Terpyridyl Complexes Research Articles

Electronic properties of Fe charge transfer complexes – A combined experimental and theoretical approach

Dye-sensitized solar cell technology holds huge potential in renewable electricity generation of the future. Due to demand urgency, ways need to be explored to reduce research time and cost. Against this background, quantum computational chemistry is illustrated to be a reliable tool at the onset of studies in this field, simulating charge transfer, spectral (solar energy absorbed) and electrochemical (ease by which electrons may be liberated) tuning of related photo-responsive dyes. Comparative experimental and theoretical DFT studies were done under similar conditions, involving an extended series of electrochemically altered phenanthrolines, bipyridyl and terpyridyl complexes of FeII. FeII/III oxidation waves vary from 0.363V for tris(3,6-dimethoxybipyridyl)FeII to 0.894V (versus Fc/Fc+) for the 5-nitrophenanthroline complex. Theoretical DFT computed ionization potentials in the bipyridyl sub-series achieved an almost 100% linear correlation with experimental electrochemical oxidation potentials, while the phenanthroline sub-series gave R2=0.95. Apart from the terpyridyl complex which accorded an almost perfect match, in general, TDDFT oscillators were computed at slightly lower energies than what was observed experimentally, while molecular HOMO and LUMO renderings reveal desired complexes with directional charge transfer propensities.

Small Organic Non–gelators Evincing Radical Control over Morphology and Rheology of a Weak Metallogel

AbstractTwo arrays of “Inorganic‐Organic Mixed Gels” (IOMGs) based on terpyridyl complexes have been synthesized combining progelator/non‐gelators with easily available, inexpensive and non‐reactive small organic non‐gelators (SOnGs). This new class of multicomponent gels displays radical changes in morphological patterns and enormous enhancement in their viscoelastic properties relative to weak metallogel (ZTP2G) derived from the progelator only. It has been unequivocally shown that twisting or coiling in gels diminishes as well as their viscoelastic strengths with simple alteration of heteroatoms, their number and positions in SOnGs. Multicomponent gelation is quite complicated considering the susceptibility of anion triggered metallogels towards various external stimuli which has been profoundly outdone. The present approach may be extremely beneficial for negating limitations in the usage of weak metallogels with promising efficacy in specified areas.

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.

Surface-confined heterometallic triads on the basis of terpyridyl complexes and design of molecular logic gates.

Surface-confined heterometallic molecular triads (SURHMTs) were fabricated on SiOx-based solid substrates using optically rich and redox-active Fe-, Os-, and Ru-based terpyridyl complexes as metalloligands and Cu(2+) ions as linkers. Optical and electrochemical studies reveal efficient electronic intramolecular communication in these assemblies. The UV-vis spectra of the triads exhibit a superposition of the metal-to-ligand charge-transfer bands of individual complexes, providing a significant enlargement of the optical window, useful for application. Similarly, cyclic voltammograms of SURHMT layers show a variety of redox peaks corresponding to individual complexes as well as multi-redox states at a low potential. Interaction of a representative SURHMT assembly with redox-active NOBF4 was investigated and used as a basis for configuring molecular logic gates.

Synthesis, characterization and biological evaluation of mixed-ligand ruthenium(II) complexes for photodynamic therapy.

This study investigated the photodynamic therapy (PDT) and anticancer activity of mixed ligand Ru(ii) terpyridyl complexes (Ru1-Ru3). The photophysical and photochemical properties, hydrophobic properties, DNA binding and DNA transcription inhibition abilities, cell uptake efficiency, cellular localization and photo-cytotoxicity were investigated. Ru1-Ru3 exhibited red luminescence between 670-710 nm and functioned as photo-sensitizers (PSs) by generating both singlet oxygen and radical ions. Without light activation, Ru1-Ru3 were located at the cytoplasm and were nontoxic to cells. However, upon light activation, Ru1-Ru3 exhibited significant photocytotoxicity. After PDT treatment, mitochondria alteration and nuclear membrane disruption occurred, which resulted in relocalization of the complexes from the cytoplasm to the nucleus. Moreover, high cellular oxidative stress caused cell necrocytosis after PDT treatment.

Luminescence Properties and Application of Versatile Coordination Compounds Based on Modified Platinum(II) Terpyridyl Complexes

Luminescence Properties and Application of Versatile Coordination Compounds Based on Modified Platinum(II) Terpyridyl Complexes

Synthesis, electrochemical characterization, and photophysical studies of structurally tuned aryl-substituted terpyridyl ruthenium(II) complexes.

Synthesis, electrochemical potentials, static emission, and temperature-dependent excited-state lifetimes of several 4'-aryl-substituted terpyridyl complexes of ruthenium(II) are reported. Synthetic tuning is explored within three conceptual series of complexes. The first series explores the impact of introducing a strong σ-donating 4,4',4″-tri-tert-butyl-2,2':6',2″-terpyridine (tbtpy) opposite to an arylated terpyridine ligand 4'-(4-methylphenyl)-2,2':6',2″-terpyridine (ttpy). It is found that (3)MLCT (triplet metal-to-ligand charge-transfer state) stabilization concomitant with (3)MC (triplet metal-centered state) destabilization in the heteroleptic parent complex [Ru(ttpy)(tbtpy)](2+) leads to an extended excited-state lifetime relative to the structurally related bis-homoleptic species [Ru(ttpy)2](2+). The second series explores the impact of introducing a carboxylic acid or a methyl ester moiety at the para-position of the arylterpyridyl ligand (R1 = R2 = H) within heteroleptic complexes as a platform for future semiconductor attachment studies. This substitution leads to further lifetime enhancements, understood as arising from (3)MLCT stabilization. Such complexes are referred to as [Ru(1)(tbtpy)](2+) (for the acid at R3) and [Ru(1')(tbtpy)](2+) (for the ester at R3). In the final series, methyl substituents are sequentially added at the R1 and R2 positions for both the acid ([Ru(2)(tbtpy)](2+) and [Ru(3)(tbtpy)](2+)) and ester ([Ru(2')(tbtpy)](2+) and [Ru(3')(tbtpy)](2+)) analogues to eventually explore dynamical electron transfer coupling at dye/semiconductor interfaces. In these complexes, sequential addition of steric bulk decreases excited state lifetimes. This can be understood to arise primarily from the increase of the (3)MLCT level, as excited-state electron delocalization is limited by inter-ring twisting in the lower-energy arylated ligand. The introduction of a dimethylated sterically encumbered ligand lead to a notable 14-fold increase in knr from [Ru(1')(tbtpy)](2+) to [Ru(3')(tbtpy)](2+) (or [Ru(1)(tbtpy)](2+) to [Ru(3)(tbtpy)](2+)).

Linear Bimetallic Alkynylplatinum(II) Terpyridyl Complexes Bearing p-Phenylene Ethynylene Oligomers: Synthesis, Characterization, Aggregation, and Photophysical Properties

The series of luminescent bimetallic alkynylplatinum(II) terpyridyl complexes [(tBu3-tpy)PtC≡C(ArC≡C)nPt(tBu3-tpy)](PF6)2 (I–IV; tBu3-tpy = 4,4′,4″-tritertbutyl-2,2′:6′,2″-terpyridine, Ar = C6H2(n-hexyloxy)2-2,5), in which two platinum(II) centers are linked by p-phenylene ethynylene oligomers, were synthesized and characterized. Their electronic absorption and luminescent behaviors were studied by steady-state spectroscopy and transient spectroscopy. Concentration-dependent emission data show that all of the complexes form self-assembled aggregates in certain concentration ranges. Complex IV, bearing a longer p-phenylene ethynylene oligomer, exhibits higher propensity in comparison to I–III to form aggregates at a concentration of >1 × 10–5 M, probably resulting from stronger metal–metal interactions and π–π stacking. All four of the complexes displayed biexponential decays with lifetimes in the range of nanoseconds in dilute solutions.

Reversible Mechanochromic Luminescence at Room Temperature in Cationic Platinum(II) Terpyridyl Complexes

Reversible mechanochromic luminescence in cationic platinum(II) terpyridyl complexes is described. The complexes [Pt(Nttpy)Cl]X2 (Nttpy = 4'-(p-nicotinamide-N-methylphenyl)-2,2':6',2″-terpyridine, X = PF6 (1), SbF6 (2), Cl (3), ClO4 (4), OTf (5), BF4 (6)) exhibit different colors under ambient light in the solid state, going from red to orange to yellow. All of these complexes are brightly luminescent at both room temperature and 77 K. Upon gentle grinding, the yellow complexes (4-6) turn orange and exhibit bright red luminescence. The red luminescence can be changed back to yellow by the addition of a few drops of acetonitrile to the sample. Crystallographic studies of the yellow and red forms of complex 5 suggest that the mechanochromic response is likely the result of a change in intermolecular Pt···Pt distances upon grinding.

Manganese carbonyl terpyridyl complexes: their synthesis, characterization and potential application as CO-release molecules

Mn(I) carbonyl terpyridyl complexes have been synthesized and characterized. The tricarbonyl derivative exhibits interesting behaviors for controlled CO-release by both thermal and photosynthetic pathways.

Surface‐Confined Heterometallic Molecular Dyads: Merging the Optical and Electronic Properties of Fe, Ru, and Os Terpyridyl Complexes

AbstractMolecular assemblies of surface‐confined heterometallic molecular dyads (SURHMDs) composed of optically rich and redox‐active Fe(pytpy)2·2PF6 (Fe‐PT), Ru(pytpy)2·2PF6 (Ru‐PT) and Os(pytpy)2·2PF6 (Os‐PT) pytpy = 4′‐(4‐pyridyl)‐2,2′:6′,2″‐terpyridyl] complexes are fabricated via bottom‐up approach on SiOx based solid supports. Pairing of the two different metal‐organic complexes at a single platform results in significant enlargement of the optical window (λ = 400–800 nm), which can be of interest for potential applications. The use of the Cu‐based linker ensures intramolecular electronic communication between these complexes. In addition, SURHMDs are electrochemically stable under large numbers of read‐write cycles (103) and exhibit multiple redox states at relatively low potentials (<1.2 V). Moreover, an electrochemical input at controlled potentials creates a mixed‐valence multicomponent system.

Induced self-assembly and disassembly of water-soluble alkynylplatinum(ii) terpyridyl complexes with “switchable” near-infrared (NIR) emission modulated by metal–metal interactions over physiological pH: demonstration of pH-responsive NIR luminescent probes in cell-imaging studies

Water-soluble alkynylplatinum(II) terpyridine complexes, [Pt{tpy(C6H4CH2NMe3-4)-4′}(CC–Ar)](OTf)2 [Ar = C6H3–(OH)2-3,5 (1), C6H4OH-4 (2), C6H3–(OMe)2-3,5 (3)], have been synthesized and characterized. The photophysical and electrochemical properties of the complexes have been studied. Complex 1 has been found to undergo aggregation at low pHs, leading to metal–metal and/or π–π interactions and the emergence of a triplet metal-metal-to-ligand charge transfer (3MMLCT) emission in the near-infrared (NIR) region, the intensity of which has been enhanced 1350-fold over that at physiological pH. Such ‘switchable’ NIR emission of complex 1 was employed in cell-imaging experiments. The pH response of the 3MMLCT emission of complex 1 in cellular compartments has been studied using experiments with fixed Madin–Darby canine kidney (MDCK) cells, while live cell-imaging experiments revealed that complex 1 could function as a NIR luminescent probe for the tracking of the location of acidic organelles such as lysosomes.

Substitution effects of Ru–terpyridyl complexes on photovoltaic and carrier transport properties in dye-sensitized solar cells

Four Ru–4,4′-dicarboxylterpyridyl (dctpy) complexes, substituted with different types of functional groups (H, F, Me, and MeO), were synthesized for dye-sensitized solar cell (DSC) applications, and the influences of the substituents on the dye-adsorption, spectral, electronic, and photovoltaic properties of the Ru–dctpy dyes were observed. UV-vis spectra of the four dyes in MeOH did not exhibit any significant differences as the substituent was changed. However, the UV spectra of dye-sensitized TiO2 films showed differences in absorbance intensities, reflecting the dye-loading amount on the TiO2 surface (Me > H > MeO > F). The photovoltaic properties of the DSCs, based on the four Ru dyes, were changed by the effects of the substituents. The Ru–Me dye exhibited the best conversion efficiency, 7.94%, with the best electron injection efficiency (τe). The Ru–F dye, in contrast, exhibited the worst efficiency, 6.29%, due to a short τe and rapid charge recombination.

Dynamics of the 3MLCT in Ru(II) Terpyridyl Complexes Probed by Ultrafast Spectroscopy: Evidence of Excited-State Equilibration and Interligand Electron Transfer

Ground- and excited-state properties of [Ru(tpy)(2)](2+), [Ru(tpy)(ttpy)](2+), and [Ru(ttpy)(2)](2+) (where tpy = 2,2':6',2″-terpyridine and ttpy = 4'-(4-methylphenyl)-2,2':6',2″-terpyridine) in room temperature acetonitrile have been investigated using linear absorption, electrochemical, and ultrafast transient pump-probe techniques. Spectroelectrochemistry was used to assign features observed in the transient spectra while single wavelength kinetics collected at a variety of probe wavelengths were used to monitor temporal evolution of the MLCT excited state. From these data, the excited-state lifetime of each complex was recovered and the rate limiting decay step was identified. In the bis-heteroleptic complex [Ru(tpy)(ttpy)](2+), photoexcitation to the (1)MLCT manifold generates both tpy-localized and ttpy-localized excited states. Accordingly, interligand electron transfer (ILET) from tpy-localized to the ttpy-localized (3)MLCT excited states is observable and the time scale has been measured to be 3 ps. For the homoleptic complex [Ru(tpy)(2)](2+), evidence for equilibration of the (3)MLCT excited-state population with the (3)MC has been observed and the time scale is reported at 2 ps.

Photophysical and electrochemical properties of platinum(ii) complexes bearing a chromophore–acceptor dyad and their photocatalytic hydrogen evolution

A series of platinum(II) complexes bearing a chromophore-acceptor dyad obtained by reacting 4-(p-bromomethylphenyl)-6-phenyl-2,2'-bipyridine or 4'-(p-bromomethylphenyl)-2,2':6',2''-terpyridine with pyridine, 4-phenylpyridine, 4,4'-bipyridine, 1-methyl-4-(pyridin-4'-yl)pyridinium hexafluorophosphate respectively, were synthesized. Their photophysical properties, emission quenching studies by Pt nanoparticles and methyl viologen, electrochemical properties and photoinduced electron-transfer reactions in a photocatalytic hydrogen-generating system containing triethanolamine and colloidal Pt without an extra electron relay, were investigated. A comparison of the rates of hydrogen production for the two photocatalytic systems, one containing a metal-organic dyad and the other comprising a 1:1 mixture of the parental platinum(II) complexes and the corresponding electron relay, showed that intramolecular electron transfer improves the photocatalytic efficiency. Compared with cyclometalated platinum(II) complexes, the related platinum(II) terpyridyl complexes exhibited poor performance for photocatalytic hydrogen evolution. An investigation into the amount of hydrogen generated by three platinum(II) complexes containing cyclometalated ligands with methyl groups located on different phenyl rings revealed that the efficiency of hydrogen evolution was affected by a subtle change of functional group on ligand, and the hydrogen-generating efficiency in the presence or absence of methyl viologen is comparable, indicating electron transfer from the excited [Pt(C^N^N)] chromophore to colloidal Pt. (1)H NMR spectroscopy of the metal-organic dyads in an aqueous solution in the presence of excess triethanolamine revealed that the dyad with a viologen unit was unstable, and a chemical reaction in the compound occurred prior to irradiation by visible light under basic conditions.

Single-Turn Helix–Coil Strands Stabilized by Metal···Metal and π–π Interactions of the Alkynylplatinum(II) Terpyridyl Moieties in meta-Phenylene Ethynylene Foldamers

Dinuclear alkynylplatinum(II) terpyridyl complexes with oligomeric bridge consisting of five repeating meta-phenylene ethynylene (mPE) units have been found to exhibit a strong tendency to fold back onto themselves to form short helical strands through the stabilization of Pt···Pt and π-π interactions. The steric bulk of the terpyridine ligands and the length of the oligomeric bridge have been found to affect the extent of the intramolecular Pt···Pt interaction that governs the stabilization of the short helical strand in solution. Their folding properties via Pt···Pt and π-π stacking interactions have been studied by (1)H NMR, 2D ROESY NMR, electronic absorption, and emission spectroscopies.

Synthesis, characterization and catalytic property of ruthenium–terpyridyl complexes

The known compound 4′-(carboxyphenyl)-2,2′:6,2″-terpyridine (LH) was prepared and complexed with RuCl 3.3H 2O. The resulting complex [Ru(LH)Cl 3] was then allowed to react separately with 2,2′-bipyridine (bpy), 1,10-phenanthroline (phen), triphenylphosphine (PPh 3) and 1,2-bis-(diphenylphosphino)ethane (dppe). The compositions of corresponding complexes [Ru(LH)bpyCl](BF 4) 1, [Ru(LH)phenCl](BF 4) 2, [Ru(LH)(PPh 3)(CH 3CN) 2] (BF 4) 2 3 and [Ru(LH)(dppe)Cl](BF 4) 4 were assigned on the basis of their FAB-mass spectra, elemental analysis, spectroscopic (IR, NMR) data and X-ray diffraction measurements. The diamagnetic, cationic complexes displayed strong MLCT transitions in the visible region with significant shift in MLCT band energy corresponding to the strength of substituted ligands. The redox behaviour of the complexes was investigated using cyclic voltammetry measurements. Among all the complexes, 3 efficiently catalyzed the synthesis of propargylamine via three components coupling reaction.

Classification of stacking interaction geometries of terpyridyl complexes

Classification of stacking interaction geometries of terpyridyl complexes

Self-Assembly of Luminescent Alkynylplatinum(II) Terpyridyl Complexes: Modulation of Photophysical Properties through Aggregation Behavior

Complexes of platinum(II) with polypyridine (that is, the multidentate ligands related to pyridine, such as bipyridine or terpyridine) have rich photophysical properties. These compounds are able to give different crystal forms in the solid state: this polymorphism is evident in the broad range of colors that can be observed in solid samples. Because of the square-planar coordination geometry of the metal center, Pt···Pt as well as π-π interactions between the chromophoric polypyridyl platinum(II) moieties are thought to contribute to the polymorphism. Owing to limited solubility, metal···metal interactions in platinum(II) polypyridyl systems had been mainly studied in the solid state, but our preparation of more soluble complexes has enabled detailed spectroscopic examinations in solution. In this Account, we describe our development of these alkynylplatinum(II) terpyridyl complexes and their unique spectral properties. A series of square-planar platinum(II) terpyridyl complexes with enhanced solubility due to the presence of the alkynyl group exhibited intense emission in solution. The lowest energy absorption and emission bands are suggested to originate from the dπ(Pt) → π*(terpy) metal-to-ligand charge transfer (MLCT) and π(C≡C-C(6)H(4)-R) → π*(terpy) ligand-to-ligand charge transfer (LLCT) transitions. In addition to polymorphism and a wide range of spectral properties, these complexes also exhibit "solvatochromism" and "solvatoluminescence". They show remarkable color changes and luminescence enhancement when the diethyl ether content in a solvent mixture is varied, even as the concentration of the platinum(II) complex is held constant. The dramatic color changes and luminescence enhancement are tentatively suggested to originate from a metal-metal-to-ligand charge transfer (MMLCT) transition: reduced solvation (caused by an increase in the fraction of diethyl ether, which is the nonsolvating component of the liquid) is thought to increase Pt···Pt and π-π stacking interactions that arise from ground-state self-assembly or aggregate formation. The absorbance and luminescence wavelengths in these solvent-induced self-assemblies are also found to be dependent on the nature of the anions. Thus, counterions play an important role in governing the degree of self-assembly and the extent of interactions within these aggregates. Several polymers carrying multiple negatively charged functional groups (under basic conditions) as well as oligonucleotides have been shown to induce the aggregation and self-assembly of the positively charged water-soluble alkynylplatinum(II) terpyridyl complexes. The driving force for the induced aggregation and self-assembly is electrostatic binding of the complex molecules to the polymer, which brings the cations into a close proximity that induces Pt···Pt and π-π interactions and gives rise to remarkable color changes and luminescence enhancement. The spectral changes are shown to be related to the properties of both the complexes and the polymers. Upon electrostatic interaction, the platinum(II) complex cations are also found to stabilize the polymers and biopolymers in a helical conformation through Pt···Pt and π-π interactions. The influence on their secondary structure is revealed by significant circular dichroism (CD) signal enhancement.

Metal Ion Complexing Properties of Dipyridoacridine, a Highly Preorganized Tridentate Homologue of 1,10-Phenanthroline

DPA (dipyrido[4,3-b;5,6-b]acridine) may be considered as a tridentate homologue of phen (1,10-phenanthroline). In this paper some of the metal ion complexing properties of DPA in aqueous solution are reported. Using UV-visible spectroscopy to follow the intense π-π* transitions of DPA as a function of pH gave protonation constants at ionic strength (μ) = 0 and 25 °C of pK(1) = 4.57(3) and pK(2) = 2.90(3). Titration of 10(-5) M solutions of DPA with a variety of metal ions gave log K(1) values as follows: Zn(II), 7.9(1); Cd(II), 8.1(1); Pb(II), 8.3(1); La(III), 5.23(7); Gd(III), 5.7(1); Ca(II), 3.68; all at 25 °C and μ = 0. Log K(1) values at μ = 0.1 were obtained for Mg(II), 0.7(1); Sr(II), 2.20(1); Ba(II), 1.5(1). The log K(1) values show that the high level of preorganization of DPA leads to complexes 3 log units more stable than the corresponding terpyridyl complexes for large metal ions such as La(III) or Ca(II), but that for small metal ions such as Mg(II) and Zn(II) such stabilization is minimal. Molecular mechanics calculations (MM) are used to show that the best-fit M-N length for coordination with DPA is 2.60 Å, accounting for the high stability of Ca(II) or La(III) complexes of DPA, which are found to have close to this M-N bond length in their phen complexes.