One-photon photophysics and two-photon absorption of 4-[9,9-di(2-ethylhexyl)-7-diphenylaminofluoren-2-yl]-2,2':6',2'-terpyridine and their platinum chloride complexes

The synthesis, one-photon photophysics and two-photon absorption (2PA) of three dipolar D-π-A 4-[9,9-di(2-ethylhexyl)-7-diphenylaminofluoren-2-yl]-2,2':6',2'-terpyridine and their platinum chloride complexes with different linkers between the donor and acceptor are reported. All ligands exhibit (1)π,π* transition in the UV and (1)π,π*/(1)ICT (intramolecular charge transfer) transition in the visible regions, while the complexes display a lower-energy (1)π,π*/(1)CT (charge transfer) transition in the visible region in addition to the high-energy (1)π,π* transitions. All ligands and the complexes are emissive at room temperature and 77 K, with the emitting excited state assigned as the mixed (1)π,π* and (1)CT states at RT. Transient absorption from the ligands and the complexes were observed. 2PA was investigated for all ligands and complexes. The two-photon absorption cross-sections (σ(2)) of the complexes (600-2000 GM) measured by Z-scan experiment are much larger than those of their corresponding ligands measured by the two-photon induced fluorescence method. The ligand and the complex with the ethynylene linker show much stronger 2PA than those with the vinylene linker.     

Synthesis and single-crystal X-ray characterization of 4,4"-functionalized 4'-(4-bromophenyl)-2,2':6',2"-terpyridines

To expand the utility of bis(terpyridine) metal connectivity, the selective symmetrical and unsymmetrical 4,4"-functionalization (-CN, -Me, -CO2Me) of 4'-(4-bromophenyl)-2,2':6',2"-terpyridines was achieved using the Kr?hnke synthesis. The final substituted 2,2':6',2"-terpyridines along with their corresponding intermediates, 4a-c, were recrystallized and characterized by 1H NMR and 13C NMR as well as X-ray crystallography; COSY correlations were also conducted to permit definitive proton assignment.     

Two-photon absorption of Zn(II) octupolar molecules

In this work we present an investigation of the non-linear optical (NLO) properties of two octupolar chromophores: [Zn(4,4'-bis(dibutylaminostyryl)-[2,2']-bipyridine)(3)](2+) and [Zn(4,4'-bis((E)-2-(N-(TEG)pyrrol-2-yl)vinyl)-[2,2']-bipyridine)(3)](2+) with Zn(ii) as the coordination center, using two-photon emission technique (TPE) in fs-pulse temporal regime. Compared to the free ligands, our results do not show a net increase in the two-photon absorption (TPA) cross-section for the octupolar complexes, once normalized to the ligand unit. This is in partial disagreement with a previous theoretical study investigating the first molecule where a significant increase of the TPA cross-section was predicted (X. J. Liu, et al., J. Chem. Phys., 2004, 120, 11 493).     

Aqueous hydrogenation of carbon dioxide catalysed by water-soluble ruthenium aqua complexes under acidic conditions

Hydrogenation of carbon dioxide (P(H2/CO2)= 5.5/2.5 MPa) into formic acid (HCOOH) under acidic conditions (pH 2.5-5.0) in water has been achieved by using water-soluble ruthenium aqua catalysts [(eta6-C6Me6)RuII(L)(OH2)]SO4 (L = 2,2'-bipyridine or 4,4'-dimethoxy-2,2' bipyridine).     

Three-dimensional nonlinear optical chromophores based on metal-to-ligand charge-transfer from ruthenium(II) or iron(II) centers

In this article, we describe a series of new complex salts in which electron-rich transition-metal centers are coordinated to three electron-accepting N-methyl/aryl-2,2':4,4' ':4',4' '-quaterpyridinium ligands. These complexes contain either Ru(II) or Fe(II) ions and have been characterized by using various techniques, including electronic absorption spectroscopy and cyclic voltammetry. Molecular quadratic nonlinear optical (NLO) responses beta have been determined by using hyper-Rayleigh scattering at 800 nm and also via Stark (electroabsorption) spectroscopic studies on the intense, visible d --> pi* metal-to-ligand charge-transfer bands. The latter experiments reveal that these putatively octupolar D(3) chromophores exhibit two substantial components of the beta tensor which are associated with transitions to dipolar excited states. Computations involving time-dependent density-functional theory and the finite field method serve to further illuminate the electronic structures and associated linear and NLO properties of the new chromophoric salts.     

Highly efficient alkene epoxidation and aziridination catalyzed by iron(II) salt + 4,4',4'-trichloro-2,2':6',2'-terpyridine/4,4'-dichloro-4'-O-PEG-OCH3-2,2':6',2'-terpyridine

"Iron(II) salt + 4,4',4'-trichloro-2,2':6',2'-terpyridine" is an effective catalyst for epoxidation and aziridination of alkenes and intramolecular amidation of sulfamate esters. The epoxidation of allylic-substituted cycloalkenes achieved excellent diastereoselectivities up to 90%. ESI-MS results supported the formation of iron-oxo and -imido intermediates. Derivitization of Cl 3terpy to O-PEG-OCH 3-Cl 2terpy renders the terpyridine unit to be recyclable, and the "iron(II) salt + 4,4'-dichloro-4'- O-PEG-OCH 3-2,2':6',2'-terpyridine" protocol can be reused without a significant loss of catalytic activity in the alkene epoxidation.     

Two-photon absorption properties of self-assemblies of butadiyne-linked bis(imidazolylporphyrin)

Supramolecular porphyrin self-assemblies have been prepared from butadiyne-linked bis(imidazolylporphyrin) by complementary coordination of imidazole to zinc, and their two-photon absorption (2PA) and higher-order nonlinear absorption properties were investigated over femtosecond time scales using an open-aperture Z-scan method. The self-assembled porphyrin dimer of the conjugated monozinc bisporphyrin 7D was shown to have a large 2PA cross section (7.6 x 10(3) GM, where 1 GM = 10(-50) cm(4) s molecule(-1) photon(-1)) at 887 nm. By comparison of this result with that for a meso-meso-linked porphyrin array without the butadiyne connection (3.7 x 10(2) GM at 964 nm), it was demonstrated that the predominant factor in this significant enhancement of the cross section was the expansion of porphyrin-porphyrin pi-conjugation. Self-coordination and monozinc metalation were also found to be contributing factors. Furthermore, a novel self-assembled porphyrin polymer 8P consisting of a biszinc complex with a mean molecular weight of M(n) = 1.5 x 10(5) Da was shown to exhibit an extraordinarily large two-photon absorption cross section (4.4 x 10(5) GM at 873 nm). Nanosecond Z-scan experiments for 7D and 8P were also undertaken and resulted in the measurement of large effective 2PA cross sections, including the excited-state absorption (2.1 x 10(5) GM for 7D and 2.2 x 10(7) GM for 8P, respectively). Finally, three-photon absorption was observed by femtosecond Z-scan experiments at 1188 nm (7.1 x 10(-89) m(6) s(2)) and 1282 nm (1.8 x 10(-89) m(6) s(2)), an observation which is the first of its kind in porphyrin chemistry.     

Transient excited-state absorption and gain spectroscopy of a two-photon absorbing probe with efficient superfluorescent properties

The synthesis, linear photophysical properties, two-photon absorption (2PA), excited-state transient absorption, and gain spectroscopy of a new fluorene derivative tert-butyl 4,4'-(4,4' (1E,1'E)-2,2'-(9,9-bis(2- (2-ethoxyethoxy)ethyl)-9H-fluorene-2,7-diyl)bis(ethene-2,1-diyl)bis(4,1 phenylene)]dipiperazine-1-carboxylate (1) are reported. The steady-state linear absorption and fluorescence spectra, along with excitation anisotropy, fluorescence lifetimes, and photochemical stability of 1 were investigated in a number of organic solvents at room temperature. The 2PA spectra of 1 with a maximum cross-section of ~ 300 GM were obtained with a 1 kHz femtosecond laser system using open-aperture Z-scan and two-photon-induced fluorescence methods. The transient excited-state absorption (ESA) and gain kinetics of 1 were investigated by a femtosecond pump-probe methodology. Fast relaxation processes (~1-2 ps) in the gain and ESA spectra of 1 were revealed in ACN solution, attributable to symmetry-breaking effects in the first excited state. Efficient superfluorescence properties of 1 were observed in a nonpolar solvent under femtosecond excitation. One- and two-photon fluorescence microscopy imaging of HCT 116 cells incubated with probe 1 was accomplished, suggesting the potential of this new probe in two-photon fluorescence microscopy bioimaging.     

A superfluorescent fluorenyl probe with efficient two-photon absorption

The linear photophysical, excited state absorption (ESA), superfluorescence, and two-photon absorption (2PA) properties of 4,4'-(1E,1'E)-2,2'-(7,7'(1E,1'E)2,2'(4,4'-sulfonylbis(4,1-phenylene))bis(ethane-2,1-diyl)bis(9,9-didecy-9H-fluorene7,2-diyl))bis(ethane-2,1-diyl)bis(N,N-diphenylaniline) (1) were investigated in organic and aqueous media with respect to its potential application in biological imaging. The analysis of linear photophysical properties revealed a rather complex nature of the main one-photon absorption band, strong solvatochromic effects in the steady-state fluorescence spectra, single-exponential fluorescence decay, and high fluorescence quantum yields in organic solvents (≈1.0). The ESA spectra of 1 suggested potential for light amplification in nonpolar media while efficient superfluorescence in cyclohexane was demonstrated. The degenerate 2PA spectra of 1 were obtained over a broad spectral range (640-900 nm), using a standard two-photon induced fluorescence method under 1 kHz femtosecond excitation. Two well defined 2PA bands with maximum 2PA cross sections up to 1700 GM in the higher energy, short wavelength band and ≈1200 GM in the lower energy, long wavelength band of 1 were shown. The potential use of 1 in bioimaging was demonstrated via one- and two-photon in vitro fluorescence imaging of HCT 116 cells.     

Strong two-photon absorption in new asymmetrically substituted porphyrins: interference between charge-transfer and intermediate-resonance pathways

We study two-photon absorption (2PA) in two series of new free-base porphyrins with 4-(diphenylamino)stilbene or 4,4'-bis-(diphenylamino)stilbene (BDPAS) attached via pi-conjugating linkers at the porphyrin meso-position. We show that this new substitution modality increases the 2PA cross section in the Soret band region (excitation wavelength 750-900 nm) of the core porphyrin by nearly 2 orders of magnitude, from sigma(2) approximately 10 GM for the meso-phenyl-substituted analogue to sigma(2) approximately 10(3) GM for the ethynyl-linked BDPAS-porphyrin dyad. The 2PA properties are quantitatively described by considering two different and interfering 2PA quantum transition pathways. The first path involves virtual transition via intermediate one-photon resonance. The second path bypasses the intermediate resonance and occurs due to a large permanent dipole moment difference between the ground and the final electronic states. To our best knowledge, this is the first experimental observation of the combined effect of these two pathways on one particular two-photon transition, resulting in quantum-interference-modulated 2PA strength.     

Temperature-induced switching of the mechanism for intramolecular energy transfer in a 2,2':6',2' '-Terpyridine-based Ru(II)-Os(II) trinuclear array

The synthesis and photophysical properties of a linear 2,2':6',2' '-terpyridine-based trinuclear Ru(II)-Os(II) nanometer-sized array are described. This array comprises two bis(2,2':6',2' '-terpyridine) ruthenium(II) terminals connected via alkoxy-strapped 4,4'-diethynylated biphenylene units to a central bis(2,2':6',2' '-terpyridine) osmium(II) core. The mixed-metal linear array was prepared using the "synthesis at metal" approach, and the Ru(II)-Ru(II) separation is ca. 50 A. Energy transfer occurs with high efficiency from the Ru(II) units to the Os(II) center at all temperatures. Forster-type energy transfer prevails in a glassy matrix at very low temperature, but this is augmented by Dexter-type electron exchange at higher temperatures. This latter process, which is weakly activated, involves long-range superexchange interactions between the metal centers. In fluid solution, a strongly activated process provides for fast energy transfer. Here, a charge-transfer (CT) state localized on the bridge is populated as an intermediate species. The CT triplet does not undergo direct charge recombination to form the ground state but transfers energy, possibly via a second CT state, to the Os(II)-based acceptor. The short tethering strap constrains the geometry of the linker, especially in a glassy matrix, such that low-temperature electron exchange occurs across a particular torsion angle of 37 degrees . The probability of triplet energy transfer depends on temperature but always exceeds 75%.     

Sensitive determination of anionic surfactants in water with trans-4-[4'-(N-methyl-N-hydroxylethylamino)-cinnamyl-N-9-(4'-(2,2':6',2''-terpyridine))-phenylmethylene]pyridine bromide by the light-absorption ratio variation approach

The light-absorption ratio variation approach was described and applied to the determination of anionic surfactants (AS) in water with a novel chromophore, trans 4-[4'-(N-methyl-N-hydroxylethylamino)-cinnamyl-N-9-(4'-(2,2':6',2'-terpyridine))-phenylmethylene]pyridine bromide (BTMHCTPP). The complexations between BTMHCTPP and sodium dodecyl sulfate (SDS) and sodium dodecylbenzenesulfonate (SDBS) at pH 3.85 were characterized by the break point approach. Results have shown that both 1BTMHCTPP:1SDS and 1BTMHCTPP:1SDBS complexes were formed, and that deltaA(r) (deltaA(r) = light-absorption ratio variation) is linear for the range of AS between 0.05 and 1.00 mg/L. The limits of detection (3sigma) are 0.045 mg/L for SDS and 0.040 mg/L for SDBS. The complexation is selective in the presence of EDTA, and it has been applied to the analysis of water samples with satisfactory results.     

Electrochemical and luminescent properties of new mononuclear ruthenium(II) and binuclear iridium(III)-ruthenium(II) terpyridine complexes.

Hexafluorophosphate salts of mononuclear complexes [Ru(II)Cl(L)(terpy)]+ (L = dmbpy (1); dpbpy (2), sambpy (3), and dpp (7), and binuclear complexes [Ru(II)2Cl2(dpp)(terpy)2]2+ (8) and [Ir(III)Ru(II)Cl2(dpp)(terpy)2]3+ (9) were prepared and characterized. Abbreviations of the ligands are bpy = 2,2'-bipyridine, dmbpy = 4,4'-dimethyl-2,2'-bipyridine, dpbpy = 4,4'-diphenyl-2,2'-bipyridine, dpp = 2,3-bis(2-pyridyl)pyrazine, sambpy = 4,4'-bis((S)-(+)-alpha-1-phenylethylamido)-2,2'-bipyridine, and terpy = 2,2':6',2'-terpyridine. The absorption spectra of 8 and 9 are dominated by ligand-centered bands in the UV region and by metal-to-ligand charge-transfer bands in the visible region. The details of their spectroscopic and electrochemical properties were investigated. In both binuclear complexes, it has been found that the HOMO is based on the Ru metal, and LUMO is dpp-based. [Ir(III)Ru(II)Cl2(dpp)(terpy)2]3+, indicating intense emission at room temperature, and a lifetime of 154 ns. The long lifetime of this bimetallic chromophore makes it a useful component in the design of supramolecular complexes.     

Expanded ligands: bis(2,2':6',2'-terpyridine carboxylic acid)ruthenium(ii) complexes as metallosupramolecular analogues of dicarboxylic acids

Ligands in which multiple metal-binding domains are linked by a metal-containing moiety rather than a conventional organic group are described as "expanded ligands". The use of 4,4'-difunctionalised {Ru(tpy)(2)} units provides a linear spacer between metal-binding domains and we have extended this motif to expanded ligands containing two carboxylic acid metal-binding domains. In this paper, we describe the synthesis and structural characterisation of ruthenium(ii) complexes of 2,2':6',2'-terpyridine-4'-carboxylic acid and 4'-carboxyphenyl-2,2':6',2'-terpyridine. The ability of the ruthenium(ii) centre to charge compensate deprotonation of the carboxylic acid leads to Zwitterionic complexes and three representative compounds have been structurally characterised.     

Electronic structures and absorption spectra of linkage isomers of trithiocyanato (4,4',4' '-tricarboxy-2,2':6,2' '-terpyridine) ruthenium(II) complexes: a DFT study

Black dye (BD), isomer 1 ([Ru(II)(H3-tctpy)(NCS)3](-1), where H3-tctpy = 4,4',4' '-tricarboxy-2,2':6,2' '-terpyridine) is known to be an excellent sensitizer for dye-sensitized solar cells and exhibits a very good near-IR photo response, compared to other ruthenium dyes. Because isothiocyanate is a linear ambidentate ligand, BD has three other linkage isomers, [Ru(H3-tctpy)(NCS)2(SCN)](-1), isomer 2 and 2', and [Ru(H3-tctpy))(SCN)3](-1), isomer 3. In this study, we have calculated the geometry of BD and its isomers by DFT. Further, we have analyzed the bonding in these isomers using NBO methods. TDDFT calculations combined with scalar relativistic zero-order regular approximations (SR-ZORA) have been carried out to simulate the absorption spectra. Calculations have been performed for the isomers both in vacuo and in solvent (ethanol). The inclusion of the solvent is found to be important to obtain spectra in good agreement with the experiment. The first absorption bands are dominated by the metal-to-ligand charge transfer (MLCT) and ligand-to-ligand charge transfer (LLCT).     

Nonlinear optical and two-photon absorption properties of octupolar tris(bipyridyl)metal complexes

The linear (absorption and emission) and nonlinear optical (NLO) properties of a series of D(3) [(Fe(II), Ru(II), Ni(II), Cu(II), Zn(II)] octupolar metal complexes featuring the 4,4'-bis[(dibutylamino)styryl]-2,2'-bipyridine ligand are reported. Zinc(II), nickel(II), and copper(II) complexes exhibit similar absorption spectra in the visible region (lambda(ILCT) = 474-476 nm) which are assigned to intraligand charge-transfer (ILCT) bands. The quadratic and cubic NLO properties are strongly influenced by the nature of the metallic center. Harmonic light scattering studies at lambda = 1.91 microm reveal that these chromophores display large first hyperpolarizabilities beta(1.91) in the range of (211-340) x 10(-30) esu; replacing the Zn(II) metal ion by Ni(II) or Cu(II) results in a decrease of the static beta(0) coefficient by a factor of 1.5-1.6. Z-scan measurements at 765 and 965 nm reveal relatively large two-photon absorption cross-sections [650 < sigma(2) < 2200 GM], showing that both beta and sigma(2) values can be tuned by simple modification of the metal ion.     

Strong cooperative enhancement of two-photon absorption in double-strand conjugated porphyrin ladder arrays

We present the two-photon absorption (2PA) spectra of a series of conjugated porphyrin oligomers containing N = 2, 4, 8, and ca. 13 monomer units, meso-meso connected with butadiyne linkers. We demonstrate that, in the coplanar double-strand arrays, self-assembled upon addition of 4,4'-bipyridyl, the conjugation length increases dramatically, leading to very strong cooperative enhancement of 2PA. We analyze the scaling of 2PA in both the double-strand and rotationally free single-strand arrays and show how the effective conjugation length in both cases is linked to the observed 2PA properties. By introducing a "conjugation signature" for the 2PA strength, we show that, in double-strand arrangement, the conjugation embraces the whole molecule up to the tetramer level, whereas in single-strand arrangement, it is always less than N, except for N = 2, but keeps increasing until N = 8. Our finding of extremely strong 2PA cross section, sigma2 approximately 105 GM, in double-strand oligomers peaking at 1.3 mum can find use for signal processing in fiber-optic devices.     

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.     

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.     

Pentafluorophenyl imidato palladium(II) complexes: catalysts for Suzuki cross-coupling reactions

Novel N-bonded imidato complexes of general formula [Pd(N-N)(C6F5)(imidate)](imidate = maleimidate, succinimidate or phthalimidate; N-N = 2,2'-bipyridine (bipy), 4,4'-dimethyl-2,2'-bipyridine (Me2bipy) or N,N,N',N'-tetramethylethylenediamine (tmeda)), [NBu4][Pd(C6F5)(H2O)(succinimidate)2] and [NBu4][Pd(C6F5)(L)(succinimidate)2](L = PPh3 or t-BuNC) have been synthesised. These complexes are air-, light- and moisture-stable. The crystal structures of [Pd(tmeda)(C6F5)(maleimidate)].H2O.0.5CHCl3, [NBu4][Pd(C6F5)(H2O)(succinimidate)2].H2O and [NBu4][Pd(C6F5)(t-BuNC)(succinimidate)2].2H2O have been determined by X-ray diffraction. Many of these new complexes are shown to be active phosphine-free palladium catalysts/precatalysts for the Suzuki cross-coupling reactions of aryl bromides and aryl chlorides with phenylboronic acid.