysis procedure (e.g., mass spectrometry). Here, we constructed a luminescent iridium(III) organometallic complex (Ir(ppy)₂(bpy)⁺; ppy = 2-phenylpyridine, bpy = 2,2^'-bipyridine)-grafted porous aromatic framework (Ir-PAF) for the first time, which can be utilized for efficient, facile, and selective detection of trace ReO₄^-/TcO₄^- in aqueous solutions. Importantly, the luminescence intensity of Ir-PAF is greatly enhanced in the presence of ReO₄^-/TcO₄^-, giving rise to a distinct turn-on sensor with the detection limit of 556.9 μg/L. Such a superior detection capability originates from the highly selective and strong interaction between ReO₄^-/TcO₄^- and Ir(ppy)₂(bpy)⁺, leading to an efficient pre-enrichment of ReO₄^-/TcO₄^- during analysis and subsequently a much weaker nonradiative decay of the luminescence of Ir(ppy)₂(bpy)⁺, as illustrated by density functional theory (DFT) calculation as well as quantum yield and fluorescence lifetime measurements. Successful quantification of trace ReO₄^- in simulated Hanford low-activity waste (LAW) solution containing large excess of Cl^-, NO₃^-, and NO₂^- was demonstrated, highlighting the bright future of luminescent PAFs in the area of chemical sensing.

Amphiphilic Gemini Iridium(III) Complex as a Mitochondria-Targeted Theranostic Agent for Tumor Imaging and Photodynamic Therapy

Clinical diagnostics and therapeutics of tumors are significantly benefitted by the development of multifunctional theranostic agents, which integrate tumor targeting, imaging, and therapeutics. However, the integration of imaging and therapy functionalities to a unimolecular framework remains a great challenge. Herein, a family of amphiphilic gemini iridium(III) complexes (GIC), Ir1-Ir6, are synthesized and characterized. The presence of quaternary ammonium (QA) groups endows GIC with adjustable water solubility and excellent self-assembly properties. Spectroscopic and computational results reveal that introducing QA groups into cyclometalating ligands (ĈN ligands) can overcome the drawback of aggregation-caused emission quenching and ensure Ir1-Ir3 with high emission intensity and excellent singlet oxygen (¹O₂) generation ability in aqueous media. Cell-based assays indicate that Ir3 shows higher cellular uptake efficiency and localizes specifically in the mitochondria, as well as exhibits outstanding photostability and an impressive phototoxicity index with satisfactory performance in mitochondria-targeted imaging and photodynamic therapy (PDT) of tumor cells. Furthermore, in vivo studies further prove that Ir3 possesses excellent antitumor activity and remarkably inhibits the growth of the HepG2 cells under PDT treatment. Consequently, this study presents a promising strategy for designing clinical application potential multifunctional iridium complex theranostic agents for mitochondria-targeted imaging and PDT in a single molecular framework.

Effects of Varying the Benzannulation Site and π Conjugation of the Cyclometalating Ligand on the Photophysics and Reverse Saturable Absorption of Monocationic Iridium(III) Complexes

A series of monocationic iridium(III) complexes, [Ir(C^N)₂(pqu)]⁺PF₆^- [pqu = 2-(pyridin-2-yl)quinoline, C^N = 2-phenylquinoline (1), 3-phenylisoquinoline (2), 1-phenylisoquinoline (3), benzo[ h]quinoline (4), 2-(pyridin-2-yl)naphthalene (5), 1-(pyridin-2-yl)naphthalene (6), 2-(phenanthren-9-yl)pyridine (7), 2-phenylbenzo[ g]quinoline (8), 2-(naphthalen-2-yl)quinoline (9), and 2-(naphthalen-2-yl)benzo[ g]quinoline (10)], were synthesized in this work. These complexes bear C^N ligands with varied degrees of π conjugation and sites of benzannulation, allowing for elucidation of the effects of the benzannulation site at the C^N ligand on the photophysics of the complexes. Ultraviolet-visible (UV-vis) absorption and emission of the complexes were systematically investigated via spectroscopic techniques and time-dependent density functional theory calculations. Their triplet excited-state absorption and reverse saturable absorption (RSA) were studied by nanosecond transient absorption (TA) spectroscopy and nonlinear transmission techniques. The fusion of phenyl ring(s) to the phenyl ring or the 4 and 5 positions of the pyridyl ring of the C^N ligand resulted in red-shifted UV-vis absorption and emission spectra in complexes 2, 5-7, 9, and 10 compared to those of the parent complex 0, while their triplet lifetimes and emission quantum yields were significantly reduced. In contrast, the fusion of one phenyl ring to the other sites of the pyridyl group of the C^N ligand showed an insignificant impact on the energies of the lowest singlet (S₁) and triplet (T₁) excited states in complexes 1, 3, and 4 but noticeably affected their TA spectral features. The fusion of the naphthyl group to the 5 and 6 and positions at the pyridyl ring did not influence the S₁ energy of complex 8 but altered the nature of the T₁ states in 8 and 10 by switching them to the benzo[ g]quinoline-localized ³π,π* state, which resulted in completely different emission and TA spectra in these two complexes. The site-dependent variations of the ground- and excited-state absorption induced strong but varied RSA from these complexes for 4.1-ns laser pulses at 532 nm, with the RSA strength decreasing in the trend of 3 > 7 ≈ 4 ≈ 9 ≈ 6 > 8 ≈ 1 ≈ 2 ≈ 5 > 10.

Modular Construction of Photoanodes with Covalently Bonded Ru- and Ir-Polypyridyl Visible Light Chromophores

1,10-phenanthroline is grafted to indium tin oxide (ITO) and titanium dioxide nanoparticle (TiO₂) semiconductors by electroreduction of 5-diazo-1,10-phenanthroline in 0.1 M H₂SO₄. The lower and upper potential limits (-0.20 and 0.15 V_SCE, respectively) were set to avoid reduction and oxidation of the 1,10-phenanthroline (phen) covalently grafted at C5 to the semiconductor. The resulting semiconductor-phen ligand (ITO-phen or TiO₂-phen) was air stable, and was bonded to Ru- or Ir- by reaction with cis-[Ru(bpy)₂(CH₃CN)₂]²⁺ (bpy = 2,2'-bipyridine) or cis-[Ir(ppy)₂(CH₃CN)₂]⁺ (ppy = ortho-C_phenyl metalated 2-phenylpyridine) in CH₂Cl₂ and THF solvent at 50 °C. Cyclic voltammetry, X-ray photoelectron spectroscopy, solid-state UV-vis, and inductively coupled plasma-mass spectrometry all confirmed that the chromophores SC-[(phen)Ru(bpy)₂]²⁺ and SC-[(phen)Ir(ppy)₂]⁺ (SC = ITO or TiO₂) formed in near quantitative yields by these reactions. The resulting photoanodes were active and relatively stable to photoelectrochemical oxidation of hydroquinone and triethylamine under neutral and basic conditions.

Highly Luminescent Cyclometalated Iridium Complexes Generated by Nucleophilic Addition to Coordinated Isocyanides

In this work, we report a new class of blue-emitting cyclometalated iridium complexes supported by acyclic diaminocarbene (ADC) ancillary ligands. These neutral, tris-chelated complexes are not obtainable via traditional synthesis routes and instead are generated through metal-mediated nucleophilic addition to a metal-bound isocyanide, which is followed by orthometalation of the ADC under mild conditions. Importantly, four of the variants exhibit efficient phosphorescence when immobilized in PMMA matrix, achieving quantum yields of 79% for blue emitters with a 2-(2,4-difluorophenyl)pyridine (F₂ppy) C^N ligand and 30-37% for orange emitters with a 2-phenylbenzothiazole (bt) C^N ligand. Electrochemical studies demonstrate significantly higher-lying HOMO levels in the ADC complexes relative to the NHC analogues, a phenomenon that results in enhanced charge-transfer character in the excited states of the ADC complexes. This study demonstrates that ADC ancillary ligands not only give rise to new structures for Ir(III)-based phosphorescent emitters but also are promising targets for use in light-emitting devices and other thin-film optical applications.

β-Diketonate ancillary ligands in heteroleptic iridium complexes: a balance between synthetic advantages and photophysical troubles

How the triplet energy of β-diketonate ancillary ligands in Ir(iii) complexes affects the phosphorescence emission: photochemical and electrochemical investigations and DFT calculations shed light on the dark triplet excited states.

Augmented pH-sensitivity absorbance of a ruthenium(ii) bis(bipyridine) complex with elongation of the conjugated ligands: an experimental and theoretical investigation

An absorbance-based sensor employing ruthenium bipyridyl with a phenanthroline-fused benzoylthiourea moiety formulated as [Ru(ii)(bpy)₂(phen-nBT)](PF₆)₂ {bpy = 2,2'-bipyridine, phen = 1,10-phenanthroline, nBT = n-benzoylthiourea} has been synthesized and characterized by elemental analyses, mass spectrometry, and infrared, ultraviolet-visible, luminescence and nuclear magnetic resonance spectroscopy. The changes in the intensity of absorption and emission of the complex induced by functionalization of the benzoylthiourea ligands with amino and carbonyl in their protonated and deprotonated forms were studied experimentally. The absorption and emission properties of the complex exhibit a strong dependence on the pH (1-11) of the aqueous medium. This work highlights the pH-sensitivity augmentation of the absorption band by elongating the conjugation length in the structure of the ruthenium bipyridine complex. The principle of this work was to design the title compound to be capable of enhancing the differences in the absorption sensitivity responses towards pH between the protonated and deprotonated complexes in the absorption measurement. Along with significant and noticeable changes in the absorption spectra, subsequent theoretical investigations specifically on the electronic and absorbance properties of the title compound were carried out in this study. Protonation of the molecule significantly stabilized the lowest-unoccupied molecular orbital (LUMO), whereas the highest-occupied molecular orbital (HOMO) is greatly destabilized upon deprotonation. A time-dependent density functional theory (TDDFT) calculation in the linear-response (-LR) regime was performed to clarify the origin of the experimentally observed linear dependence of absorption intensity upon pH (1-11). The MLCT band exhibits hyperchromic shift at low pH as indicated by the large transition dipole moment and a wider distribution of the response charge of the molecule, which is induced by the stabilization of the electrostatic potential at the carbonyl moiety by protonation. This study provides the possibility of employing theoretical information to gain insight into the origin of the optical absorption obtained experimentally. The ruthenium complex was designed with an elongated ligand conjugation length and exhibited a tremendously large change in the absorption intensity of the protonated and deprotonated forms, which therefore demonstrates its feasibility as an indicator molecule especially for absorbance measurements.

Spectroscopic, Electrochemical and DFT Studies of Phosphorescent Homoleptic Cyclometalated Iridium(III) Complexes Based on Substituted 4-Fluorophenylvinyl- and 4-Methoxyphenylvinylquinolines

This study reports the synthesis and comparative investigation of the substituent effects of a new series of highly luminescent homoleptic tris-cyclometalated iridium(III) complexes of the type [Ir(N^˄C)₃]. These are based on two ligand type derivatives comprising of 4-fluorophenylvinylquinolines and 4-methoxyphenylvinylquinolines with electron-donating and/or electron-withdrawing groups as aryl substituents at 2-position. The structures of the ligands and their complexes were characterized by means of FT-IR, UV-Vis and NMR spectrometry complemented with photoluminescence and cyclic voltammetry. The photophysical properties of 2-aryl-4-(4-fluorophenylvinyl)quinoline and its corresponding complex were also studied using the density functional theory method. The photoluminescent properties of the ligands and the corresponding complexes showed high fluorescent intensities and quantum yields in solvents of different polarities. The photoluminescence spectra of the complexes in solid film, showed common transmission curves at longer wavelengths maximum (λ_em = 697 nm) possibly originating from the interference of scattered light of higher-order transmission of monochromators.

Synthesis, structures, photophysical and catalytic properties of benzothienyl iridium(III) complexes

Bisbenzothienyl iridium(III) complexes, [Ir(bt)2(PR3)]X (bt: 2-phenylbenzo[ d]thiazole, R = n-Bu or Ph, X = OTf, BF4 or SbF6) are reported, two of which, (R = n-Bu or Ph, X = OTf), have been characterised by X-ray crystallography. The complexes are thermally stable and their photophysical properties are presented, together with their catalytic activity in the “borrowing hydrogen reaction” of alcohols with amines.

Photoluminescence and electroluminescence of an iridium(iii) complex with 2′,6′-bis(trifluoromethyl)-2,4′-bipyridine and 2-(5-phenyl-1,3,4-thiadiazol-2-yl)phenol ligands

Efficient greenish yellow OLEDs based on an iridium(iii) complex containing electron transport ligands of 2′,6′-bis(trifluoromethyl)-2,4′-bipyridine and 2-(5-phenyl-1,3,4-thiadiazol-2-yl)phenol show a maximum current efficiency of 54.5 cd A⁻¹and a maximum external quantum efficiency of 16.1%.

Bis-cyclometalated iridium complexes with electronically modified aryl isocyanide ancillary ligands

Bis-cyclometalated iridium complexes with electronically modified aryl isocyanide ligands are described, and the effects on the photophysical properties are noted.

Photoluminescence and electroluminescence of iridium(iii) complexes with 2′,6′-bis(trifluoromethyl)-2,4′-bipyridine and 1,3,4-oxadiazole/1,3,4-thiadiazole derivative ligands

Highly efficient OLEDs based on green and orange iridium(iii) complexes based on 2′,6′-bis(trifluoromethyl)-2,4′-bipyridine and 2-(5-(4-(trifluoromethyl)phenyl)-1,3,4-oxadiazol-2-yl)phenol show peak current efficiencies of 74.8 and 41.0 cd A⁻¹, respectively, with low efficiency roll-off.

Two-photon absorption properties and (1)O2 generation ability of Ir complexes: an unexpected large cross section of [Ir(CO)2Cl(4-(para-di-n-butylaminostyryl)pyridine)]

The new complexes cis-[Ir(CO)2Cl(4-(para-di-n-butylaminostyryl)pyridine)] () and [Ir(cyclometallated-2-phenylpyridine)2(4,4'-(para-di-n-butylaminostyryl)-2,2'-bipyridine)][PF6] () were synthesized and fully characterized along with the known complex Ir(cyclometallated-2-phenylpyridine)2(5-Me-1,10-phenanthroline)][PF6] (). Remarkably, complex , with an Ir(i) centre, displays fluorescence - as opposed to the phosphorescence typical of many Ir(iii) complexes - with a modestly high quantum yield in solution, opening a new route for the design of iridium-based emitters which should not be limited to the +3 oxidation state. It is also characterized by an unexpectedly large two-photon absorption (TPA) cross section, an order of magnitude higher than that previously reported for Ir(iii) or Pt(ii) complexes. The great potential of cyclometallated Ir(iii) complexes for photodynamic therapy was confirmed, with and showing a good singlet oxygen generation ability, coupled with a modest TPA activity for .

Luminogenic iridium azide complexes

The synthesis and characterization of luminogenic, bioorthogonal iridium probes is described. These probes exhibit long photoluminescence lifetimes amenable to time-resolved applications. A simple, modular synthesis via 5-azidophenanthroline allows structural variation and allows optimization of cell labeling.