Expanded bite angles in tridentate ligands. Improving the photophysical properties in bistridentate RuII polypyridine complexes

New Tridentate Ligand Affords a Long-Lived 3MLCT Excited State in a Ru(II) Complex: DNA Photocleavage and 1O2 Production

Two new complexes, [Ru(tpy)(qdppz)](PF6)2 (1; qdppz = 2-(quinolin-8-yl)dipyrido[3,2-a:2',3'-c]phenazine, tpy = 2,2':6',2″-terpyridine) and [Ru(qdppz)2](PF6)2 (2), were investigated for their potential use as phototherapeutic agents through their ability to photosensitize the production of singlet oxygen, 1O2, upon irradiation with visible light. The complexes exhibit strong Ru(dπ) → qdppz(π*) metal-to-ligand charge transfer (MLCT) absorption with maxima at 485 and 495 nm for 1 and 2 in acetone, respectively, red-shifted from the Ru(dπ) → tpy(π*) absorption at 470 nm observed for [Ru(tpy)2]2+ (3) in the same solvent. Complexes 1 and 3 are not luminescent at room temperature, but 3MLCT emission is observed for 2 with maximum at 690 nm (λexc = 480 nm) in acetone. The lifetimes of the 3MLCT states of 1 and 2 were measured using transient absorption spectroscopy to be ∼9 and 310 ns in methanol, respectively, at room temperature (λexc = 490 nm). The bite angle of the qdppz ligand is closer to octahedral geometry than that of tpy, resulting in the longer lifetime of 2 as compared to those of 1 and 3. Arrhenius treatment of the temperature dependence of the luminescence results in similar activation energies, Ea, from the 3MLCT to the 3LF (ligand-field) state for the two complexes, 2520 cm-1 in 1 and 2400 cm-1 in 2. However, the pre-exponential factors differ by approximately two orders of magnitude, 2.3 × 1013 s-1 for 1 and 1.4 × 1011 s-1 for 2, which, together with differences in the Huang-Rhys factors, lead to markedly different 3MLCT lifetimes. Although both 1 and 2 intercalate between the DNA bases, only 2 is able to photocleave DNA owing to its 1O2 production upon irradiation with ΦΔ = 0.69. The present work highlights the profound effect of the ligand bite angle on the electronic structure, providing guidelines for extending the lifetime of 3MLCT Ru(II) complexes with tridentate ligands, a desired property for a number of applications.

Preparation of Substituted Pyridines via a Coupling of β-Enamine Carbonyls with Rongalite-Application for Synthesis of Terpyridines

A Hantzsch-type strategy for the synthesis of 2,3,5,6-tetrasubstituted pyridines via an oxidative coupling of β-enamine carbonyl compounds with rongalite was developed. This method employs rongalite as a C1 unit for the assembly of a pyridine ring at C-4 position, offering a facile method for the preparation of substituted pyridine derivatives with a broad functional group tolerance. In particular, this method allows us to prepare terpyridine derivatives, which are important ligands or structural fragments for catalysts and 3D metal–organic frameworks.

Manganese(I) Complex with Monodentate Arylisocyanide Ligands Shows Photodissociation Instead of Luminescence

Recently reported manganese(I) complexes with chelating arylisocyanide ligands exhibit luminescent metal-to-ligand charge-transfer (MLCT) excited states, similar to ruthenium(II) polypyridine complexes with the same d6 valence electron configuration used for many different applications in photophysics and photochemistry. However, chelating arylisocyanide ligands require substantial synthetic effort, and therefore it seemed attractive to explore the possibility of using more readily accessible monodentate arylisocyanides instead. Here, we synthesized the new Mn(I) complex [Mn(CNdippPhOMe2)6]PF6 with the known ligand CNdippPhOMe2 = 4-(3,5-dimethoxyphenyl)-2,6-diisopropylphenylisocyanide. This complex was investigated by NMR spectroscopy, single-crystal structure analysis, high-resolution electrospray ionization mass spectrometry (HR-ESI-MS) measurements, IR spectroscopy supported by density functional theory (DFT) calculations, cyclic voltammetry, and time-resolved as well as steady-state UV-vis absorption spectroscopy. The key finding is that the new Mn(I) complex is nonluminescent and instead undergoes arylisocyanide ligand loss during continuous visible laser irradiation into ligand-centered and charge-transfer absorption bands, presumably owed to the population of dissociative d-d excited states. Thus, it seems that chelating bi- or tridentate binding motifs are essential for obtaining emissive MLCT excited states in manganese(I) arylisocyanides. Our work contributes to understanding the basic properties of photoactive first-row transition metal complexes and could help advance the search for alternatives to precious metal-based luminophores, photocatalysts, and sensors.

In-Depth Studies of Ground- and Excited-State Properties of Re(I) Carbonyl Complexes Bearing 2,2':6',2″-Terpyridine and 2,6-Bis(pyrazin-2-yl)pyridine Coupled with π-Conjugated Aryl Chromophores

In the current work, comprehensive photophysical and electrochemical studies were performed for eight rhenium(I) complexes incorporating 2,2':6',2″-terpyridine (terpy) and 2,6-bis(pyrazin-2-yl)pyridine (dppy) with appended 1-naphthyl-, 2-naphthyl-, 9-phenanthrenyl, and 1-pyrenyl groups. Naphthyl and phenanthrenyl substituents marginally affected the energy of the MLCT absorption and emission bands, signaling a weak electronic coupling of the appended aryl group with the Re(I) center. The triplet MLCT state in these complexes is so low lying relative to the triplet ³IL_aryl that the thermal population of the triplet excited state delocalized on the organic chromophore is ineffective. The attachment of the electron-rich pyrenyl group resulted in a noticeable red shift and a significant increase in molar absorption coefficients of the lowest energy absorption of the resulting Re(I) complexes due to the contribution of intraligand charge-transfer (ILCT) transitions occurring from the pyrenyl substituent to the terpy/dppy core. At 77 K, the excited states of [ReCl(CO)₃(Lⁿ-κ²N)] with 1-pyrenyl-functionalized ligands were found to have predominant ³IL_pyrene/³ILCT_{pyrene→terpy} character. The ³IL/³ILCT nature of the lowest energy excited state of [ReCl(CO)₃(4'-(1-pyrenyl)-terpy-κ²N)] was also evidenced by nanosecond transient absorption and time-resolved emission spectroscopy. Enhanced room-temperature emission lifetimes of the complexes [ReCl(CO)₃(Lⁿ-κ²N)] with 1-pyrenyl-substituted ligands are indicative of the thermal activation between ³MLCT and ³IL/³ILCT excited states. Deactivation pathways occurring upon light excitation in [ReCl(CO)₃(4'-(1-naphthyl)-terpy-κ²N)] and [ReCl(CO)₃(4'-(1-pyrenyl)-terpy-κ²N)] were determined by femtosecond transient absorption studies.

Trifluoromethyl substitution enhances photoinduced activity against breast cancer cells but reduces ligand exchange in Ru(ii) complex

A series of five ruthenium complexes containing triphenyl phosphine groups known to enhance both cellular penetration and photoinduced ligand exchange, cis-[Ru(bpy)2(P(p-R-Ph)3)(CH3CN)]2+, where bpy = 2,2'-bipyridine and P(p-R-Ph)3 represent para-substituted triphenylphosphine ligands with R = -OCH3 (1), -CH3 (2) -H (3), -F (4), and -CF3 (5), were synthesized and characterized. The photolysis of 1-5 in water with visible light (λ irr ≥ 395 nm) results in the substitution of the coordinated acetonitrile with a solvent molecule, generating the corresponding aqua complex as the single photoproduct. A 3-fold variation in quantum yield was measured with 400 nm irradiation, Φ 400, where 1 is the most efficient with a Φ 400 = 0.076(2), and 5 the least photoactive complex, with Φ 400 = 0.026(2). This trend is unexpected based on the red-shifted metal-to-ligand charge transfer (MLCT) absorption of 1 as compared to that of 5, but can be correlated to the substituent Hammett para parameters and pK a values of the ancillary phosphine ligands. Complexes 1-5 are not toxic towards the triple negative breast cancer cell line MDA-MB-231 in the dark, but 3 and 5 are >4.2 and >19-fold more cytotoxic upon irradiation with blue light, respectively. A number of experiments point to apoptosis, and not to necrosis or necroptosis, as the mechanism of cell death by 5 upon irradiation. These findings provide a foundation for understanding the role of phosphine ligands on photoinduced ligand substitution and show the enhancement afforded by -CF3 groups on photochemotherapy, which will aid the future design of photocages for photochemotherapeutic drug delivery.

Terpyridine-Based 3D Metal-Organic-Frameworks: A Structure-Property Correlation

Design, synthesis, and applications of metal-organic frameworks (MOFs) are among the most salient fields of research in modern inorganic and materials chemistry. As the structure and physical properties of MOFs are mostly dependent on the organic linkers or ligands, the choice of ligand system is of utmost importance in the design of MOFs. One such crucial organic linker/ligand is terpyridine (tpy), which can adopt various coordination modes to generate an enormous number of metal-organic frameworks. These frameworks generally carry physicochemical characteristics induced by the π-electron-rich (basically N-electron-rich moiety) terpyridines. In this minireview, the construction of 3D MOFs associated with symmetrical terpyridines is discussed. These ligands can be easily derivatized at the lateral phenyl (4'-phenyl) position and incorporate additional organic functionalities. These functionalities lead to some different binding modes and form higher dimensional (3D) frameworks. Therefore, these 3D MOFs can carry multiple features along with the characteristics of terpyridines. Some properties of these MOFs, like photophysical, chemical selectivity, photocatalytic degradation, proton conductivity, and magnetism, etc. have also been discussed and correlated with their frameworks.

Green-Light Activation of Push-Pull Ruthenium(II) Complexes

Synthesis, characterization, electrochemistry, and photophysics of homo- and heteroleptic ruthenium(II) complexes [Ru(cpmp)2 ]2+ (22+ ) and [Ru(cpmp)(ddpd)]2+ (32+ ) bearing the tridentate ligands 6,2''-carboxypyridyl-2,2'-methylamine-pyridyl-pyridine (cpmp) and N,N'-dimethyl-N,N'-dipyridin-2-ylpyridine-2,6-diamine (ddpd) are reported. The complexes possess one (32+ ) or two (22+ ) electron-deficient dipyridyl ketone fragments as electron-accepting sites enabling intraligand charge transfer (ILCT), ligand-to-ligand charge transfer (LL'CT) and low-energy metal-to-ligand charge transfer (MLCT) absorptions. The latter peak around 544 nm (green light). Complex 22+ shows 3 MLCT phosphorescence in the red to near-infrared spectral region at room temperature in deaerated acetonitrile solution with an emission quantum yield of 1.3 % and a 3 MLCT lifetime of 477 ns, whereas 32+ is much less luminescent. This different behavior is ascribed to the energy gap law and the shape of the parasitic excited 3 MC state potential energy surface. This study highlights the importance of the excited-state energies and geometries for the actual excited-state dynamics. Aromatic and aliphatic amines reductively quench the excited state of 22+ paving the way to photocatalytic applications using low-energy green light as exemplified with the green-light-sensitized thiol-ene click reaction.

RK, Pillegowda M, Periyasamy G, Suchetan PA, Butcher RJ, Foro S, Nagaraju G. Synthesis, crystal structures, photophysical, electrochemical studies, DFT and TD-DFT calculations and Hirshfeld analysis of new 2,2′:6′,2′′-terpyridine ligands with pendant 4′-(trimethoxyphenyl) groups and their homoleptic ruthenium complexes

[Ru(L1)₂](PF₆)₂ (1) and [Ru(L2)₂](PF₆)₂ (2): X-ray structures, CH⋯F/O, OH⋯F/N, CH⋯O/π, π⋯π interactions, absorption and emission spectra, DFT/TD-DFT, Hirshfeld analysis.

Structural, electrochemical and photophysical behavior of Ru(ii) complexes with large bite angle sulfur-bridged terpyridyl ligands

Sulfur-bridged terpyridyl ligands expand the bite angles in Ru(ii) species leading to geometries very close to that of a “perfect” octahedron. Altering the donor strength of substituents results in systematic tuning of the redox properties.

H/D solvent isotope effects on the photoracemization reaction of enantiomeric the tris(2,2′-bipyridine)ruthenium(ii) complex and its analogues

This work assessed solvent isotope effects on the photoracemization rate and emission lifetime for [Ru(bpy)₃]²⁺ (bpy = 2,2′-bipyridine) in water.

The Important Role of Coordination Geometry on Photophysical Properties of Blue-Green Emitting Ruthenium(II) Diisocyano Complexes Bearing 2-Benzoxazol-2-ylphenolate

A series of blue-green emitting Ru^II diisocyano complexes containing 2-benzoxazol-2-ylphenolate (PBO) have been prepared. The complexes were isolated under varied reaction conditions in two isomeric forms, i.e., trans,trans,trans- (1) and cis,trans,cis- (2), with varied ligand coordination geometry above the Ru^II center. The photoluminescence of the isomeric complexes has been compared and tuned by the systematic variation of the electronic properties of the isocyanides. The cis,trans,cis- isomers exhibit structureless emission in the blue-green region (471-517 nm) upon excitation at λ_ex > 400 nm in dichloromethane solution at room temperature. Both isomeric forms show similarly structured greenish emission at 499-523 nm on excitation at λ_ex > 355 nm in a methanol/ethanol (4:1) glassy medium at 77 K. On careful comparison with the corresponding absorption and electrochemical data, it is suggested that the solution emission of the cis,trans,cis- isomers (2) at room temperature is originated from the metal-to-ligand charge transfer (MLCT), while a ligand-centered (LC) parentage is assigned for the emission in a glassy state for both isomeric forms. In line with the above experimental results, DFT calculation demonstrates the change in the nature and relative energy of the HOMOs and LUMOs with respect to the varied ligand coordination geometry and π-accepting ability of the isocyanides.

High-Yielding Syntheses of Multifunctionalized RuII Polypyridyl-Type Sensitizer: Experimental and Computational Insights into Coordination

Ru^II complexes based on functionalized 2,6-di(quinolin-8-yl)pyridine (dqp) ligands feature excellent photophysical and geometrical properties, thus suggesting dqp ligands as ideal surrogates for 2,2'-bipyridine (bpy) or 2,2':6',2″-terpyridine (tpy). However, the synthesis of multifunctionalized [Ru(dqp)₂]²⁺-based complexes is often low-yielding, which has hampered their practical value to date. In this study, a universal high-yielding route was explored and corroborated by a mechanistic investigation based on ¹H NMR, MS, and density functional theory. With application of high-boiling but less-coordinating solvents (i.e., DMF) during the coordination of dqp by the precursor [Ru(dqp)(MeCN)₃]²⁺, the required reaction temperature is lowered considerably (by 30 °C). In comparison to tpy, the reaction rate for dqp is further reduced which is assigned to the higher steric demand upon the coordination process. Namely, the onset of coordination of a tpy derivative at 60 °C and of dqp at 90 °C is significantly milder than in previous protocols. The versatility of the procedure is demonstrated by the high-yielding syntheses of multifunctionalized Ru^II complexes reaching up to 90%, whereby the presence of hydroxyl groups and losses during purification may lower the isolated yields substantially. In addition, the same strategy of high-boiling but less-coordinating solvents enabled a milder one-pot protocol to prepare [Ru(dqp)₂]²⁺ from a [Ru(MeCN)₆]²⁺ source, i.e., without the need for in situ reduction or halide abstraction as typical for Ru^IIICl₃ hydrate. Hence, the developed protocol benefits from an improved thermal tolerance of sensitive functional groups, which may be applicable also to related polypyridyl-type ligands.

Ultrafast Energy Transfer in Dinuclear Complexes with Bridging 1,10-Phenanthroline-5,6-Dithiolate

We report herein the preparation and characterization of dinuclear complexes with the bridging ligand 1,10-phenanthroline-5,6-dithiolate (phendt^2-) bearing Ru(bpy)₂ or Ir(ppy)₂ at the diimine moiety and Ni(dppe), Ni(dppf), CoCp, RhCp*, and Ru( p-Me-ⁱPr-benzene) at the dithiolate unit. In comparison with the mononuclear precursors used in the synthesis, all dinuclear complexes were characterized by absorption and photoluminescence spectroscopy as well as cyclic voltammetry. Because of the beneficial spectral and electrochemical properties of the Ir/Co complex for a light-driven charge separation, this complex was investigated in detail by time-resolved luminescence {nanosecond (ns)-resolution} and transient absorption spectroscopy {femtosecond (fs)-resolution}. All measurements supported by DFT calculations show that the observed effective luminescence quenching by the dithiolate coordinated metal is caused by an ultrafast singlet-singlet Dexter energy transfer.

Comparing Isomeric Tridentate Carbazole-Based Click Ligands: Metal Complexes and Redox Chemistry

Two novel bis(triazolyl)carbazole ligands Hbtc1 (3,6-di(tert-butyl)-1,8-bis[(1-(3,5-di(tert-butyl)phenyl)-1,2,3-triazol-4-yl)]-9H-carbazole) and Hbtc2 (3,6-di(tert-butyl)-1,8-bis[(4-(3,5-di(tert-butyl)phenyl)-1,2,3-triazol-1-yl)]-9H-carbazole), differing in the regiochemistry of triazole attachment, have been synthesized by Cu-catalyzed azide-alkyne cycloaddition, the so-called "click-reactions". Metalation with Ru, Zn, and Ni precursors led to the formation of M(btc)₂ complexes (M=Ru, Zn, Ni), with two deprotonated ligands coordinating to the metal center in tridentate fashion, forming almost perfectly octahedral coordination spheres. The redox properties of M(btc)₂ complexes have been investigated by cyclic voltammetry, UV/Vis spectroscopy, spectroelectrochemistry, and chemically. The CV of the ruthenium complexes revealed three quasi-reversible one-electron oxidation processes, one assigned as the Ru^II/III couple and two originating from ligand-based oxidations. The CVs of both Zn and Ni complexes contained only two oxidation waves corresponding to the oxidation of the two ligands. The oxidation potentials of complexes derived from Hbtc1 ligands were found to be 300-400 mV lower than those of the corresponding complexes derived from Hbtc2, reflecting the significant difference in donation through the N(2) or N(3) atom of the triazole moiety.

Coordination chemistry in the design of heterogeneous photocatalysts

Heterogeneous catalysts have been widely used for photocatalysis, which is a highly important process for energy conversion, owing to their merits such as easy separation of catalysts from the reaction products and applicability to continuous chemical industry and recyclability. Yet, homogenous photocatalysis receives tremendous attention as it can offer a higher activity and selectivity with atomically dispersed catalytic sites and tunable light absorption. For this reason, there is a major trend to combine the advantages of both homogeneous and heterogeneous photocatalysts, in which coordination chemistry plays a role as the bridge. In this article, we aim to provide the first systematic review to give a clear picture of the recent progress from taking advantage of coordination chemistry. We specifically summarize the role of coordination chemistry as a versatile tool to engineer catalytically active sites, tune light harvesting and maneuver charge kinetics in heterogeneous photocatalysis. We then elaborate on the common fundamentals behind various materials systems, together with key spectroscopic characterization techniques and remaining challenges in this field. The typical applications of coordination chemistry in heterogeneous photocatalysis, including proton reduction, water oxidation, carbon dioxide reduction and organic reactions, are highlighted.

Microsecond 3MLCT excited state lifetimes in bis-tridentate Ru(ii)-complexes: significant reductions of non-radiative rate constants

In this paper we report the photophysical properties of a series of bis-tridentate Ru^II-complexes, based on the dqp-ligand (dqp = 2,6-di(quinolin-8-yl)pyridine), which display several microsecond long excited state lifetimes for triplet metal-to-ligand charge transfer (³MLCT) at room temperature. Temperature dependence of the excited state lifetimes for [Ru(dqp)₂]²⁺ and [Ru(dqp)(ttpy)]²⁺ (ttpy = 4'-tolyl-2,2':6',2''-terpyridine) is reported and radiative and non-radiative rate constants for the whole series are reported and discussed. We can confirm previous assumptions that the near-octahedricity of the bis-dqp complexes dramatically slows down activated decay at room temperature, as compared to most other and less long-lived bis-tridentate Ru^II-complexes, such as [Ru(tpy)₂]²⁺ with τ = 0.25 ns at room temperature (tpy = 2,2':6',2''-terpyridine). Moreover, the direct non-radiative decay to the ground state is comparatively slow for ∼700 nm room-temperature emission when considering the energy-gap law. Analysis of the 77 K emission spectra suggests that this effect is not primarily due to smaller excited state distortion than that for comparable complexes. Instead, an analysis of the photophysical parameters suggests a weaker singlet-triplet mixing in the MLCT state, which slows down both radiative and non-radiative decay.

A multidonor-photosensitizer-multiacceptor triad for long-lived directional charge separation

The modular assembly of a directional photoredox-active multidonor-photosensitizer-multiacceptor (D_n-P-A_m) architecture is presented. The triad assembly features a central Ru(ii) sensitizer equipped with pendant polymer chains consisting of multiple triarylamine (pTARA) and naphthalene diimide (pNDI) units, respectively. Upon excitation, the efficient formation (>96%) of charge separation (CS) was observed featuring similar CS lifetimes (400 ns) as related molecular triads. In contrast, a significant additional longer-lived CS component (2400 ns, 30%) is observed indicating multiple contributing pathways.

A renaissance of ligand-to-metal charge transfer by cerium photocatalysis

Diverse alcohols, serving as substrates or co-catalysts, and Ce(iv) achieve photoinduced LMCT to generate highly active alkoxy radicals, which opens a new avenue for many difficult HAT reactions.

A low-spin Fe(iii) complex with 100-ps ligand-to-metal charge transfer photoluminescence

Transition-metal complexes are used as photosensitizers, in light-emitting diodes, for biosensing and in photocatalysis. A key feature in these applications is excitation from the ground state to a charge-transfer state; the long charge-transfer-state lifetimes typical for complexes of ruthenium and other precious metals are often essential to ensure high performance. There is much interest in replacing these scarce elements with Earth-abundant metals, with iron and copper being particularly attractive owing to their low cost and non-toxicity. But despite the exploration of innovative molecular designs, it remains a formidable scientific challenge to access Earth-abundant transition-metal complexes with long-lived charge-transfer excited states. No known iron complexes are considered photoluminescent at room temperature, and their rapid excited-state deactivation precludes their use as photosensitizers. Here we present the iron complex [Fe(btz)₃]³⁺ (where btz is 3,3'-dimethyl-1,1'-bis(p-tolyl)-4,4'-bis(1,2,3-triazol-5-ylidene)), and show that the superior σ-donor and π-acceptor electron properties of the ligand stabilize the excited state sufficiently to realize a long charge-transfer lifetime of 100 picoseconds (ps) and room-temperature photoluminescence. This species is a low-spin Fe(iii) d⁵ complex, and emission occurs from a long-lived doublet ligand-to-metal charge-transfer (²LMCT) state that is rarely seen for transition-metal complexes. The absence of intersystem crossing, which often gives rise to large excited-state energy losses in transition-metal complexes, enables the observation of spin-allowed emission directly to the ground state and could be exploited as an increased driving force in photochemical reactions on surfaces. These findings suggest that appropriate design strategies can deliver new iron-based materials for use as light emitters and photosensitizers.

Asymmetric Cyclometalated RuII Polypyridyl-Type Complexes with π-Extended Carbanionic Donor Sets

A series of novel cyclometalated Ru^II complexes were investigated featuring the tridentate dqp ligand platform (dqp is 2,6-di(quinolin-8-yl)pyridine), in order to utilize the octahedral coordination mode around the Ru center to modulate the electrochemical and photophysical properties. The heteroleptic complexes feature C₁ symmetry due to symmetry breaking by the peripheral five- or six-membered carbanionic chelate (phenyl, naphthyl, or anthracenyl units). The chelation mode is controlled by the steric effects and C-H activation selectivity of the ligand, which prompted the development of a general synthesis protocol. The optimized conditions to achieve high overall yields (55-75%) involve NaHCO₃ as the base and an simplified purification protocol: i.e., facile chromatographic separation using commercially available amino-functionalized silica applying nonaqueous salt-free conditions to omit the necessity of counterion exchange. The structural, photophysical, and electrochemical properties were studied in depth, and the results were corroborated by density functional theory (DFT) calculations. Steady state and time-resolved spectroscopy revealed red-shifted absorption (up to 750 nm) and weak IR emission (800-1000 nm) combined with prolonged emission lifetimes (up to 20 ns) in comparison to classical tpy-based (tpy is 2,2':6',2″-terpyridine) complexes. An enhanced stability was observed by blocking the reactive positions of the carbanionic ligand framework, while the reactive positions may be exploited for further functionalization.

Spectroelectrochemical properties of a Ru(ii) complex with a thiazolo[5,4-d]thiazole triarylamine ligand

A new electroactive bridging ligand based on the donor (triarylamine) and acceptor (thiazolothiazole) units has been designed and incorporated into a diruthenium complex.

An Overview Of Photosubstitution Reactions Of Ru(II) Imine Complexes And Their Application In Photobiology And Photodynamic Therapy

This article is a short review that presents a short review of photosubstitution reactions of Ru(II) imine complexes and illustrates their use in the development of therapeutic agents. The review begins with an overview of the photophysical behavior and common photoreactions of Ru(II) imine complexes, with select examples from the literature since the 1960s. It is followed by a more detailed picture of the application of knowledge gained over the years in the development of Ru(II) complexes for photobiology and photodynamic therapy.

In Situ Spectroelectrochemical Investigations of RuII Complexes with Bispyrazolyl Methane Triarylamine Ligands

The synthesis and characterization of two triarylamine ligands, 4-(di(1H-pyrazol-1-yl)methyl)-N-(4-(di(1H-pyrazol-1-yl)methyl)phenyl)-N-phenylaniline (TPA-2bpm) and tris(4-(di(1H-pyrazol-1-yl)methyl)phenyl)amine (TPA-3bpm), containing the bispyrazolylmethane moiety and its RuII terpyridine complexes are presented. The redox properties of the ligands and RuII complexes are explored in detail through cyclic and square-wave voltammetry in addition to in situ UV-vis-near infrared, electron paramagnetic resonance, and fluorescence spectroelectrochemistry. It was demonstrated that the triarylamine radical cation was able to be generated, and further, TPA-2bpm underwent an electrochemically induced dimerization process.

Terpyridine and Quaterpyridine Complexes as Sensitizers for Photovoltaic Applications

Terpyridine and quaterpyridine-based complexes allow wide light harvesting of the solar spectrum. Terpyridines, with respect to bipyridines, allow for achieving metal-complexes with lower band gaps in the metal-to-ligand transition (MLCT), thus providing a better absorption at lower energy wavelengths resulting in an enhancement of the solar light-harvesting ability. Despite the wider absorption of the first tricarboxylate terpyridyl ligand-based complex, Black Dye (BD), dye-sensitized solar cell (DSC) performances are lower if compared with N719 or other optimized bipyridine-based complexes. To further improve BD performances several modifications have been carried out in recent years affecting each component of the complexes: terpyridines have been replaced by quaterpyridines; other metals were used instead of ruthenium, and thiocyanates have been replaced by different pinchers in order to achieve cyclometalated or heteroleptic complexes. The review provides a summary on design strategies, main synthetic routes, optical and photovoltaic properties of terpyridine and quaterpyridine ligands applied to photovoltaic, and focuses on n-type DSCs.

Spectroscopic signatures of ligand field states in {Ru(II)(imine)} complexes

Ligand field (LF) states have been present in discussions on the photophysics and photochemistry of ruthenium-iminic chromophores for decades, although there is very little documented direct evidence of them. We studied the picosecond transient absorption (TA) spectroscopy of four {Ru(II)(imine)} complexes that respond to the formula trans-[Ru(L)4(X)2], where L is either pyridine (py) or 4-methoxypyridine (MeOpy) and X is either cyanide or thiocyanate. Dicyano compounds behave as most ruthenium polypyridines and their LF states remain silent. In contrast, in the dithiocyanate complexes we found clear spectroscopic evidence of the participation of LF states in the MLCT decay pathway. These states are of donor and acceptor character simultaneously and this is manifested in the presence of MLCT and LMCT transient absorption bands of similar energy. Spectroelectrochemical techniques supported the interpretation of the absorption features of MLCT states, and DFT methods helped to assign their spectroscopic signatures and provided strong evidence on the nature of LF states.

Synthesis of heteroleptic terpyridyl complexes of Fe(ii) and Ru(ii): optical and electrochemical studies

Heteroleptic terpyridyl complexes of Fe(ii) and Ru(ii) are synthesized. They are characterized using complimentary techniques and their optical and electrochemical properties are studied. A detailed computational study was also performed.

Energy transfer and formation of long-lived 3MLCT states in multimetallic complexes with extended highly conjugated bis-terpyridyl ligands

Multimetallic complexes with extended conjugated ligands show efficient energy transfer to the lowest excited states and prolonged Fe(ii) ³MLCT lifetimes.

Azadipyrromethene cyclometalation in neutral RuII complexes: photosensitizers with extended near-infrared absorption for solar energy conversion applications

In the on-going quest to harvest near-infrared (NIR) photons for energy conversion applications, a novel family of neutral ruthenium(ii) sensitizers has been developed by cyclometalation of an azadipyrromethene chromophore.