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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.

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.

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.

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...

An effective strategy was developed for the synthesis of new 2,2′-bipyridine ligands, symmetrical and unsymmetrical 6,6′-binicotinates, and 2,2′-bipyridine-5-carboxylates, from 4-propargylisoxazoles. The synthesis of symmetrical 2,2′-disubstituted 6,6′-binicotinates was achieved using the Eglinton reaction of 5-methoxy-4-(prop-2-yn-1-yl)isoxazoles with Cu(OAc)2, followed by Fe(NTf2)2/Au(NTf2)tBuXPhos-catalyzed isomerization of the so-formed mixture of isoxazole/azirine-substituted biacetylenic intermediates. Unsymmetrical 2,2′-disubstituted 6,6′-binicotinates were prepared via a copper-free Sonogashira coupling of 5-methoxy-4-(prop-2-yn-1-yl)isoxazoles with 6-bromonicotinates to give methyl 6-(3-(5-methoxyisoxazol-4-yl)prop-1-ynyl)pyridine-3-carboxylates, followed by a transformation of the propargylisoxazole moiety of the adduct into the pyridine fragment under Fe(II)/Au(I) relay catalysis conditions. 6-(Pyrid-2-yl)nicotinates were synthesized by a Stille-type coupling of 2-(tributylstannyl)pyridine with...

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.

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.

The six-coordinated silver(I) complex [Au

Two iridium [Ir(N^C)

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.

A series of novel diimine (N∧N) ligands containing developed aromatic [2,1-a]pyrrolo[3,2-c]isoquinoline system have been prepared and used in the synthesis of Ir(III) luminescent complexes. In organic solvents, the ligands display fluorescence which depends strongly on the nature of solvents to give moderate to strong orange emission in aprotic solvents and shows a considerable blue shift and substantial increase in emission intensity in methanol. Insertion of electron-withdrawing and -donating substituents into peripheral phenyl fragment has nearly no effect onto emission parameters. The ligands were successfully used to prepare the metalated [Ir(N∧C)2(N∧N)]+ complexes (where N∧C = phenylpyridine (N∧C-1), p-tolylpyridine (N∧C-2), 2-(benzo[b]thiophen-2-yl)pyridine (N∧C-3), 2-benzo[b]thiophen-3-yl)pyridine (N∧C-4), and methyl 2-phenylquinoline-4-carboxylate (N∧C-5)) using standard synthetic procedures. The complexes obtained display moderate to strong phosphorescence in organic solvents; the emission chara...

The encapsulation and/or surface modification can stabilize and protect the phosphorescence bio‐probes but impede their intravenous delivery across biological barriers. Here, a new class of biocompatible rhenium (ReI) diimine carbonyl complexes is developed, which can efficaciously permeate normal vessel walls and then functionalize the extravascular collagen matrixes as in situ oxygen sensor. Without protective agents, ReI‐diimine complex already exhibits excellent emission yield (34%, λ em = 583 nm) and large two‐photon absorption cross‐sections (σ 2 = 300 GM @ 800 nm) in water (pH 7.4). After extravasation, remarkably, the collagen‐bound probes further enhanced their excitation efficiency by increasing the deoxygenated lifetime from 4.0 to 7.5 µs, paving a way to visualize tumor hypoxia and tissue ischemia in vivo. The post‐extravasation functionalization of extracellular matrixes demonstrates a new methodology for biomaterial‐empowered phosphorescence sensing and imaging., Biocompatible rhenium (ReI) diimine carbonyl complexes functionalize the extravascular collagen matrixes as in situ oxygen sensor. After tail‐vein delivery and vessel penetration, the probe can bind extravascular collagens and achieve stabilization enhanced two‐photon phosphorescence yields. Increased deoxygenated phosphorescence lifetime from 4.0 to 7.5 µs paves a way to visualize tumor hypoxia and tissue ischemia in vivo.

A series of Au(I) alkynyl complexes containing a novel N-donor ligand (2-phenylpyrido[2,1-a]pyrrolo[3,2-c]isoquinoline) coordinated through pyrrol-nitrogen has been synthesized and characterized using X-ray crystallography and NMR spectroscopy. The compounds obtained are luminescent in solution and in solid state, and emission intensity depends on the nature of alkynyl ligand to give values of quantum yield equal 8.0 and 6.5% for the complexes 3 and 4, respectively in dichloromethane solution at room temperature. The emission observed is ligand centred fluorescence that is not typical for the complexes of this type, which usually display phosphorescence determined by strong spin-orbit coupling with the heavy metal ion. DFT calculations of the complexes electronic structure showed that contribution of the gold orbitals into the states responsible for emission is nearly negligible that results in low intersystem crossing rate and suppression of phosphorescence in the complexes studied.

The first example of trinuclear copper(I) and silver(I) pyrazolates adducts with a tertiary diphosphine (Ph2PCH2PPh2) retaining trimeric [MPz]3 core is reported. Despite rather strong M-P bonding, the complexes are able to undergo the dissociation of one M-P bond leading to the "merry-go-round" movement of P atoms over the M3 triangle. The copper complex displays emission from 1MLCT and 3MLCT states. The triplet and singlet states are separated by a relatively small energy gap (1080 cm-1) that triggers the thermally activated delayed fluorescence (TADF) behavior and leads to the worthy quantum yield of 41% at 298 K. The silver complex in the solid state and frozen solution shows dual emission originating from the 1IL and 3MLCT states that is dictated by the much higher energy difference between the emissive singlet and triplet as well as by the essentially different nature of these states.

Stimuli-responsive metal complexes are extensively studied due to their promising properties for various practical applications. In many cases, stimuli-induced response is provoked by phase transitions, which completely modify electronic properties of chromophoric center to give substantial modification of the phase emissive properties. However, complexity of the systems hinders theoretical calculations, which could be used to interpret the emission response, even at qualitative level. In this study, we apply a joint experimental and theoretical approach to model the luminescence switching of a vapochromic Au–Cu organometallic supramolecular complex in solution, amorphous, and crystal state. We have investigated luminescence spectra and emission anisotropy of the complex in solution, polymer gel, amorphous, and crystal states. The excitation and emission energies of the complex in vacuum and crystal state have been calculated using QM and QM/MM approaches. The results show that (1) the red shift of emissi...

A high yield synthesis of fluorescent benzo, thieno, and furo [c]-fused methyl 7-aryl-6H-pyrrolo[3,4-c]pyridazine-5-carboxylates, including unprecedented heterocyclic skeletons, was performed by the transformation of methyl 4-aminopyrrole-2-carboxylate into the corresponding diazo compound, followed by intramolecular azo coupling under acid conditions onto a nucleophilic aryl or hetaryl group in the 3-position. Azo coupling is completely regioselective and, according to DFT calculations, a kinetically controlled reaction. N-Methylation of 1,3-disubstituted 2H-pyrrolo[3,4-c]cinnolines occurs selectively at N5 under kinetic control, leading exclusively to 5-methyl-5H-pyrrolo[3,4-c]cinnoline derivatives.

In the present work we obtained a series of NIR luminescent platinum(II) complexes with a pincer N^N^C ligand based on the conjugated {benzoimidazo[1,2-a]pyrazine} system with the [Pt(N^N^C)L]n+ structural motif (L = phosphine, alkynyl or pyridine-type ligands). We have also synthesized two complexes with bidentate phosphines that demonstrate different types of coordination: 1) as chelating ligand (in case of 1,2-bis(diphenylphosphino)benzene), that led to de-coordination of pyridine ring of N^N^C ligand and formation of a [Pt(N^C)dppb]+ complex; 2) as a bridging ligand (in case of bis(diphenylphosphino)methane) between two {Pt(N^N^C)} fragments in a dimeric complex of type [{Pt(N^N^C)}2dppm]2+. The complexes obtained were fully characterized using spectroscopic methods, and their ground-state structures and photophysical properties were studied by DFT and TD DFT methods. According to the data obtained the aromatic {benzoimidazo[1,2-a]pyrazine} fragment plays a key role in the photophysics of this type of complexes and the triplet 3LC state located at the N^N^C ligand proved to be the only emissive state in all the complexes prepared. Unexpectedly variations in the nature of the ligands occupying the fourth coordination position in the square-planar structural motif, changes in the mode of the N^N^C ligand coordination and even the Pt-Pt bond formation did not result in significant variations of the emission profile. The photophysical behavior of these complexes has been analyzed using DFT calculations, which are in complete agreement with the experimental data and confirmed that the lowest relaxed triplet configuration responsible for the phosphorescence in the complexes studied is located at the N^N^C ligand.

A new heterocyclic system, pyrido[2,1-a]pyrrolo[3,2-c]isoquinoline, was synthesized via Pd-catalyzed intramolecular cyclization of 1-[1-benzyl-2-(2-bromophenyl)-1H-pyrrol-3-yl]pyridin-1-ium bromides. The heterocycles obtained display stimuli responsive fluorescence in solution depending on the nature of the solvent. The strongest blue shift of the emission maxima and growth in luminescence intensity was observed in protic solvents and upon addition of proton donors to solutions of compounds in aprotic solvents. The effect of proton donors on emission characteristics was explained by DFT calculations in terms of H-complex formation with the nucleophilic centres of the molecular skeleton.

The growing attention to the luminescent nanocarriers is strongly stimulated by their potential application as drug delivery systems and by the necessity to monitor their distribution in cells and tissues. In this communication we report on the synthesis of amphiphilic polypeptides bearing C-terminal phosphorescent label together with preparation of nanoparticles using the polypeptides obtained. The approach suggested is based on a unique and highly technological process where the new phosphorescent Pt-cysteine complex serves as initiator of the ring-opening polymerization of α-amino acid N-carboxyanhydrides to obtain the polypeptides bearing intact the platinum chromophore covalently bound to the polymer chain. It was established that the luminescent label retains unchanged its emission characteristics not only in the polypeptides but also in more complicated nanoaggregates such as the polymer derived amphiphilic block-copolymers and self-assembled nanoparticles. The phosphorescent nanoparticles display no cytotoxicity and hemolytic activity in the tested range of concentrations and easily internalize into living cells that makes possible in vivo cell visualization, including prospective application in time resolved imaging and drug delivery monitoring.

A rational approach to the synthesis of cage-like compounds has been realized to build a new family of sulfido-phosphane Au(i) polynuclear complexes. Ditopic phosphane ligands with an extended aromatic system were used to obtain cage compounds with a clearly determined geometry. Au(i) complexes have been fully characterised in solution using spectroscopy methods, and DFT optimisation of the molecular structure gives additional arguments in favour of the suggested structural patterns. All complexes obtained are luminescent in solution and in the solid state, and display multiple emissions with an unusual combination of two phosphorescence bands and one fluorescence band. DFT calculations show that multiple emissions were mainly determined by

A rational approach to the synthesis of cage-like compounds has been realized to build a new family of sulfido-phosphane Au(i) polynuclear complexes. Ditopic phosphane ligands with an extended aromatic system were used to obtain cage compounds with a clearly determined geometry. Au(i) complexes have been fully characterised in solution using spectroscopy methods, and DFT optimisation of the molecular structure gives additional arguments in favour of the suggested structural patterns. All complexes obtained are luminescent in solution and in the solid state, and display multiple emissions with an unusual combination of two phosphorescence bands and one fluorescence band. DFT calculations show that multiple emissions were mainly determined by IL and metal perturbed IL transitions. The ratio of singlet and triplet emission components depends on the distance between the ligand chromophoric centre and Au(i)., This research has been supported by grants of the Russian Foundation for Basic Research 16-33-60109, 14-03-00970 and the Russian Presidential scholarship SP-2534.2016.1. The financial support from the Academy of Finland (grant 268993, I. O. K.) is acknowledged. The work was carried out using equipment of the Analytical Centre for Nano- and Biotechnologies (Peter the Great St Petersburg Polytechnic University with financial support from the Ministry of Education and Science of Russian Federation); and Centres for Magnetic Resonance, for Optical and Laser Materials Research, for Chemical Analysis and Materials Research, and Computer Centre (Research park of St Petersburg State University).

Tetranuclear AuI–FeII dimetallic and AuI–CuI–FeII trimetallic complexes bearing ferrocenyl (Fc) groups have been assembled by using two triphosphane ligands, namely, (PPh2CH2)2PPh (dpmp) and (PPh2)3CH (tppm). The compositions and structural type of the clusters are dependent on the stereochemistry of the P donor ligands. The complexes [tppmAu3Cu(C2R)3]PF6 [R = Fc (1) and 4-C6H4-Fc (2)] adopt a trigonal pyramidal {Au3Cu} arrangement of the coordinating metal core, whereas for the compounds with the linear triphosphane [Au4(dpmp)2(C2R)2](PF6)2 [R = Fc (3) and 4-C6H4-Fc (4)], a planar rhomboidal {Au4} framework was found. Clusters 1–4 were characterized by NMR spectroscopy and ESI-MS measurements. The solid-state structures of 1, 3, and 4 have been determined by X-ray crystallography. The electrochemical properties of 1–4 were studied and revealed redox processes attributed to the Fc functions. Oxidation of the Fc units in 1, 2, and 4 occurs independently. In 3, an electron transfer process mediated by the {Au4} metal core was observed.

A family of triphosphine gold–copper clusters bearing aliphatic and hydroxyaliphatic alkynyl ligands of general formula [HC(PPh2)3Au3Cu(C2R)3]+ (R = cyclohexyl (1), cyclopentyl (2), But (3), cyclohexanolyl (4), cyclopentanolyl (5), 2,6-dimethylheptanolyl (6), 2-methylbutanolyl (7), diphenylmethanolyl (8)) was synthesized via a self-assembly protocol, which involves treatment of the (AuC2R)n acetylides with the (PPh2)3CH ligand in the presence of Cu+ ions and NEt3. Addition of Cl– or Br– anions to complex 8 results in coordination of the halides to the copper atoms to give neutral HC(PPh2)3Au3CuHal(C2COHPh2)3 derivatives (Hal = Cl (9), Br (10)). The title compounds were characterized by NMR and ESI-MS spectroscopy, and the structures of 1, 4, 7, and 8 were determined by single-crystal X-ray diffraction analysis. The photophysical behavior of all of the complexes has been studied to reveal moderate to weak phosphorescence in solution and intense emission in the solid state with a maximum quantum yield of 80...

Reactions of the [(tppm)Au3Cl3] [tppm = tris(diphenylphosphanyl)methane] precursor and CuI ions with a stoichiometric amount of the corresponding linear mono- [HC2(C6H4)nC6H5; n = 1, 2] and diacetylenes [HC2(C6H4)nC2H; n = 1–3] that contain extended polyaryl moieties afford a series of luminescent heterometallic complexes with a common structural motif based on the {(AuC2)3Cu} cluster core. The complexes obtained were characterized by using X-ray crystallography and NMR spectroscopy. All compounds studied display dual singlet and triplet luminescence, the former component of which can be completely suppressed in concentrated solution by a self-absorption phenomenon. The results of the photophysical measurements together with the quantum chemical calculations (PBE0-DFT level of theory) indicate that singlet emission originates mainly from copper-perturbed intraligand transitions, whereas the phosphorescence can be assigned to the {(AuC2)3Cu} core-centered transitions. Due to the low contribution of the gold atoms to the orbitals responsible for the singlet and triplet emission, the emissive excited states are very weakly coupled, thereby resulting in a negligible energy transfer between these excited states.

A series of tri- and tetranuclear phosphine complexes of d(10) metal ions supported by the polydentate ligands, bis(diphenylphosphinomethyl)phenylphosphine (PPP) and tris(diphenylphosphinomethyl)phosphine (PPPP), were synthesized. All the compounds under study, [AuM2(PPP)2](3+) (M = Au (1), Cu (2), Ag (3)), [M4(PPPP)2](4+) (M = Ag (4), Au (5)), [AuAg3(PPPP)2](4+) (6), and [Au2Cu2(PPPP)2(NCMe)4](4+) (7), were characterized crystallographically. The trinuclear clusters 1-3 contain a linear metal core, while in the isostructural tetranuclear complexes 4-6 the metal framework has a plane star-shaped arrangement. Cluster 7 adopts a structural motif that involves a digold unit bridged by two arms of the PPPP phosphines and decorated two spatially separated Cu(I) ions chelated by the remaining P donors. The NMR spectroscopic investigation in DMSO solution revealed the heterometallic clusters 2, 3, and 6 are stereochemically nonrigid and undergo reversible metal ions redistribution between several species, accompanied by their solvation-desolvation. The complexes 1-3 and 5-7 exhibit room temperature luminescence in the solid state (Φem = 6-64%) in the spectral region from 450 to 563 nm. The phosphorescence observed originates from the triplet excited states, determined by the metal cluster-centered dσ* → pσ transitions.

A family of supramolecular cage molecules has been obtained via self-assembly of the phosphine-gold coordination complexes following an aurophilicity-driven aggregation approach. Use of the di- (PP) or tridentate (PPP) phosphine ligands Pn (n = 2, 3) with rigid polyaromatic backbones leads to clean formation of the coordination Pn(Au(tht))n(n+) species, sequential treatment of which with H2O/NEt3 and excess of H2NBu(t) gives the finite 3D structures of two major types. The cylindrical-like hexametallic cages [(PPAu2)3(μ3-NBu(t))2](2+) are based on the diphosphines PP = 1,4-bis(diphenylphosphino)benzene (1), 4,4'-bis(diphenylphosphino)biphenyl (2), 4,4"-bis(diphenylphosphino)terphenyl (3), while the triphosphine PPP (1,3,5-tris(diphenylphosphinophenyl)benzene) produces a tetrahedral dodecagold complex [(PPPAu3)4(μ3-NBu(t))4](4+) (4). The cages 1-4 have been studied using the ESI-MS and (1)H, (31)P NMR spectroscopy, and the crystal structures of 1 and 4 were determined by an X-ray diffraction study. The NMR spectroscopic investigations showed that cylindrical complexes 1-3 undergo twisting-like interconversion of the helical P ↔ M isomers in solution, while 4 is a stereochemically rigid compound retaining its axially chiral architecture. The difference in dynamic behavior was rationalized using computational studies with density functional methods.

A new series of homoleptic alkynyl complexes, [{Au2Cu2(C2R)4}n] (R=C3H7O (1), C6H11O (2), C9H19O (3), C13H11O (4)), were obtained from Au(SC4H8)Cl, Cu(NCMe)4PF6, and the corresponding alkyne in the presence of a base (NEt3). Complexes 1-4 aggregate upon crystallization into polymeric chains through extensive metallophilic interactions. The cluster that contains fluorenolyl functionalities, C13H9O (5), crystallizes in its molecular form as a disolvate, [Au2Cu2(C2C13H9O)4]·2THF. The substitution of weakly bound THF molecules with pyridine molecules leads to the complex [Au2Cu2(C2C13H9O)4]·2py (6), thus giving two polymorphs in the solid state. Such structural diversity is established through metal-chain and hydrogen-bond formation, which depends on the stereochemical characteristics of the organic ligands. More interestingly, this solid-state structural arrangement affords good emission properties, such as intensity and spectroscopic profile, which are otherwise very weakly emissive in solution. Metallophilic aggregation of the {Au2Cu2} cluster units, as observed in the crystals, results in dramatic enhancement of the room-temperature phosphorescence, thereby reaching a maximum quantum efficiency of 95% (4). A theoretical approach further indicates a synergistic effect of the array of the metal chain upon aggregation, which greatly enhances the spin-orbit coupling and, hence, the phosphorescence, thereby opening up a new direction in the field of aggregate-enhanced emission.

The reactions between trinuclear gold complex tppmAu 3Cl 3 (tppm = tris(diphenylphosphino)methane), arylacetylenes HC 2C 6H 4X and Cu + under basic conditions result in formation of the heterometallic complexes [tppm(AuC 2C 6H 4X) 3Cu] +, X = H (1), COOMe (2), CN (3), OMe (4), NH 2 (5). These compounds belong to one structural motif and consist of the heterometallic {(AuC 2C 6H 4X) 3Cu} core stabilized by the tridentate phosphine. Compounds 1-5 were characterized by polynuclear NMR and IR spectroscopy, ESI-MS and single-crystal X-ray analysis. Luminescence properties of these complexes have been studied and revealed a substantial red shift of the emission maxima with the increase in the electron donicity of the alkynyl ligands substituents in the 550-680 nm range. The theoretical calculations of the electronic structures showed that variations of the substituents on the alkynyl ligands display very little effect on the molecular structural parameters but show appreciable influence on the orbital energies and luminescence characteristics of the compounds under study. © 2012 The Royal Society of Chemistry., The authors greatly appreciate the financial support of Saint- Petersburg State University research grant 12.37.132.2011, the University of Eastern Finland (Russian–Finnish collaborative project), the Russian Foundation for Basic Research grants 11- 03-00974, 11-03-00541, and 11-03-92010.

Coordination of P,N indolyl-phosphine ligands to Au(I), Ag(I) and Cu(I) metal ions under weakly basic conditions results in easy deprotonation of the indolyl N-H function and effective formation of a family of homo- and heterobimetallic complexes MM'(PPh(2)C(9)H(7)N)(2) (M = M' = Au (2), Ag (5); M = Au, M' = Cu (3), Ag (4)). The latter (4) exists as an inseparable mixture of four different complexes, which are in equilibrium driven by slow dynamics. The reaction of silver(I) and copper(I) ions with PPh(2)(C(9)H(8)N) affords a rare tetranuclear Z-shaped cluster Ag(2)Cu(2)(PPh(2)C(9)H(7)N)(4) (6), which exhibits red luminescence in solid state (650 nm) and a weak dual emission in solution with the main component in the near-IR region (746 nm).

Two iridium [Ir(NC)(2)(NN)](+) complexes with the diimine NN ligand containing a long polymethylene hydrophobic chain were synthesized and characterized by using NMR and ESI mass-spectrometry: NN - 2-(1-hexadecyl-1H-imidazol-2-yl)pyridine, NC - methyl-2-phenylquinoline-4-carboxylate (Ir1) and 2-phenylquinoline-4-carboxylic acid (Ir2). These complexes were used to prepare the luminescent PEGylated DPPC liposomes (DPPC/DSPE-PEG2000/Ir-complex = 95/4.5/1 mol%) using a thin film hydration method. The narrowly dispersed liposomes had diameters of about 110 nm. The photophysics of the complexes and labeled liposomes were carefully studied. Ir1 and Ir2 give red emission (lambda(em) = 667 and 605 nm) with a lifetime in the microsecond domain and quantum yields of 4.8% and 10.0% in degassed solution. Incorporation of the complexes into the liposome lipid bilayer results in shielding of the emitters from interaction with molecular oxygen and partial suppression of excited state nonradiative relaxation due to the effect of the relatively rigid bilayer matrix. Delivery of labeled liposomes to the cultured ARPE-19 cells demonstrated the usefulness of Ir1 and Ir2 in cellular imaging. Labeled liposomes were then injected intravitreally into rat eyes and imaged successfully with optical coherence tomography and funduscopy. In conclusion, iridium complexes enabled the successful labeling and imaging of liposomes in cells and animals.