Cyclometalated Ligand Research Articles

Platinum(II) acetimino cyclometalated complexes derived from room temperature ammonia activation

Two Pt(II) rollover cyclometalated complexes, [Pt(bpyPh‐H)(DMSO)Me] (1) and [Pt(bpyPh‐H)(DMSO)Cl] (2), where bpyPh‐H is the C3‐deprotonated 6‐phenyl‐2,2’‐bipyridine, were reacted with aqueous ammonia in acetone at room temperature. In the case of the electron‐poor complex 2 simple substitution of DMSO gave the amino complex [Pt(bpyPh‐H)(NH3)Cl] (4), whereas the electron‐rich complex 1 produced the rare acetimine complex [Pt(bpyPh‐H)(HN=CMe2)Me] (3), stable both in solution and in the solid state. The result is noteworthy, as the condensation product of acetone and ammonia, acetimine, is not stable under mild conditions. The reaction likely requires a Pt(II) electron‐rich complex and the presence of a carbon donor in trans position. An analogous reaction occurs with methylamine, allowing the synthesis of the secondary imine complex [Pt(bpyPh‐H)(MeN=CMe2)Me], 5. Starting from this finding a series of cyclometalated acetimine complexes [Pt(N^C)(HN=CMe2)Me] were isolated and characterized with other classical and rollover cyclometalated ligands with an array of different electronic and steric properties, indicating a possible extension of the reaction to various cyclometalated ligands. A preliminary study on the antimicrobial and antitumor properties of complex 3, taken as a model for this class, showed no significant effects against Gram‐positive, Gram‐negative bacteria, or yeasts, but found activity in vitro against HT29 colon cancer cell line.

Achieving deep red to near-infrared emission in dinuclear platinum (II) complexes with the donor-π-acceptor-type cyclometalated ligand

A novel deep red-emitting dinuclear platinum (II) complex, (TPA2niq)2Pt2(C8OXT)2, featuring a donor-π-acceptor (D-π-A) type ligand, was synthesized and characterized. Here, TPA2niq represents the 4-(tert-butyl)-N-(4-(tert-butyl)phenyl)-N-(4-(6-(isoquinolin-1-yl)naphthalen-2-yl)phenyl)aniline unit, while C8OXT was the abbreviation for the bridging ligand 5-(4-octyloxyphenyl)-1,3,4-oxadiazole-2-thiol. Its photophysical, electrochemical, and electroluminescent characteristics were primarily studied. It was found that (TPA2niq)2Pt2(C8OXT)2 exhibited a saturated deep red emission with a peak at 686 nm in dichloromethane. Furthermore, the (TPA2niq)2Pt2(C8OXT)2-doped polymer electroluminescent devices (PLEDs), fabricated through a solution process, exhibited outstanding electroluminescence (EL) properties, with an emission peak at 684 nm, a maximum external quantum efficiency (EQE) of 3.78%, and a maximum radiant emittance of 4478 mW/Sr/m2. By incorporating the D-π-A type ligand into the dinuclear platinum (II) complex, the PLEDs achieved efficient deep red emission.

Ir(III)‐Based Photosensitizer‐Loaded M1 Macrophage Exosomes for Synergistic Photodynamic Therapy

AbstractThe synthesis of organic photosensitizers with effective reactive oxygen species (ROS) generation remains one of the urgent needs for cancer therapy. In this study, a simple strategy is developed to endow the intrinsic non‐photosensitizer fluorophores with profound ROS‐generating ability upon light irradiation. This strategy is featured by introducing donor–acceptor (D‐A) structured fluorophores as auxiliary ligands into the Ir(III) metal complex, which provides the Ir(III) metal center‐based triplet state (T1) as an energy level springboard to efficiently enhance the energy transition to the D‐A ligand‐based triplet state (T1'). The energy level difference between T1 and T1' can be regulated through altering the cyclometalated ligands of Ir(III), facilitating the energy transfer from T1 to T1' for augmented ROS generation. To improve the pharmacological properties of the obtained D‐A coordinated Ir(III) complex, it is incorporated with the exosomes extracted from M1 phenotype macrophages (M1‐Exos). The generated nanocomplexes are able to trigger synergistic photodynamic therapy, facilitating the reprogramming of tumor‐associated macrophages and eradicating the tumors in mice. This study provides a general strategy to transform non‐photosensitizer fluorophores into effective photosensitizers for biomedical applications.

Phosphorescent cyclometalated iridium(III) complexes incorporated into polynorbornene polymeric platform as potential probes for assessments of oxygen in cancer cells

Phosphorescent transition metal complexes are considered as promising probes for oxygen sensing in living cells and tissues. Red light-emitting complexes are more valuable because the red irradiation better penetrates into biological tissues. In the present study, far-red light-emitting iridium(III) complexes PnIr1-PnIr4 on polyoxanorbornene platform were synthesized and their oxygen sensing properties were tested in water and in cells in vitro. Iridium(III) complexes incorporated into polymeric platform contained 1-(thien-2-yl)isoquinoline cyclometalating ligands and norbornene-substituted picolinate (PnIr1) and diimine (PnIr2-PnIr4) ancillary ligands. The quantum yields and phosphorescence lifetimes of the synthesized polymeric iridium probes in degassed water solutions were 1.5–2 times higher than in aerated solutions demonstrating oxygen-dependent quenching of phosphorescence. Of the four probes, PnIr1 easily penetrated into cultured cancer cells grown as monolayer and 3D spheroids and showed reliable response to hypoxia with increase of lifetime from 1.31 to 3.06 µs. Good water solubility, far-red oxygen-sensitive emission and low cytotoxicity make the new probe a promising tool for intracellular oxygen assessments in cancer research.

Synthesis and Luminescent Properties of Zwitterionic Platinum Bis‐Phosphine Complexes Based on a Pendant Closo‐Monocarborane Cluster

ABSTRACTThe synthesis, structures and photophysical properties of a series of zwitterionic platinum complexes are reported. These cyclometalated complexes have the general structure Pt(C^N)(P^P), where C^N is a cyclometalating ligand with a pendant monocarborane cluster and P^P is a bis‐phosphine ligand (dppe or dppb). Their solid‐state structures have been characterized by x‐ray diffraction, and no Pt–Pt interactions are observed. All complexes are emissive at room temperature in solid states with quantum yields of 0.06–0.58 in PMMA films. The emission energy of these complexes is governed by the nature of the C^N cyclometalated ligands, allowing the emission to be tuned from blue to green. In particular, the introduction of an anionic carborane unit provokes a more than twofold improvement in the photoluminescence quantum yield of [Pt(CB11‐ppy)(dppe)] (3b) compared to the parent cationic complex [Pt(ppy)(dppe)]+. In addition, density functional theory (DFT) calculations were performed on the ground states and first triplet excited states of 1a, 2a, and 3a for interpretation of the observed photophysical properties.

Ultrafast Near‐Infrared Luminescence from Cyclometalated Iridium(III) Complexes with Indirubin as Ancillary Ligand

AbstractBeing a constitutional isomer of the indigo dye, indirubin has been known as a purple colourant for a long time. On the other hand, its structural and photophysical properties as ligand in metal complexes are virtually unexplored. Herein, for the first time, we utilized indirubin as ancillary chelator to develop two new heteroleptic iridium(III) complexes equipped with two 2‐phenylpyridine units as archetypical cyclometalating ligands. These new complexes display fully reversible oxidation and reduction processes, and show a panchromatic absorption extending up to 900 nm in acetonitrile solution at 298 K. Moreover, an unexpected broad and unstructured emission band is detected for both complexes in the near‐infrared region, peaking at approx. 1100 nm and having a lifetime of approx. 60 ps; such an emission is attributed to a ligand‐centred triplet excited state (3LC) located on the indirubin ligand itself, as proved by DFT calculations. These findings may pave the way for further exploration of the indirubin dye as a ligand for different types of metal centres to create efficient near‐infrared triplet emitters without the need for difficult synthetic procedures.

Exploring the Photophysics and Photocatalytic Activity of Heteroleptic Rh(III) Transition-Metal Complexes Using High-Throughput Experimentation.

High-throughput synthesis and screening (HTSS) methods were used to investigate the photophysical properties of 576 heteroleptic Rh(III) transition-metal complexes through measurement of the UV-visible absorption spectra, deaerated excited-state lifetime, and phosphorescent emission spectra. While 4d transition-metal photophysics are often highly influenced by deleterious metal-centered deactivation channels, the HTSS of structurally diverse cyclometalating and ancillary ligands attached to the metal center facilitated the discovery of photoactive complexes exhibiting long-lived charge-transfer phosphorescence (0.15-0.95 μs) spanning a substantial portion of the visible region (546-620 nm) at room temperature. Further photophysical and electrochemical investigations were then carried out on select complexes with favorable photophysics to understand the underlying features controlling these superior properties. Heteroleptic Ir(III) complexes with identical ligand morphology were also synthesized to compare these features to this family of well understood chromophores. A number of these Rh(III) complexes contained the requisite properties for photocatalytic activity and were consequently tested as photocatalysts (PCs) in a water reduction system using a Pd water reduction cocatalyst. Under certain conditions, the activity of the Rh(III) PC actually surpassed that of the Ir(III) PC, uncovering the potential of this often-overlooked class of transition metals as both efficient photoactive chromophores and PCs.

Synthesis and Performance of Deep-Red Phosphorescent Iridium Complexes with Pyrone as an Auxiliary Ligand.

Two bis-cyclometalated heteroleptic iridium complexes incorporating 1-phenylisoquinoline (piq) as the main cyclometalating ligand and 3-hydroxy-2-methyl-4-pyrone (ma) or 2-ethyl-3-hydroxy-4H-pyran-4-one (ema) as the auxiliary ligand, namely Ir(piq)2(ma) (Ir-1) and Ir(piq)2(ema) (Ir-2), were developed and applied as deep-red phosphors in organic light-emitting diodes (OLEDs). The two auxiliary ligands had similar influences on the photophysical, electrochemical, and electroluminescent properties of the iridium complexes. Ir(piq)2(ma) (Ir-1) showed better luminescence performance in a simple phosphorescent OLED compared to the traditional red iridium complex Ir(piq)2(acac) and exhibited a current efficiency of 9.39 cd A-1 (EQE of 12.09%). In contrast, Ir(piq)2(ema) exhibited an efficiency of 8.6 cd A-1 (EQE of 10.19%).

Synthesis and bonding in platinum(II) complexes with cyclometalated carbene and isoelectronic bis(phosphino)metallocene ligands

Four cycloplatinated complexes of the type [Pt(C^C*){M(η5-C5H4PPh2)2-κ2P,P'}][PF6]n (M = Fe, n = 1; M = Co, n = 2), where C^C* is 2-(3-methylimidazol-2- ylidene-1-yl-κC2)phenyl-κC1 and similar cyclometalated ligands bearing an additional aromatic ring and phenyl substituents at the imidazol-2-ylidene unit, were prepared and structurally characterized by spectroscopic methods (NMR and ESI MS), elemental analysis, cyclic voltammetry and DFT calculations. Experimental structural parameters and DFT calculations consistently indicate differentiation of the Pt-bound phosphine groups due to unlike trans influence of the phenyl and carbene donor moieties at the cyclometalated ligand in these compounds

Cyclometallated Imides as Templates for the H‐Bond Directed Iridium‐Catalyzed Asymmetric Hydrogenation of N‐Methyl, N‐Alkyl and N‐Aryl Imines

AbstractA combined computational and experimental approach allowed us to develop overall the most selective catalyst for the direct hydrogenation of N‐methyl, N‐alkyl and N‐aryl imines described to date. Iridium catalysts with a cyclometallated cyclic imide group provide selectivity of up to 99 % enantiomeric excess. Computational studies show that the selectivity results from the combined effect of H‐bonding of the imide C=O with the substrate iminium ion and a stabilizing π–π interaction with the cyclometallated ligand. The cyclometallated ligand thus exhibits a unique mode of action, serving as a template for the H‐bond directed approach of the substrate which results in enhanced selectivity. The catalyst (2) has been synthesized and isolated as a crystalline air‐stable solid. X‐ray analysis of 2 confirmed the structure of the catalyst and the correct position of the imide C=O groups to engage in an H‐bond with the substrate. 19F NMR real‐time monitoring showed the hydrogenation of N‐methyl imines catalyzed by 2 is very fast, with a TOF of approx. 3500 h−1.

Cyclometallated Imides as Templates for the H-Bond Directed Iridium-Catalyzed Asymmetric Hydrogenation of N-Methyl, N-Alkyl and N-Aryl Imines.

A combined computational and experimental approach allowed us to develop overall the most selective catalyst for the direct hydrogenation of N-methyl, N-alkyl and N-aryl imines described to date. Iridium catalysts with a cyclometallated cyclic imide group provide selectivity of up to 99 % enantiomeric excess. Computational studies show that the selectivity results from the combined effect of H-bonding of the imide C=O with the substrate iminium ion and a stabilizing π-π interaction with the cyclometallated ligand. The cyclometallated ligand thus exhibits a unique mode of action, serving as a template for the H-bond directed approach of the substrate which results in enhanced selectivity. The catalyst (2) has been synthesized and isolated as a crystalline air-stable solid. X-ray analysis of 2 confirmed the structure of the catalyst and the correct position of the imide C=O groups to engage in an H-bond with the substrate. 19F NMR real-time monitoring showed the hydrogenation of N-methyl imines catalyzed by 2 is very fast, with a TOF of approx. 3500 h-1.

High‐Efficiency and Long‐Lifetime Near‐Infrared OLEDs Based on Iridium Complexes with Enhanced Horizontal Emitting Dipole Orientation

AbstractHigh‐efficiency and long‐lifetime near‐infrared (NIR) organic light‐emitting diodes (OLEDs) are rarely reported. Herein, three efficient NIR Ir(III) complexes 1–3 are developed with specially designed cyclometallated ligands based on pyrido[3,4‐b]pyrazine and oriented substitutions along the Ir─N bond axis. Electron‐deficient pyrazine ring effectively stabilizes LUMO energy, leading to significant emission bathochromic shift. Importantly, for complexes 2 and 3, oriented substitutions along the direction of the Ir─N bond axis considerably enhance the horizontal emitting dipole orientation ratio up to 90%. Their OLEDs demonstrate high maximum external quantum efficiencies (EQEs), negligible efficiency roll‐offs, superior radiance, and long lifetimes. The maximum EQEs and radiances of devices are 9.84% and 158 W Sr−1 m−2 at 725 nm for 1, 6.98% and 14.03 W Sr−1 m−2 at 760 nm for 2, and 12.49% and 18.94 W Sr−1 m−2 at 735 nm for 3, respectively. The device lifetime LT97 at 10 mA cm−2 is 453 h for complex 2, which sets a champion lifetime for NIR‐OLEDs. This work demonstrates that pyrido[3,4‐b]pyrazine is a desired building block for robust NIR emitting Ir(III) complexes, providing a superior paradigm to combine high efficiency, negligible roll‐off, and long device lifetime simultaneously toward practical applications.

Tuning Excited State Character in Iridium(III) Photosensitizers and Its Influence on TTA-UC.

A series of mixed ligand, photoluminescent organometallic Ir(III) complexes have been synthesized to incorporate substituted 2-phenyl-1H-naphtho[2,3-d]imidazole cyclometalating ligands. The structures of three example complexes were categorically confirmed using X-ray crystallography each sharing very similar structural traits including evidence of interligand hydrogen bond contacts that account for the shielding effects observed in the 1H NMR spectra. The structural iterations of the cyclometalated ligand provide tuning of the principal electronic transitions that determine the visible absorption and emission properties of the complexes: emission can be tuned in the visible region between 550 and 610 nm and with triplet lifetimes up to 10 μs. The nature of the emitting state varies across the series of complexes, with different admixtures of ligand-centered and metal-to-ligand charge transfer triplet levels evident. Finally, the use of the complexes as photosensitizers in triplet-triplet annihilation energy upconversion (TTA-UC) was investigated in the solution state. The study showed that the complexes possessing the longest triplet lifetimes showed good viability as photosensitizers in TTA-UC. Therefore, the use of an electron-withdrawing group on the 2-phenyl-1H-naphtho[2,3-d]imidazole ligand framework can be used to rationally promote TTA-UC using this class of complex.

Luminescent color control and electroluminescent characteristics of iridium(III) complexes containing a four-membered chelating ring from ancillary ligand

Six dpppy (P,P-diphenyl-N-(pyridin-2-yl)phosphinic amide)- and dppq (P,P-diphenyl-N-(quinolin-2-yl)phosphinic amide)-based iridium(III) complexes 1a, 1b, 2a, 2b, 3a and 3b containing four-membered chelate architecture were synthetized. Their crystal structure and photophysical properties were investigated. The crystal structure shows that two coordinating N atoms from the ancillary ligand dpppy and dppq form a four-membered chelate architecture with the centered iridium(III). By changing the substituent groups and conjugation of the cyclometalated ligand, the control of the luminescent color of the complexes was achieved. In CH2Cl2 solution, complexes 1a, 1b, 2a, 2b, 3a and 3b emitted phosphorescence peaked at 509, 506, 479, 478, 620 and 618 nm with CIE color coordinates of (0.29, 0.60), (0.27, 0.61), (0.13, 0.37), (0.14, 0.35), (0.67, 0.33) and (0.67, 0.33), respectively. The quantum chemical calculation shows that their emitting light is primarily from 3LC π−π* states of the cyclometalated ligand. Electroluminescent devices with dual light-emitting layers were fabricated and exhibited mild efficiency roll-off.

Rigidity‐Enhanced Narrowband Iridium(III) Complexes with Finely‐Optimized Emission Spectra for Efficient Pure‐Red Electroluminescence

AbstractAttaining phosphorescent materials with narrowband emission is crucial for advancing wide‐color‐gamut organic light‐emitting diode (OLED). Herein, a rigid modification strategy is introduced for iridium(III) complexes to achieve the narrowband red emission with negligible 0–1 peak. By introducing the rigid indolo[3,2,1‐jk]carbazole (ICz) into the cyclometalated ligand, Ir(III) complexes, ICziq‐Ir and ICzqz‐Ir, exhibit pure red phosphorescence with emission peaks at 608 and 613 nm and full widths at half‐maximum (FWHMs) of 37 and 38 nm (0.12 and 0.13 eV) in toluene, respectively. Furthermore, the specific site modification of ICzqz‐Ir greatly suppresses the high‐frequency vibration of the structure, resulting in the narrowband photoluminescent spectrum close to the Gaussian distribution with superior color purity. The OLEDs utilizing ICziq‐Ir and ICzqz‐Ir demonstrate maximum external quantum efficiencies of 21.4 and 17.8% as well as mild efficiency roll‐off. Remarkably, the electroluminescence spectra exhibit similar narrowband red emission with FWHMs of 37 and 43 nm and CIE coordinates of (0.65, 0.35) and (0.66, 0.34), attesting to the excellent color purity of the phosphorescent OLEDs.

Bimetallic H2 Addition and Intramolecular Caryl-H Activation Mediated by an Iron-Zinc Hydride.

Heteronuclear Fe(μ-H)Zn hydride Cp*Fe(1,2-Cy2PC6H4)HZnEt (3) undergoes reversible intramolecular Caryl-H reductive elimination through coupling of the cyclometalated phosphinoaryl ligand and the hydride, giving rise to a formal Fe(0)-Zn(II) species. Addition of CO intercepts this equilibrium, affording Cp*(Cy2PPh)(CO)Fe-ZnEt that features a dative Fe-Zn bond. Significantly, this system achieves bimetallic H2 addition, as demonstrated by the transformation of the monohydride Fe(μ-H)Zn to a deuterated dihydride Fe-(μ-D)2-Zn upon reaction with D2.

Ligand Regulation Strategy to Modulate ROS Nature in a Rhodamine-Iridium(III) Hybrid System for Phototherapy.

The efficacy of photodynamic therapy (PDT) is highly dependent on the photosensitizer features. The reactive oxygen species (ROS) generated by photosensitizers is proven to be associated with immunotherapy by triggering immunogenic cell death (ICD) as well. In this work, we establish a rhodamine-iridium(III) hybrid model functioning as a photosensitizer to comprehensively understand its performance and potential applications in photodynamic immunotherapy. Especially, the correlation between the ROS generation efficiency and the energy level of the Ir(III)-based excited state (T1'), modulated by the cyclometalating (C∧N) ligand, is systematically investigated and correlated. We prove that in addition to the direct population of the rhodamine triplet state (T1) formed through the intersystem crossing process with the assistance of a heavy Ir(III) metal center, the fine-tuned T1' state could act as a relay to provide an additional pathway for promoting the cascade energy transfer process that leads to enhanced ROS generation ability. Moreover, type I ROS can be effectively produced by introducing sulfur-containing thiophene units in C∧N ligands, providing a stronger M1 macrophage-activation efficiency under hypoxia to evoke in vivo antitumor immunity. Overall, our work provides a fundamental guideline for the molecular design and exploration of advanced transition-metal-based photosensitizers for biomedical applications.

Solution-processed orange organic light-emitting diodes based on phosphorescent iridium(III) complexes with coumarin 6 as the main ligand

Four ionic orange phosphorescent iridium(III) complexes (Ir1, Ir2, Ir3, Ir4) were successfully synthesized using coumarin 6 as the cyclometalated ligand and 2,2′-bipyridine (bpy) derivatives with different number and position of methyl groups as the auxiliary ligand. The effects of substituents in the auxiliary ligands on their properties were systematically investigated. These four complexes exhibited orange emission at wavelengths of 590, 588, 587, and 586 nm, respectively, with excellent solubility and remarkable photophysical properties in different solvents. Furthermore, they were further applied in the organic light-emitting diodes (OLEDs) based on solution method. The maximum luminance of the devices based on Ir1/Ir2/Ir3/Ir4 reached 1907.0/932.6/760.8/519.3 cd/m2, with corresponding maximum current efficiency (CE), power efficiency (PE), and external quantum efficiency (EQE) values of 1.56/1.71/1.97/1.52 cd/A, 0.33/0.32/0.35/0.27 lm/W, and 0.77/0.82/0.90/0.72 %, respectively. Although there is room for improvement in the performance of OLEDs, this strategy inspires us to modulate the novel photoluminescent and electroluminescent properties of iridium(III) complexes through rational modifications of their ancillary ligands.

Regioselective C(sp2)-C(sp3) Coupling Mediated by Classical and Rollover Cyclometalation

By taking advantage of a sequence of oxidative addition/reductive elimination reactions, Pt(II) cyclometalated derivatives are able to promote a rare C(sp2)-C(sp3) bond coupling, resulting in the production of novel methyl-substituted pyridines and bipyridines. Starting from 6-phenyl-2,2′-bipyridine, the step-by-step full sequence of reactions has been followed, leading to the unprecedented 3-methyl-6-phenyl-2,2′-bipyridine, which was isolated and fully characterized. The synthesis involves the following steps: (1) rollover cyclometalation to give the starting complex [Pt(N^C)(DMSO)Me]; (2) the synthesis of a more electron-rich complex [Pt(N^C)(PPh3)Me] by the substitution of DMSO with triphenylphosphine; (3) oxidative addition with methyl iodide to give the Pt(IV) complex [Pt(N^C)(PPh3)(Me)2(I)]; (4) iodide abstraction with silver tetrafluoborate to give an unstable pentacoordinate intermediate, which rapidly evolves through a carbon–carbon reductive coupling, forming a new C(sp3)-C(sp2) bond; (5) finally, the extrusion and characterization of the newly formed 3-methyl-6-phenyl-2,2′-bipyridine. The reaction has been therefore extended to a well-known classical cyclometalating ligand, 2-phenylpyridine, demonstrating that the method is not restricted to rollover derivatives. Following the same step-by-step procedure, 2-phenylpyridine was converted to 2-o-tolyl-pyridine, displaying the potential application of the method to the larger family of classical cyclometalated complexes. The application of this protocol may be useful to convert an array of heterocyclic compounds to their methyl- or alkyl-substituted analogs.

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.