Structures of two haptotropic isomers generated by the sliding of 1,3,5-triene ligands on a Pd-Pd-Pd chain

Two haptotropic isomers of [Pd(3)(mu(3)-DMVC)(2)(CH(3)CN)(2)][BF(4)](2) (DMVC = 1,2-di-(E)-carbomethoxyvinylcyclopentene) were structurally determined by X-ray crystallographic analyses; a monoclinic crystal contained a symmetric sandwich complex (mu(3)-eta(2):eta(2):eta(2)-coordination of DMVC ligands) and a triclinic crystal contained an unsymmetric sandwich complex (mu(3)-eta(2):eta(3):eta(1)-coordination of DMVC ligands), where the latter are connected to each other by C-HO hydrogen bonds.     

Synthesis and characterization of conjugated polymers containing a carbazole moiety

Two series of conjugated polymers with a carbazole moiety were synthesized by Knovenagel and Wittig condensations. The chemical structure, thermogravimetric, photophysical and electrochemical properties of the polymers were characterized by ¹H‐NMR, IR, GPC, TG, UV‐vis, FL, and CV. The results indicated that PBM is the most thermally stable one and PBP is the most thermally instable one. The absorption and emission properties of the polymers were adjusted by the modification of chemical structures. The quenching effect of cyano group and oxygen atom results in the lower fluorescence quantum efficiency. The fitted emission spectra suggested that the emission spectra of all the polymers come from different vibronic transitions and aggregation emission. Copyright © 2008 John Wiley & Sons, Ltd.     

Photoinduced charge separation and recombination in a conjugated polymer-semiconductor nanocrystal composite

Semiconductor nanocrystals and conjugated polymers are classes of well-known materials with optoelectronic properties. We demonstrate that in a nanocrystalline TiO₂/poly(p-phenylene vinylene) (PPV) composite, excitons photogenerated in the polymer can be dissociated at the interface between the components, with electrons transferred to the nanocrystals. We show this and also follow the subsequent recombination using a time-resolved microwave conductivity technique. Recombination proceeds in a complex manner with roughly half of the initial amplitude decaying in 600 ns and the remainder in a biexponential process with time constants and relative amplitudes of 4.3 (0.7) and 80 μs (0.3). Photovoltaic devices were made from the composite films and their properties are discussed in light of the measured recombination rate and a simple carrier transport model.     

An efficient synthetic approach to highly conjugated porphyrin-based assemblies containing a bipyridine moiety

[structure: see text] An efficient and potential stepwise strategy involving the mixed sequence of Stille and Wittig-Horner reactions was used for the preparation of a polyene-substituted bis-porphyrin incorporating a bipyridine moiety.     

Novel conjugated copolymers based on dithiafulvalene moiety for bulk heterojunction solar cells

New conjugated copolymers, P1‐P3 , based on dithiafulvalene‐fused entity and different conjugated segments have been synthesized. Incorporation of electron‐deficient conjugated segments into the conjugated copolymers results in red shifting the absorption band and lowering the hole mobility. Bulk heterojunction solar cells using on these polymers as the donor and [6,6]‐phenyl‐C61 ‐butyric acid methyl ester (PC₆₁BM) as the acceptor were fabricated by solution process. The cells based on the blend of P1‐P3 /PC₆₁BM (1:1, w/w) have power conversion efficiencies (PCEs) ranging from 0.53 to 0.93%. Among these, the cell of P1 /PC₆₁BM exhibited the highest open‐circuit voltage at 0.85 V, and the cell of P3/PC₆₁BM exhibited the best PCE at 0.93% with the short‐circuit current (J_SC) of 4.88 mA/cm². © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Spin-orbit coupling in chelates with conjugated ligands

In the paper the spin-orbit coupling in chelates with conjugated ligands has been studied theoretically. The proposed models were used for the calculation of the lifetime of the ³₂ electron-transfer triplet state of the complex ion Ru(phen) ₃ ⁺² .     

Synthesis and characterization of novel conjugated polymers based on 3-cyclobutene-1,2-dione moiety

Three novel conjugated polymers bearing 3,4-bis（4-hexylthiophen-2-yl）-3-cyclobutene-1,2-dione unit in their main chain have been synthesized successfully in good yields through Suzuki or Stille coupling reaction.Their molecular structures have been confirmed by FT-IR,¹H NMR and ¹³C NMR.All these copolymers exhibit broad and strong absorption bands in UV-vis region,and their optical band gaps are calculated to be 1.6-2.0 eV.suggesting that they have good coverage with the solar spectrum.These polymers have good thermostability and solubility in common organic solvents.Moreover,all these objective macromolecules possess high electron affinity of～3.8 eV determined from cyclic voltammetry measurement,implying that they are potential n-type polymeric photovoltaic materials.     

Photoinduced intramolecular proton transfer of phenol-containing ligands and their zinc complexes

N,N'-Bis(salicylidene)hydrazine (L(I)), a bis-2-hydroxybenzene-type ligand H2L, its tert-butyl derivative (L(II)), and the corresponding Zn2+ complexes of the type Zn2(LH)2L (Zn-I and Zn-II) were synthesized. The molecular structure of Zn-II was determined by X-ray crystallography at -170 degrees C. The photoreactions of the four compounds in solution were studied by time-resolved UV-vis spectroscopy using nanosecond laser pulses. A weak but strongly Stokes shifted fluorescence signal of the ligands L(I) or L(II) is suggested to be due to excited-state intramolecular proton transfer (ESIPT) from the phenolic hydroxy group to the nitrogen of the methine bond in analogy to the fast enol --> keto tautomerization of other 2-hydroxybenzenes. A transient with the maximum at 480 nm, bleaching at 370 nm, and a lifetime of 0.01-0.3 ms is attributed to the trans-keto tautomer, formed via internal conversion. The decay occurs via trans --> cis isomerization and proton back-transfer to the enol form. Quenching by water indicates a proton-catalyzed reaction. To account for similar fluorescence and transient properties in the cases of the Zn2+ complexes, a photoinduced tautomerism at one of the two free phenolic hydroxy groups is proposed. The rapid ESIPT followed by a relatively slow relaxation process is reversible.     

Chiral NHC ligands bearing a pyridine moiety in copper-catalyzed addition of diethylzinc to nitroalkenes

Chiral N-heterocyclic carbenes, derived from amino acids containing a pyridine ring, are effective ligands in the enantioselective copper-catalyzed addition of diethylzinc to β-nitroalkenes, which provides access to chiral nitroalkanes. The advantages of this process include high yields, broad and complementary substrate scope, and good to high enantioselectivities.     

Photoinduced DNA cleavage by cyclopentadienyl metal complexes conjugated to DNA recognition elements

[structure: see text]. DNA recognition elements have been attached to CpW(CO)3CH3 and CpW(CO)3Ph, which produce methyl and phenyl radicals that cleave DNA upon photolysis. The inclusion of binding moieties in 3 increases the efficiency but not the selectivity of strand scission over that seen in the simple unfunctionalized complex, while 11 cleaves preferentially at T sites within AT-rich tracts.     

Synthesis and characterization of novel conjugated polymers based on 3-cyclobutene-l,2-dione moiety

Three novel conjugated polymers bearing 3,4-bis(4-hexylthiophen-2-yl)-3-cyclobutene-1,2-dione unit in their main chain have been synthesized successfully in good yields through Suzuki or Stille coupling reaction.Their molecular structures have been confirmed by FT-IR,~1H NMR and ~(13)C NMR.All these copolymers exhibit broad and strong absorption bands in UV-vis region,and their optical band gaps are calculated to be 1.6-2.0 eV.suggesting that they have good coverage with the solar spectrum.These polymers...     

A stable zerovalent palladium chain enveloped by a pi-electron sheath of conjugated polyene ligands

A surprisingly stable homoleptic Pd(0)(4) chain complex of non-activated olefins was isolated and structurally characterized by X-ray crystallographic analysis, and the unique structure and bonding are compared to those of the corresponding dicationic [Pd(4)](2+) chain sandwich complex.     

Synthesis and characterization of highly conjugated, chiral bridging ligands

This paper describes the synthesis of four chiral derivatives of the electronically highly conjugated tetra-2-pyridylpyrazine (TPPZ) bridging ligand, which are denoted (R)- and (S)-4,5- and 5,6-pineno-tetra-2-pyridylpyrazine (PTPPZ). Preparation of these ligands was undertaken through the use of commercially available, enantiomerically pure (1R)- and (1S)-alpha-pinene, which was functionalized and subsequently employed in a Krohnke pyridine synthesis involving a furan-substituted pyridinium salt to yield a chiral, furan-substituted pyridyl intermediate. Oxidative degradation and subsequent reduction of this furan led to a chiral, substituted 2-pyridylaldehyde, which underwent a pyridoin condensation followed by cyclization to produce the final PTPPZ ligands.     

Photoinduced enhancement in the luminescence of hydrophilic quantum dots coated with photocleavable ligands

In search of strategies to photoactivate the luminescence of semiconductor quantum dots, we devised a synthetic approach to attach photocleavable 2-nitrobenzyl groups to CdSe-ZnS core-shell quantum dots coated with hydrophilic polymeric ligands. The emission intensity of the resulting nanostructured constructs increases by more than 60% with the photolysis of the 2-nitrobenzyl appendages. Indeed, the photoinduced separation of the organic chromophores from the inorganic nanoparticles suppresses an electron-transfer pathway from the latter to the former and is mostly responsible for the luminescence enhancement. However, the thiol groups anchoring the polymeric envelope to the ZnS shell also contribute to the photoinduced emission increase. Presumably, their photooxidation eliminates defects on the nanoparticle surface and promotes the radiative deactivation of the excited quantum dots. This effect is fully reversible but its magnitude is only a fraction of the change caused by the photocleavage of the 2-nitrobenzyl groups. In addition, these particular quantum dots can cross the membrane of model cells and their luminescence increases by ~80% after the intracellular photocleavage of the 2-nitrobenzyl quenchers. Thus, photoswitchable luminescent constructs with biocompatible character can be assembled combining the established photochemistry of the 2-nitrobenzyl photocage with the outstanding photophysical properties of semiconductor quantum dots and the hydrophilic character of appropriate polymeric ligands.     

Structure and reactivity of new phosphine ligands containing the hemi-labile sulfone moiety

New heterofunctional phosphine ligands have been synthesised, incorporating the substitutionally labile sulfone and sulfonamide moieties as chelating groups, which display activity in the palladium-catalysed Suzuki and amination cross-coupling reactions. Single-crystal X-ray diffraction studies of the complexes formed with [Pd(mu-Cl)(dmba)] (dmba-H = N,N-dimethylbenzylamine) highlight the coordinating nature of these ligands; showing the formation of a bis chelate complex through a six-membered Pd-P-C-C-S-O ring with the sulfonamide class of ligands.     

Photochemistry of A1E, a retinoid with a conjugated pyridinium moiety: competition between pericyclic photooxygenation and pericyclization

The photochemistry of the retinoid analogue A1E shows an oxygen and solvent dependence. Irradiation of A1E with visible light (lambda(irr) = 425 nm) in methanol solutions resulted in pericyclization to form pyridinium terpenoids. Although the quantum yield for this cyclization is low (approximately 10(-4)), nevertheless the photochemical transformation occurs with quantitative chemical yield with remarkable chemoselectivity and diastereoselectivity. Conversely, irradiation of A1E under the same irradiation conditions in air-saturated carbon tetrachloride or deuterated chloroform produced a cyclic 5,8-peroxide as the major product. Deuterium solvent effects, experiments utilizing endoperoxide, phosphorescence, and chemiluminescence quenching studies strongly support the involvement of singlet oxygen in the endoperoxide formation. It is proposed that, upon irradiation, in the presence of oxygen, A1E acts as a sensitizer for generation of singlet oxygen from triplet oxygen present in the solution; the singlet oxygen produced reacts with A1E to produce cyclic peroxide. Thus, the photochemistry of A1E is characterized by two competing reactions, cyclization and peroxide formation. The dominant reaction is determined by the concentration of oxygen, the concentration of A1E, and the lifetime of singlet oxygen in the solvent employed. If the lifetime of singlet oxygen in a given solvent is long enough, then oxidation (peroxide formation) is the major reaction. If the singlet oxygen produced is quenched by the protonated solvent molecules faster than singlet oxygen reacts with A1E, then cyclization dominates.     

Ruthenium molecular wires with conjugated bridging ligands: onset of band formation in linear inorganic conjugated oligomers

We have prepared and characterized a series of multimetallic oligomers of Ru using the pi-conjugated bridging ligand tetra-2-pyridyl-1,4-pyrazine (tppz), as well as mixed-ligand complexes with terpyridine end caps, and analyzed their electrochemical and spectroscopic properties, comparing them with modern computational electronic structure methods. The results suggest that the high degree of metal-metal interunit communication in these linear oligomers yields low HOMO-LUMO gaps, high delocalization, and the onset of "quasi-band" features, all indicative that these compounds should be excellent molecular wire materials. Recent spectroscopic and excited-state analyses of these and related compounds focus on optically accessible states, which ignore optically silent frontier electronic states more relevant to nanoelectronic applications.     

Synthesis of conjugated polymers containing anthracene moiety and their electro‐optical properties

Both fully conjugated polymer poly[2‐methoxy‐5‐(2‐ethylhexyloxy)‐1,4‐phenylene vinylene‐alt‐9,10‐anthrylene vinylene] [poly(MEHPV‐AV)] and conjugated/nonconjugated block copolymers poly(alkanedioxy‐2‐methoxy‐1,4‐phenylene‐1,2‐ethenylene‐9,10‐anthrylene‐1,2‐ehthenylene‐3‐methoxy‐1,4‐phenylene)[poly(BFMPx‐AV), (x = 4, 8, and 12)] were synthesized by Horner–Emmons reaction utilizing potassium tert‐butoxide. Of these synthesized polymers poly(BFMP4‐AV) and poly(BFMP8‐AV), which has four and six methylene groups as solubility spacer in the main chain exhibited liquid crystalline to isotropic transition in addition to the two first order transitions. Light‐emitting diode (LED)s made from the organic solvent soluble poly(BFMP12‐AV) as emitting layer showed blue shift in the emission spectrum compared to the one made from fully conjugated poly(MEHPV‐AV). Although poly(BFMP12‐AV) had higher barrier to the electron injection from cathode than poly(MEHPV‐AV), the luminance efficiency of LED made from poly(BFMP12‐AV) was about 25 times higher than the one made from poly(MEHPV‐AV), which had fully conjugated structure. LEDs fabricated by both poly(BFMP12‐AV) and poly(MEHPV‐AV) exhibited Stoke's shift in the range of 155 to 168 nm from the absorption maximum due to the excimer formation between the ground and excited state anthracene groups. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3173–3180, 2000     

Synthesis and characterization of soluble conjugated polymers having pyrene moiety in the main chain

Three new alternating conjugated polymers consisting of pyrene and 3‐dodecylthiophene ( PPyMT ), 4,4′‐didodecyl‐2,2′‐bithiophene ( PPyBT ), or 9,9‐didodecylfluorene ( PPyFlu ) moieties have been prepared using Suzuki coupling reaction or Sugimoto approaches. The polymers were readily soluble in common organic solvents and exhibited good thermal stability in nitrogen and air atmospheres. The structures and optical properties of the polymers were characterized by NMR, FTIR, XRD, UV–vis, and fluorescence spectroscopy. PPyMT and PPYBT showed blue‐light emission in solution, whereas PPyFlu performed blue‐light emitting in film state. The polymers exhibited an intermolecular aggregation and structural ordering due to pyrene–pyrene π–π stacking interaction. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010