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In this study, the synthesis, photophysical characterization, and (photo)biological assessment of functional rhenium(I)- and platinum(II)-based complexes are presented. These compounds feature anionic 1,2,4-triazolylpyridine-based chromophores and neutral βC-based monodentate coligands, specifically 9H-pyrido[3,4-b]indole (nHo) or 9-methyl-9H-pyrido[3,4-b]indole (MenHo), which have been chosen to promote their biological activity. The impact of transition metal cations, coordination geometries, substitution patterns of the luminophore and coligands on the properties of these complexes was thoroughly assessed, encompassing photoluminescence and singlet dioxygen (1O2) quantum yields, excited state lifetimes, and (non)radiative rate constants, across various temperatures and phases. Superior photophysical characteristics were attained by the Pt(II)-based complexes, while effective capabilities as photosensitizers of 1O2were observed for all coordination compounds. Incorporation of these complexes into a polymeric matrix (PMMA) significantly enhanced their luminescence efficiencies by preventing diffusional quenching arising from triplet dioxygen (3O2). Furthermore, a comprehensive (photo)cytotoxicity study on human telomerase reverse transcriptase (hTERT)-immortalized cells was conducted to assess the potential applications of these complexes in photodynamic therapy. In summary, a versatile platform for designing photofunctional materials with photosensitizing properties is offered by this coordination chemical approach. Precise control of photophysical and (photo)biological attributes is achievable through the careful selection of metal centers, substitution patterns, and ancillary ligands.

In an effort to develop transition metal complexes with efficient phosphorescence, we synthesized cyclometalated complexes [M(N∧C∧N)Cl] (M = Pd or Pt) with amine groups NH(C6H5) at the two ortho-positions of the pyridyl rings (HLNHPh) or NH(C6H5CH2) (HLNHBn) for intramolecular hydrogen bonding with the Cl–coligand. Single-crystal X-ray diffractometry confirmed the hydrogen bonding and showed a distorted square planar geometry around the metal centers with τ4values of around 0.25 due to marked distortion of the Cl–coligand from the coordination plane. Long-wavelength UV–vis absorption energies are increased for Pt vs Pd. The Pt(II) complexes are intense triplet emitters in solution at 298 K (λmax= 520 nm) and at 77 K. The Pd(II) derivatives showed vibrationally structured phosphorescence bands in a frozen glassy matrix at 77 K resembling those of the Pt complexes but were nonemissive in liquid solutions at 298 K. The DFT-optimized electronic structures of the complexes show comparable geometries in their singlet ground state (S0) and in the first triplet (T1) excited states. Both are distorted by a combination of steric repulsion of the bulky ortho-RNH groups of the tridentate N∧C∧N ligands, the Cl–coligand, and the N–H···Cl···H–N hydrogen bonds.

The synthesis as well as the structural and photophysical characterization of two isoleptic bis-cyclometalated Pt(II) and Pd(II) complexes, namely [PtL] and [PdL], bearing a tailored dianionic tetradentate ligand (L2–) are reported. The isostructural character and intermolecular interactions of [PtL] and [PdL] were assessed by NMR spectroscopy and X-ray diffraction analysis. Both complexes show fully ligand-controlled aggregation, demonstrating that a judicious molecular design can tune the photophysical properties. In fact, by introduction of fluorine atoms on defined positions and methoxy groups on complementary sites, metal–metal interactions can be forced by a head-to-tail stacking. Hence, [PtL] shows luminescence from metal-perturbed ligand-centered or from metal-metal-to-ligand charge-transfer triplet states in diluted solutions, in frozen glasses and in crystals, with high photoluminescence quantum yields and long lifetimes in the microsecond range. At room temperature (RT) in concentrated fluid solutions, the palladium analogue [PdL] surprisingly emits luminescence from aggregated species involving supramolecular interactions. Time-resolved photoluminescence and transient absorption spectroscopies demonstrated that ultrafast intersystem crossing occurs for both metals, which outruns any competitive relaxation pathway from the photoexcited singlet state. Furthermore, we demonstrate that the radiationless deactivation can be suppressed in frozen glassy matrices at 77 K and by intermolecular interactions in fluid solutions at RT. In both cases and as indicated by density functional theory calculations, the lowest emissive state acts as an energy trap from which the thermal population of dissociative states with formal occupation of an antibonding Pd-centered 4dx2–y2orbital is suppressed. This occurs as the energy gap between the emissive and the dark states surpasses kT.

Fluoride is a natural contaminant of water – that endangers many people worldwide when present in concentrations higher than 2ppm. Here, fluoride removal by four different nanostructured colloidal particles (SiO2@ZrO2nc, SiO2@ZrO2c, @ZrO2nc, and @ZrO2c) was measured in batch systems within a period of 24h. Surprisingly, these materials removed fluoride from the water solutions and reached equilibrium in less than 10min. The combination of high specific surface and fast fluoride removal placed these materials among the top materials currently known in fluoride removal. Also, the impact of element leaching was measured and quantified. The influence of time, pH, and fluoride concentration on leaching of Zr and Si was evaluated with a response surface methodology. Leaching of Zr and Si continued for several hours and depended on first-order, quadratic and cross-product coefficients. Previous studies of fluoride removal with zirconium oxide often assumed that a decrease in fluoride concentration in the solution indicated that fluoride was bound to the surface of the oxide. Zirconium oxide's solubility in water is low, but not zero. Hence, Zr might have formed soluble fluorocomplexes. This is the first report of fluoride removal with zirconium oxide that studied the leaching of the solid to exclude the formation of soluble fluorocomplexes.

In this work, we describe the synthesis as well as structural, photophysical, and theoretical investigation of a new coordination chemical concept involving rhenium(I) complexes bearing monoanionic 1,2,4-triazolylpyridine-based bidentate chromophores. The X-ray diffractometric analysis of single crystals revealed particular packing features: the trifluoromethylated exemplar displayed two kinds of arrangements of the coordination centers, where the bidentate ligands at the edges of the unit cell are staggered parallel to each other, whereas those inside show antiparallel stacking with respect to the external ligands. On the other hand, the complexes bearing an adamantyl substituent yield a linear arrangement, where the bulky moiety of one luminophore points to the pyridine center of the adjacent ligand of the neighboring complex while including methanol molecules hydrogen-bonded to the triazolato unit. We observed that the photophysical properties of the complexes (photoexcited-state lifetimes, photoluminescence maxima and quantum yields) can be adjusted by tuning of the substitution pattern at the bidentate luminophore as well as by variation of the monodentate coligand. The photoluminescence spectra and photoexcited-state lifetimes of the crystalline phases were measured by phosphorescence lifetime micro(spectro)scopy. Interestingly, the vibrationally resolved emission spectra of the crystals closely resemble those of diluted frozen glassy matrixes at 77 K, in contrast with the broad bands observed in amorphous solids and in fluid solutions, where the charge-transfer character is enhanced. While the photoluminescence quantum yields (ΦL) reach up to 15%, the complexes are able to attain up to 55% efficiency regarding the photosensitization of 1O2(ΦΔ), depending on the combination of luminophore and coligand. Theoretical calculations showed that the photoexcited triplet (T1) state has a metal–ligand-to-ligand charge-transfer character, where promotion to the excited electronic configuration shortens the Re(I)–N bond involving the bidentate triazolylpyridine while stretching the three fac-CO–Re(I) bonds as well as the linkage to the axial monodentate coligand. The calculated vertical (Evl) and 0–0 (E(0–0)) radiative transition energies are in very good agreement with the experimental values (Eexplum).

Two isoleptic complexes involving Pd(II) and Pt(II) centres with a tetradentate luminophoric ligand were adsorbed onto Laponite (LAP), yielding H2O-dispersible nanohybrids with remarkable photoexcited state properties. The adsorption promoted rigidification of the coordination compounds and suppression of roto-vibrational deactivation pathways, thus enhancing the performance of the molecular species. Interestingly, room temperature phosphorescence was achieved in the case of the Pd(II)-containing nanohybrid along with a marked 3O2sensitivity, whereas the photoluminescence of the Pt(II)-based material showed only a mild dependence on the presence of 3O2while reaching up to 37% quantum yield.

In this work, the synthesis, structural and photophysical characterization of six phosphorescent H2O-soluble Pt(II) complexes are reported while addressing their emission maxima, photoluminescence quantum yields (ΦL), lifetimes (τ), aggregation tendency, and microenvironment sensitivity as a function of the substitution pattern on the main tridentate luminophore. Different ancillary ligands, namely, a trisulfonated phosphane and maltohexaose-conjugated pyridines (with or without amide bridges), were introduced and evaluated for the realization of switch-on-photoluminescent labels reporting on the microenvironment sensed in biofilms of Gram+and Gram–models, namely, Staphylococcus aureusand Escherichia coli. With the aid of confocal luminescence micro(spectro)scopy, we observed that selected complexes specifically interact with the biofilms while leaving planktonic cells unlabeled. By using photoluminescence lifetime imaging microscopy, excited-state lifetimes within S. aureusbiofilms were measured. The photoluminescence intensities were drastically boosted, and the excited state lifetimes were significantly prolonged upon binding to the viscous biofilm matrix, mainly due to the suppression of radiationless deactivation pathways upon shielding from physical quenching processes, such as interactions with solvent molecules and 3O2. The best performances were attained for non-aggregating complexes with maltohexaose targeting units and without amide bridges. Notably, in the absence of the maltodextrin, a hydrophobic adamantyl moiety suffices to attain a sizeable labeling capacity. Moreover, photoluminescence studies showed that selected complexes can also effectively interact with E. colibiofilms, where the bacterial cells are able to partially uptake the maltodextrin-based agents. In summary, the herein introduced concepts enable the development of specific biofilm reporters providing spatial resolution as well as lifetime- and spectrum-based readouts. Considering that most theragnostic agents reported so far mainly address metabolically active bacteria at the surface of biofilms but without reaching cells deeply immersed in the matrix, a new platform with a clear structure-property correlation is provided for the early detection of such bacterial arrays.

In this work, for the first time, the comparative use of P-, As-, and Sb-based ligands in phosphorescent coordination compounds is reported toward new coordination chemical concepts in the design and realization of tailored triplet emitters with nonconventional elements. By means of spectroscopic, X-ray diffractometric, and quantum-chemical methods, we reconstructed the nature of the chemical bonds as well as the influence of the increasingly heavy elements on the photoexcited state properties, which were correlated with the hybridization and polarizability of the pnictogen atoms (Pn). In particular, we elucidated the structural and photophysical properties of a series of homologous Pt(II) complexes with monodentate ancillary ligands based on group 15 elements, namely P, As, and Sb. Six coordination compounds bearing tridentate dianionic 2,6-bis(1H-1,2,4-triazol-5-yl)pyridine luminophoric pincer ligands bearing either CF3or tBumoieties on the triazole rings along with triphenylpnictogens (PnPh3) as monodentate ancillary ligands ([CF3/Pn]or [tBu/Pn], respectively) have been investigated. The electron donating or withdrawing effect of the peripheral substituent (tBuvs. CF3, respectively) and its influence on the bonding, crystal packing as well as the excited state energies and lifetimes was assessed in fluid solutions, frozen glassy matrices, amorphous solids, and crystalline phases. A progressively red-shifted phosphorescence was observed with increasing atomic number along with a growing compensation of hybridization defects upon coordination of the Pnatom to the Pt(II) center. The change of molecular geometry of the PnPh3unit upon complexation was extrapolated to predict the structural and excited state characteristics of the Bi-based analogues, which according to DFT calculations should be stable species and are the subject of ongoing synthetic efforts. In general, we envisage the use of these ligands for the relativistic enhancement of radiative deactivation rate processes, especially if Bi-based s-orbitals participate on the bond with the metal center, paving the road toward novel coordination compounds using abundant elements with high spin–orbit coupling for sustainable electroluminescent devices.

In this work, we synthesized two tailored phosphorescent Pt(II) complexes bearing a cyclometalating tridentate thiazole-based C^N*N pincer luminophore (L) and exchangeable chlorido ([PtCl(L)]) or cyanido ([PtCN(L)]) coligands. While both complexes showed photoluminescence from metal-perturbed ligand-centered triplet states (3MP-LC), [PtCN(L)]reached the highest phosphorescence quantum yields and displayed a significant sensitivity toward quenching by 3O2. We encapsulated them into two Zn-based metal–organic frameworks, namely, MOF-5and ZIF-8. The incorporation of the organometallic compounds in the resulting composites [PtCl(L)]@ZIF-8, [PtCN(L)]@ZIF-8, [PtCl(L)]@MOF-5, and [PtCN(L)]@MOF-5was verified by powder X-ray diffractometry, scanning electron microscopy, time-resolved photoluminescence spectroscopy and microscopy, as well as N2- and Ar-gas sorption studies. The amount of encapsulated complex was determined by graphite furnace atomic absorption spectroscopy, showing a maximum loading of 3.7 wt %. If compared with their solid state forms, the solid-solution composites showed prolonged 3O2-sensitive excited state lifetimes for the complexes at room temperature, reaching up to 18.4 μs under an Ar atmosphere, which is comparable with the behavior of the complex in liquid solutions or even frozen glassy matrices at 77 K.

The adsorption of a Re(CO)3(phen)-poly(4-vinylpyridine) polymer, RePVP, on multiwall carbon nanotubes surfaces is studied by transmission electron microscopy and absorption spectroscopy in combination with chemometric techniques in MeOH/H2O solvent mixture. Nanohybrid structures like a shish-kebab (NHSK) are observed by TEM when RePVP is wrapped around carbon nanotubes (CNTs) surfaces. The association between RePVP and CNTs studied by absorption spectroscopy suggests the coexistence of CNTs with a high or low content of adsorbed RePVP on their surface. In the absence of CNTs, the photophysical properties of RePVP (i.e., luminescence quantum yield, ΦL, and amplitude-weighted average lifetimes, ⟨τ⟩) are strongly dependent on the morphology of the polymer as witnessed by the dependence of ΦLon the concentration of RePVP (CRePVP) and the fact that in CH3CN ΦLand ⟨τ⟩ are sensitive to O2while in a MeOH/H2O solvent mixture they are not. In the NHSK, an energy-transfer process between excited −[Re(CO)3(phen)]+* pendent chromophores and the CNTs surface, with static and dynamic components, is responsible for the quenching of the RePVP luminescence by CNTs.

In this work, we have explored Re(I) complexes featuring triphenylpnictogen (PnPh3, Pn= P, As, or Sb)-based coligands and bidentate (neutral or monoanionic) luminophores derived from 1,10-phenantroline (phen), as well as from 2-(3-(tert-butyl)-1H-1,2,4-triazol-5-yl)pyridine (H(N-tBu)). The effect of the increasingly heavy elements on the structural parameters, photoexcited-state properties, and electrochemical behavior as well as the hybridization defects and polarization of the Pnatoms was related to the charges of the main luminophores (i.e., phenvs N-tBu) and explored in terms of photoluminescence spectroscopy, X-ray diffractometry, and quantum-chemical methods. Therefore, an in-depth analysis of the bonding, crystal packing, excited-state energies, and lifetimes was assessed in liquid solutions, frozen glassy matrices, and crystalline phases along with a semiquantitative photoactivation study. Notably, by changing the main ligand from phento N-tBu, an increase in radiative and radiationless deactivation rates (krand knr, respectively) at 77 K together with a faster photoinduced CO release and fragmentation at room temperature was detected. In addition, a progressively red-shifted phosphorescence was observed with the growing atomic number of the pnictogen atom, along with a boost in krand knrat 77 K. Down the Vthmain group and upon coordination of the Pnatom to the Re(I) center, an increasingly prominent jump of s-orbital participation on the binding sxp3.00-orbitals of the Pnatoms is evidenced. Based on these findings, the ability of these complexes to act as tunable photoluminescent labels able to perform as light-driven CO-releasing molecules is envisioned.

A family of Pt(II) complexes bearing monoanionic C^N^N ligands as luminophoric units as well as a set of monodentate ligands derived from allenylidene and carbene species were synthesized and characterized in terms of structure and photophysical properties. In addition, we present the extraordinary molecular structure of a phosphorescent complex carrying an allenylidene ligand. Depending on the co-ligand, an effect can be observed in the photoluminescence lifetimes and quantum yields as well as in the radiative and radiation less deactivation rate constants. Their correlation with the substitution pattern was analyzed by comparing the photoluminescence in fluid solution at room temperature and in frozen glassy matrices at 77 K. Moreover, in order to gain a deeper understanding of the electronic states responsible for the optical properties, density functional theory calculations were performed. Finally, the cytotoxicity of the complexes was evaluated in vitro, showing that the cationic complexes exhibit strong effects at low micromolar concentrations. The calculated half-maximum effective concentrations (EC50values) were 4 times lower in comparison to the established antitumor agent oxaliplatin. In contrast, the neutral species are less toxic, rendering them as potential bioimaging agents.

Efficient shielding of phosphorescent transition metal complexes against diffusion-controlled collisional quenching by triplet molecular dioxygen as well as reduction of microenvironment-related radiationless deactivation pathways is crucial for their applications in bioimaging and optoelectronics. In this report, we present a straightforward yet efficient approach to safeguard emissive triplet states from external influences by adsorbing phosphorescent Pt(II) complexes onto a layered nanoclay, namely Laponite. These hybrids facilitate the dispersion of otherwise insoluble transition metal complexes in aqueous media while shielding them from physical quenching. Self-assembly of the nanoclay and intermolecular stacking between molecules adsorbed at different nanodisc units are mirrored in the photophysical, colloidal, and morphological properties of the hybrids, which were herein characterized by steady-state and time-resolved photoluminescence spectroscopy, dynamic light scattering, and atomic force microscopy. We also show that the hybrids are noncytotoxic and can be exploited as luminescent reporters in spectrally resolved phosphorescence lifetime imaging implemented by confocal optical microscopy.