Tuning the gas phase redox properties of copper(II) ternary complexes of terpyridines to control the formation of nucleobase radical cations

Electrospray ionization (ESI) tandem mass spectrometry (MS/MS) of ternary copper(II) complexes of [Cu(terpyX)(M)]2+ (where terpyX = is a substituted 2,2':6',2'-terpyridine ligand; M = the nucleobases: adenine, guanine, thymine and cytosine) was examined as a means of forming radical cations of nucleobases in the gas phase. The following substituents were examined: 4'-NMe2-2,2':6',6'-terpyridine; 4'-OH-2,2':6',6'-terpyridine; 4'-F-2,2':6',6'-terpyridine; 2,2':6',6'-terpyridine; 4'-Cl-2,2':6',6'-terpyridine; 4'-Br-2,2':6',6'-terpyridine; 4'-CO2H-2,2':6',6'-terpyridine; 4'-NO2-2,2':6',6'-terpyridine and 6,6'-dibromo-2',2:6',2'-terpyridine. Each of the ternary complexes [Cu(terpyX)(M)]2+ was mass selected and subjected to collision induced dissociation (CID) in a quadrupole ion trap. The types of fragmentation reactions observed for these complexes depend on the nature of the substituent on the terpyridine ligand, while the yields of the radical cations of the nucleobases follow the order of their ionization energies (IEs): G (lowest IE) > A > C > T (highest IE). In general, radical cation formation is favoured for electron withdrawing substituents (e.g. NO2) while loss of the neutral nucleobase is favoured for electron donating substituents (e.g. NMe2). Loss of the protonated nucleobase is a major fragmentation pathway for the OH substituted terpyridine system, consistent with its ability to bind to a metal centre as a deprotonated ligand. Crystal structure determinations of (6,6'-dibromo-2',2:6',2'-terpyridine)bis(nitrato)copper(II) and diaqua(4'-oxo-2,2':6',6'-terpyridine)copper(II) nitrate monohydrate were performed and correlated with the ESI results.     

Effect of adenine moiety on DNA binding property of copper(II)-terpyridine complexes

Two novel copper(ii) terpyridine complexes, [Cu(atpy)(NO(3))(H(2)O)](NO(3)).3H(2)O () and [Cu(ttpy)(NO(3))(2)] () (atpy = 4'-p-N9-adeninylmethylphenyl-2,2':6,2'-terpyridine; ttpy = 4'-p-tolyl-2,2':6,2'-terpyridine) have been prepared and structurally characterized by X-ray crystallography. Both complexes show a CuN(3)O(2) coordination in a square pyramidal (4 + 1) geometry with terpyridine acting as an equatorial ligand. For complex , intermolecular AA base pairing interaction is observed between N(6) and N(1) of adjacent adenines with N(6)N(1) of 3.027(7) A. A molecular dynamics simulation of the DNA binding of two complexes showed that the adenine moiety plays an important role in the intercalation of into DNA. This is verified by UV, fluorescence, circular dichroism and flow linear dichroism studies. The promotional effect from the adenine moiety to the intracellular DNA binding of complex is also confirmed by the inductively coupled plasma mass (ICP-MS) spectrometry data which showed a significant higher copper content in DNA isolated from complex treated MCF-7 and HeLa cells.     

Synthesis of soluble bis-terpyridine ligands bearing ethynylene-phenylene spacers

Soluble and rigid terpyridine-based ditopic ligands bearing one to five phenylene/ethynylene modules have been synthesized by way of a stepwise procedure. Each module is attached to the terpyridine unit via an ethynylene fragment and functionalized at the 4-position with an additional ethynylene connector and in the 2,5-positions with two flexible dodecyloxy chains. The synthetic protocol is based on sequential Pd(0)-catalyzed cross-coupling reactions between a terpyridine subunit grafted with the necessary diethynyl/phenyl or ethynylphenyl/bromide appendage. For ditopic ligands displaying an even number of phenyl/ethynylene modules, the final step involves a single cross-coupling reaction between 4'-ethynylene-2,2':6',6' '-terpyridine and the appropriate bromo derivative. In the case of the ligands having an odd number of phenylene/ethynylene fragments, a double cross-coupling reaction between an extended dibromopolyphenylene intermediate and 4'-ethynylene-2,2':6',6' '-terpyridine or 1-(4'-ethynylene-2,2':6',2' '-terpyridine)-4-ethynylene-2,5-didodecyloxy-benzene is required. For ligands I-V, optimal preparative conditions were found with [Pd(0)(PPh(3))(4)] (6 mol %) in n-propylamine at 70 degrees C. Oxidative dimerization of the 1-(4'-ethynylene-2,2':6',2' '-terpyridine)-4-ethynylene-2,5-didodecyloxybenzene derivative in the presence of cupric salts and oxygen gives the corresponding homoditopic ligand II(2)() bearing a central diphenyldiacetylene spacer. Spectroscopic data for the new oligomers are discussed in terms of the extent of pi-electron conjugation. Upon increasing the number of phenylene/ethynylene modules, there is a progressive lowering in energy of absorption and fluorescence transitions.     

Self-assembled monolayers of Ru/Os dinuclear complexes: probing monolayer structure and interaction energies by electrochemical means

Monolayers of [Ru(bpy)2(micro-1)M2][PF6]4 salts (M = Os, Ru; bpy = 2,2'-bipyridine, 1 = 4'-(2,2'-bipyridin-4-yl)-2,2':6',2' '-terpyridine, tpy = 2,2':6',2' '-terpyridine, and 2 = 4'-(4-pyridyl)-2,2':6',2' '-terpyridine) were self-assembled on platinum and investigated by fast-scan electrochemistry. The electrochemistry of the complexes in solution and confined to the surface in self-assembled monolayers (SAMs) exhibited an almost ideal behavior. Scan-rate-dependent measurements of the peak current density (jp) were used to determine interaction energies within the monolayer. It is shown that the tpy coordination sites of the dinuclear complexes interact more strongly within the SAM than the bipyridine-coordinated fragments. This result was supported by peak potential shifts, which are due to interaction forces in SAMs. The alignment of the rodlike complexes relative to the surface is discussed, and the results of molecular mechanics calculations indicate that the species adopt a tilted orientation.     

Preparations and characterizations of bichromophoric systems composed of a ruthenium polypyridine complex connected to a difluoroborazaindacene or a zinc phthalocyanine chromophore

This paper describes the synthesis of a new series of molecules composed of a ruthenium cation liganded by a chloro or a thiocyanato, a 4,4'-(diethoxycarbonyl)-2,2'-bipyridine, and a 2,2':6',2' '-terpyridine substituted in its 4' position by a difluoroborazaindacene or a zinc phthalocyanine. A set of conditions are reported to conveniently synthesize these dyads by a Stille cross-coupling reaction between the trimethyltin derivative of the organic chromophore and the corresponding ruthenium complex with 4'-bromo-2,2':6',2' '-terpyridine and 4,4'-(diethoxycarbonyl)-2,2'-bipyridine. The dyads were studied by UV-visible absorption spectroscopy, steady-state fluorescence, and electrochemistry. The results of these studies indicate strong electronic coupling between the zinc phthalocyanine unit and the ruthenium complex but weakly electronically coupled systems in the case of dyads containing a difluoroborazaindacene unit. The new bichromophoric systems display strong absorbance in the visible spectrum. An efficient quenching of the fluorescence of the organic chromophore by the nearby ruthenium complex was also observed in all of the dyads. In dyads connected to the borazaindacene, excitation spectra indicate efficient photoinduced energy transfer from the borazaindacene to the ruthenium complex.     

Synthesis, characterization and electrochemistry of 4'-functionalized 2,2':6',2'-terpyridine ruthenium(II) complexes and their biological activity

The synthesis and characterization of Ru(II) terpyridine complexes derived from 4'-functionalized 2,2':6',2'-terpyridine ligands by a multi step procedure have been described. The complexes are redox-active, showing both metal-centred (oxidation) and ligand-centred (reduction) processes. The antibacterial and antifungal activity of the synthesized ruthenium(II) complexes [Ru(attpy)2](PF6)2 (attpy = 4'-(4-acryloyloxymethylphenyl)-2,2':6',2'-terpyridine); [Ru(mttpy)2](PF6)2 (mttpy = 4'-(4-methacryloyloxymethylphenyl)-2,2':6',2'- terpyridine); [Ru(mttpy)(MeOPhttpy)](PF6)2 (MeOPhttpy = 4'-(4-methoxyphenyl)-2,2':6',2'-terpyridine); and [Ru(mttpy)(ttpy)](PF6)2 (ttpy = 4'-(4-methylphenyl)-2,2':6',2'-terpyridine) were tested against four human pathogens (Proteus vulgaris, Proteus mirabilis, Pseudomonas aeruginosa and Escherichia coli) and five plant pathogens (Curvularia lunata, Fusarium oxysporum, Fusarium udum, Macrophomina phaseolina and Rhizoctonia solani) by the well diffusion method and MIC values of the complexes are reported. A biological study of the complexes indicated that the complexes [Ru(mttpy)2](PF6)2 and [Ru(mttpy)(MeOPhttpy)](PF6)2 exhibit very good activity against most of the test pathogens and their activity is better than those of some of the commercially available antibiotics like tetracycline and the fungicide carbendazim.     

Chiral hybrid metal-organic dendrimers

[structure: see text] New chiral terpyridines containing Frechét-type dendrons have been readily synthesized by coupling dendritic benzyl bromide and 4'-[6-(2,2'-dihydroxy-1,1'-binaphthyl)]-2,2':6'2' '-terpyridine. These chiral dendritic terpyridines were used to efficiently construct high molecular weight hybrid metal-organic dendrimers based on the Ru(II)-bis(terpy) linkage. Preliminary fluorescence measurements show generation-dependent fluorescence quenching behavior of 3,5-dimethoxybenzyl peripherals by the [Ru(terpy)(2)](2+) unit.     

Synthesis and redox behavior of biferrocenyl-functionalized ruthenium(II) terpyridine gold clusters

Spectroscopic and electrochemical characterizations of ferrocene- and biferrocene-functionalized terpyridine octanethiolate monolayer-protected clusters were investigated and reported. The electrochemical measurements of Ru2+ coordinated with 4'-ferrocenyl-2,2':6',2' '-terpyridine and 4'-biferrocenyl-2,2':6',2' '-terpyridine complexes were dominated by the Ru2+/Ru3+ redox couple (E(1/2) at approximately 1.3 V), Fe(2+)/Fe(3+) redox couples (E(1/2) from approximately 0.6 to approximately 0.9 V), and terpy/terpy-/terpy2- redox couples (E(1/)(2) at ca. -1.2 and ca. -1.4 V). The substantial appreciable variations detected in the Ru2+/Ru3+ and Fe2+/Fe3+ oxidation potentials indicate that there is an interaction between the Ru2+ and Fe2+ metal centers. The coordination of the Ru2+ metal center with 4'-ferrocenyl-2,2':6',2' '-terpyridine and 4'-biferrocenyl-2,2':6',2' '-terpyridine leads to an intense 1[(d(pi)Fe)6] --> 1[d(pi)Fe)5(pi*terpyRu)1] transition in the visible region. The 1[(d(pi)Fe)6] -->1[d(pi)Fe)5(pi*terpyRu)1] transition observed at approximately 510 nm revealed that there was a qualitative electronic coupling between metal centers. The coordination of the Ru2+ transition metal center lowers the energy of the pi*terpy orbitals, causing this transition.     

Dearomatization and functionalization of terpyridine by lutetium(III) alkyl complexes

Lutetium(III)-bis(alkyl) and -tris(alkyl) fragments supported by either 2,2':6',2' '-terpyridine or 4,4',4' '-tri-tert-butyl-2,2':6',2' '-terpyridine are not stable and undergo facile 1,3-alkyl migration under ambient conditions resulting in dearomatization and ortho (2' or 6') functionalization of the terpyridyl ligand, clearly demonstrating that the terpyridyl ligand framework is not as innocent as previously thought.     

Electrocatalytic reduction of CO2 to CO by polypyridyl ruthenium complexes

Electrocatalytic reduction of CO(2) by [Ru(tpy)(bpy)(solvent)](2+) (tpy = 2,2':6',2'-terpyridine, bpy = 2,2'-bipyridine) and its structural analogs is initiated by sequential 1e(-) reductions at the tpy and bpy ligands followed by rate limiting CO(2) addition to give a metallocarboxylate intermediate. It undergoes further reduction and loss of CO.     

Synthesis and properties of the elusive ruthenium(II) complexes of 4'-cyano-2,2':6',2' '-terpyridine

The heteroleptic and homoleptic ruthenium(II) complexes of 4'-cyano-2,2':6',2' '-terpyridine are synthesized by palladium catalyzed cyanation of the corresponding Ru(II) complexes of 4'-chloro-2,2':6',2' '-terpyridine. The introduction of the strongly electron-withdrawing cyano group into the Ru(tpy)(2)(2+) moiety dramatically changes its photophysical and redox properties as well as prolongs its room temperature excited-state lifetime.     

Electrocatalytic properties of guanine, adenine, guanosine-5'-monophosphate, and ssDNA by Fe(II) bis(2,2':6',2'-terpyridine), Fe(II) tris(1,10-phenanthroline), and poly-Fe(II) tris(5-amino-1,10-phenanthroline)

The electrocatalytic oxidations of guanine, adenine, guanosine-5'-monophosphate(GMP) and ssDNA were performed in the presence of Fe(II) bis(2,2':6',2'-terpyridine) and Fe(II) tris(1,10-phenanthroline) complexes as homogeneous catalysts by cyclic voltammetric methods. The Fe(II/III) redox couple of these compounds is responsible for their catalytic properties. The electrocatalytic oxidation current of above substrates were developed from the anodic peak currents of Fe(II) bis(2,2':6',2'-terpyridine) and Fe(II) tris(1,10-phenanthroline) complexes at about +0.93 V and 0.97 V, respectively. The electrocatalytic oxidative properties of guanine by Fe(II) bis(2,2':6',2'-terpyridine) complex was measured by amperometry method using the rotating disk electrodes. Electropolymerization of Fe(II) tris(5-amino-1,10-phenanthroline) complex produced thin polymer films on gold and glassy carbon electrodes. The electrochemical quartz crystal microbalance (EQCM) and cyclic voltammetry were used to study the in situ growth of the polymer. The poly(FeII(5-NH(2)-1,10-phen)(3)) exhibited a good electrocatalytic oxidation towards guanine and also for the mixture of guanine and adenine too.     

Unusual frequency dispersion effects of the nonlinear optical response in highly conjugated (polypyridyl)metal-(porphinato)zinc(II) chromophores

The syntheses and electrooptic properties of a new family of nonlinear optical chromophores are reported. These species feature an ethyne-elaborated, highly polarizable porphyrinic component and metal polypyridyl complexes that serve as integral donor and acceptor elements. Examples of this structural motif include ruthenium(II) [5-(4'-ethynyl-(2,2';6',2' '-terpyridinyl))-10,20-bis(2',6'-bis(3,3-dimethyl-1-butyloxy)phenyl)porphinato]zinc(II)-(2,2';6',2' '-terpyridine)(2+) bis-hexafluorophosphate (Ru-PZn); osmium(II) [5-(4'-ethynyl-(2,2';6',2'-terpyridinyl))-10,20-bis(2',6'-bis(3,3-dimethyl-1-butyloxy)phenyl)porphinato]zinc(II)-(2,2';6',2'-terpyridine)(2+) bis-hexafluorophosphate (Os-PZn); ruthenium(II) [5-(4'-ethynyl-(2,2';6',2'-terpyridinyl))-15-(4'-nitrophenyl)ethynyl-10,20-bis(2',6'-bis(3,3-dimethyl-1-butyloxy)phen-yl)porphinato]zinc(II)-(2,2';6',2' '-terpyridine)(2+) bis-hexafluorophosphate (Ru-PZn-A); osmium(II) [5-(4'-ethynyl-(2,2';6',2' '-terpyridinyl))-15-(4'-nitrophenyl)ethynyl-10,20-bis(2',6'-bis(3,3-dimethyl-1-butyloxy)phenyl)porphinato]zinc(II)-(2,2';6',2' '-terpyridine)(2+) bis-hexafluorophosphate (Os-PZn-A); and ruthenium(II) [5-(4'-ethynyl-(2,2';6',2' '-terpyridinyl))osmium(II)-15-(4'-ethynyl-(2,2';6',2'-terpyridinyl))-10,20-bis (2',6'-bis(3,3-dimethyl-1-butyloxy)phenyl)porphinato]zinc(II)-bis(2,2';6',2'-terpyridine)(4+) tetrakis-hexafluorophosphate (Ru-PZn-Os). The frequency dependence of the dynamic hyperpolarizability of these compounds was determined from hyperRayleigh light scattering (HRS) measurements carried out at fundamental incident irradiation wavelengths (lambda(inc)) of 800, 1064, and 1300 nm. These data show that (i) coupled oscillator photophysics and metal-mediated cross-coupling can be exploited to elaborate high beta(0) supermolecules that exhibit significant excited-state electronic communication between their respective pigment building blocks; (ii) high-stability metal polypyridyl compounds constitute an attractive alternative to electron releasing dialkyl- and diarylamino groups, the most commonly used donor moieties in a wide range of established nonlinear optical dyes; (iii) this design strategy enables ready elaboration of chromophores having extraordinarily large dynamic hyperpolarizabilities (beta(lambda) values) at telecommunication relevant wavelengths; and (iv) porphyrin B- and Q-state-derived static hyperpolarizabilities (beta(0) values) can be designed to have the same or opposite sign in these species, thus providing a new means to regulate the magnitude of lambda(inc)-specific dynamic hyperpolarizabilities.     

cis-[Ru(2,2':6',2' '-terpyridine)(DMSO)Cl(2)]: useful precursor for the synthesis of heteroleptic terpyridine complexes under mild conditions

[Ru(II)(terpy)(DMSO)Cl(2)] complexes were synthesized as a 5/1 mixture of cis and trans isomers, and their reactivities with CO and with substituted 2,2':6',2' '-terpyridine (terpy) moieties have been investigated. The structure of a trans isomer and its CO adduct have been unambiguously assigned by spectroscopy and X-ray diffraction. The [Ru(terpy)(terpy-Br)](2+) complex prepared either from the cis-[Ru(II)(terpy)(DMSO)Cl(2)] or from the cis-[Ru(II)(terpy-Br)(DMSO)Cl(2)] precursor appeared to be reactive in cross-coupling reactions promoted by low-valent palladium(0) and is an attractive target for the stepwise synthesis of polynuclear complexes bearing vacant coordination sites (terpy-Br for 4'-bromo-2,2':6',2' '-terpyridine). Several bipyridine, phenanthroline, and bipyrimidine complexes were prepared this way and their optical and redox properties determined and discussed.     

Highly conjugated (polypyridyl)metal-(porphinato)zinc(II) compounds: long-lived, high oscillator strength, excited-state absorbers having exceptional spectral coverage of the near-infrared

Transient dynamical studies of ruthenium(II) [5-(4'-ethynyl-(2,2';6',2' '-terpyridinyl))-10,20-bis(2',6'-bis(3,3-dimethyl-1-butyloxy)phenyl)porphinato]zinc(II)-(2,2';6',2' '-terpyridine)2+ bis-hexafluorophosphate (Ru-PZn), osmium(II) [5-(4'-ethynyl-(2,2';6',2' '-terpyridinyl))-10,20-bis(2',6'-bis(3,3-dimethyl-1-butyloxy)phenyl)porphinato]zinc(II)-(2,2';6',2' '-terpyridine)2+ bis-hexafluorophosphate (Os-PZn), ruthenium(II) [5-(4'-ethynyl-(2,2';6',2' '-terpyridinyl))-15-(4'-nitrophenyl)ethynyl-10,20-bis(2',6'-bis(3,3-dimethyl-1-butyloxy)phenyl)porphinato]zinc(II)-(2,2';6',2' '-terpyridine)2+ bis-hexafluorophosphate (Ru-PZn-A), osmium(II) [5-(4'-ethynyl-(2,2';6',2' '-terpyridinyl))-15-(4'-nitrophenyl)ethynyl-10,20-bis(2',6'-bis(3,3-dimethyl-1-butyloxy)phenyl)porphinato]zinc(II)-(2,2';6',2' '-terpyridine)2+ bis-hexafluorophosphate (Os-PZn-A), and ruthenium(II) [5-(4'-ethynyl-(2,2';6',2' '-terpyridinyl))-ruthenium(II)-15-(4'-ethynyl-(2,2';6',2' '-terpyridinyl))-10,20-bis(2',6'-bis(3,3-dimethyl-1-butyloxy)phenyl)porphinato]zinc(II)-bis(2,2';6',2' '-terpyridine)4+ tetrakis-hexafluorophosphate (Ru-PZn-Ru), and ruthenium(II) [5-(4'-ethynyl-(2,2';6',2' '-terpyridinyl))-osmium(II)-15-(4'-ethynyl-(2,2';6',2' '-terpyridinyl))-10,20-bis(2',6'-bis(3,3-dimethyl-1-butyloxy)phenyl)porphinato]zinc(II)-bis(2,2';6',2' '-terpyridine) tetrakis-hexafluorophosphate (Ru-PZn-Os) show that these highly conjugated supermolecular chromophores feature electronically excited states that absorb over broad NIR spectral windows with considerable oscillator strength and manifest lifetimes (1-50 mus) that are extraordinarily long relative to those of classic low band-gap organic materials. The excited-state absorptive domains of these strongly coupled multipigment ensembles can be extensively modulated. For sequential one-photon absorptive processes, these compounds evince large sigmae, sigmae/sigmag, and sigmae - sigmag values. As the combination of all these properties within single chromophoric entities have heretofore lacked precedent within the NIR, these and closely related structures may find particular utility in a variety of technologically important optical-limiting applications.     

A single centre water splitting dye complex adsorbed on rutile TiO2(110): photoemission, x-ray absorption, and optical spectroscopy

A single centre water splitting dye complex (aqua(2,2'-bipyridyl-4,4'-dicarboxylic acid)-(2,2':6',6'-terpyridine)Ruthenium(II)), along with a related complex ((2,2'-bipyridyl-4,4'-dicarboxylic acid)-(2,2':6',6'-terpyridine)chloride Ruthenium(II)), has been investigated using photoemission and compared to molecules with similar structures. Dye molecules were deposited in situ using ultra-high vacuum electrospray deposition, which allows for the deposition of thermally labile molecules, such as these dye molecules. Adsorption of the dye molecules on the rutile TiO(2)(110) surface has been studied using core-level and valence photoemission. Core-level photoemission spectra reveal that each complex bonds to the surface via deprotonation of its carboxylic acid groups. A consideration of the energy level alignments reveals that both complexes are capable of charge transfer from the adsorbed molecules to the conduction band of the rutile TiO(2) substrate.     

From encapsulation to polypseudorotaxane: unusual anion networks driven by predesigned metal bis(terpyridine) complex cations

Solvothermal reactions of CuSCN, metal (Mn2+, Fe2+, Co2+, Ni2+, Cu2+) sulfate, and terpyridine (2,2':6',2' '-terpyridine or 4'-p-tolyl-2,2':6',2' '-terpyridine) in the presence of triphenylphosphine yielded a series of hybrid coordination compounds, in which in situ formed metal bis(terpyridine) complex cations are encapsulated by a 3D anionic network or entangled by 2D heartlike networks, forming encapsulation or polypseudorotaxane supramolecules. The complex cations play a role as template to direct the fabrication of the structures.     

Ruthenium-complex-catalyzed regio- and stereoselective linear codimerization of 2-norbornenes with acrylic compounds

A linear codimerization of 2-norbornenes with acrylic compounds such as acrylates and an acrylamide proceeded efficiently by ruthenium catalyst systems, RuCl3(tpy)/Zn (tpy = 2,2':6',2' '-terpyridine) or [RuCl2(C6H6)]2/Zn in a primary or secondary alcoholic solvent, to afford the corresponding exo-trans-2-norbornylacrylates as major products regio- and stereoselectively along with a small amount of cis isomers. The reaction of 2,5-norbornadiene with methyl acrylate also gave the linear exo-trans codimer, which was effectively catalyzed by the addition of triarylphosphines to the RuCl3(tpy)/Zn catalyst system.     

Terpyridine Metal Complexes as Building Blocks for Supramolecular Assemblies and Polymers: Thermal Stabilities and Thin Film Preparation

5,5'-Dimethyl-2,2':6',2'-terpyridine complexes with various transition metal ions like Zn(II), Co(II), Mn(II) and Hg(II) were investigated concerning their thermal properties. A significant dependency of the thermal stability (5% weight loss) of the complexes depending on the kind of metal ion used could be observed ranging from 315 to 390 °C. Furthermore, self-assembled thin films of such metallo-supramolecular Hg(II) complexes were prepared and characterized by synchrotron based X-ray reflectivity and fluorescence techniques.     

Convenient and efficient synthesis of functionalized oligopyridine ligands bearing accessory pyrromethene-BF2 fluorophores

The synthesis of stable and highly luminescent pyridine-, bipyridine-, phenanthroline-, bipyrimidine-, and terpyridine-based ligands bearing one or two 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (bodipy) modules has demonstrated the advantages of three different protocols which have been adapted in light of the chemical stability of the alkyne-grafted starting building blocks and the chemical reactivity of the bromo-substituted starting materials. A classical method of condensation of aldehydes or acid chlorides with Kryptopyrrole has been used for direct linkage of a bodipy to the oligopyridinic platform. For the phenylethynyl-linked molecules, direct coupling between the bodipy-phenyliodo and the stable 4'-ethynyl-2,2':6',2' '-terpyridine, 6,6' '-diethynyl-2,2':6',2' '-terpyridine, 5-ethynyl-2,2'-bipyridine, 5,5'-diethynyl-2,2'-bipyridine, 6,6'-diethynyl-2,2'-bipyridine, and 5,5'-diethynyl-2,2'-bipyrimidine substrates is feasible and is promoted by Pd catalysts and sonication. This procedure provides the advantages of efficiency, versatility, and rapidity. A second set of experimental conditions is required to produce the 4-substituted pyridine, 3,8-disubstituted-1,10-phenanthroline, and 5,5' '-disubstituted-2,2':6',2' '-terpyridine derivatives. Cross coupling of a bodipy-phenylethynyl molecule with the bromo-substituted partners takes place smoothly with the pyridine but with low yields in the other cases due to the efficient formation of the homocoupled diphenylbutadiyne bodipy compounds. A third convenient protocol enabled the preparation of these target molecules in a one-pot reaction where the deprotection of the alkyne was conducted in situ by a phase-transfer process with aqueous NaOH and with Et(3)BnN(+)Cl(-) as mediator and the cross-coupling reaction realized in the benzene phase with [Pd(PPh(3))(4)] as catalyst and CuI as co-reagent. The nascent acid was quenched in the aqueous phase. This method is much more efficient when a trimethylsilyl protecting group is used instead of a propargylic alcohol. The pyridino-bodipy bases were alkylated smoothly in good yields in the presence of methyl iodide. The photophysical and electrochemical properties for these new molecules have been investigated and are discussed in terms of substitution patterns of the bipyridine and terpyridine platforms. In the pyridinium salt 18, the fluorescence from the first singlet excited state at lambda(em) = 547 nm is totally quenched at the expense of a low-lying charge-transfer emitting state located at lambda(em) = 660 nm.