Cationic Iridium Complexes Research Articles

Anchoring a Sulfonate Group to an Electron‐Transporting Molecule by an Alkyl Chain and Its Use as the Counter Anion in a Phosphorescent Cationic Iridium Complex

An electron-transporting anion prepared by anchoring a sulfonate group onto an electron-transporting molecule through a flexible alkyl chain and its use as the counter anion in a cationic iridium complex is reported. The flexible alkyl chain improves the solubility of the bulky anion in water or in polar organic solvents. The anion exhibits similar photophysical and electrochemical properties to the parent electron-transporting molecule. Within the complex, the anion does not disturb the phosphorescence of the cation in the solid film. Solution-processed small-molecule organic light-emitting diodes (OLEDs) using the complex as the dopant show superior performances over the reference device using the conventional complex with a PF6 - counter anion. It is revealed that anchoring anionic groups to optoelectronically active molecules with flexible alkyl chains is a feasible approach to develop optoelectronically active anions for assembling ion pairs with advanced optoelectronic properties.

Vacuum-Deposited versus Spin-Coated Emissive Layers for Fabricating High-Performance Blue-Green-Emitting Diodes.

The electroluminescent characteristics of two sublimable cationic iridium(III) complexes that bear the same coordinated iridium(III) cation but different tetraphenylborate-type negative counterions have been investigated. Blue-green-emitting devices were successfully fabricated from these complexes using various preparation processes, namely, spin-coating and vacuum evaporation deposition. Experiments indicated that devices with vacuum-deposited emissive layers showed superior photoelectric properties relative to devices with spin-coated emissive layers, including a maximum current efficiency of 27.91 cd A-1 , an external quantum efficiency of 10.48 %, a power efficiency of 27.73 lm W-1 and the highest luminance of up to 25.34×103 cd m-2 , whereas the turn-on voltages were quite low. The overall device performance surely ranks among the best of phosphorescent organic light-emitting diodes based on ionic transition-metal complexes.

Potassium Binding Adjacent to Cationic Transition-Metal Fragments: Unusual Heterobimetallic Adducts of a Calix[4]arene-Based Thione Ligand.

The synthesis of cationic rhodium and iridium complexes of a bis(imidazole-2-thione)-functionalized calix[4]arene ligand and their surprising capacity for potassium binding are described. In both cases, uptake of the alkali metal into the calix[4]arene cavity occurs despite adverse electrostatic interactions associated with close proximity to the transition-metal fragment [Rh+···K+ = 3.715(1) Å; Ir+···K+ = 3.690(1) Å]. The formation and constituent bonding of these unusual heterobimetallic adducts have been interrogated through extensive solution and solid-state characterization, examination of the host-guest chemistry of the ligand and its upper-rim unfunctionalized calix[4]arene analogue, and use of density functional theory based energy decomposition analysis.

Multifunctional Cationic Iridium(III) Complexes Bearing 2-Aryloxazolo[4,5-f][1,10]phenanthroline (N^N) Ligand: Synthesis, Crystal Structure, Photophysics, Mechanochromic/Vapochromic Effects, and Reverse Saturable Absorption.

A series of 2-aryloxazolo[4,5-f][1,10]phenanthroline ligands (N^N ligands) and their cationic iridium(III) complexes (1-11, aryl = 4-NO2-phenyl (1), 4-Br-phenyl (2), Ph (3), 4-NPh2-phenyl (4), 4-NH2-phenyl (5), pyridin-4-yl (6), naphthalen-1-yl (7), naphthalen-2-yl (8), phenanthren-9-yl (9), anthracen-9-yl (10), and pyren-1-yl (11)) were synthesized and characterized. By introducing different electron-donating or electron-withdrawing substituents at the 4-position of the 2-phenyl ring (1-5), or different aromatic substituents with varied degrees of π-conjugation (6-11) on oxazolo[4,5-f][1,10]phenanthroline ligand, we aim to understand the effects of terminal substituents at the N^N ligands on the photophysics of cationic Ir(III) complexes using both spectroscopic methods and quantum chemistry calculations. Complexes with the 4-R-phenyl substituents adopted an almost coplanar structure with the oxazolo[4,5-f][1,10]phenanthroline motif, while the polycyclic aryl substituents (except for naphthalen-2-yl) were twisted away from the oxazolo[4,5-f][1,10]phenanthroline motif. All complexes possessed strong absorption bands below 350 nm that emanated from the ligand-localized 1π,π*/1ILCT (intraligand charge transfer) transitions, mixed with 1LLCT (ligand-to-ligand charge transfer)/1MLCT (metal-to-ligand charge transfer) transitions. At the range of 350-570 nm, all complexes exhibited moderately strong 1ILCT/1LLCT/1MLCT transitions at 350-450 nm, and broad but very weak 3LLCT/3MLCT absorption at 450-570 nm. Most of the complexes demonstrated moderate to strong room temperature phosphorescence both in solution and in the solid state. Among them, complex 7 also manifested a drastic mechanochromic and vapochromic luminescence effect. Except for complexes 1 and 4 that contain NO2 or NPh2 substituent at the phenyl ring, respectively, all other complexes exhibited moderate to strong triplet excited-state absorption in the spectral region of 440-750 nm. Moderate to very strong reverse saturable absorption (RSA) of these complexes appeared at 532 nm for 4.1 ns laser pulses. The RSA strength followed the trend of 7 > 11 > 9 > 3 > 2 ≈ 4 > 5 ≈ 10 ≈ 6 ≈ 8 > 1. The photophysical studies revealed that the different 2-aryl substituents on the oxazole ring impacted the singlet and triplet excited-state characteristics dramatically, which in turn notably influenced the RSA of these complexes.

Synthesis, characterization and photophysical properties of a new Cu2+ selective phosphorescent sensor

A new Cu(II) selective phosphorescent sensor based on a cationic iridium(III) complex was synthesized and characterized. Compared with other commonly coexisting metal ions, the Ir(III) complex displayed significant phosphorescence quenching for detecting Cu2+ with a 1:1 stoichiometry in MeOH/H2O (1:1, v/v) solution. Upon addition of Cu2+, the rapid quenching of emission intensity provided a sensitive method for detection of Cu2+. The corresponding detection limit was determined to be 7.6 × 10−8 M and the association constant between the Ir(III) complex and Cu2+ was calculated to be 0.31 × 105 M−1. Luminescence imaging experiments demonstrated that this Ir(III) complex was cell permeable and suitable for monitoring intracellular Cu2+ in living Hela cells by confocal microscopy.

Application of an orange–yellow emitting cationic iridium(III) complex in GaN-based warm white light-emitting diodes

An orange–yellow emitting cationic iridium(III) complex [(ptpy)2Ir(BCP)]PF6 (ptpy: 2-(p-tolyl)pyridine; BCP: bathocuproine) was synthesized. [(ptpy)2Ir(BCP)]PF6 exhibited high thermal stability with the thermal decomposition temperature (T d) of 375 °C, with the temperature increasing from 20 to 100 °C, the photoluminescent intensity of [(ptpy)2Ir(BCP)]PF6 decreased to 79.9%. It can be efficiently excited by blue light (λmax = 457 nm) of GaN chip, and a series of GaN-based light-emitting diodes (LEDs) were fabricated by using it as phosphors blended in silicone at different blending concentrations. At 1.0 wt.%, a cold white LED was obtained, the corresponding color rendering index (CRI) was 77.1, correlated color temperature (CCT) was 6278 K, luminous efficiency (η L) was 68.4 lm W−1, and Commission Internationale de L’Eclairage (CIE) value was (0.32, 0.25). At 2.0 wt.%, a neutral white LED was obtained, the corresponding CRI was 74.2, CCT was 4737 K, η L was 75.4 lm W−1, and CIE value was (0.34, 0.27). At 2.5, 3.0, 4.0 and 5.0 wt.%, four warm white LEDs were obtained, among them, the maximum η L was 85.8 lm W−1 (at 4.0 wt.%), the maximum CRI was 73.7 (at 2.5 wt.%), their CCT changed between 3410 K and 2328 K, the CIE values were (0.37, 0.30), (0.41, 0.34), (0.46, 0.39) and (0.49, 0.41) respectively. The results suggest [(ptpy)2Ir(BCP)]PF6 is a promising phosphor candidate for white LEDs, especially for warm white LEDs.

Electronic nature of the emitting triplet in SF5-substituted cationic Ir(III) complexes

A theoretical density functional theory study has been performed on a family of cationic iridium(III) complexes of the form [Ir(C^N)2(dtBubpy)]+ (dtBubpy = 4,4′-di-tert-butyl-2,2′-bipyridine), that incorporate 2-phenylpyridine (1, 2) and 1-phenylpyrazole (3, 4) cyclometallating C^N ligands functionalized with SF5 groups. The goal is to investigate the effect that the inclusion of SF5 groups in meta (1, 3) and para position (2, 4) with respect to the Ir–C bond has on the electronic nature of the emitting triplet state and the emission wavelength. The attachment of the electron-withdrawing groups induces the stabilization of the molecular orbitals localized on the C^N ligands and, in particular, of the highest-occupied molecular orbital (HOMO). This stabilization enlarges the energy gap between the HOMO and the lowest-unoccupied molecular orbital (LUMO), and shifts to higher energies the metal-to-ligand charge transfer (MLCT) triplet described by the HOMO → LUMO excitation. As a consequence, a triplet state of ligand-centered (LC) nature becomes the lowest-energy triplet excited state for all the four complexes. For complexes 1 and 2, the state is centered on the C^N ligands (3LCC^N) and the introduction of the SF5 groups in para causes a greater effect than their insertion in meta. Substitution of the pyridine ring by a pyrazole ring in complexes 3 and 4 destabilizes the 3LCC^N states and the lowest-energy triplet involves the diimine N^N ligand (3LCN^N). Theoretical calculations therefore predict that the electronic nature of the lowest-lying triplet drastically changes in passing from the unsubstituted complex (3MLCT) to complexes 1 and 2 (3LCC^N) and to complexes 3 and 4 (3LCN^N). These changes help to rationalize the aspect of the emission spectra and the shift to the blue of the emission wavelength. The appearance of low energy 3LC triplets centered on the ancillary ligand, whose energy is hardly affected by changes in the C^N ligands structure, constitutes a limit to blue-shift the phosphorescence emission in this kind of complexes.

High-color-rendering-index white polymer light-emitting electrochemical cells based on ionic host-guest systems: Utilization of blend films of blue-fluorescent cationic polyfluorenes and red-phosphorescent cationic iridium complexes

Abstract The authors present high-color-rendering-index (CRI) white polymer light-emitting electrochemical cells (PLECs) based on ionic host-guest systems. PLECs were fabricated with blend films composed of a blue fluorescent cationic π-conjugated polymer, poly(9,9-bis[6′-(N,N,N,-trimethylammonium)hexyl]fluorine-co-alt-1,4-phenylene)bromide (PFN+Br−), used as a host, and a red phosphorescent cationic iridium complex, [Ir(ppy)2(biq)]+(PF6)− (where (ppy)− = 2-phenylpyridinate and biq = 2,2′-biquinoline), used as a guest. By optimizing the composition of PFN+Br− and [Ir(ppy)2(biq)]+(PF6)− in the active layers, white light emission with Commission Internationale de l'Eclairage (CIE) coordinates of (x = 0.28, y = 0.31) and a very high CRI of 95.8 was achieved through mixing of blue and red light at an applied voltage of 4.0 V. The white light emissions were obtained at a low [Ir(ppy)2(biq)]+(PF6)− concentration (PFN+Br−:[Ir(ppy)2(biq)]+(PF6)− = 1:0.01 (mass ratio)), showing that [Ir(ppy)2(biq)]+(PF6)− acts as a suitable energy acceptor. The emission mechanism of the ionic host-guest PLECs can be explained by Forster resonance energy transfer (FRET) and Dexter energy transfer (DET) from the excited PFN+Br− to [Ir(ppy)2(biq)]+(PF6)−. Utilization of ionic host-guest PLECs is a very promising method for realizing white light-emitting devices with very high CRI.

Yellow light-emitting electrochemical cells utilizing iridium(III) phenanthroimidazole complexes

ABSTRACTThe utilization of cationic iridium complexes in light-emitting electrochemical cells (LECs) have drawn remarkable attention over other metal complexes, because of their large ligand-field splitting energies (LFSEs). Herein, we report two new cationic iridium complexes using phenanthroimidazole derivatives as ancillary ligand, namely, [Ir(ppy)2(ptpphim)]PF6 (complex 1) and [Ir(meppy)2(ptpphim)]PF6 (complex 2). The photoluminescence (PL) emission spectra in acetonitrile solution show yellow emission for complex 1 (540 nm) and complex 2 (561 nm). LECs were fabricated and emitted yellow light with the CIE coordinates of (0.46, 0.52) and (0.49, 0.50) for complex 1 and 2, respectively. Complex 1 shows the higher current efficiency of 0.56 cd A−1 than complex 1 (0.26 cd A−1) due to the lower current current density of the former. The use of phenanthroimidazole with a bulky tetraphenyl methane group reduce the intermolecular interactions between the iridium complexes, thereby enhancing device performances.

Iridium-catalyzed sp3 C–H Alkylation of 3-Carbonyl-2-(alkylamino)pyridines with Alkenes

Iridium-catalyzed C–H alkylation of 3-carbonyl-2-(alkylamino)pyridines via secondary sp3 C–H activation adjacent to the nitrogen atom, with terminal alkenes proceeded to give the corresponding α-secondary amines in high yields. The reaction was efficiently catalyzed by a cationic iridium complex coordinated with 1,5-cyclooctadiene.

Synthesis, physicochemical properties, thermal analysis and biological application of phosphorescent cationic iridium(III) complexes

Cyclometalating iridium(III) complexes with formula, [Ir(cpy)2(biim)Cl] 1, [Ir(cpy)2(bpy)Cl] 2 and [Ir(cpy)2(dppe)Cl] 3 (where, cpy=9-(pyridine-2-yl)-9H-carbazole, biim=biimidazole, bpy=2,2′-bipyridine, dppe=1,2-bis(diphenylphosphino)ethane) were synthesized and characterized by elemental analysis, 1H, 13C NMR, and ESI-Mass spectral studies. The complex 1–3 show their emissions in green emitting region (λPL,max=536–580nm), and the emission maxima can be tuned by changing the ancillary ligand. The phosphorescent line shape indicates that the emissions originate predominantly from 3MLCT states with little admixture of ligand-based 3(π-π∗) excited states. These complexes exhibited biexponential phosphorescence decays with relatively short lifetimes of 0.40–12.35µs in solution state at room temperature and the relaxation dynamics of 1–3 are O2 dependent. The electrochemical and thermal properties were systematically evaluated. Binding of these complexes (1–3) with calf thymus DNA was investigated by UV–Vis, fluorescence, circular dichroic spectroscopy, viscosity measurements and computer aided molecular docking studies. The binding constant of complexes (1–3) with ct-DNA obtained by UV–Vis absorption studies were 2.28×104, 1.98×104 and 2.98×104M−1, respectively. The result indicated that the complexes (1–3) were able to bind to DNA with different binding affinity in the order: 3>1>2. Complexes (1–3) also exhibit a good binding propensity to bovine serum albumin (BSA). Gel electrophoresis assay demonstrated that complexes (1–3) cannot promote the cleavage ability of the pBR322 plasmid DNA or plasmid pBluescript II KS+ DNA or pUC19 DNA in the presence of the reducing agent 3-mercaptopropionic acid. The cytotoxicity studies of complexes 1–3 were tested in vitro on in human cervical cancer cell line (HeLa) and they found to be active. We propose that the phosphorescent iridium(III) complexes (1–3) are possible candidates for the green phosphors in organic light emitting diodes (OLEDs) applications as well as better anticancer agents.

Phosphorescent Cationic Iridium(III) Complexes with 1,3,4-Oxadiazole Cyclometalating Ligands: Solvent-Dependent Excited-State Dynamics

To elucidate the nature of low-lying triplet states and the effect of ligand modifications on the excited-state properties of functional cationic iridium complexes, the solvent-dependent excited-state dynamics of two phosphorescent cationic iridium(III) complexes, namely [Ir(dph-oxd)2(bpy)]PF6 (1) and [Ir(dph-oxd)2(pzpy)]PF6 (2), were investigated by femtosecond and nanosecond transient absorption spectroscopy. Upon photoexcitation to the metal-to-ligand charge-transfer (MLCT) states, the excited-state dynamics shows a rapid process (τ=0.7−3 ps) for the formation of solvent stabilized 3MLCT states, which significantly depends on the solvent polarity for both 1 and 2. Sequentially, a relatively slow process assigned to the vibrational cooling/geometrical relaxation and a long-lived phosphorescent emissive state is identified. Due to the different excited-state electronic structures regulated by ancillary ligands, the solvation-induced stabilization of the 3MLCT state in 1 is faster than that in 2. The present results provide a better sight of excited-state relaxation dynamics of ligand-related iridium(III) complexes and solvation effects on triplet manifolds.

Warm White Light-Emitting Diodes Based on a Novel Orange Cationic Iridium(III) Complex

A novel orange cationic iridium(III) complex [(TPTA)2Ir(dPPOA)]PF6 (TPTA: 3,4,5-triphenyl-4H-1,2,4-triazole, dPPOA: N,N-diphenyl-4-(5-(pyridin-2-yl)-1,3,4-oxadiazol-2-yl)aniline) was synthesized and used as a phosphor in light-emitting diodes (LEDs). [(TPTA)2Ir(dPPOA)]PF6 has high thermal stability with a decomposition temperature (Td) of 375 °C, and its relative emission intensity at 100 °C is 88.8% of that at 25°C. When only [(TPTA)2Ir(dPPOA)]PF6 was used as a phosphor at 6.0 wt % in silicone and excited by a blue GaN (GaN: gallium nitride) chip (450 nm), an orange LED was obtained. A white LED fabricated by a blue GaN chip (450 nm) and only yellow phosphor Y3Al5O12:Ce3+ (YAG:Ce) (1.0 wt % in silicone) emitted cold white light, its CIE (CIE: Commission International de I’Eclairage) value was (0.32, 0.33), color rendering index (CRI) was 72.2, correlated color temperature (CCT) was 6877 K, and luminous efficiency (ηL) was 128.5 lm∙W−1. Such a cold white LED became a neutral white LED when [(TPTA)2Ir(dPPOA)]PF6 was added at 0.5 wt %; its corresponding CIE value was (0.35, 0.33), CRI was 78.4, CCT was 4896 K, and ηL was 85.2 lm∙W−1. It further became a warm white LED when [(TPTA)2Ir(dPPOA)]PF6 was added at 1.0 wt %; its corresponding CIE value was (0.39, 0.36), CRI was 80.2, CCT was 3473 K, and ηL was 46.1 lm∙W−1. The results show that [(TPTA)2Ir(dPPOA)]PF6 is a promising phosphor candidate for fabricating warm white LEDs.

Fluorine-free blue-emitting cationic iridium complexes with oxadiazole-type cyclometalating ligands and their use in light-emitting electrochemical cells

Fluorine-free, blue-emitting cationic iridium complexes, namely [Ir(Tipr-dphoxd)2(bpy)]PF6 (1) and [Ir(Tipr-dphoxd)2(pzpy)]PF6 (2), which use 2-phenyl-5-(2,4,6-triisopropylphenyl)-1,3,4-oxadiazole (Tipr-dphoxd) as the cyclometalating ligand (CΛN) and 2,2’-bipyridine (bpy) or 2-(1H-pyrazol-1-yl)pyridine (pzpy) as the ancillary ligands (NΛN), have been synthesized and fully characterized. In solution, complex 1 emits efficient blue-green light centered at 505 nm with notable charge-transfer (CT) (Ir/CΛN → NΛN) character; while in the lightly doped film, it emits efficient sky-blue light peaked at 474 and 502 nm with much CΛN-centered 3π-π∗ character. In both solution and films, complex 2 always emits sky-blue light peaked around 468 nm and 500 nm with dominant CΛN-centered 3π-π∗ character. The sky-blue light emission from complexes 1 and 2 is among the bluest reported for fluorine-free, blue-emitting cationic iridium complexes. Theoretical calculations reveal that complex 1 bears energetically close-lying CT and CΛN-centered 3π-π∗ states, and its emission can arise from either or both of them; while for complex 2, its emission always comes from the lowest-lying CΛN-centered 3π-π∗ state. Because the CT state contributes considerably to the emission of complex 1, complex 1 exhibits more rapid radiative decays, higher luminescent efficiencies and shorter excited-state lifetimes than complex 2 in both the solution and lightly doped film. Complexes 1 and 2 have been tested as emitting materials in solid-state light-emitting electrochemical cells (LECs), with red-shifted electroluminescence compared to the photoluminescence. The green-yellow LEC based on complex 1 and the blue-green LEC based on complex 2 show peak current efficiencies of 12.4 and 5.0 cd A−1, respectively.

Tuning the Ground State and Excited State Properties of Monocationic Iridium(III) Complexes by Varying the Site of Benzannulation on Diimine Ligand.

Extending π-conjugation of the diimine ligand (N^N ligand) via benzannulation is a common way to tune the absorption and emission energies of cationic iridium(III) complexes. However, it can cause either a red- or blue-shift of the absorption and emission bands depending on the site of benzannulation. To understand the mechanism of changes in optical transitions upon benzannulation on the diimine ligand, a series of new cationic iridium(III) complexes [Ir(dppi)2(N^N)]PF6 (1-6) (where dppi =1,2-diphenylpyreno[4,5-d]imidazole; N^N = 2-(pyridin-2-yl)quinoline (1), 2-(pyridin-2-yl)[7,8]benzoquinoline (2), 2,2'-bisquinoline (3), 2-(quinolin-2-yl)[7,8]benzoquinoline (4), 2-(pyridin-2-yl)[6,7]benzoquinoline (5), 2-(quinolin-2-yl)[6,7]benzoquinoline (6)) containing diimine ligand with varied degrees of π-conjugation via benzannulation at different sites of the 2-(pyridin-2-yl)quinoline ligand were synthesized. Experimental results and density functional theory (DFT) calculations revealed that benzannulation at the 6,7-position of quinoline and/or the 5',6'-position of pyridine (3, 5, and 6) induced red-shifts in their absorption and emission bands with respect to the parent complex 1; while benzannulation at the 7,8-position of quinoline resulted in blue-shifts (2 vs 1 and 4 vs 3). This phenomenon was rationalized by the symmetry of the frontier molecular orbitals at the site of benzannulation, which stabilized or destabilized the lowest unoccupied molecular orbital (LUMO) upon interactions with 1,3-butadiene, while the energy of the highest occupied molecular orbital (HOMO) remained nearly the same. This discovery would enable a rational design of organic or organometallic compounds that have predetermined absorption and emission energies.

Tuning the photophysical properties of cationic Ir(III) complexes containing oxazoline-based ancillary ligand

ABSTRACTTwo new cationic iridium(III) complexes were synthesized and characterized using oxazoline based ancillary ligand, namely, [Ir(dfppy)2(ibpo)]PF6 (Complex 1) and [Ir(ppz)2(ibpo)]PF6 (Complex 2), where dfppy is 2-(2,4-difluorophenyl)pyridine, ppz is 1-phenylpyrazole, and ibpo is (S,S)-2,2’-isopropylidene-bis(4-phenyl-2-oxazoline). The absorption, emission, and cyclic voltammetry of the complexes were investigated. Photoluminescence (PL) emission spectra of the complexes in acetonitrile solutions were measured which displays intense photoluminescence maxima in blue (Complex 1) and green (Complex 2) region of the visible spectrum. Light-emitting electrochemical cells (LECs) were fabricated utilizing these complexes and investigated their electroluminescent properties. The devices based on both complexes exhibit green electroluminescence with Commission Internationale de l'Eclairage (CIE) coordinates of (0.46, 0.49) and (0.38, 0.50) for Complexes 1 and 2, respectively.

Exploring Site Selectivity of Iridium Hydride Insertion into Allylic Alcohols: Serendipitous Discovery and Comparative Study of Organic and Organometallic Catalysts for the Vinylogous Peterson Elimination

The vinylogous Peterson elimination of a broad range of primary, secondary, and tertiary silylated allylic alcohols by two distinct and complementary catalytic systems—a cationic iridium complex and a Bronsted acid—is reported. These results are unexpected. Nonsilylated substrates are typically isomerized into aldehydes and silylated allylic alcohols into homoallylic alcohols with structurally related iridium complexes. Although several organic acids and bases are known to promote the vinylogous Peterson elimination, the practicality, mildness, functional group tolerance, and generality of both catalysts are simply unprecedented. Highly substituted C═C bonds, stereochemically complex scaffolds, and vicinal tertiary and quaternary (stereo)centers are also compatible with the two methods. Both systems are stereospecific and enantiospecific. After optimization, a vast number of dienes with substitution patterns that would be difficult to generate by established strategies are readily accessible. Importantly,...

Preparation of Peapod Polymer via the Supramolecular Chain Formation by Tris(spiroborate) Twin Bowl

Successive guest-containing tubular polymer was prepared by the olefin metathesis polymerization of tris(spiroborate) twin bowl after the formation of supramolecular polymer. The cationic iridium(III) complexes were topologically fixed inside the polymer to form a peapod-like structure. The polymer was evaluated by SEC, ICP-AES, and DLS analyses, and string-like structures were found in the AFM observation of the peapod polymer.

Di-/trinuclear cationic Ir(III) complexes: Design, synthesis and application for highly sensitive and selective detection of TNP in aqueous solution

Novel di- and trinuclear cationic iridium(III) complexes with flexible chain functionalized triazole–pyridine moieties as bridging ligands, namely DC-Ir and TC-Ir, were successfully synthesized and their photophysical and electrochemical properties studied. Despite DC-Ir and TC-Ir have different numbers of iridium(III) cores, the almost identical emissions in both solutions and aggregation states were observed. Theoretical calculations were performed to investigate their electronic structures and rationalize the photophysical and electrochemical behaviors. Compared with the emission in the solution, they exhibit enhanced photoluminescence in the aggregation states. Benefiting from the high emission in aqueous solution, DC-Ir and TC-Ir were employed as the “turn-off” sensors to detect the explosives. The results reveal that DC-Ir and TC-Ir show fast and highly sensitive and selective detection towards 2,4,6-trinitrophenol (TNP) owing to the efficient photo-induced electron transfer as well as the strong electrostatic interaction.

Lessons learned in tuning the optoelectronic properties of phosphorescent iridium(iii) complexes.

This perspective illustrates our approach in the design of heteroleptic cationic iridium(iii) complexes for optoelectronic applications, especially as emitters in electroluminescent devices. We discuss changes in the photophysical properties of the complexes as a consequence of modification of the electronics of either the cyclometalating (C^N) or the ancillary (N^N) ligands. We then broach the impact on these properties as a function of modification of the structure of both types of ligands. We explain trends in the optoelectronic behaviour of the complexes using a combination of rationally designed structure-property relationship studies and theoretical modelling that serves to inform subsequent ligand design. However, we have found cases where the design paradigms do not always hold true. Nevertheless, all these studies contribute to the lessons we have learned in the design of heteroleptic cationic phosphorescent iridium(iii) complexes.