Electron acceptors of the fluorene series. 10.(1) novel acceptors containing butylsulfanyl, butylsulfinyl, and butylsulfonyl substituents: synthesis, cyclic voltammetry, charge-transfer complexation with anthracene in solution, and X-ray crystal structures of two tetrathiafulvalene complexes

2,4,5,7-Tetranitro-9-fluorenone (1b) reacts readily with n-butanethiol in dipolar aprotic solvents with selective substitution of nitro groups by butylsulfanyl groups in positions 2 and 7 (2, 3); the 2,5-isomer 4 was formed only as a minor product (<1%). Condensation of fluorenones 2-4 with malononitrile yielded 9-dicyanomethylene derivatives 5-7, which showed strong intramolecular charge transfer (lambda approximately 510-560 nm) and were found to sensitize the photoconductivity of carbazole-containing polymer films. Oxidation of sulfides 2-4 gave sulfoxide 8 or sulfones 9-11, which then were converted into their corresponding dicyanomethylene derivatives 12-15. All these novel acceptors showed three reversible single-electron reduction waves (cyclic voltammetry) yielding radical anion, dianion, and radical trianion; moreover, acceptors 13-15 showed also a fourth reduction wave, representing reversible tetraanion formation. Substitution of the oxygen of the carbonyl group in the fluorenones by a dicyanomethylene group increased the thermodynamic stability (K(SEM) growth) of the radical anion; K(SEM) ranged from 3 x 10(5) to 3 x 10(9) M(-1). CV measurements characterize compounds 3, 4 (EA = 1. 86-1.89 eV) as poor acceptors, 2, 6-11 (EA = 2.13-2.31 eV) as moderate acceptors, and 5, 12-15 (EA = 2.53-2.66 eV) as strong electron acceptors. Charge-transfer complex (CTC) formation between acceptors 9, 10, 13, 14, and anthracene as a donor was monitored by the appearance of additional low-energy bands in the visible region (CTC bands) of their electron absorption spectra. Increasing the EA of the acceptors from 9-fluorenones to the corresponding 9-dicyanomethylenefluorenes increases the complexation constants K(CTC) by 2.5-3 times, while sulfonyl substituents present substantial steric hindrance for complexation (as compared to the nitro group), decreasing K(CTC) values. Two CTCs for acceptors 14 and 17 with tetrathiafulvalene (TTF) were obtained, and their structures were solved by single-crystal X-ray diffractometry, giving the stoichometries 14:TTF, 2:3, and 17:TTF:PhCl, 1:1:0.5. In the former complex the packing motif is a mixed.DDAD'A. stack; in the latter complex the D and A moieties form unusually close CT pairs, which pack in a herringbone motif.     

Tuning of redox potentials for the design of ruthenium anticancer drugs -- an electrochemical study of [trans-RuCl(4)L(DMSO)](-) and [trans-RuCl(4)L(2)](-) complexes, where L = imidazole, 1,2,4-triazole, indazole

The electrochemical behavior of [trans-RuCl(4)L(DMSO)](-) (A) and [trans-RuCl(4)L(2)](-) (B) [L = imidazole (Him), 1,2,4-triazole (Htrz), and indazole (Hind)] complexes has been studied in DMF, DMSO, and aqueous media by cyclic voltammetry and controlled potential electrolysis. They exhibit one single-electron Ru(III)/Ru(II) reduction involving, at a sufficiently long time scale, metal dechlorination on solvolysis, as well as, in organic media, one single-electron reversible Ru(III)/Ru(IV) oxidation. The redox potential values are interpreted on the basis of the Lever's parametrization method, and particular forms of this linear expression (that relates the redox potential with the ligand E(L) parameter) are proposed, for the first time, for negatively (1-) charged complexes with the Ru(III/II) redox couple center in aqueous phosphate buffer (pH 7) medium and for complexes with the Ru(III/IV) couple in organic media. The E(L) parameter was estimated for indazole showing that this ligand behaves as a weaker net electron donor than imidazole or triazole. The kinetics of the reductively induced stepwise replacement of chloride by DMF were studied by digital simulation of the cyclic voltammograms, and the obtained rate constants were shown to increase with the net electron donor character (decrease of E(L)) of the neutral ligands (DMSO < indazole < triazole < imidazole) and with the basicity of the ligated azole, factors that destabilize the Ru(II) relative to the Ru(III) form of the complexes. The synthesis and characterization of some novel complexes of the A and B series are also reported, including the X-ray structural analyses of (Ph(3)PCH(2)Ph)[trans-RuCl(4)(Htrz)(DMSO)], [(Ph(3)P)(2)N][trans-RuCl(4)(Htrz)(DMSO)], (H(2)ind)[trans-RuCl(4)(Hind)(DMSO)], and [(Hind)(2)H][trans-RuCl(4)(Hind)(2)].     

Electrochemistry of microparticles of tris (2,2′-bipyridine) ruthenium(II) hexafluorophosphate

The electrochemical behaviour of tris(2,2′-bipyridine)ruthenium(II) hexafluorophosphate (Ru(II)) microparticles, immobilised on a graphite electrode and adjacent to an aqueous electrolyte solution, has been studied by cyclic voltammetry and an in situ spectroelectrochemical technique. The solid Ru(II) complex exhibits one reversible redox couple with a formal potential (E_f) of 1.1 V versus Ag¦AgCl. The continuous cyclic voltammetric experiments showed that the Ru(II) microparticles are stable during the electrochemical conversions. The in situ spectroelectrochemical study showed that the absorbance at 463 nm decreased due to the oxidation of Ru(II) to Ru(III). Upon reduction, the growth of absorbance at 463 nm was observed due to the formation of Ru(II) complex and this process was reversible.     

Ruthenium(II) coordination chemistry of a fused donor-acceptor ligand: synthesis, characterization, and photoinduced electron-transfer reactions of [{Ru(bpy)2}(n)(TTF-ppb)](PF6)(2n) (n = 1, 2)

A pi-extended, redox-active bridging ligand 4',5'-bis(propylthio)tetrathiafulvenyl[i]dipyrido[2,3-a:3',2'-c]phenazine (L) was prepared via direct Schiff-base condensation of the corresponding diamine-tetrathiafulvalene (TTF) precursor with 4,7-phenanthroline-5,6-dione. Reactions of L with [Ru(bpy)(2)Cl(2)] afforded its stable mono- and dinuclear ruthenium(II) complexes 1 and 2. They have been fully characterized, and their photophysical and electrochemical properties are reported together with those of [Ru(bpy)(2)(ppb)](2+) and [Ru(bpy)(2)(mu-ppb)Ru(bpy)(2)](4+) (ppb = dipyrido[2,3-a:3',2'-c]phenazine) for comparison. In all cases, the first excited state corresponds to an intramolecular TTF --> ppb charge-transfer state. Both ruthenium(II) complexes show two strong and well-separated metal-to-ligand charge-transfer (MLCT) absorption bands, whereas the (3)MLCT luminescence is strongly quenched via electron transfer from the TTF subunit. Clearly, the transient absorption spectra illustrate the role of the TTF fragment as an electron donor, which induces a triplet intraligand charge-transfer state ((3)ILCT) with lifetimes of approximately 200 and 50 ns for mono- and dinuclear ruthenium(II) complexes, respectively.     

Synthesis, characterization and electron transfer properties of some picolinate complexes of ruthenium

In aqueous solution ruthenium trichloride reacted with picolinic acid (Hpic) in the presence of a base to afford [Ru(pic)₃]. In solution it shows intense ligand-to-metal charge transfer transitions near 310 and 370 nm, together with a low-intensity absorption near 2000 nm. [Ru(pic)₃] is one-electron paramagnetic and shows a rhombic ESR spectrum in 1:1 dimethylsulphoxide-methanol solution at 77 K. The distortions from octahedral symmetry have been calculated by ESR data analysis. The axial distortion is larger than the rhombic one. In acetonitrile solution it shows a reversible ruthenium(III)-ruthenium(II) reduction at −0.09 V vs. SCE and a reversible ruthenium(III)-ruthenium(IV) oxidation at 1.52 V vs. SCE. Chemical or electrochemical reduction of [Ru^III(pic)₃] gives [Ru^II(pic)₃]⁻, which in solution shows intense MLCT transitions near 360, 410 and 490 nm, and is converted back to [Ru(pic)₃] by exposure to air. Reaction of [Ru(pic)₃] with 8-quinolinol (HQ) in dimethylsulphoxide solution affords [RuQ₃]. [Ru(bpy)(pic)₂] (bpy = 2,2′-bipyridine) has been prepared by the reaction of Hpic with [Ru(bpy)(acac)₂]Cl (acac = acetylacetonate ion) in ethyleneglycol. It is diamagnetic and in solution shows intense MLCT transitions near 370, 410 and 530 nm. In acetonitrile solution it shows a reversible ruthenium(II)-ruthernium(III) oxidation at 0.44 V vs. SCE and a reversible one-electron reduction of bpy at − 1.64V vs. SCE.     

Two trinuclear Ru(II) complexes of hetero-tritopic bridging ligands: synthesis,characterization, theoretical calculations,photophysical and electrochemical properties

Two hetero-tritopic bridging ligands L¹ and L² based on 2,2′-bipyridine and 1,10-phenanthroline moieties, and their corresponding Ru(II) complexes [{Ru(bpy)₂}₃(µ₃?L¹)](PF₆)₆ and [{Ru(bpy)₂}₃(µ₃?L²)](PF₆)₆ (bpy = 2,2′-bipyridine), were synthesized. The molecular structures of both complexes were deduced by ¹H NMR, ESI-MS, ESI-HRMS, elemental analyses, and IR spectroscopy. Quantum calculations on the free bridging ligands and their complexes are also presented. Both complexes display MLCT absorptions at around 454 nm, and emissions at around 613 nm in CH₃CN solution at room temperature and at around 590 nm in EtOH–MeOH glassy matrix at 77 K. Cyclic and differential pulse voltammetry studies of both complexes reveal one reversible Ru(II)-centered oxidation and three reversible ligand-centered reductions, in each case.     

Half-sandwich ruthenium(II)-arene complexes: synthesis,spectroscopic studies,biological properties,and molecular modeling

In search for antitumor metal-based drugs that would mitigate the severe side-effects of cisplatin, Ru(II) complexes are gaining increasing recent interest. In this work, we report on the synthesis, characterization (¹H- and ¹³C-NMR, FT-IR), and cytotoxicity studies of two new half-sandwich organometallic Ru(II) complexes of the general formula [Ru(η⁶-arene)(XY)Cl](PF₆) where arene?=?benzene or toluene and XY?=?bidentates: dipyrido[3,2-a:2′,3′-c]phenazine (dppz) or 2-(9-anthryl)-1H-imidazo[4,5-f][1,10]phenanthroline (aip), which are bound to Ru(II) via two phenanthroline-N atoms in a characteristic “piano-stool” configuration of Ru(II)-arene complexes—as confirmed by vibrational and NMR spectra. In addition, cytotoxic studies were performed for similar half-sandwich organometallic [Ru(η⁶-p-cymene)(Me₂dppz)Cl]PF₆ complex (Me₂dppz = 11,12-dimethyl-dipyrido[3,2-a:2′,3′-c]phenazine). This study is complemented with elaborate modeling with density functional theory (DFT) calculations, which provided insight into reactive sites of Ru(II) structures, further detailed by molecular docking on the B-DNA dodecamer, which identified binding sites and affinities: most pronounced for the [Ru(η⁶-benzene)(aip)Cl](PF₆) in both A-T and G-C regions of the DNA minor groove. Cytotoxic activity was probed versus tumor cell lines B16, C6, and U251 (B16 mouse melanoma, C6 rat glioma, U251 human glioblastoma) and non-tumor cell line HACAT (HACAT normal human keratinocytes).     

Synthesis and reactivity of silylated tetrathiafulvalenes

Novel organosilylated tetrathiafulvalenes (TTFs) possessing Si-H or Si-Si bonds have been synthesised. The crystal structures of several derivatives have been determined by X-ray diffraction, including that of dimeric (Si(2)Me(4))(TTF)(2) () incorporating a diatomic SiMe(2)-SiMe(2) linker. Cyclic voltammetry measurements in all cases show two oxidation waves. DFT calculations were performed to rationalize the absence of an electronic communication between the two TTF moieties of through the disilanyl spacer. The reactivity of the Si-H bond has been exploited to prepare the dinuclear complex [{Ru(CO)(4)}(2){mu-(Me(2)Si)(4)TTF}] (), starting from Ru(3)(CO)(12) and TTF(SiMe(2)H)(4) (). Treatment of with 2 equiv. of PPh(3) or dppm results in selective substitution of a CO ligand trans to a SiMe(2) group to afford mer-[{Ru(PPh(3))(CO)(3)}(2){mu-(Me(2)Si)(4)TTF}] () and mer-[{Ru(CO)(3)}(2)(eta(1)-dppm){mu-(Me(2)Si)(4)TTF}] (). Attempts to transform the Si-H bonds of some TTF(SiMe(2)H)(n) (n = 1, 2) into Si-O functions using stoichiometric amounts of water in the presence of tris(dibenzylideneacetone)dipalladium(0) were unsuccessful. Quantitative cleavage of the C(TTF)-Si bond was observed instead of formation of TTF-based-siloxanes. Essays of catalytic bis-silylation of phenylacetylene with and TTF(SiMe(2)-SiMe(3)) () in the presence of Pd(OAc)(2)/1,1,3,3-tetramethylbutylisocyanide failed. Again, cleavage of the C(TTF)-Si bond was noticed.     

Synthesis,characterization and catalytic,cytotoxic and antimicrobial activities of two novel cyclotriphosphazene‐based multisite ligands and their Ru(II) complexes

Two novel cyclotriphosphazene ligands ( 2 and 3 ) bearing 3‐oxypyridine groups and their corresponding Ru(II) complexes ( 4 and 5 ) were synthesized and their structures were characterized using Fourier transform infrared, ¹H NMR and ³¹P NMR spectroscopic data and elemental analysis. The Ru(II) complexes were used as catalysts for catalytic transfer hydrogenation of p‐substituted acetophenone derivatives in the presence of KOH. Additionally, the cytotoxic activities of compounds 2 , 3 , 4 , 5 were evaluated against PC3 (human prostate cancer), DLD‐1 (human colorectal cancer), HeLa (human cervical cancer) and PNT1A (normal human prostate) cell lines. Finally the antimicrobial activities of compounds 2 , 3 , 4 , 5 were evaluated against a panel of Gram‐positive and Gram‐negative bacteria and yeast cultures. The complexes showed efficient catalytic activity towards transfer hydrogenation of acetophenone derivatives, especially those bearing electron‐withdrawing substituents on the para‐position of the aryl ring. The compounds were found to have moderate to high cytotoxic and antimicrobial activities, and Ru(II) complexation enhanced both cytotoxic and antimicrobial activities in comparison with the parent compounds. Copyright © 2015 John Wiley & Sons, Ltd.     

Synthesis,structure and electrochemical properties of a family of organoruthenium complexes

Reaction of N-(2′-hydroxyphenyl)benzaldimines (abbreviated in general as H₂L-R, where R stands for the para-substituent in the benzaldehyde fragment and H stands for the dissociable hydrogen atoms) with [Ru(PPh₃)₂(CO)₂Cl₂] affords a family of organoruthenium complexes of the type [Ru(PPh₃)₂(CO)(L-R)] where the N-(2′-hydroxyphenyl)benzaldimine ligand is coordinated to the metal center as tridentate C,N,O-donor. Structure of a representative complex has been determined by X-ray crystallography. All the [Ru(PPh₃)₂(CO)(L-R)] complexes are diamagnetic, and show characteristic ¹H NMR signals and moderately intense MLCT transitions in the visible region. Cyclic voltammetry of the [Ru(PPh₃)₂(CO)(L-R)] complexes shows a reversible Ru(II)–Ru(III) oxidation within 0.38–0.68 V versus SCE, followed by an irreversible oxidation of the coordinated benzaldimine ligand within 1.09–1.27 V versus SCE. An irreversible reduction of the coordinated benzaldimine ligand is also observed near −1.1 V versus SCE. Potential of the Ru(II)–Ru(III) oxidation is observed to be sensitive to the nature of para-substituent R.     

Spectrophotometric study of the ruthenium(III,II)–2,2′,2″- terpyridine system

Ruthenium(III) reacts with 2,2′,2″-terpyridine in aqueous solution at pH 3.0–4.5, when heated at 85 °C for 2 min, giving a green cationic complex with an absorbance maximum at 690 nm. The color is stable for at least 25 h. The system conforms to Beer's law. The optimal range for measurement (1.00-cm optical path) is 2–10 p.p.m. Ru; the molar absorptivity is 8.3 ·10³. Ruthenium(II) reacts with terpyridine at pH 5.5 to develop an amber cationic complex (absorption maximum at 475 nm) on heating at 95° C for 45 min. The color is apparently stable indefinitely. The system conforms to Beer's law; the optimal range is 1–5 p.p.m. Ru; the molar absorptivity is 1.45·10⁴ l mol^?1 cm^?1. Common anions do not interfere; separation as RuO₄ is necessary when iron and a few other transition cations are present. The green complex, a strong oxidant, is converted to the ruthenium(II) complex by oxidation of water, slowly at room temperature, or more quickly by longer heating and/or higher temperature, and by increase of pH. The Ru(II) complex can be converted to the Ru(III) complex by strong oxidants such as Ce(IV). In the amber complex, the reaction ratio is 1 Ru: 2 terpyridine, in which the ligand is tridentate, whereas in the green complex the reaction ratio is 1 Ru : 3 terpyridine, the latter acting only as a bidentate ligand. Short gentle warming of a mixture of ruthenium(III) and terpyridine first produces a transient unidentified blue-colored species (absorbance at 790 nm).     

Photoreactions of tris(2,2'-bipyridyl)-ruthenium(II) with peroxydisulfate in deoxygenated aqueous solution in the presence of nucleic acid components, polynucleotides, and DNA

Abstract— The photobleaching of excited tris(2,2′-bipyridyl)-ruthenium(II), *Ru(bpy)₃²⁺, by peroxydis-ulfate in the presence of DNA and a series of polynucleotides, mononucleosides (uridine, cytidine, adenosine, guanosine), and purine or pyrimidine bases was studied in deoxygenated aqueous solution at room temperature. A reaction scheme is proposed which is confirmed by data obtained from mixing experiments with Ru(III) and bleaching measurements of Ru(II) using either continuous visible light or a nanosecond laser pulse (353 nm). The primary photobleaching step is the formation of Ru(bpy)₃²⁺ and the SO₄^- radical anion. In the presence of nucleic acids the two oxidizing species are formed in close proximity to the strand, since we used conditions where the Ru(bpy) ₃²⁺ ion is bound to the strand. Concerning the secondary reactions two clear cases (and several more complex cases) can be distinguished. On addition of uracil to the Ru(bpy)₃²⁺/S₂O₈^2- system the quantum yield for photobleaching is not significantly changed (φ^rel? 0.95), whereas it drops to virtually zero for guanosine-containing substrates, including DNA. The former result is explained by a reaction of SO₄^- with uracil leading to theN–1 radical which oxidizes Ru(II) to Ru(IIl). In contrast, the guanine moiety reacts with Ru(III) converting it into Ru(II). Therefore, in the presence of S₂O₈^2- and a substrate carrying a guanine moiety, Ru(bpy₃²⁺ acts as a photocatalyst.     

Chromo‐Fluorogenic Detection of Nitroaromatic Explosives by Using Silica Mesoporous Supports Gated with Tetrathiafulvalene Derivatives

Three new hybrid gated mesoporous materials ( SN₃‐1 , SNH₂‐2 , and SN₃‐3 ) loaded with the dye [Ru(bipy)₃]²⁺ (bipy=bipyridine) and capped with different tetrathiafulvalene (TTF) derivatives (having different sizes and shapes and incorporating different numbers of sulfur atoms) have been prepared. The materials SN₃‐1 and SN₃‐3 are functionalized on their external surfaces with the TTF derivatives 1 and 3 , respectively, which were attached by employing the “click” chemistry reaction, whereas SNH₂‐2 incorporates the TTF derivative 2 , which was anchored to the solid through an amidation reaction. The final gated materials have been characterized by standard techniques. Suspensions of these solids in acetonitrile showed “zero release”, most likely because of the formation of dense TTF networks around the pore outlets. The release of the entrapped [Ru(bipy)₃]²⁺ dye from SN₃‐1 , SNH₂‐2 , and SN₃‐3 was studied in the presence of selected explosives (Tetryl, TNT, TNB, DNT, RDX, PETN, PA, and TATP). SNH₂‐2 showed a fairly selective response to Tetryl, whereas for SN₃‐1 and SN₃‐3 dye release was found to occur with Tetryl, TNT, and TNB. The uncapping process in the three materials can be ascribed to the formation of charge‐transfer complexes between the electron‐donating TTF units and the electron‐accepting nitroaromatic explosives. Finally, solids SNH₂‐2 and SN₃‐1 have been tested for Tetryl detection in soil with good results, pointing toward a possible use of these or similar hybrid capped materials as probes for the selective chromo‐fluorogenic detection of nitroaromatic explosives.     

Synthesis,characterization and cyclic voltammetric studies of monopicolinate complexes of ruthenium(II)

Summary Two stable monopicolinate complexes of ruthenium(II), [Ru(bipy)₂(pic)]ClO₄ and [Ru(pap)₂(pic)]ClO₄ [bipy = 2,2-bipyridine, pic = picolinate anion, pap = 2-(phenylazo)-pyridine], were prepared and characterized. The complexes are diamagnetic and behave as 1:1 electrolytes in MeCN solution. In the i.r. spectra, they show characteristic vibrations of bipy or pap, pic and ClO _inf4 ^p– . In MeCN solution, both complexes display three intense absorption bands in the visible region, which have been assigned to metal-to-ligand charge-transfer transitions. Each complex shows a reversible ruthenium(II)-ruthenium(III) oxidation in MeCN, the formal potential (E _inf298 ^p0 ) being 0.75 V versus a saturated calomel reference electrode (SCE) for [Ru-(bipy)₂(pic)]⁺ and 1.44 V versus SCE for [Ru(pap)₂(pic)]⁺. Multiple reductions of the coordinated bipy and pap ligands have also been observed.Author to whom all correspondence should be directed.     

Heteroligand bipyridyl-pyridylbenzimidazole Ru(II) complexes. Synthesis,structural characterization,and investigation of electronic structure

Ruthenium(II) complexes with pyridylbenzimidazole derivatives were synthesized and investigated by NMR (¹H and ¹H-¹H COSY), mass, and electronic spectroscopy. Proceeding from quantum-chemical calculations by the density functionsl methods the analysis was performed of electronic and geometric structure of free ligands and Ru(II)complexes, and the electron absorption spectra of complexes under study were interpreted. Compared to [Ru(bpy)₃]²⁺ (bpy = 2,2′-bipyridyl) the charge transfer band in the visible range of the electronic spectra of the complexes in question suffered a red shift by ～10 nm, and its intensity in the absorption maximum is several times smaller. The introduction of acceptor substituents into the benzene ring of the pyridylbenzimidazole ligand did not affect significantly the spectral properties of the complexes.     

Building up 1‐D, 2‐D,and 3‐D Polyiodide Frameworks by Finely Tuning the Size of Aryls on Ar‐S‐TTF in the Charge‐Transfer (CT) Complexes of Ar‐S‐TTFs and Iodine

The arylthio‐substituted tetrathiafulvalenes (Ar‐S‐TTFs) are electron donors having three reversible states, neutral, cation radical, and dication. The charge‐transfer (CT) between Ar‐S‐TTFs ( TTF1 — TTF3 ) and iodine (I₂) is reported herein. TTF1 — TTF3 show the CT with I₂ in the CH₂Cl₂ solution, but they are not completely converted into cation radical state. In CT complexes of TTF1 — TTF3 with I₂, the charged states of Ar‐S‐TTFs are distinct from those in solution. TTF1 is at cation radical state, and TTF2 — TTF3 are oxidized to dication. The iodine components in complexes show various structures including 1‐D chain of V‐shaped (I₅)^–, and 2‐D and 3‐D iodine networks composed of I₂ and (I₃)^–.     

Second‐order nonlinear optical responses switching of N∧N∧N ruthenium carboxylate complexes with proton‐electron transfer

In this article, the nonlinear optical (NLO) switching action of Ru(III/II) carboxylate complexes was investigated by density functional theory (DFT). Among the studied complexed, Ru(III)PhCOO^? has the largest β value of 4972 × 10^?30 esu. Through the proton transfer (PT) process, the ? COOH group of Ru(III)PhCOOH and Ru(III)COOH complexes can form the ? COO^? group. Then, ? COO^? group acts as a strong donor and Ru(III) acts as an acceptor, which may be the most favorably used in the development of metal complexes NLO material. The redox NLO switching and PT NLO switching of Ru(III)PhCOO^?, Ru(III)PhCOOH, Ru(II)PhCOO^?, and Ru(II)PhCOOH complexes have been studied. The β value of Ru(III)PhCOO^? complex is ～36 and ～48 times larger than those of reduced Ru(II)PhCOO^? and Ru(II)PhCOOH, respectively. Note that the β value of deprotonated Ru(III)PhCOO^? is ～215 times larger than that of Ru(III)PhCOOH. The molecular electrostatic potential analysis also confirms that Ru(III)PhCOOH may have poor performance in the second‐order NLO response. In addition, the TDDFT calculations show that the ligand to metal charge transfer transition lead to the largest β value of the Ru(III)PhCOO^? complex. This investigation provides important insight into the remarkably large NLO properties and NLO switching of Ru(III/II) carboxylate complexes. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem 000: 000–000, 2011     

Redox,spectroscopic, photo-induced ligand exchange,and DNA interaction studies of a new Ru(II)Pt(II) bimetallic complex

A new bimetallic complex, [Ru(biq)₂(dpp)PtCl₂](PF₆)₂ (where biq = 2,2′-biquinoline and dpp = 2,3-bis(2-pyridyl)pyrazine), containing a cis-PtCl₂ moiety coupled to a sterically strained Ru(II)-based chromophore was designed, synthesized, and investigated with respect to its spectroscopic, redox, photo-induced ligand exchange, and DNA-interaction properties. The electrochemistry of the designed complex was found to be consistent with the bridging coordination of the dpp ligand and formation of the bimetallic complex. The complex displays intense ligand-based π → π* transitions in the UV region and metal-to-ligand charge-transfer transitions (MLCT) in the visible region. The loss of bridging coordination of the dpp ligand and formation of complexes, [Ru(biq)₂(CH₃CN)₂]²⁺ and [Pt(dpp)(CH₃CN)₂]²⁺ was observed when an acetonitrile solution of the metal complex was irradiated with visible light (λ_irr ≥ 550 nm). The designed complex displays covalent binding with DNA in dark through the cis-PtCl₂ moiety, as confirmed by agarose gel electrophoresis. Upon photoirradiation, the complex dissociates into two DNA-binding moieties and displays covalent binding through: (i) a cis-PtL₂ subunit of [Ptdpp(L)₂]²⁺ and (ii) open coordination sites of the ruthenium of [Ru(biq)₂(L)₂]²⁺ (L = solvent). The designed complex represents the first Ru(II)Pt(II) complex that undergoes photo-induced ligand exchange and displays multifunctional interactions with DNA upon photoirradiation.     

Quantum Mechanical and Experimental Validation that Cyclobis(paraquat‐p‐phenylene) Forms a 1:1 Inclusion Complex with Tetrathiafulvalene

The promiscuous encapsulation of π‐electron‐rich guests by the π‐electron‐deficient host, cyclobis(paraquat‐p‐phenylene) (CBPQT⁴⁺), involves the formation of 1:1 inclusion complexes. One of the most intensely investigated charge‐transfer (CT) bands, assumed to result from inclusion of a guest molecule inside the cavity of CBPQT⁴⁺, is an emerald‐green band associated with the complexation of tetrathiafulvalene (TTF) and its derivatives. This interpretation was called into question recently in this journal based on theoretical gas‐phase calculations that reinterpreted this CT band in terms of an intermolecular side‐on interaction of TTF with one of the bipyridinium (BIPY²⁺) units of CBPQT⁴⁺, rather than the encapsulation of TTF inside the cavity of CBPQT⁴⁺. We carried out DFT calculations, including solvation, that reveal conclusively that the CT band emerging upon mixing TTF with CBPQT⁴⁺ arises from the formation of a 1:1 inclusion complex. In support of this conclusion, we have performed additional experiments on a [2]rotaxane in which a TTF unit, located in the middle of its short dumbbell, is prevented sterically from interacting with either one of the two BIPY²⁺ units of a CBPQT⁴⁺ ring residing on a separate [2]rotaxane in a side‐on fashion. This [2]rotaxane has similar UV/Vis and ¹H NMR spectroscopic properties with those of 1:1 inclusion complexes of TTF and its derivatives with CBPQT⁴⁺. The [2]rotaxane exists as an equimolar mixture of cis‐ and trans‐isomers associated with the disubstituted TTF unit in its dumbbell component. Solid‐state structures were obtained for both isomers, validating the conclusion that the TTF unit, which gives rise to the CT band, resides inside CBPQT⁴⁺.     

Tripodal Ru(II) complexes with conjugated and non-conjugated rigid-rod bridges for semiconductor nanoparticles sensitization

Three tripodal Ru(II)-polypyridyl complexes have been synthesized as models to study long-range electron transfer in TiO₂ semiconductor nanoparticles thin films, in particular to study the effect of the conjugation of the bridge containing the Ru complex and for distance dependence studies. The tripodal sensitizers, which are 1,3,5,7-tetraphenyladamantane derivatives having three COOMe anchoring groups and one rigid-rod bridge substituted with a Ru(II) complex, are the longest prepared to date (Ru-to-footprint distance ∼24 Å). Two have a rigid-rod bridge made of two p-ethynylphenylene units (Ph-E)₂ capped with a 4-2,2′-bipyridyl (bpy) ligand or a 5-1,10-phenanthrolinyl (phen) ligand for the Ru complex. The third tripod, which contains a bpy ligand for the Ru complex, has one bicyclo[2.2.2]octylene (Bco) unit in place of a p-phenylene (Ph) unit and is the first example of a tripodal sensitizer with a non-conjugated bridge.