Intraligand Charge Transfer Research Articles

A new heteroleptic phosphorescent cuprous complex supported by a BINAP ligand: synthesis, structure, luminescence properties and theoretical analyses

Luminescent cuprous complexes are an important class of coordination compounds due to their relative abundance, low cost and ability to display excellent luminescence. The heteroleptic cuprous complex solvate rac-(acetonitrile-κN)(3-aminopyridine-κN)[2,2'-bis(diphenylphosphanyl)-1,1'-binaphthyl-κ2P,P']copper(I) hexafluoridophosphate dichloromethane monosolvate, [Cu(C5H6N2)(C2H3N)(C44H32P2)]PF6·CH2Cl2, conventionally abbreviated as [Cu(3-PyNH2)(CH3CN)(BINAP)]PF6·CH2Cl2, (I), where BINAP and 3-PyNH2 represent 2,2'-bis(diphenylphosphanyl)-1,1'-binaphthyl and 3-aminopyridine, respectively, is described. In this complex solvate, the asymmetric unit consists of a cocrystallized dichloromethane molecule, a hexafluoridophosphate anion and a complete racemic heteroleptic cuprous complex cation in which the cuprous centre, in a tetrahedral CuP2N2 coordination, is coordinated by two P atoms from the BINAP ligand, one N atom from the 3-PyNH2 ligand and another N atom from a coordinated acetonitrile molecule. The UV-Vis absorption and photoluminescence properties of this heteroleptic cuprous complex have been studied on polycrystalline powder samples, which had been verified by powder X-ray diffraction before recording the spectra. Time-dependent density functional theory (TD-DFT) calculations and a wavefunction analysis reveal that the orange-yellow phosphorescence emission should originate from intra-ligand (BINAP) charge transfer mixed with a little of the metal-to-ligand charge transfer 3(IL+ML)CT excited state.

Breaking the barrier: an osmium photosensitizer with unprecedented hypoxic phototoxicity for real world photodynamic therapy.

Hypoxia presents a two-fold challenge in the treatment of cancer, as low oxygen conditions induce biological changes that make malignant tissues simultaneously more aggressive and less susceptible to standard chemotherapy. This paper reports the first metal-based photosensitizer that approaches the ideal properties for a phototherapy agent. The Os(phen)2-based scaffold was combined with a series of IP-nT ligands, where phen = 1,10-phenanthroline and IP-nT = imidazo[4,5-f][1,10]phenanthroline tethered to n = 0-4 thiophene rings. Os-4T (n = 4) emerged as the most promising complex in the series, with picomolar activity and a phototherapeutic index (PI) exceeding 106 in normoxia. The photosensitizer exhibited an unprecedented PI > 90 (EC50 = 0.651 μM) in hypoxia (1% O2) with visible and green light, and a PI > 70 with red light. Os-4T was also active with 733 nm near-infrared light (EC50 = 0.803 μM, PI = 77) under normoxia. Both computation and spectroscopic studies confirmed a switch in the nature of the lowest-lying triplet excited state from triplet metal-to-ligand charge transfer (3MLCT) to intraligand charge transfer (3ILCT) at n = 3, with a lower energy and longer lifetime for n = 4. All compounds in the series were relatively nontoxic in the dark but became increasingly phototoxic with additional thiophenes. These normoxic and hypoxic activities are the largest reported to date, demonstrating the utility of osmium for phototherapy applications. Moreover, Os-4T had a maximum tolerated dose (MTD) in mice that was >200 mg kg-1, which positions this photosensitizer as an excellent candidate for in vivo applications.

New scu topological MOF based on azolyl-carboxyl bifunctional linker: Gas adsorption and luminescence properties

The self-assembly of Zn2+ ion and an azolyl-carboxyl bifunctional ligand, 4,6-bis(triazol-1-yl)isophthalic acid (H2btzip), give rise to one three-dimensional (3D) porous metal-organic framework (MOF), [Zn(btzip)(H2O)0.5]·H2O (1). The MOF shows a rare (4,8)-connected scu net containing 1D channels, based on 4-connecetd ligands and 8-connected [Zn(COO)2(H2O)] dimers. Owing to the decoration of uncoordinated N atoms in porous walls, 1 can selectively capture CO2 molecules over CH4 with high adsorption heat and considerable selectivity. The different adsorption sites for CO2 in 1 were deeply explored by simulations. In addition, 1 also displays strong solid-state luminescence that is from the intraligand charge transfer.

Design of a pillar-layered metal-organic framework as high-performance fluorescence sensor for nitroaromatic compounds

A ternary luminescent cadmium-triazolate-carboxylate framework, [(CH3)2NH2][Cd(1245-BTC)0.5(3S-TRZ)] (SNNU-111, 1245-BTC ​= ​1245-benzenetetra- carboxylic acid, 3S-TRZ ​= ​3-mercaptotriazole) was successfully designed in this work. X-ray single crystal diffraction results show that Cd atoms are connected by 3S-TRZ ligands to form 2D wave-like layers, which are further extended by 1245-BTC linkers to generate the 3D pillar-layered architecture of SNNU-111. Solid-state and solution photoluminescence both showed that the emissions of SNNU-111 was ascribed to the intraligand charge transfer in 1245-BTC. Benefited from this process, SNNU-111 MOF can act as excellent fluorescence sensor to quantitatively detect involved nitroaromatics including nitrobenzene (NB), 1,2-dinitrobenzene (1,2-DNB), 1,3-dinitrobenzene (1,3-DNB), 2,4-dinitrotoluene (DNT), 2,4,6-trinitrotoluene (TNT), and 2,4,6-trinitrophenol (PA) through the fluorescence quenching. The corresponding quenching coefficient (Ksv) values are of 1.0 ​× ​104-1.7 ​× ​104 ​M−1, which surpass the performance of many reported sensors. Specially, the Ksv value of 1.2 ​× ​104 ​M−1 for NB is nearly the highest one among all MOF sensors up to now. On the other hand, SNNU-111 sensor also exhibits good sensitivity to nitroaromatics with the detection limits as low as 1.61–5.77 ​ppm. Overall, the definite pillar-layered structure, fast response and high sensitivity make SNNU-111 a promising fluorescent sensor to detect nitroaromatic compounds.

Picolinate-appended tacn complexes for bimodal imaging: Radiolabeling, relaxivity, photophysical and electrochemical studies

Based on our previous works involving two 1,4,7-triazacyclononane (tacn)-based ligands Hno2py1pa (1-Picolinic acid-4,7-bis(pyridin-2-ylmethyl)-1,4,7-triazacyclononane) and Hno1pa (1-Picolinic acid-1,4,7-triazacyclononane), we report here the synthesis of analogues bearing picolinate-based π-conjugated ILCT (Intra-Ligand Charge Transfer) transition antenna (HL1, HL2), using regiospecific N-functionalization of the tacn skeleton and their related transition metal complexes (e.g. Cu2+, Zn2+ and Mn2+). Coordination properties as well as their photophysical and electrochemical properties were investigated in order to quantify the impact of such antenna on the luminescent or relaxometric properties of the complexes. The spectroscopic properties of the targeted ligands and metal complexes have been studied using UV–Vis absorption and fluorescence spectrocopies. While the zinc complex formed with HL1 possesses a moderate quantum yield of 5%, complexation of Cu2+ led to an extinction of the luminescence putatively attributed to a photo-induced electron transfer, as supported by spectroscopic and electrochemical evidences. The [Mn(L2)]+ complex is characterized by a fluorescence quantum yield close to 8% in CH2Cl2. The potential interest of such systems as bimodal probes has been assessed from radiolabeling experiments conducted on HL1 and 64Cu2+ as well as confocal microscopy analyses and from relaxometric studies carried out on the cationic [Mn(L2)]+ complex. These results showed that HL1 can be used for radiolabeling, with a radiochemical conversion of 40% in 15 min at 100 °C. Finally, the relaxivity values obtained for [Mn(L2)]+, r1p = 4.80 mM−1·s−1 and r2p = 8.72 mM−1·s−1, make the Mn(II) complex an ideal candidate as a probe for Magnetic Resonance Imaging.

Synthesis, characterization and DFT studies of complexes bearing [Re(CO)3]+ core and reactivity towards cyanide ion

Mononuclear rhenium(I) complexes having fac-[Re(CO)3]+ core of general formula fac-[Re(CO)3(L)Cl] have been synthesized in excellent yield by reacting [Re(CO)5Cl] with L1 and L2in a ratio of 1:1 in toluene under inert atmosphere. Here L1 and L2 are N-((quinolin-2-yl)methylene)-9H-fluoren-2-amine and N-((anthracen-10-yl)methylene)quinolin-8-amine respectively. Spectroscopic measurements such as NMR, ESI-MS and IR spectroscopy were used to ensure the formations of desired complexes. Molecular structures of fac-[Re(CO)3(L1)Cl] and fac-[Re(CO)3(L2)Cl] were confirmed by single-crystal X-ray diffraction. The ligands are emissive whereas the metal complexes are weak emitter. A remarkable change in absorption as well as emission behavior was observed in complex 2 upon addition of cyanide ion. Interruption in intraligand charge transfer in complex 2 is the probable reason for the obvious change in spectral response of the same. 1H NMR titration was performed as the evidence of the previously stated fact. The ground and excited-state geometries, absorption properties of rhenium(I) complexes were examined by DFT and TDDFT methods. The natural transition orbital (NTO) and analysis reveal the nature of excitations.

Energy transfer in ternary TbEDTA chelates with a series of dipicolinic acid derivatives

The energy transfer in lanthanoid chelates was studied using the ternary TbEDTA (EDTA = ethylenediaminetetraacetic acid) chelates with several dipicolinic acid derivatives (pyridine-2,6-dicarboxylic acid (L1, dpa), 4-(9H-fluoren-3-yl)pyridine-2,6-dicarboxylic acid (L2), 4-(dibenzo [b,d]furan-2-yl)pyridine-2,6-dicarboxylic acid (L3), 4-(dibenzo [b,d]thiophen-2-yl)pyridine-2,6-dicarboxylic acid (L4) and 4-(9H-carbazol-3-yl)pyridine-2,6-dicarboxylic acid (L5)) and spectroscopic methods (absorption and luminescence spectroscopy and the effect of argon treatment and temperature on luminescence lifetime(s)). The results revealed that the ILCT (intra-ligand charge transfer) state is inefficient in exciting the Tb(III) ion and the emissive states of the ligands, as well as the triplet states, act as quenching states by receiving energy back transfer from the Tb(III) ion. The stability constants for these ternary complexes were also determined.

A water-soluble 1,8-naphthyridine-based imidazolium molecular gripper for fluorescence sensing and discriminating of GMP

A selective receptor for sensing and discriminating of GMP is useful not only in the energy metabolism but also in the processes of DNA replication and transcription-related to GMP; such a receptor is presently rare especially in a pure water environment. Herein, a novel 1,8-naphthyridine-based tripodal imidazolium gripper-like molecular served as a “turn-on” fluorescent receptor (TINP) was designed and synthesized for selective sensing and discriminating GMP from structurally similar GNPs (N = D and T) and XMPs (X = U, T, A, and C) in 100% aqueous solution. TINP consists of 1,8-naphthyridines and imidazolium cations. 2-acetylamino-1,8-naphthyridine was chosen as fluorophore and tri-hydrogen bonds interactions sites for the nucleobase guanine. Imidazolium cations were identified as the phosphate part receiving moieties and communicators, while the three imidazolium cations also served as indispensable water-soluble parts. GMP caused a remarkable fluorescence enhancement (ca. 6.5-fold) with a quantum yield (Φf) of 0.26 at 399 nm, displaying an efficient “turn on” behavior. The sensing mechanisms and fluorescence response were explained by Job's plot, NMR spectroscopic analysis, and theoretical calculations. The “turn-on” fluorescent property for GMP can be attributed to photoinduced electron transfer (PeT) transitions with some mixed intraligand charge-transfer (ILCT) transitions. Finally, the preliminary results of cell experiments show that the receptor can be applied for the imaging of GMP in living mammalian cells.

Fast-Response, Highly Air-Stable, and Water-Resistant Organic Photodetectors Based on a Single-Crystal Pt Complex.

Organic semiconductors demonstrate several advantages over conventional inorganic materials for novel electronic and optoelectronic applications, including molecularly tunable properties, flexibility, low-cost, and facile device integration. However, before organic semiconductors can be used for the next-generation devices, such as ultrafast photodetectors (PDs), it is necessary to develop new materials that feature both high mobility and ambient stability. Toward this goal, a highly stable PD based on the organic single crystal [PtBr2 (5,5'-bis(CF3 CH2 OCH2 )-2,2'-bpy)] (or "Pt complex (1o)") is demonstrated as the active semiconductor channel-a material that features a lamellar molecular structure and high-quality, intraligand charge transfer. Benefitting from its unique crystal structure, the Pt-complex (1o) device exhibits a field-effect mobility of ≈0.45 cm2 V-1 s-1 without loss of significant performance under ambient conditions even after 40 days without encapsulation, as well as immersion in distilled water for a period of 24 h. Furthermore, the device features a maximum photoresponsivity of 1 × 103 A W-1 , a detectivity of 1.1 × 1012 cm Hz1/2 W-1 , and a record fast response/recovery time of 80/90 µs, which has never been previously achieved in other organic PDs. These findings strongly support and promote the use of the single-crystal Pt complex (1o) in next-generation organic optoelectronic devices.

Synthesis, Characterization and Molecular Docking Studies of Mn (II) Complex of Sulfathiazole

Sulfathiazole (SFTZ) is an antibacterial drug that contains the organosulfur compounds. It is used as a short-acting sulfa drug. The metal complexes of sulfa-drug have gained considerable importance due to their pronounced biological activity. The sulfa-drugs have received great attention because of their therapeutic applications against bacterial infections. Mn(II) complex of sulfathiazole was synthesized by the reaction of sulfathiazole with MnCl2.4H2O. The Mn (II) complex was characterized based on UV, IR, 1H NMR Spectroscopy and x-ray powder diffraction. The electronic spectrum of the ligand showed intra charge transfer which was assigned to the chromophores present in the ligand, while that of the complex suggested intra ligand charge transfer (ILCT) and ligand to metal charge transfer (LMCT). In the IR spectrum of sulfathiazole, the N-H stretch of SO2NH appeared at 3255.23 cm-1. In the IR spectrum of the metal complex, this band was absent. This suggested the deprotonation of the N-H of SO2NH during the complexation reaction. This showed that sulfathiazole acted as a monodentate ligand. 1H NMR spectrum of [Mn(SFTZ)] complex showed the involvement of the nitrogen atom of SO2NH. The crystal structure of [Mn(SFTZ)] complex belongs to monoclinic system, space group P1, with cell parameters of a= 4.519Å, b = 8.704Å, c = 12.608Å, V = 493.5Å3, β = 95.69º. Molecular docking suggested that the ligand/complex bonded effectively with the E.coli and S.aureus because their global binding energies were negative. The binding interactions of ligand/complex with E. coli and S. aureus were predicted. Molecular docking predicted the feasibility of the biochemical reactions before experimental investigation. It was concluded that sulfathiazole behaved as a monodentate ligand towards Mn (II) ion. The binding energy and interaction of [Mn(SFTZ)] with E.coli and S. aureus have also shown that inhibition of the bacterial species is feasible. The mechanism of action of [Mn(SFTZ)] with E. coli and S. aureus is now well understood.

Electronic Communication within Flexible Bisdithiolene Ligands Bridging Molybdenum Centers

Bimetallic molybdenum dithiolene complexes involving two flexible ditopic conjugated linkers have been synthesized and characterized by electrochemistry, spectroelectrochemistry, and single crystal X-ray diffraction. The electrochemical investigations evidence that the two metallic bisdithiolene moieties are electronically coupled in the monocationic state. DFT and TD-DFT calculations further suggest that the intervalence charge transfer within both monocations is essentially localized on the ligand and can be described as an intraligand charge transfer (ILCT).

Bonding Interactions in Uranyl α-Diimine Complexes: A Spectroscopic and Electrochemical Study of the Impacts of Ligand Electronics and Extended Conjugation.

Uranyl complexes of aryl-substituted α-diimine ligands gbha (UO2-1a-f) and phen-BIAN (UO2-2a-f) [gbha (1) = glyoxal bis(2-hydroxyanil); phen-BIAN (2) = N,N'-bis(iminophenol)acenaphthene; R = OMe (a), t-bu (b), H (c), Me (d), F (e), and naphthyl (f)] were designed, prepared, and characterized by X-ray diffraction, FT-IR, NMR, UV-vis, and electrochemical methods. These ligand frameworks contain a salen-type O-N-N-O binding pocket but are redox-noninnocent, leading to unusual metal complex behaviors. Here, we describe three solid-state structures of uranyl complexes UO2-1b, UO2-1c, and UO2-1f and observe manifestations of ligand noninnocence for the U(VI) complexes UO2-1b and UO2-1c. The impacts of accessible π-systems and ligand substitution on the axial uranium-oxo interactions were evaluated spectroscopically via the intraligand charge-transfer (ILCT) processes that dominate the absorption spectra of these complexes and through changes to the asymmetric (ν3) O═U═O stretching frequency. This, in combination with electrochemical data, reveals the effects of the inclusion of the conjugated acenaphthene backbone and the importance of ligand electronic structure on uranyl's bonding interactions.

Proton-Coupled Oxidation of Aldimines and Stabilization of H-Bonded Phenoxyl Radical-Phenol Skeletons.

Stable phenoxyl radicals H-bonded to phenols were successfully isolated. The effect of the intermolecular H-bonding to the concerted proton coupled electron transfer (CPET) reactions of the aldimines and the stability and spin distribution of the H-bonded phenoxyls are reported. Salts of iminium-phenol derivatives as cations and the corresponding imine-phenolato derivatives coordinated to zinc(II) as anions, [ZnII(ArRO)Cl2]-[ArROH2]+, were isolated, where ArOH are aldimine derivatives. Notably, [ZnII(ArRO)Cl2]-[ArROH2]+ salts undergo CPET reactions in air affording phenoxyl analogues, [ZnII(ArOH)Cl2].ArO●·CH3CN. [ZnII(ArRO)Cl2]-[ArROH2]+ salts incorporate intermolecular iminium-phenolato, [(Zn)Ar-O--+HN═CH-] H-bonds, while [ZnII(ArOH)Cl2].ArO●·CH3CN moieties contain intermolecular phenoxyl-phenol, [Ar-O-HO-Ar]●, H-bonds. The phenoxyls are presented in two forms, [(Zn)Ar-O●---HO-Ar (zinc phenoxyl) ↔ (Zn)Ar-OH---●O-Ar (free phenoxyl)]. In crystals, the spin density scatters on both phenolic fragments corresponding to a delocalized state, while in solution the latter form has been calculated as a ground electronic state. The X-band EPR spectra of crystals, solutions and frozen glasses were analyzed. The powder spectra at g = 2.0030 ± 0.0005 and the frozen glass spectra at g = 2.0075 ± 0.0003 follow the hyperfine patterns due to 14N (I = 1) nuclei. In fluid solutions, the g values of the hyperfine signals due to 14N and 1H nuclei are 2.0078 ± 0.0001. 1-3 exhibit absorption bands at 350-390 nm due to π → π* intraligand charge transfer (ILCT) transitions, while the radical species, in addition to π → π transitions at 405-440 nm, display phenol to phenoxyl intervalence charge transfer (IVCT) transitions at 600-650 nm. The cyclic voltammograms (CVs) of 1-3 depend on the scan rates; at lower scan rates (100-400 mV/s) the CPET reactions occur at -0.92 to -0.96 V versus Fc+/Fc couple, whereas at higher scan rates (1000-2400 mV/s), the oxidation occurs by the electron transfer (ET) path at 0.05-0.12 V. Thus, a potential shift of ∼1.0 V is recorded due to CPET reactions facilitated by H-bonding.

A new series of three-coordinate cuprous complexes formed by steric hindrance of a phosphine ligand: Synthesis, structure characterization, properties and TD-DFT calculations

Four new three-coordinate cuprous complexes with a CuN2P core, 1-QBO, 2-Phen, 3-MePBO, 4-QBI, were designed and synthesized by utilizing a steric hindrance of phosphine ligand o-Anisyl3P [QBO = 2-(2′-quinolyl)benzoxazole, Phen = 1,10-Phenanthroline, MePBO = 5-methyl-2-(2′-pyridyl)-benzoxazole, QBI = 2-(2′-quinolyl)benzimidazole, o-Anisyl3P = tri(2-methoxyphenyl)-phosphine]. As a counterpart to 1-QBO, a four-coordinate complex 5-QBOP2 has also been synthesized with a CuN2P2 core. All complexes were characterized by single-crystal X-ray diffraction, spectroscopic analysis (IR, UV–Vis), elemental analysis, and photoluminescence study. Single-crystal X-ray diffraction revealed that complexes 1–4 all adopt trigonal CuN2P coordination geometry with one phosphine and one diimine ligand. Their UV–Vis absorption spectra exhibit concentration dependences of absorption edge shift. Time-dependent density functional theory (TD-DFT) calculations reveal that their S1 states and the peak transition states can be mainly assigned as ligand–ligand & metal–ligand charge transfer (L′LCT + MLCT) and intra-ligand charge transfer (ILCT) states, respectively. It is noteworthy that all three-coordinate complexes 1–4 do not display obvious photoluminescence (PL), whereas the PL of four-coordinate complex 5 is turned on by an extra coordination of a phosphine ligand to 1. This PL complex has also been synthesized and characterized as 5-QBOP2 from 1-QBO. This model of three-coordinate to four-coordinate change with PL turn-on behavior could be used for sensing volatile organic compounds (VOCs).

Synthesis, EPR study and photophysical properties of a mononuclear Fe(III) Schiff base complex functionalized by 3,6-di-tert-butyl-carbazole moieties

An azomethine iron(III) complex containing 3,6-di-tert-butyl-carbazole fragments on periphery with a PF6ˉ counter-ion was synthesized and characterized by a wide range of experimental techniques. According to the X-ray powder diffraction data, the unit cell contains four molecules, which adopt a facial isomeric form. EPR spectroscopy revealed the presence of only high-spin (HS) iron(III) centers in the temperature range between 3.8 and 300 K. At low temperatures, the majority of complexes form the supramolecular dimers, wherein the two HS iron(III) centers are weakly antiferromagnetically coupled, but an increase in temperature causes the cleavage of intermolecular hydrogen bonds and results in the formation of a monomeric packing structure. The thermal stability and phase behavior were studied by thermogravimetric analysis and differential scanning calorimetry. The UV/Vis absorption properties were studied in dichloromethane and rationalized by time-dependent density functional theory calculations. Upon excitation at 345 nm, the complex exhibits intense fluorescence centered at 449 nm. A single emission band was assigned to a πcarb–π* intraligand charge-transfer excited state. In addition to a significant Stokes shift (104 nm), a high fluorescence quantum yield (54%) was observed.

Luminescent mononuclear and dinuclear cycloplatinated (II) complexes comprising azide and phosphine ancillary ligands

A new series of cycloplatinated (II) complexes with general formulas of [Pt (bhq)(N3)(P)] [bhq = deprotonated 7,8‐benzo[h]quinoline, P = triphenyl phosphine (PPh3) and methyldiphenyl phosphine], [Pt (bhq)(P^P)]N3 [P^P = 1,1‐bis (diphenylphosphino)methane (dppm) and 1,2‐bis (diphenylphosphino)ethane] and [Pt2(bhq)2(μ‐P^P)(N3)2] [P^P = dppm and 1,2‐bis (diphenylphosphino)acetylene] is reported in this investigation. A combination of azide (N3−) and phosphine (monodentate and bidentate) was used as ancillary ligands to study their influences on the chromophoric cyclometalated ligand. All complexes were characterized by nuclear magnetic resonance spectroscopy. To confirm the presence of the N3− ligand directly connected to the platinum center, complex [Pt (bhq)(N3)(PPh3)] was further characterized by single‐crystal X‐ray crystallography. The photophysical properties of the new products were studied by UV–Vis spectroscopy in CH2Cl2 and photoluminescence spectroscopy in solid state (298 or 77 K) and in solution (77 K). Using density functional theory calculations, it was proved that, in addition to intraligand charge‐transfer (ILCT) and metal‐to‐ligand charge‐transfer (MLCT) transitions, the L′LCT (L′ = N3, L = C^N) electronic transition has a remarkable contribution in low energy bands of the absorption spectra (for complexes [Pt (bhq)(N3)(P)] and [Pt2(bhq)2(μ‐P^P)(N3)2]). It is indicative of the determining role of the N3− ligand in electronic transitions of these complexes, specifically in the low energy region. In this regard, the photoluminescence studies indicated that the emissions in such complexes originate from a mixed 3ILCT/3MLCT (intramolecular) and also from aggregations (intermolecular).

Realization of Highly Efficient Red Phosphorescence from Bis-Tridentate Iridium(III) Phosphors.

Bis-tridentate Ir(III) metal complexes bring forth interesting photophysical properties, among which the orthogonal arranged, planar tridentate chelates could increase the emission efficiency due to the greater rigidity and, in the meantime, allow strong interligand stacking that could deteriorate the emission efficiency. We bypassed this hurdle by design of five bis-tridentate Ir(III) complexes (1-5), to which both of their monoanionic ancillary and dianionic chromophoric chelate were functionalized derivative of 2-pyrazolyl-6-phenylpyridine, i.e. pzpyphH2 parent chelate. Hence, addition of phenyl substituent to the pyrazolyl fragment of pzpyphH2 gave rise to the precursors of monoanionic chelate (A1H-A3H), on which the additional tert-butyl and/or methoxy groups were introduced at the selected positions for tuning their steric and electronic properties, while precursors of dianionic chelates was judiciously prepared with an isoquniolinyl central unit on pziqphH2 in giving the red-shifted emission (cf. L1H2 and L2H2). Factors affected their photophysical properties were discussed by theoretical methods based on DFT and TD-DFT calculation, confirming that the T1 excited state of all investigated Ir(III) complexes shows a mixed metal-to-ligand charge transfer (MLCT), intraligand charge transfer (ILCT), ligand-to-ligand charge transfer (LLCT), and ligand-centered (LC) transition character. In contrast, the poor quantum yield of 3 is due to the facilitation of the nonradiative decay in comparison to the radiative process. As for potential OLED applications, Ir(III) complex 2 gives superior performance with max. efficiencies of 28.17%, 41.25 cd·A-1 and 37.03 lm·W-1, CIEx,y = 0.63, 0.37 at 50 mA cm-2, and small efficiency roll-off.

A New Class of Homoleptic and Heteroleptic Bis(terpyridine) Iridium(III) Complexes with Strong Photodynamic Therapy Effects.

Six homo- or heteroleptic tricationic Ir(R1-tpy)(R2-tpy)3+ complexes (Ir1-Ir6, R1/R2 = Ph, 4'-N(CH3)2Ph, pyren-1-yl, or 4'-{2-[2-(2-methoxyethoxy)ethoxy]ethoxy}Ph, tpy = 2,2';6',2"-terpyridine) were synthesized and tested for photodynamic therapy (PDT) effects. The ground- and excited-state characteristics of these complexes were studied systematically via spectroscopic methods and quantum chemistry calculations. All complexes possessed intraligand charge transfer (1ILCT) / metal-to-ligand charge transfer (1MLCT) dominated transition(s) in their low-energy absorption bands, which red-shifted with the increased electron-releasing strength of the R1/R2 substituent. Five of the complexes exhibited ligand-centered 3 π,π*/3ILCT/3MLCT emission. With a stronger electron-releasing R1/R2 substituent, the degree of charge transfer contribution increased, leading to a decrease of the emission quantum yield. When the 4'-N(CH3)2Ph substituent was introduced on both tpy ligands, the emission of Ir3 was completely quenched. Our study on the transient absorption of these complexes demonstrated that they all possessed broadband triplet excited-state absorption in the 400-800 nm region. Pyrenyl substitution of one or more tpy ligands, as in Ir4 and Ir5, increased the lifetimes of the lowest triplet excited state and the singlet oxygen (1O2) production efficiencies. Ir1-Ir5 were nontoxic toward SK-MEL-28 cells, with photocytotoxicities that varied from 0.18 to 153 µM. Among them, Ir4 had the highest 1O2 quantum yield (0.81) in cell-free conditions, showing the largest photocytotoxicity against SK-MEL-28 cells for Ir(III) PSs to date, and was the most efficient generator of reactive oxygen species (ROS) in vitro. Ir4 possessed a very large phototherapeutic index (PI = dark EC50 / light EC50) of >1657, the largest reported for an Ir(III) complex photosensitizer upon broadband visible light (400-700 nm) activation. Ir4 also exhibited a very strong PDT effect toward MCF-7 breast cancer cells and its xenograft tumor model. Upon 450-nm light activation, Ir4 dramatically inhibited the xenograft tumor growth and exhibited negligible side effects upon PDT treatment.

Silver-nitrilotriacetate coordination polymers: Supra-molecular and photoluminescence properties

Three new coordination polymers (CPs), [Ag3(nta)(azpy)3(H2O)]n·5H2O, 1, [Ag3(nta)(bpa)2.5]n·5.5H2O, 2 and [Ag6(nta)2(tmdp)5]n·17H2O, 3 (where nta = nitrilotriacetate, azpy = 4,4′-azobipyridine, bpa = 1,2-di(4-pyridyl)ethane and tmdp = 4,4′-trimethylenedipyridine) have been synthesized and characterized by different techniques viz. elemental analysis, PXRD, IR, UV–vis and X-ray crystallography. Single crystal X-ray studies reveal that CP 1 is one-dimensional structure whereas, 2 and 3 are two-dimensional and three-dimensional structures respectively. By altering the flexibility of bipyridine ligands, different coordination behaviour of nta was observed and also dimensionality of CPs changed from 1D to 3D. A supra-molecular 3D structure of 1 was generated because of π⋯π interactions. The argentophilic interactions involved in the formation of 2D and 3D structures of 2 and 3 respectively. The photoluminescent properties of CPs 1–3 were studied in a solid state at room temperature. CPs 1 and 2 showed emission bands at 432 and 401 nm respectively because of intra-ligand charge transfer transitions. In the case of 1, the emission band is red-shifted with respect to azpy since of π-π stacking in the solid state. CP 3 showed emission in the visible region at 488 nm, is due to the promotion of the lone pair of electrons of the metal to the π* orbital of the ligand.

Synthesis, Characterization and Complexation Behaviour of Chloroquine towards Ti (II) Ion

Aims: Chloroquine is a member of the drug class 4-aminoquinoline used for the prevention and treatment of malaria in areas where malaria is known to be sensitive to its effects.
 Our aim is to synthesize the chloroquine – titanium complex and to study its coordination behavior.
 Place and Duration of Study: Department of Chemistry, Michael Okpara University of Agriculture, Umudike, 2019.
 Methodology: Ti(II) complex of chloroquine was synthesized by the reaction of chloroquine phosphate with titanium(IV) oxide. The metal complex was characterized based on UV, IR and 1H NMR Spectroscopy.
 Results: The UV spectrum of the complex suggested intra ligand charge transfer (ILCT), ligand to metal charge transfer (LMCT), and d-d transition. The IR spectrum of the complex showed the involvement of amine and imine group in coordination to Ti. This showed that chloroquine acted as a bidentate ligand. 1H NMR of the spectrum further showed the involvement of the amine group in coordination.
 Conclusion: The ability of chloroquine to sequestrate Ti (II) ion has been assured. This drug can be used to chelate Ti ions from solution, environment, and biological system.