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Cyclometallated platinum(ii) species with ancillary acyclic diaminocarbene ligands work as efficient green emitting components of OLED devices.

Application of NIR (near-infrared) emitting transition metal complexes in biomedicine is a rapidly developing area of research. Emission of this class of compounds in the “optical transparency windows” of biological tissues and the intrinsic sensitivity of their phosphorescence to oxygen resulted in the preparation of several commercial oxygen sensors capable of deep (up to whole-body) and quantitative mapping of oxygen gradients suitable for in vivo experimental studies. In addition to this achievement, the last decade has also witnessed the increased growth of successful alternative applications of NIR phosphors that include i) site-specific in vitro and in vivo visualization of sophisticated biological models ranging from 3D cell cultures to intact animals; ii) sensing of various biologically relevant analytes, such as pH, reactive oxygen and nitrogen species, RedOx agents, etc.; iii) several therapeutic applications such as photodynamic (PDT), photothermal (PTT), and photoactivated cancer (PACT) therapies as well as their combinations with other therapeutic and imaging modalities to yield new variants of combined therapies and theranostics. Nevertheless, emerging applications of these compounds in experimental biomedicine and their implementation as therapeutic agents practically applicable in PDT, PTT, and PACT face the challenges related to critically important improvement of their photophysical and physico-chemical characteristics. This review outlines the current state of the art, achievements of the last decade and stresses the most promising trends, major prospectives, and challenges in the design of NIR phosphors suitable for biomedical applications.

A series of diphosphine Re(I) complexes Re1–Re4 have been designed via decoration of the archetypal core {Re(CO)2(N^N)} through the installations of the phosphines P0 and P1 bearing the terminal double bond, where N^N = 2,2′-bipyridine (N^N1), 4,4′-di-tert-butyl-2,2′-bipyridine (N^N2) or 2,9-dimethyl-1,10-phenanthroline (N^N3) and P0 = diphenylvinylphosphine, and P1 = 4-(diphenylphosphino)styrene. These complexes were copolymerized with the corresponding N-vinylpyrrolidone-based Macro-RAFT agents of different polymer chain lengths to give water-soluble copolymers of low-molecular p(VP-l-Re) and high-molecular p(VP-h-Re) block-copolymers containing rhenium complexes. Compounds Re1–Re4, as well as the copolymers p(VP-l-Re) and p(VP-h-Re), demonstrate phosphorescence from a 3MLCT excited state typical for this type of chromophores. The copolymers p(VP-l-Re#) and p(VP-h-Re#) display weak sensitivity to molecular oxygen in aqueous and buffered media, which becomes almost negligible in the model physiological media. In cell experiments with CHO-K1 cell line, p(VP-l-Re2) and p(VP-h-Re2) displayed significantly reduced toxicity compared to the initial Re2 complex and internalized into cells presumably by endocytic pathways, being eventually accumulated in endosomes. The sensitivity of the copolymers to oxygen examined in CHO-K1 cells via phosphorescence lifetime imaging microscopy (PLIM) proved to be inessential.

Five square-planar [Pt(C^N*N'^C')] complexes (Pt1-Pt5) with novel nonsymmetric tetradentate ligands (L1-L5) were synthesized and characterized. Varying the structure of the metalating aromatic systems result in substantial changes in photophysical properties and intermolecular interaction mode of the complexes in solution and in solid state. The complexes are strongly emissive in tetrahydrofuran solution, with the band maxima ranging from 560 to 690 nm. Three of these complexes (Pt1, Pt2, Pt4) afford nanospecies upon injection of their solution into water, which show aggregation-induced emission (AIE) with a strong red shift of emission bands. In the solid state, crystalline samples of these complexes demonstrate mechanochromism upon grinding with a bathochromic shift of the emission. DFT and TD-DFT computational analysis of monomeric Pt1-Pt5 in solution and model dimeric emitters formed through intermolecular interaction of Pt1, Pt2, Pt4 molecules allowed assignment of observed AIE to the

Strongly blue fluorescent 1-phenyl-2-(pyridin-2-yl)-1H-phenanthro[9,10-d]imidazole (L1) is a facile block for the construction of multichromophore organic molecules, and simultaneously serves as a chelating diimine ligand. The coordination of L1 to zinc halides enhances the intraligand charge transfer and decreases the emission energy. For the iodide derivative, intra- and intermolecular heavy atom effects lead to a dual singlet–triplet emission with a temperature-dependent ratio of fluorescence and phosphorescence bands in the crystalline state. Decoration of the anthracene core with pyridyl-phenanthroimidazole units (L2 and L3) changes the localization of the lowest energy electronic transitions to the former polyaromatic motif. The solid-state photophysical characteristics of L2 and L3-based compounds strongly depend on the intermolecular interactions between the constituting π-systems (phenanthrene and anthracene), which are perturbed by the ZnX2 coordinated fragments. Modulation of π-stacking contacts in these molecular materials containing L2 and L3 chromophores forms a basis for dynamic optical properties, responsive to mechanical, thermal, or chemical stimuli.

Luminescent cyclometalated complexes [M(C^N^N)CN] (M=Pt, Pd; HC^N^N=pyridinyl- (M=Pt 1, Pd 5), benzyltriazolyl- (M=Pt 2), indazolyl- (M=Pt 3, Pd 6), pyrazolyl-phenylpyridine (M=Pt 4)) decorated with cyanide ligand, have been explored as nucleophilic building blocks for the construction of halogen-bonded (XB) adducts using IC6 F5 as an XB donor. The negative electrostatic potential of the CN group afforded CN⋅⋅⋅I noncovalent interactions for platinum complexes 1-3; the energies of XB contacts are comparable to those of metallophilic bonding according to QTAIM analysis. Embedding the chromophore units into XB adducts 1-3⋅⋅⋅IC6 F5 has little effect on the charge distribution, but strongly affects Pt⋅⋅⋅Pt bonding and π-stacking, which lead to excited states of MMLCT (metal-metal-to-ligand charge transfer) origin. The energies of these states and the photoemissive properties of the crystalline materials are primarily determined by the degree of aggregation of the luminophores via metal-metal interactions. The adduct formation depends on the nature of the metal and the structure of the metalated ligand, the variation of which can yield dynamic XB-supported systems, exemplified by thermally regulated transition 3↔3⋅⋅⋅IC6 F5 .

The combined action of ultraviolet irradiation and microwave heating onto acetonitrile solution of [Re( NN )(CO)3 (NCMe)]OTf ( NN =phenantroline and neocuproine) afforded cis,trans-Re( NN )(CO)2 (NCMe)2 ]+ acetonitrile derivatives. Substitution of relatively labile NCMe with a series of aromatic N-donor ligands (pyridine, pyrazine, 4,4'-bipyridine, N-methyl-4,4'-bipyridine) gave a novel family of the diimine cis,trans-[Re( NN )(CO)2 (L)2 ]+ complexes. Photophysical studies of the obtained compounds in solution revealed unusually high absorption across the visible region and NIR phosphorescence with emission band maxima ranging from 711 to 805 nm. The nature of emissive excited states was studied using DFT calculations to show dominant contribution of 3 MLCT (dπ(Re)→π*( NN )) character. Electrochemical (CV and DPV) studies of the monocationic diimine complexes revealed one reduction and one oxidation wave assigned to reduction of the diimine moiety and oxidation of the rhenium center, respectively.

Herein we report on the synthesis, structural characterization and photophysical properties of cyclometalated Pt(II) complexes [Pt(N^C)(PPh2(C6H4COOH))Cl] (where N^C ligands are 2-phenylpyridine, (2-benzofuran-3-yl)pyridine, and (2-benzo[b]tiophen-3-yl)pyridine) and their conjugates with the histidine-containing RRRRRRRRRRHVLPKVQA peptide. This peptide contains the RHVLPKVQA sequence, which is responsible for antiamyloid activity, and the Arg9 RRRRRRRRR domain, which shows improved translocation through cell membranes. The chemistry underpinning the conjugation is regioselective complexation between Pt(II) complexes and histidine residue in the peptide. The prepared conjugates have been characterized using high-resolution mass spectrometry and NMR spectroscopy. It was shown that the conjugates are easily soluble in aqueous media and display emission band profiles essentially similar to those of the starting complexes but considerably higher luminescence quantum yield and much longer phosphorescence lifetime. MTT assay on HeLa cell culture revealed no cytotoxicity up to 10 μM after 24 h of incubation. Ex vivo and in vivo neuroimaging experiments on both wild and amyloid peptide expressing strains of Drosophila melanogaster revealed that the conjugates penetrate the blood-brain barrier and are evenly distributed throughout the brain independently of the strain used.

A series of iridium complexes with various cyclometalated ligands and phosphines [Ir(N^C)2(PR3)Cl], where N^C = 2-(benzothiophen-3-yl)pyridine and 2-phenylpyridine and R = phenyl and p-methoxyphenyl, were obtained. It was shown that the complexes of this type react with imidazole under mild conditions. The phosphine and chloride ligands are consecutively substituted to give imidazole-containing derivatives. The photophysical properties of all the synthesized compounds were investigated in detail. The imidazole-containing complexes demonstrate efficient triplet luminescence in solution with quantum yields up to 60%, which is sensitive to molecular oxygen.

The six-coordinated silver(I) complex [Au2Ag(μ-(PPh2)2py)2(OTf)2](OTf), 4 (py = pyridine, OTf = CF3SO3), and the five-coordinated silver(I) complex [Au2Ag(acetone)(μ-(PPh2)2py)2](PF6)3, 6, were prepared by the reaction of the precursor complexes 1(OTf)2 and 1(PF6)2, in which 1 = [Au2(μ-(PPh2)2py)2]2+, with 1 equiv of Ag(OTf) in dichloromethane and excess of Ag(PF6) in a mixture of dichloromethane/acetone, respectively. Also, the five-coordinated silver(I) complex [Au2Ag(μ-(PPh2)2py)2(py)(OTf)](OTf)2, 5, was obtained by the reaction of 4 with pyridine. The clusters 4-6 were characterized using multinuclear NMR spectroscopy and elemental microanalysis. The single-crystal X-ray diffraction analysis revealed the octahedral and distorted square pyramidal geometries around the silver(I) centers in the crystal structures of 4 and 6, respectively; a dynamic structure was observed for cluster 5 due to pendulum motion of the Ag(pyridine) moiety, which was anchored in the metallomacrocyclic unit [Au2(μ-(PPh2)2py)2]2+. Although the crystal structure of 6 did not display disorders for the silver atom and the acetone ligand similar to that observed for 5, the low-temperature NMR spectroscopies and calculations show a dynamic structure for cluster 6 due to linear motion of the Ag(acetone) moiety. The reaction of the precursor complex 1(PO2F2)2 with 2 equiv of Ag(PO2F2) yielded the tetranuclear Au2Ag2 cluster [Au2Ag2(PO2F2)2(μ-(PPh2)2py)2](PO2F2)2, 7, with a planar-shaped {Au2Ag2} metal core in which alternating Au and Ag atoms occupy the tetragon vertices and showed a strong argentophillic interaction between the silver(I) centers. All clusters 4-7 are emissive in the solid state, and the origins of their emissive excited states were determined using time-dependent density functional theory calculations. Cluster 7 showed a dual phosphorescence emission, which displays strong dependence of the contributions of each emissive component onto the excitation wavelength.

A family of diimine (N^N) and cyclometalating (N^C) ligands based on a phenanthro-imidazole aromatic system: 2-pyridyl-1H-phenanthro[9,10-d]imidazole (N^N); 2-R-1-phenyl-1H-phenanthro[9,10-d]imidazole, R = phenyl (N^C4), 3-iodophenyl (N^C5) and 4-nitrophenyl (N^C6) were prepared. It was found that N^C4 and N^C5 show π–π* fluorescence typical of aromatic systems of this sort, whereas the donor–acceptor architecture of N^C6 leads to strong emission solvatochromism and acidochromism, indicating the charge transfer character of the fluorescence observed. Six iridium(III) complexes (1–6) [Ir(N^C#)2(N^N)]+, where # = 1–6 and N^C1 = 2-phenylpyridine, N^C2 = 2-(benzo[b]thiophen-2-yl)pyridine, and N^C3 = methyl 2-phenylquinoline-4-carboxylate, were also synthesized and characterized. The complexes obtained display moderate to bright phosphorescence with quantum yields up to 46% in degassed solution. The photophysical characteristics of 1–6 were studied in detail. DFT and TD DFT calculations were used for the assignment of electronic transitions responsible for the absorption and emission of these compounds. The variations in the cyclometalating ligand structure give rise to rich photophysics of the complexes obtained. It was found that the orbitals of both N^C and N^N ligands make a major contribution to the formation of emissive excited states and a delicate balance between the energy of the ligands’ frontier orbitals determines the emission character.

The synthesis of phosphorescent transition metal complexes with emission in the near infrared (NIR) region, appreciable quantum yields, compatibility with physiological media and suitability for application as effective oxygen sensors in biological systems is still a challenge in the field of synthetic organometallic chemistry. In addition to the sufficiently high requirements in photophysics, they also have to meet strict conditions for biocompatibility and selectivity of sensory responses in a multicomponent biological medium. Building on our previous research, we have synthesized three novel iridium [Ir(N^C)2(N^N)]+ complexes (N^C – metalated ligands based on benzothienyl-phenanthridine core; N^N – pyridine-triazole diimine chelate), with their periphery decorated with 1, 2 or 3 relatively small “double-tail” oligo(ethylene glycol) (OEG) {–C(O)NHCH(CH2OC2H4OC2H4OCH3)2} functions. All these complexes display desirable photophysical characteristics: excitation at the high energy limit of the “window of transparency”, NIR emission at ca. 710–720 nm, rather high quantum yields (13–15% in degassed methanol solution) and strong lifetime responses to variations in oxygen concentration. However, the study of their behavior in model biological systems (human serum albumin (HSA) and fetal bovine serum (FBS) solutions) by gel permeation chromatography and absorption/luminescence spectroscopy showed that only the complex bearing OEG functions at all three chelate ligands is compatible with the requirements of imaging experiments, i.e. it is water soluble and bleaching stable, has low toxicity and its sensory response is insensitive to the presence of the components of biological media, temperature, and pH. The sensing properties of this molecular probe were studied in detail and test imaging experiments in phosphorescence lifetime imaging (PLIM) mode were carried out on cancer cell cultures. We demonstrate that this probe is accumulated in the cell cytoplasm and exhibits low cytotoxicity at concentrations up to 125 μM. Phosphorescence lifetime imaging microscopy (PLIM) of live mouse colorectal cancer cells (CT26) and human oral squamous carcinoma (SCC-4) stained with the probe has shown lifetimes in the 1.35–2.51 μs interval with pronounced responses to oxygen under hypoxic conditions, thus providing the basis for qualitative detection of hypoxia and semi-quantitative oxygen concentration measurements.

In this work, we report on the synthesis of the two highly thermosensitive Eu complexes ([(tta)3Eu(NN1)] (Eu1) and [(tta)3Eu(NN2)] (Eu2), where tta is thenoyltrifluoroacetone, NN1 is 3-phenyl-2-(pyridin-2-yl)pyrido[2,1-a]pyrrolo[3,2-c]isoquinoline, and NN2 is 1-phenyl-2-(pyridin-2-yl)-1H-phenanthro[9,10-d]imidazole), and preparation of luminescent thermosensitive nanomaterial (latex nanothermometer, LNT). LNT design and preparation were based on the application of Eu2 and copolymerization of butyl and methyl methacrylates in the presence of the complex, surfactant (cetyltrimethylammonium bromide), and cosurfactant (acetone). Optimization of nanoemulsion polymerization conditions allowed us to obtain strongly luminescent nanoparticles with a narrow size distribution (D = 75 nm; PDI = 0.05). Moreover, the resulting LNT particles feature nonuniform distribution of Eu2, which localizes mainly inside the nanoparticles while the outer layer lacks the complex. As a result, the developed LNT demonstrates monoexpo...

In this communication, we propose a new strategy and present the dual pH/O2 lifetime sensor based on covalent conjugation of fluorescein (pH sensor) and orthometalated iridium complex (O2 sensor) to human serum albumin (HSA). The resulting conjugate demonstrates biocompatibility, low toxicity, fast cellular uptake, and displays independent lifetime responses onto variations in media acidity and oxygen concentration that makes it suitable for application as effective pH/O2 probe in luminescent microscopy by using FLIM/PLIM detection mode. The concept applicability has been exemplified by dual spatially and temporally localized intracellular sensing of pH and O2 concentration in living cells.

Near-infrared (NIR) molecular emitters based on transition-metal complexes have attracted growing attention due to their potential application for in vivo and in vitro bioimaging experiments. Their...

The series of chelating phosphine ligands, which contain bidentate P2 (bis[(2-diphenylphosphino)phenyl] ether, DPEphos; 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene, Xantphos; 1,2-bis(diphenylphosphino)benzene, dppb), tridentate P3 (bis(2-diphenylphosphinophenyl)phenylphosphine), and tetradentate P4 (tris(2-diphenylphosphino)phenylphosphine) ligands, was used for the preparation of the corresponding dinuclear [M(μ2-SCN)P2]2 (M = Cu, 1, 3, 5; M = Ag, 2, 4, 6) and mononuclear [CuNCS(P3/P4)] (7, 9) and [AgSCN(P3/P4)] (8, 10) complexes. The reactions of P4 with silver salts in a 1:2 molar ratio produce tetranuclear clusters [Ag2(μ3-SCN)(t-SCN)(P4)]2 (11) and [Ag2(μ3-SCN)(P4)]22+ (12). Complexes 7–11 bearing terminally coordinated SCN ligands were efficiently converted into derivatives 13–17 with the weakly coordinating –SCN:B(C6F5)3 isothiocyanatoborate ligand. Compounds 1 and 5–17 exhibit thermally activated delayed fluorescence (TADF) behavior in the solid state. The excited states of thiocyanate species are dominated by the ligand to ligand SCN → π(phosphine) charge transfer transitions mixed with a variable contribution of MLCT. The boronation of SCN groups changes the nature of both the S1 and T1 states to (L + M)LCT d,p(M, P) → π(phosphine). The localization of the excited states on the aromatic systems of the phosphine ligands determines a wide range of luminescence energies achieved for the title complexes (λem varies from 448 nm for 1 to 630 nm for 10c). The emission of compounds 10 and 15, based on the P4 ligand, strongly depends on the solid-state packing (λem = 505 and 625 nm for two crystalline forms of 15), which affects structural reorganizations accompanying the formation of electronically excited states., Copper(I) and silver(I) thiocyanate complexes containing di-, tri-, and tetraphosphine ligands show efficient TADF in the solid state, dominated by the ligand to ligand SCN → π(phosphine) charge transfer, which is changed to d,p(M, P) → π(phosphine) transitions for the isothiocyanatoborate derivatives. The wide variation of the emission color from blue (448 nm) to red-orange (630 nm) is attributed to the nature of the P-donor ligands and the packing effects, influencing structural distortions in the excited state.

Single molecule luminophores capable of multiple emissions are essential for the development of new materials with unconventional photophysical behavior. In this work, a family of diphosphine ligands PPh2–PAH–PPh2 with variable polyaromatic hydrocarbon (PAH) spacers (PAH = 9,10-anthracene L1, 1,4-naphthalene L2, 2,6-naphthalene L3, and their diethynyl congeners L4–L6) were employed to prepare gold(I) complexes (RC2Au)PPh2–PAH–PPh2(AuC2R) (1–22), containing a selection of alkynyl groups. Investigation of their optical properties indicates that compounds with anthracene-based diphosphines (1–4 and 13–16) display only 1IL (ππ*) fluorescence with Φem up to 93%. The naphthalene and diethynyl-naphthalene diphosphine complexes (5–12 and 17–22), however, demonstrate panchromatic emission in the solid state and in solution featuring well-separated low and high energy signals, which originate from 1IL (ππ*) and 3IL (ππ*) transitions along with certain contribution from metal to ligand and ligand to ligand charge transfers.

Self-assembly of β-diketonate (Htta = thenoyl(trifluoro)acetone) and 4,4′-azopyridine (Azo-py) with neodymium(III) ions in the presence of methanol resulted in the formation of mononuclear complex [NdIII(TTA)3(MeOH)2]·0.5Azo-py (A) in which two asymmetric units are linked by Azo-py through hydrogen bonding via methanol. A reveals near-infrared emission (NIR) centred at about 895 and 1056 nm, in the 10–370 K temperature range, originating from the two emissive transitions on Nd(III) from 4F3/2 to 4I9/2 and 4I11/2 levels, respectively. Furthermore, the NIR luminescence intensity of A at room temperature augments two times upon thermal elimination of one coordinated methanol molecule. The thermally activated A exhibits single centre ratiometric thermometer behaviour in a wide temperature range from 10 to 300 K. Moreover, fluorescence properties of A were compared to another mononuclear complex [NdIII(TTA)3(4-OHpy)(H2O)] (B). Assembly A also exhibits field-induced slow magnetic relaxation properties with an energy barrier of ΔE/kB = 19.7(7) K and an attempt time of relaxation, τ0 = 3.7(8) × 10−7 s for fresh sample A, and ΔE/kB = 27.3 K and τ0 = 8.5(0) × 10−8 for assembly A after thermal treatment at 370 K.

The reactions of labile [Re(diimine)(CO)3(H2O)]+ precursors (diimine = 2,2′-bipyridine, bpy; 1,10-phenanthroline, phen) with dicyanoargentate anion produce the dirhenium cyanide-bridged compounds [{Re(diimine)(CO)3}2CN)]+ (1 and 2). Substitution of the axial carbonyl ligands in 2 for triphenylphosphine gives the derivative [{Re(phen)(CO)2(PPh3)}2CN]+ (3), while the employment of a neutral metalloligand [Au(PPh3)(CN)] affords heterobimetallic complex [{Re(phen)(CO)3}NCAu(PPh3)]+ (4). Furthermore, the utilization of [Au(CN)2]−, [Pt(CN)4]2–, and [Fe(CN)6]4–/3– cyanometallates leads to the higher nuclearity aggregates [{Re(diimine)(CO)3NC}xM]m+ (M = Au, x = 2, 5 and 6; Pt, x = 4, 7 and 8; Fe, x = 6, 9 and 10). All novel compounds were characterized crystallographically. Assemblies 1–8 are phosphorescent both in solution and in the solid state; according to the DFT analysis, the optical properties are mainly associated with charge transfer from Re tricarbonyl motif to the diimine fragment. The energy of this p...

New simple, fast, effective and environmentally friendly one-pot method for the synthesis of extensively used tetrakis(acetonitrile)copper(I) complexes with BF4−, PF6− and ClO4− counterions is invented and optimized. The approach suggested allows using water as solvent and minimizes amounts of toxic organic reagents in the synthetic protocol.

Three novel template bis-bidentate ligands based on {3,6-di(thien-2-yl)pyridazine} skeleton and four binuclear Pt(II) complexes containing these metalating templates were synthesized and characterized including photophysical study of two emissive compounds. These complexes display phosphorescence from triplet excited state localized primarily at the thienyl-pyridazine aromatic system, the emission bands being unusually strong shifted (ca. 100 nm/4380 cm−1) to the NIR region compared to analogous phenyl-pyridazine complexes. The absorption and emission characteristics of the complexes were analyzed by using DFT and TD DFT calculations. The results of calculations confirm that emission originates from a mixture of 3LC, 3MLCT, 3LLCT with major contribution of the former excited state and show reasonable agreement with the experimental data.

Synthesis of biocompatible near infrared phosphorescent complexes and their application in bioimaging as triplet oxygen sensors in live systems are still challenging areas of organometallic chemistry. We have designed and synthetized four novel iridium [Ir(N^C)2(N^N)]+ complexes (N^C–benzothienyl-phenanthridine based cyclometalated ligand, N^N–pyridin-phenanthroimidazol diimine chelate), decorated with oligo(ethylene glycol) groups to impart these emitters’ solubility in aqueous media, biocompatibility, and to shield them from interaction with bio-environment. These substances were fully characterized using NMR spectroscopy and ESI mass-spectrometry. The complexes exhibited excitation close to the biological “window of transparency”, NIR emission at 730 nm, and quantum yields up to 12% in water. The compounds with higher degree of the chromophore shielding possess low toxicity, bleaching stability, absence of sensitivity to variations of pH, serum, and complex concentrations. The properties of these probes as oxygen sensors for biological systems have been studied by using phosphorescence lifetime imaging experiments in different cell cultures. The results showed essential lifetime response onto variations in oxygen concentration (2.0–2.3 μs under normoxia and 2.8–3.0 μs under hypoxia conditions) in complete agreement with the calibration curves obtained “in cuvette”. The data obtained indicate that these emitters can be used as semi-quantitative oxygen sensors in biological systems.

A family of diimine (N^N) and cyclometalating (N^C) ligands based on a phenanthro-imidazole aromatic system: 2-pyridyl-1H-phenanthro[9,10-d]imidazole (N^N); 2-R-1-phenyl-1H-phenanthro[9,10-d]imidazole, R = phenyl (N^C4), 3-iodophenyl (N^C5) and 4-nitrophenyl (N^C6) were prepared. It was found that N^C4 and N^C5 show π-π* fluorescence typical of aromatic systems of this sort, whereas the donor-acceptor architecture of N^C6 leads to strong emission solvatochromism and acidochromism, indicating the charge transfer character of the fluorescence observed. Six iridium(iii) complexes (1-6) [Ir(N^C#)2(N^N)]+, where # = 1-6 and N^C1 = 2-phenylpyridine, N^C2 = 2-(benzo[b]thiophen-2-yl)pyridine, and N^C3 = methyl 2-phenylquinoline-4-carboxylate, were also synthesized and characterized. The complexes obtained display moderate to bright phosphorescence with quantum yields up to 46% in degassed solution. The photophysical characteristics of 1-6 were studied in detail. DFT and TD DFT calculations were used for the assignment of electronic transitions responsible for the absorption and emission of these compounds. The variations in the cyclometalating ligand structure give rise to rich photophysics of the complexes obtained. It was found that the orbitals of both N^C and N^N ligands make a major contribution to the formation of emissive excited states and a delicate balance between the energy of the ligands' frontier orbitals determines the emission character.

The six-coordinated silver(I) complex [Au

Two NIR emitting platinum [Pt(N^N^C)(phosphine)] and iridium [Ir(N^C)2(N^N)]+, complexes containing reactive succinimide groups were synthesized and characterized with spectroscopic methods (N^N^C ...

Non-invasive optical techniques on the basis of quenching of phosphorescence by molecular oxygen represent a powerful tool to perform mapping of oxygen content in biological systems. The development of phosphorescent oxygensensitive probes suitable for biological applications, especially in vivo, remains a challenging task. In this paper we applied for biological investigations one novel and one previously published Ir(III)-based complexes. This complexes demonstrate low cytotoxicity at the concentrations ≤70 μM and good uptake by cultured cancer cells. Both compounds were primarily located within the cytoplasm. Using TCSPC-based phosphorescence lifetime macro-imaging in vivo, we found that IR-2 complex shows detectable phosphorescence in tumor tissue in mice upon local injection. These results illustrate the high potential of organometallic complexes under study for mapping of oxygen level in cells and tissues.

Two iridium [Ir(N^C)

This work describes interaction of a family of [Pt(N∧C)(PR3)Cl] complexes with imidazole (Im), possible application of this chemistry for regioselective labeling of proteins through imidazole rings of histidine residues and employment of the resulting phosphorescent products in bioimaging. It was found that the complexes containing aliphatic phosphines display reversible substitution of chloride ligand for imidazole function that required considerable excess of imidazole to obtain full conversion into the substituted [Pt(ppy)(PR3)(Im)] product, whereas the substitution in the complexes with aromatic phosphines readily proceeds in 1:1.5 mixture of reagents. Rapid, selective, and quantitative coordination of imidazole to the platinum complexes enabled regioselective labeling of ubiquitin. X-ray protein crystallography of the {[Pt(ppy)(PPh3)]/ubiquitin} conjugate revealed direct bonding of the platinum center to unique histidine-68 residue through the nitrogen atom of imidazole function, the coordination bei...

Albumins are very promising carrier family for various types of small functional molecules, including (pro)drugs, sensors, and imaging agents. In this study, we demonstrate that one of the most crucial features of albumin—its ability to internalize into cancer cells—is strongly affected by its aggregation state. We used 14 different luminescent complexes (polynuclear heterometallic Ag(I)-Au(I) and Cu(I)-Au(I) clusters and a series of mononuclear water-soluble and hydrophobic Pt(II) complexes) able to form either covalent conjugates or non-covalent adducts with human serum albumin (HSA) to investigate the impact of preparation conditions on aggregation behavior of HSA. We demonstrated that preparation of non-aggregated HSA-based conjugates/adducts requires compliance with rather strict reaction conditions (aqueous solution with as low as possible organic co-solvent content and complex/HSA molar ratio not exceeding some critical value) while bypassing these rules (e.g., using the reaction mixtures enriched by organic solvent, high complex/HSA molar ratio or bulky hydrophobic molecules) may lead to HSA aggregation or even instability of the conjugates in solution. Further, we showed that non-aggregated HSA conjugates with water-soluble Pt complex easily internalize into cancer HeLa cells, while fully aggregated non-covalent HSA adducts with heterometallic Cu-Au clusters do not. Ultimately, in this study, we put forward two major points. First, we formulate general rules providing simple preparation route for non-aggregated cell-penetrable HSA-based conjugates, particularly, phosphorescent probes. Second, we demonstrate that the aggregation state of albumin is a very important parameter, which should be controlled while preparing its conjugates.

Combining the star-shaped alkynyl ligands with low-nuclearity gold-copper triphosphane clusters produces 3D metallocage aggregates, which demonstrate room temperature phosphorescence in solution (max Φem =0.6). Their luminescence mainly originates from cluster-localized metal-to-ligand charge transfer excited state. These supramolecular assemblies can be easily converted into the isostructural gold-silver congeners by the direct exchange of the metal ions. Such modification of the terminal metal cores switches the emission to the intraligand (alkyne) electronic transitions of the triplet manifold, that represents an unusual optical functionality among the metallocycle/metallocage complexes.