Enhancing the photophysical properties of Ru(II) complexes by specific design of tridentate ligands

Photo-release of acetonitrile in ruthenium(II) complexes with various substituted terpyridine ligands

The photo-release of acetonitrile is investigated in a series of ruthenium(II) complexes of the general formula [Ru(R-phtpy)(acac)(MeCN)](PF6) (phtpy stands for 4'-phenyl-2,2':6',2''-terpyridine, and R = Et2N, Me2N, MeO, Me, H, NO2). The experimental quantum yields of photo-release (ϕMeCN = MeCN released/photons absorbed) increases with the donating capability of R, with values ranging from ϕMeCN = 0 (NO2) to ϕMeCN = 0.05 (Et2N). The origin of this effect is investigated computationally using the density functional theory and compared to those reported recently by our group on related [Ru(R-phtpy)(acac)(NO)](PF6) species capable of causing photo-release of NO. In the present case, the capability for MeCN release appears related to the relative energies of the metal-centered (3MC) vs. metal-ligand-charge-transfer (3MLCT) triplet states. The 3MC state, in which the Ru-NC distance is elongated to 4.2 Å, is expected to be responsible for the release. Additionally, four crystal structures are reported for the compounds in which R = Et2N, MeO, H, and NO2.

Fine-Tuning the Excited-State Dynamics of Heteroleptic Ruthenium(II) Polypyridyl Complexes with Systematic Variation of Benzazole-Substituted 8-Hydroxyquinolines

A series of structurally related bistridentate heteroleptic Ru(II) polypyridyl complexes, [RuII(ttpy)(8-HQLS/N/O)]+ (Ru1-Ru3), were synthesized, where ttpy = p-tolyl terpyridine and 8-HQLS/N/O are monoanionic N^N^O-donor tridentate ligands (8-HQLX), derived from 8-hydroxyquinoline (8-HQ), namely, 8-HQLS = 2-(2'-benzothiazole)-8-hydroxyquinoline, 8-HQLN = 2-(2'-benzimidazole)-8-hydroxyquinoline, and 8-HQLO = 2-(2'-benzoxazole)-8-hydroxyquinoline. The electronic structures of these rigid ligands were systematically tuned by varying the noncoordinating heteroatoms (S, O, NH) in the five-membered heterocyclic ring, impacting the electronic properties, redox potentials, excited-state lifetime/dynamics, and deactivation pathways and photophysical behavior of the corresponding Ru(II) complexes. Notably, [RuII(ttpy)(8HQLN)]+ (Ru2) exhibited an excited-state lifetime (τ > 1 ns in CH3CN at RT) surpassing that of the homoleptic complex [Ru(ttpy)2]2+ (τ ∼ 0.62 ns), despite its more distorted octahedral geometry. These heteroleptic complexes (Ru1-Ru3) showed extended excited-state lifetimes compared to their homoleptic counterpart Ru4. The complexes displayed absorption in the red region, which is favorable for phototherapeutic applications. Their relative singlet oxygen (1O2) quantum yields (ΦΔ) in CH3CN ranged from 0.03 to 0.10. Given their reasonable excited-state lifetimes and 1O2 generation ability, these Ru(II) complexes demonstrated potential as photocatalysts for organic substrates, as evidenced by their effectiveness in the photooxidation of PPh3 to Ph3P=O as a model reaction.

Molecular engineering and electrolyte optimization strategies for enhanced performance of Ru(ii) polypyridyl-sensitized DSSCs

Dye-sensitized solar cells (DSSCs) are a leading third-generation solar cell technology due to their low cost, ease of fabrication, and tunable photoelectrochemical properties. Among DSSC components, the photosensitizer plays a crucial role in light absorption and charge generation, with Ru(ii)-polypyridyl complexes standing out due to their superior photostability, broad absorption spectra, and efficient charge injection. This review provides a comprehensive analysis of molecular engineering strategies for Ru(ii)-polypyridyl photosensitizers, emphasizing ligand modifications to design and develop novel Ru(ii) photosensitizers with prolonged excited-state lifetimes, reduced charge recombination, enhanced light-harvesting capabilities, and improved overall solar-to-power conversion efficiency (PCE). In addition, cyclometallated polypyridyl Ru(ii) complexes are explored as promising alternatives to Ru(ii) complexes incorporating labile thiocyanate (SCN) ligands for DSSCs, which offer improved stability. The relationship between the molecular structure of Ru(ii) photosensitizers and their photovoltaic characteristics is analyzed by examining key factors that influence their photovoltaic performance, including light-harvesting efficiency, fine-tuning ground and excited state oxidation potentials (GSOP/ESOP), extending excited state lifetimes, and minimizing charge recombination. Additionally, the impact of co-adsorbents, electrolyte additives, and interfacial engineering on DSSC performance is explored. Emphasis is placed on optimizing redox electrolytes beyond conventional iodide/triiodide (I-/I- 3) systems to minimize energy loss and enhance PCE. By carefully considering those challenges, this review lays the groundwork for the rational design of next-generation DSSCs that are more efficient, stable, and commercially viable.

Leveraging Metal Complexes for Microsecond Lifetime-Based Chloride Sensing

Chloride is the most abundant anion in cells and plays many critical roles in maintaining cellular homeostasis. However, current chloride indicators are rare with inherent sensitivity in their emission properties, such as vulnerability to pH changes or short emission lifetimes. These limitations restrict their application in aqueous media and imaging. In this work, we employed a transition-metal complex bearing pyridinium as a recognition unit for chloride and studied the phosphorescence emission properties. Iridium(III) complex 1 was synthesized as an alternative chloride-sensitive luminophore. The conjugable design also allows customization for the desired applications. Complex 1 exhibited high sensitivity and selectivity in chloride sensing across different physiological environments, regardless of pH fluctuation and ionic strength. Additionally, complex 1 featured a microsecond emission lifetime. The chloride sensing ability of complex 1 can be measured through both the luminescence intensity and long-lived phosphorescent lifetime, providing an alternative potential route for chloride imaging. The analogue 1b was successfully applied in the imaging of Cl- in cellular environments and showed dose-dependent responses in both live and fixed cells.

Remarkable Increase in the Rate of Trans-Cis Photoisomerization of Os(II)-Terpyridine Complexes via Oxidation and Reduction

Luminescent homoleptic Os(II)-terpyridine complexes comprising stilbene-appended naphthalene, anthracene, and pyrene motifs are designed in this work, and their photophysical, electrochemical, and photoisomerization behaviors are extensively investigated. All complexes exhibit intense spin-allowed singlet metal-to-ligand charge transfer (1MLCT) bands in the visible (496-500 nm) and weaker spin-forbidden singlet-to-triplet 3MLCT transitions in the 600-700 nm range. They display moderate emission at room temperature with lifetimes in the range of 84.5-112.5 ns. Electrochemical studies reveal a reversible Os2+/Os3+ oxidation couple within 0.93-0.96 V, alongside multiple reversible or quasi-reversible reduction peaks associated with terpyridine units in between -1.10 and -1.85 V. The stilbene motifs facilitate reversible trans-cis photoisomerization under alternative treatment with visible and UV light, enabling the complexes to function as photomolecular switches in the near-infrared domain. Interestingly, a remarkable increase in the rate of photoisomerization has been achieved via oxidation as well as reduction of the complexes, which, in turn, induces multistep switching involving reversible oxidation-reduction and trans-cis isomerization. Computational investigations are also conducted on all three conformations {trans-trans (t-t), trans-cis (t-c), and cis-cis (c-c)} of the complexes to gain insight into their electronic structures and for accurate assignment of their absorption and emission spectral bands.

Effect of the Appended Morpholinyl Group on Photophysical Behavior of Mono- and Bis-cyclometalated Terpyridine Iridium(III) Chromophores

This paper provides extensive studies of [IrCl(Ph-py)(morph-C6H4-terpy-κ3N)]PF6 (1A), [Ir(Ph-py)2(morph-C6H4-terpy-κ2N)]PF6 (2A), [IrCl(Ph-py)(Ph-terpy-κ3N)]PF6 (1B), and [Ir(Ph-py)2(Ph-terpy-κ2N)]PF6 (2B) designed to demonstrate the possibility of controlling the photophysical properties of mono- and bis-cyclometalated complexes [IrCl(Ph-py)(R-C6H4-terpy-κ3N)]PF6 and [Ir(Ph-py)2(R-C6H4-terpy-κ2N)]PF6 through a remote electron-donating substituent introduced into the 4'-position of 2,2':6',2″-terpyridine (terpy) via the phenyl linker. The attachment of the morpholinyl (morph) group was evidenced to induce dramatic changes in the emission characteristics of the monocyclometalated Ir(III) systems with meridionally coordinated R-C6H4-terpy ligand (κ3N). In solution, the obtained complex [IrCl(Ph-py)(morph-C6H4-terpy-κ3N)]PF6 was found to be a rare example of dual-emissive Ir(III) systems. Within the series [Ir(Ph-py)2(R-C6H4-terpy-κ2N)]PF6 bearing the R-C6H4-terpy ligand bound to the central ion in a bidentate coordination mode, the appended electron-donating morpholinyl group induced a minor effect on the emission maximum, but it was found to be an effective tool for extending the excited-state lifetime, further prolonging with the increase of solvent polarity. The results of this work are of high significance for better understanding the push-pull effect and dual-emission phenomena in Ir-based luminophores, as well as developing chromophores with prolonged emission lifetimes.

From the Design of Innovative Ti-Pt Heterometallic Complexes to the Development of Highly Anti-Proliferative Water-Soluble Cationic Titanocenes

Two innovative early/late Ti-Pt-heterobimetallic complexes were synthesized, characterized, and screened in cell-based assays using several human (SW480 and MDA-MB-231) and murine cancer cell lines (CT26 and EMT6) as well as a non-cancerous cell line (HMEC). The combination of the two metals - titanium(IV) and platinum (IV) - in a single molecule led to a synergistic biological activity (higher anti-proliferative properties than a mixture of each of the corresponding monometallic complexes). This study also investigated the benefits of associating a metal-free terpyridine moiety (with intrinsic biological activity) with a water-soluble titanocene fragment. The present work reveals that these combinations results in water-soluble titanocene compounds displaying an anti-proliferative activity down to the submicromolar level. One of these complexes induced an antitumor effect in vivo in CT26 tumor bearing BALB/C mice. The terpyridine moiety was also used to track the complex in vitro by multiphoton microscopy imaging.

Naphthalene Diimide and Bis-Heteroleptic Ru(II) Complex-Based Hybrid Molecule with 3-in-1 Functionalities

Multipurpose applications of a newly developed homobimetallic Ru(II) complex, Ru-NDI[PF6]4, which incorporates 1,10-phenanthroline and triazole-pyridine ligands and linked via a (-CH2-)3 spacer to the reputed anion-π interacting NDI system, are described. Solution-state studies of the bimetallic complex, including EPR, PL, UV-vis, and NMR experiments, reveal two sequential one-electron transfers to the NDI unit, generating NDI⋅- and NDI2- in the presence of F- selectively. This process inhibits the primary electron transfer from Ru(II) to the NDI unit, thereby allowing the 3MLCT-based emission of the complex to be recovered, resulting in a corresponding ten-fold increase in luminescence intensity. DFT and TD-DFT computational studies further elucidate the experimentally observed absorption spectra of the complex. Secondly, CT-DNA binding studies with the complex are performed using various spectroscopic analyses such as UV-vis, PL, and CD. Comparative DNA binding studies employing EB and molecular docking reveal that the binding with CT-DNA occurs through both intercalative and groove binding modalities. Thirdly, the photocatalytic activities of the complex towards C-C, C-N, and C-O bond formation in organic cross-coupling reactions, including the amidation of α-keto acids to amines and the oxidation of alcohol to aldehydes, are also demonstrated.

Spectro-electrochemical study of iron and ruthenium bis-terpyridine complexes with methyl viologen-like subunits as models for supramolecular polymers

Metallo-supramolecular polyelectrolytes (MEPE) have a variety of attractive properties concerning electrochromism, spin-crossover, rheology, and cell differentiation. Previous studies suggest that these polynuclear structures can be regarded as an assembly of individual subunits and mononuclear complexes can act as models. In this study, we synthesize a monotopic and a ditopic terpyridine ligand with pyridinium units as well as the corresponding iron and ruthenium MEPEs and their mononuclear counterparts. UV-vis studies show that the mononuclear complexes have similar absorption properties to MEPEs. Furthermore, all complexes and MEPEs exhibit electrochromic behavior. Yet only the MEPEs can be deposited on different substrates using a layer-by-layer approach which makes them attractive for applications as electrochromic devices. However, the low solubility particularly of the ruthenium MEPE, renders characterization in solution impractical. Hence, the use of mononuclear complexes with similar monotopic ligands as presented herein can act as a first instance to evaluate the properties of corresponding MEPEs, facilitating the development of metallo-supramolecular materials.

Ruthenium(II) Polypyridyl Complexes with Benzoxazole Derivatives and Non-Innocent Ligands as Effective Antioxidants in Human Neuroblasts

Ruthenium(II) polypyridyl complexes continue to raise increasing interest for the encouraging results in several biomedical areas. Considering their vast chemical-physical repertoire, in particular the possibility to switch from the sensitization of reactive oxygen species (ROS) to ROS-scavenging abilities by tuning the nature of their ligands, it is therefore surprising that their potential as antioxidants has not been largely investigated so far. Herein, we explored the antioxidant behaviour of the novel ruthenium compound [Ru(dbpy)(2,3-DAN)Cl]PF6 (Ru1), featuring a benzoxazole derivative (dpby=2,6-bis(4-methyl-2-benzoxazolyl)pyridine) and the non-innocent 2,3-diamminonaftalene (2,3-DAN) ligand, along with the reference tpy-containing analogue [Ru(tpy)(2,3-DAN)Cl]PF6 (Ru2) (tpy=2,2':6',2''-terpyridine). Following the synthesis and the electrochemical characterization, chemical antioxidant assays highlighted the beneficial role of dpby for the ROS-scavenging properties of Ru1. These data have been corroborated by the highest protective effect of Ru1 against the oxidative stress induced in SH-SY5Y human neuroblastoma, which exerts pro-survival and anti-inflammatory actions. The results herein reported highlight the potential of Ru1 as pharmacological tool in neurodegenerative diseases and specially prove that the antioxidant properties of such compounds are likely the result of a non-trivial synergetic action involving the bioactive ligands in their chemical architectures.

Synthesis and structural characterizations of three carbonyl(α-diimine)hydrido(triphenylphosphine)ruthenium(II) complexes with derivatives of 1,10-phenanthroline

Three new ruthenium(II) polypyridyl complexes containing α-diimine ligands, namely, carbonylhydrido(1,10-phenanthroline-κ2N,N)bis(triphenylphosphine-κP)ruthenium(II) hexafluorophosphate, [RuH(C12H8N2)(C18H15P)2(CO)]PF6, carbonylhydrido(2,9-dimethyl-1,10-phenanthroline-κ2N,N)bis(triphenylphosphine-κP)ruthenium(II) hexafluorophosphate, and carbonylhydrido(4,7-dimethyl-1,10-phenanthroline-κ2N,N)bis(triphenylphosphine-κP)ruthenium(II) hexafluorophosphate, both [RuH(C14H12N2)(C18H15P)2(CO)]PF6, were synthesized and characterized by spectroscopic and X-ray diffraction methods. In these complexes, the ruthenium(II) ion adopts a distorted octahedral geometry. There are no intermolecular hydrogen bonds in the crystal structures of the analysed complexes and Hirshfeld surface analysis showed that the H...H contacts constitute a high percentage, close to 50%, of the intermolecular interactions.

The Role of Intraligand Charge Transfer Processes in Iridium(III) Complexes with Morpholine-Decorated 4'-Phenyl-2,2':6',2″-terpyridine

To investigate the impact of the electron-donating morpholinyl (morph) group on the ground- and excited-state properties of two different types of Ir(III) complexes, [IrCl3(R-C6H4-terpy-κ3N)] and [Ir(R-C6H4-terpy-κ3N)2](PF6)3, the compounds [IrCl3(morph-C6H4-terpy-κ3N)] (1A), 4[Ir(morph-C6H4-terpy-κ3N)2](PF6)3 (2A), [IrCl3(Ph-terpy-κ3N)] (1B) and [Ir(Ph-terpy-κ3N)2](PF6)3 (2B) were obtained. Their photophysical properties were comprehensively investigated with the aid of static and time-resolved spectroscopic methods accompanied by theoretical DFT/TD-DFT calculations. In the case of bis-terpyridyl iridium(III) complexes, the attachment of the morpholinyl group induced dramatic changes in the absorption and emission characteristics, manifested by the appearance of a new, very strong visible absorption tailing up to 600 nm, and a significant bathochromic shift in the emission of 2A relative to the model chromophore. The emission features of 2A and 2B were found to originate from the triplet excited states of different natures: intraligand charge transfer (3ILCT) for 2A and intraligand with a small admixture of metal-to-ligand charge transfer (3IL-3MLCT) for 2B. The optical properties of the mono-terpyridyl iridium(III) complexes were less significantly impacted by the morpholinyl substituent. Based on UV-Vis absorption spectra, emission wavelengths and lifetimes in different environments, transient absorption studies, and theoretical calculations, it was demonstrated that the visible absorption and emission features of 1A are governed by singlet and triplet excited states of a mixed MLLCT-ILCT nature, with a dominant contribution of the first component, that is, metal-ligand-to-ligand charge transfer (MLLCT). The involvement of ILCT transitions was reflected by an enhancement of the molar extinction coefficients of the absorption bands of 1A in the range of 350-550 nm, and a small red shift in its emission relative to the model chromophore.

Cyclometalated and NNN Terpyridine Ruthenium Photocatalysts and Their Cytotoxic Activity

The cyclometalated terpyridine complexes [Ru(η2-OAc)(NC-tpy)(PP)] (PP = dppb 1, (R,R)-Skewphos 4, (S,S)-Skewphos 5) are easily obtained from the acetate derivatives [Ru(η2-OAc)2(PP)] (PP = dppb, (R,R)-Skewphos 2, (S,S)-Skewphos 3) and tpy in methanol by elimination of AcOH. The precursors 2, 3 are prepared from [Ru(η2-OAc)2(PPh3)2] and Skewphos in cyclohexane. Conversely, the NNN complexes [Ru(η1-OAc)(NNN-tpy)(PP)]OAc (PP = (R,R)-Skewphos 6, (S,S)-Skewphos 7) are synthesized in a one pot reaction from [Ru(η2-OAc)2(PPh3)2], PP and tpy in methanol. The neutral NC-tpy 1, 4, 5 and cationic NNN-tpy 6, 7 complexes catalyze the transfer hydrogenation of acetophenone (S/C = 1000) in 2-propanol with NaOiPr under light irradiation at 30 °C. Formation of (S)-1-phenylethanol has been observed with 4, 6 in a MeOH/iPrOH mixture, whereas the R-enantiomer is obtained with 5, 7 (50-52% ee). The tpy complexes show cytotoxic activity against the anaplastic thyroid cancer 8505C and SW1736 cell lines (ED50 = 0.31-8.53 µM), with the cationic 7 displaying an ED50 of 0.31 µM, four times lower compared to the enantiomer 6.

Photophysical Studies of Helicate and Mesocate Double-Stranded Dinuclear Ru(II) Complexes

The metal-ligand charge transfer (3MLCT) and phosphorescence-quenching metal-centered (3MC) states of the helicate and mesocate diastereoisomers of a double-stranded dinuclear polypyridylruthenium(II) complex have been investigated using ultrafast transient absorption spectroscopy. At 294 K, transient signals of the helicate decayed significantly slower than those of the mesocate, whereas at 77 K, no clear contrast in kinetics was observed. Contributions to excited-state decay from high-lying 3MLCT states were identified at both temperatures. Spectroscopic data (294 K) suggest that the 3MC state of the helicate lies above the 3MLCT and that the reverse is true for the mesocate; this was further validated by density functional theory calculations. The stabilization of the 3MC state relative to the 3MLCT state in the mesocate was explained by a reduction in ligand field strength due to distortion near the ligand bridge, which causes further deviation from octahedral geometry compared to the helicate. This work illustrates how minor structural differences can significantly influence excited state dynamics.

Control of Photoisomerization Kinetics via Multistage Switching in Bimetallic Ru(II)-Terpyridine Complexes

In this study, we carried out detailed experimental and theoretical investigation on photophysical, electrochemical, and photoisomerization behaviors of a new array of luminescent binuclear Ru(II) complexes derived from a phenylene-vinylene-substituted terpyridyl ligand possessing RT lifetimes within 60.3-410.5 ns. The complexes experienced trans-to-cis isomerization in MeCN on irradiation with visible light, accompanied by significant changes in their absorption and emission spectral profiles. The reverse cis-to-trans process is also possible with the use of ultraviolet (UV) light. On conversion from trans to cis isomers, the emission intensity increases substantially, while for the reverse process, luminescence quenching occurs. Thus, "off-on" and "on-off" emission switching is facilitated upon treatment with visible and UV light alternatively. By the use of chemical oxidants (ceric ammonium nitrate and potassium permanganate) and reductants (metallic sodium) as well as light of appropriate wavelengths, multistate switching phenomena involving reversible oxidation-reduction and trans-cis isomerization have been achieved. Interestingly, the rate of this multistate photoswitching process becomes much faster compared to only two-state trans-cis isomerization of these complexes. Density functional theory (DFT) and time-dependent-DFT (TD-DFT) calculations are also performed to obtain a clear picture of the electronic environment of the complexes and also for the appropriate assignment of absorption and emission spectral bands.

Phototoxicity of Tridentate Ru(II) Polypyridyl Complex with Expanded Bite Angles toward Mammalian Cells and Multicellular Tumor Spheroids

Tridentate ligand-coordinated ruthenium (II) polypyridyl complexes with large N-Ru-N bite angles have been shown to promote ligand field splitting and reduce singlet-triplet state mixing leading to dramatically extended emission quantum yields and lifetimes under ambient conditions. These effects are anticipated to enhance their photoinduced singlet oxygen production, promoting prospects for such complexes as type II phototherapeutics. In this contribution, we examined this putative effect for [Ru(bqp)(bqpCOOEt)]2+, Ru-bqp-ester, a heteroleptic complex containing bqp = [2,6-bi(quinolin-8-yl)pyridine], a well-established large bite angle tridentate ligand, as well as its peptide conjugates [Ru(bqp)(bqpCONH-ahx-FrFKFrFK(Ac)-CONH2)]5+ (Ru-bqp-MPP) and [Ru(bqp) (bqp)(CONH-ahx-RRRRRRRR-CONH2)]10+ (Ru-bqp-R8) that were prepared in an effort to promote live cell/tissue permeability and targeting of the parent. Membrane permeability of both parent and peptide conjugates were compared across 2D cell monolayers; A549, Chinese hamster ovary, human pancreatic cancer (HPAC), and 3D HPAC multicellular tumor spheroids (MCTS) using confocal microscopy. Both the parent complex and peptide conjugates showed exceptional permeability with rapid uptake in both 2D and 3D cell models but with little distinction in permeability or distribution in cells between the parent or peptide conjugates. Unexpectedly, the uptake was temperature independent and so attributed to passive permeation. Both dark and photo-toxicity of the Ru(II) complexes were assessed across cell types, and the parent showed notably low dark toxicity. In contrast, the parent and conjugates were found to be highly phototoxic, with impressive phototoxic indices (PIs) toward HPAC cell monolayers in particular, with PI values ranging from ∼580 to 760. Overall, our data indicate that the Ru(II) parent complex and its peptide conjugates show promise at both cell monolayers and 3D MCTS as photosensitizers for photodynamic therapy.

Low-Temperature Observation of the Excited-State Decay of Ruthenium-(Mono-2,2':6',2″-Terpyridine) Ions with Innocent Ligands: DFT Modeling of an 3MLCT-3MC Intersystem Crossing Pathway

The synthesis, electrochemistry, and photophysical characterization of five 2,2':6',2″-terpyridine ruthenium complexes (Ru-tpy complexes) is reported. The electrochemical and photophysical behavior varied depending on the ligands, i.e., amine (NH₃), acetonitrile (AN), and bis(pyrazolyl)methane (bpm), for this series of Ru-tpy complexes. The target [Ru(tpy)(AN)₃]²⁺ and [Ru(tpy)(bpm)(AN)]²⁺ complexes were found to have low-emission quantum yields in low-temperature observations. To better understand this phenomenon, density functional theory (DFT) calculations were performed to simulate the singlet ground state (S₀), T_e, and metal-centered excited states (³MC) of these complexes. The calculated energy barriers between T_e and the low-lying ³MC state for [Ru(tpy)(AN)₃]²⁺ and [Ru(tpy)(bpm)(AN)]²⁺ provided clear evidence in support of their emitting state decay behavior. Developing a knowledge of the underlying photophysics of these Ru-tpy complexes will allow new complexes to be designed for use in photophysical and photochemical applications in the future.

Synthesis and Theoretical and Photophysical Study on a Series of Neutral Ruthenium(II) Complexes with Donor-Metal-Accepter Configuration

In order to construct a new type of ruthenium(II) terpyridine complexes with activated triplet metal-centered (³MC) states, as well as stabilized triplet metal-to-ligand charge transfer (³MLCT) states, conducive to fine emissive performances, Ru-1, Ru-2, Ru-3, and Ru-4 were synthesized. Compared with the [Ru(terpyridine)₂]²⁺ prototype (0.25 ns), this series of ruthenium(II) terpyridine complexes exhibit lengthened excited state lifetime (43.3 ns for Ru-1, 52.7 ns for Ru-2, 43.6 ns for Ru-3, and 53.4 ns for Ru-4). Interfragment charge transfer analysis illustrates the electron transfer direction of the four complexes, manifesting their intramolecular charge transfer characteristic. When excited, their lowest-lying triplet states are assigned as ³MLCT based on spin-density surface distribution. The singlet excited states and ³MLCT states were thoroughly studied by UV-visual absorption and nanosecond time-resolved transient absorption spectra, respectively. Photoluminescence spectra revealed their weak broadband near-infrared emission at room temperature and red phosphorescence at 77 K. The low molecular weight and the good thermal stability make Ru-1 and Ru-2 suitable for vaporization coating, while the fine solubility in common organic solvents makes Ru-3 and Ru-4 suitable for solution processing. Furthermore, the intrinsic electroneutrality and favorable energy levels endow them with new potential to be applied in the optoelectronic field.

Synthesis, Crystallographic Structure, Theoretical Analysis, Molecular Docking Studies, and Biological Activity Evaluation of Binuclear Ru(II)-1-Naphthylhydrazine Complex

Ruthenium(II)-arene complexes have gained significant research interest due to their possible application in cancer therapy. In this contribution two new complexes are described, namely [{RuCl(η⁶-p-cymene)}₂(μ-Cl)(μ-1-N,N'-naphthyl)]X (X = Cl, 1; PF₆, 2), which were fully characterized by IR, NMR, and elemental microanalysis. Furthermore, the structure of 2 in the solid state was determined by a single crystal X-ray crystallographic study, confirming the composition of the crystals as 2·2MeOH. The Hirshfeld surface analysis was employed for the investigation of interactions that govern the crystal structure of 2·2MeOH. The structural data for 2 out of 2·2MeOH was used for the theoretical analysis of the cationic part [{RuCl(η⁶-p-cymene)}₂(μ-Cl)(μ-1-N,N'-naphthyl)]⁺ (2a) which is common to both 1 and 2. The density functional theory, at B3LYP/6-31+G(d,p) basis set for H, C, N, and Cl atoms and LanL2DZ for Ru ions, was used for the optimization of the 2a structure. The natural bond orbital and quantum theory of atoms in molecules analyses were employed to quantify the intramolecular interactions. The reproduction of experimental IR and NMR spectra proved the applicability of the chosen level of theory. The binding of 1 to bovine serum albumin was examined by spectrofluorimetry and molecular docking, with complementary results obtained. Compound 1 acted as a radical scavenger towards DPPH^• and HO^• radicals, along with high activity towards cancer prostate and colon cell lines.

Terpyridine Diphosphine Ruthenium Complexes as Efficient Photocatalysts for the Transfer Hydrogenation of Carbonyl Compounds

The cationic achiral and chiral terpyridine diphosphine ruthenium complexes [RuCl(PP)(tpy)]Cl (PP=dppp (1), (R,R)-Skewphos (2) and (S,S)-Skewphos (3)) are easily obtained in 85-88 % yield through a one-pot synthesis from [RuCl2 (PPh3 )3 ], the diphosphine and 2,2':6',2''-terpyridine (tpy) in 1-butanol. Treatment of 1-3 with NaPF6 in methanol at RT affords quantitatively the corresponding derivatives [RuCl(PP)(tpy)]PF6 (PP=dppp (1 a), (R,R)-Skewphos (2 a) and (S,S)-Skewphos (3 a)). Reaction of [RuCl2 (PPh3 )3 ] with (S,R)-Josiphos or (R)-BINAP in toluene, followed by treatment with tpy in 1-butanol and finally with NaPF6 in MeOH gives [RuCl(PP)(tpy)]PF6 (PP=(S,R)-Josiphos (4 a), (R)-BINAP (5 a)) isolated in 78 % and 86 % yield, respectively. The chiral derivatives have been isolated as single stereoisomers and 3 a, 4 a have been characterized by single crystal X-ray diffraction studies. The tpy complexes with NaOiPr display high photocatalytic activity in the transfer hydrogenation (TH) of carbonyl compounds using 2-propanol as the only hydrogen donor and visible light at 30 °C, at remarkably high S/C (up to 5000) and TOF values up to 264 h-1 . The chiral enantiomers 2, 2 a and 3, 3 a induce the asymmetric photocatalytic TH of acetophenone, affording (S)- and (R)-1-phenylethanol with 51 and 52 % ee, respectively, in a MeOH/2-propanol mixture.

Instantaneous High-Resolution Visual Imaging of Latent Fingerprints in Water Using Color-Tunable AIE Pincer Complexes

Instant visualization of latent fingerprints is developed by using a series of water-soluble terpyridine zinc complexes as aggregation-induced emission probes in pure water, under UV light or ambient sunlight. By simply soaking, or spraying with an aqueous solution of the probe, bright yellow fluorescence images with high contrast and resolution are readily developed on various surfaces including tinfoil, glass, paper, steel, leather, and ceramic tile. Remarkably, latent fingerprints can be visualized within seconds including details of whorl and sweat pores. The color of emission can be tuned from blue to orange by modifying the pincer ligands, allowing direct imaging under sunlight. These inexpensive, water-resistant, and color-tunable probes provide a practical approach for latent fingerprints recording and analysis, security protection, as well as criminal investigation in different scenarios.

Unexpected Boost in Activity of a Cu(I) Photosensitizer by Stabilizing a Transient Excited State

In this study, we present a slight but surprisingly successful structural modification of the previously reported heteroleptic Cu(I) photosensitizer Cubiipo ([(xantphos)Cu(biipo)]PF₆; biipo = 16H-benzo-[4',5']-isoquinolino-[2',1':1,2]-imidazo-[4,5-f]-[1,10]-phenanthrolin-16-one). As a key feature, biipo bears a naphthalimide unit at the back, which is directly fused to a phenanthroline moiety to extend the conjugated π-system. This ligand was now altered to include two additional methyl groups at the 2,9-positions at the phenanthroline scaffold. Comparing the novel Cudmbiipo complex to its predecessor, ultrafast transient absorption spectroscopy reveals the efficient suppression of a major deactivation pathway by stabilization of a transient triplet state. Furthermore, quantitative measurements of singlet oxygen evolution in solution confirmed that a larger fraction of the excited-state population is transferred to the photocatalytically active ligand-centered triplet ³LC state with a much longer lifetime of ∼30 μs compared to Cubiipo (2.6 μs). In addition, Cudmbiipo was compared with the well-established reference complex Cubcp ([(xantphos)Cu(bathocuproine)]PF₆) in terms of its photophysical and photocatalytic properties by applying time-resolved femto- and nanosecond absorption, step-scan Fourier transform infrared (FTIR), and emission spectroscopies. Superior light-harvesting properties and a greatly enhanced excited-state lifetime with respect to Cubcp enable Cudmbiipo to be more active in exemplary photocatalytic applications, i.e., in the formation of singlet oxygen and the isomerization of (E)-stilbene.

Recent Advances in Photorelease Complexes for Therapeutic Applications”

Photorelease complexes represent a class of agents for which UV-visible light triggers the expulsion of a specfic molecule that is intrinsically part of the inner coordination sphere or held in...

Dinuclear 2,4-di(pyridin-2-yl)-pyrimidine based ruthenium photosensitizers for hydrogen photo-evolution under red light

In this study, we report two dinuclear Ru(II) complexes C1 and C2 and compare them to their mononuclear analogues Ref1 and Ref2. The dinuclear species exhibit a much stronger absorption, longer excited-state lifetimes and higher luminescence quantum yields than the mononuclear complexes. In addition, C1 and C2 are easier to reduce. An estimation of the driving forces for the electron transfer processes relevant to photocatalytic hydrogen evolution suggests that C1 and Ref2 possess similar activity as photosensitizer (PS). Yet, the improved photophysical properties of C1 make it a more promising candidate for hydrogen evolution. In hydrogen evolution experiments, C1 indeed exhibits increased activity as PS, however, the catalytic system loses its activity after only a few hours. C2 is less active than the mononuclear complexes despite its superior photophysical properties. This observation is attributed to a lack of driving force for the electron transfer towards the catalyst. Further studies of the dinuclear complex C1 show that it is indeed the PS, which decomposes under the catalytic conditions, presumably due to the electron transfer towards the catalyst being the rate-limiting step.