Herein, a novel pH-responsive phosphorescent probe based on cyclometalated iridium(III) complex is reported. To prevent oxygen quenching of phosphorescence and to improve the probe biocompatibility, the complex is covalently conjugated with a water-soluble block-copolymer that also increases its pH sensitivity. The resulting polymeric nanoprobe demonstrates a strong response of the phosphorescence lifetime onto pH variations in physiological range. Cellular experiments with Chinese hamster ovary (CHO-K1) cells show the predominant internalization of the probe in acidified cell compartments, endosomes and lysosomes. The analysis of phosphorescence lifetime imaging microscopy data confirms applicability of the sensor for monitoring of intra- and extracellular pH in cell cultures.

Binuclear transition-metal complexes based on conjugated systems containing coordinating functions are potentially suitable for a wide range of applications, including light-emitting materials, sensors, light-harvesting systems, photocatalysts, etc., due to energy-transfer processes between chromophore centers. Herein we report on the synthesis, characterization, photophysical, and theoretical studies of relatively rare rhenium(I) and rhenium(I)-iridium(III) dyads prepared by using the nonsymmetrical polytopic ligands (NN2 and NN3) with the strongly conjugated phenanthroline and imidazole-quinoline/pyridine coordinating fragments. Availability of these different diimine chelating functions and targeted synthetic procedures allowed one to obtain a series of mononuclear (Re and Ir) and binuclear (Re-Re and Re-Ir) metal complexes with various modes of {Re(CO)3Cl} and {Ir(NC)2} metal fragment coordination. The obtained compounds were characterized by 1D 1H and 2D (COSY and NOESY) NMR spectroscopy, mass spectrometry, elemental analysis, and X-ray diffraction crystallography. The photophysical study of the complexes (absorption, excitation and emission spectra, quantum yields, and excited-state lifetimes) showed that their emission parameters display strong dependence on the manner of metal center coordination to the diimine bidentate functions. The mononuclear complexes with an unoccupied imidazole-quinoline/pyridine fragment [Re(NN2), Re(NN3), and Ir(NC2)2(NN2)] or those containing a coordinated {Ir(NC)2} fragment in this position [Ir(NC2)2(NN1) and Re(NN2)Ir(NC1)2-Re(NN2)Ir(NC4)2] exhibit moderate-to-intense phosphorescence (quantum yields vary from 3% to 56% in a degassed solution), whereas the complexes containing a {Re(CO)3Cl} moiety in the imidazole-quinoline/pyridine position [Re2(NN2), Re2(NN3), and Ir(NC2)2(NN2)Re] demonstrate a strong reduction in the phosphorescence efficiency with a quantum yield of ≪0.1%. Quenching of the phosphorescence in the latter types of emitters is discussed in terms of a strong decrease in the radiative rate constants for these complexes compared to their analogues mentioned above, while the nonradiative constants remain nearly unchanged. Theoretical density functional theory (DFT) and time-dependent DFT (TD DFT) calculations, including evaluation of the radiative rate constants for the couple of structurally analogous complexes with and without a {Re(CO)3Cl} moiety coordinated to the imidazole-quinoline/pyridine chelating function, confirmed the observed trend in the variation of the emission intensity.

In this work nine novel heteroleptic Ir(III) complexes of general formulae [Ir(N perpendicular to C #)(2)(O perpendicular to O #)] containing four different cyclometallating and four beta-diketonate ligands were synthesized and fully characterized. Six of them display phosphorescence in the deep red and NIR regions with quantum yields reaching 24.6 % in degassed solution for one of the NIR emitters. Variation in the nature of orthometalating ligands results in dramatic changes in photophysical behavior: the compounds containing 2-phenylpyridine (N perpendicular to C 1) and 2-(benzo[b]thiophen-2-yl)pyridine (N perpendicular to C 2) ligands give non-emissive complexes, whereas those with methyl 2-phenylquinoline-4-carboxylate (N perpendicular to C 3) and 6-(benzo[b]thiophen-2-yl)phenanthridine) (N perpendicular to C 4) are luminescent, but display different character of electronic transitions responsible for absorption and emission. Complexes with the N perpendicular to C 3 ligand luminesce from (LC)-L-3 excited state and do not change their emission characteristics upon variations in the nature of beta-diketonates. On the contrary, the compounds based on the N perpendicular to C 4 cyclometalating ligand emit from the excited state with considerable contribution of (MLCT)-M-3 character and show systematic bathochromic shift of absorption and emission bands upon increase in electron donicity of O perpendicular to O # ligands. This conclusion was supported by DFT and TD-DFT calculations and by the analysis of correlations between the C-13 chemical shift of the diketonate C(H) carbon and emission maxima of the compounds under study.

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(diphe-nylphosphino)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)}(2)dppm](2+). The complexes obtained were fully character-ized 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.

Two NIR-emitting platinum [Pt(NANAC)-(phosphine)] and iridium [Ir(N<^>C)2(N<^>N)](+) complexes containing reactive succinimide groups were synthesized and characterized with spectroscopic methods (N<^>N<^>C, 1-phenyl-3-(pyridin-2-yl)-benzo [4,5]imidazo [1,2-a] pyrazine, N<^>C, 6-(2-b enzothi enyl)-phenanthridine, phosphine-3-(diphenylphosphaneyl) propanoic acid N-hydroxysuccinimide ether, and N<^>N, 4-oxo-4-((1-(pyridin-2-yl)-1H-1,2,3-triazol-4-yl)methoxy)butanoic acid N-hydroxysuccinimide ether). Their photophysics were carefully studied and analyzed using time-dependent density functional theory calculations. These complexes were used to prepare luminescent micro-and nanopartides with the "core-shell" morphology, where the core consisted of biodegradable polymers of different hydrophobicity, namely, poly(nplactic add), poly(epsilon-caprolactone), and poly(omega-pentadecalactone), whereas the shell was formed by covalent conjugation with poly(L-lysine) covalently labeled with the platinum and iridium emitters. The surface of the species was further modified with heparin to reverse their charge from positive to negative values. The micropartides' size determined with dynamic laser scanning varies considerably from 720 to 1480 nm, but the nanoparticles' diameter falls in a rather narrow range, 210-230 nm. The species with a poly(L-lysine) shell display a high positive (>30 mV) zeta-potential that makes them essentially stable in aqueous media. Inversion of the surface charge to a negative value with the heparin cover did not deteriorate the species' stability. The iridium- and platinum-containing particles displayed emissions the spectral patterns of which were essentially similar to those of unconjugated complexes, which indicate retention of the chromophore nature upon binding to the polymer and further immobilization onto polyester micro- and nanoparticles for drug delivery. The obtained particles were tested to determine their ability to penetrate into different cells types: cancer cells, stem cells, and fibroblasts. It was found that all types of particles could effectively penetrate into all cells types under investigation. Nanopartides were shown to penetrate into the cells more effectively than microparticles. However, positively charged nanoparticles covered with poly(L-lysine) seem to interact with negatively charged proteins in the medium and enter the inner part of the cells less effectively than nanopartides covered with poly(L-lysine)/heparin. In the case of micropartides, the species with positive zeta-potentials were more readily up-taken by the cells than those with negative values.

New N^N and N^C luminescent ligands with solvatochromic behavior and their iridium complexes were synthesized, characterized and investigated.

This paper presents synthesis and photophysical investigation of a very rare type of the ReI diimine complexes, [Re(diimine)(CO)3(OPR3)]+, R = Ph, Cy; diimine – phenanthroline and neocuproine, containing monodentate (unsupported) phosphine oxide ligands. The obtained compounds have been structurally characterized in solid phase by using XRD crystallography, which revealed unusual distortions in the pseudo octahedral rhenium environment, which may be ascribed to intramolecular interligand (phosphine oxide – diimine) interaction rather than to crystal packing effect. Optimization of the ground state structure of these molecules with the DFT method also confirmed intramolecular origin of the observed structural peculiarities. The complexes display phosphorescence in solution and in solid state with the quantum yield up to 11 % and 14 %, respectively, which originates from 3MLCT excited state as demonstrated by DFT calculations. Comparative analysis of the ligand (L) effect onto emission energy in the [Re(neocuproine)(CO)3(L)] complexes (L = PPh3, NCMe, OPPh3, Cl–) showed that the position of emission wavelength in the corresponding complexes qualitatively correlates with cumulative donor ability of these ligands that is in complete agreement with the 3MLCT character of emission.

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 photophysical characteristics (large Stokes shift and lifetime in the microsecond domain) offer some important advantages in comparison to organic fluorophores and may provide better imaging resolution and higher sensitivity: for example, in mapping the oxygen concentration in biological objects. We have synthesized a series of [Ir(N<^>C)(2)(N<^>N)](+) complexes with emission in the NIR region (N<^>C = (2-benzothienyl)-phenanthridine and 6-(2-benzothienyl)phenanthridine-2-carboxylic acid; N<^>N = functionalized pyridine-triazole chelates), which also display a considerable red shift of their excitation spectra to the window of transparency. The flexible protocol for the synthesis of the N<^>N ligands makes possible wide variations in the peripheral ligand environment: e.g., insertion of hydrophilic carboxyl group and further attachment of the other biologically relevant functions. The compounds obtained were completely characterized using spectroscopic methods, and their ground-state structures and photophysical properties were studied by DFT and TD DFT methods. To analyze the behavior of these emitters in biological systems, we investigated their interaction with human serum albumin (HSA), as the most abundant serum protein. It was found that these complexes readily form noncovalent {HSA-complex} adducts by embedding into hydrophobic cavities of this protein that also induced its partial aggregation. The complexes demonstrated preferential redistribution toward aggregated forms of HSA; the complex:HSA molar ratio did not exceed 1:3 for nonaggregated species. It was also shown that interaction of the hydrophobic complexes with albumin and the resulting aggregation dramatically change their important photophysical parameters such as emitter lifetime and its sensor response onto molecular oxygen.

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 photo physical 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 (LC)-L-3, (MLCT)-M-3, (LLCT)-L-3 with major contribution of the former excited state and show reasonable agreement with the experimental data.

A series of ruthenium(II) p-cymene complexes bearing 2‑(1,2,4‑triazol‑3‑yl)pyridines was obtained. A simple and efficient 1H NMR spectroscopic criterion for determining coordination mode of the 2‑(1,2,4‑triazol‑3‑yl)pyridines as ligands in the complexes is described. The validity of the criterion is corroborated by DFT calculations using B3LYP functional and mixed LANL2DZ/6-31**G basis set. Also, the influence of the size of the substituent in 5-position of the triazole ring on linkage isomers' ratio is discussed.