Synthesis of Organic and Water Soluble Poly(1,4-phenylenevinylenes) Containing Carboxyl Groups: Living Ring-Opening Metathesis Polymerization (ROMP) of 2,3-Dicarboxybarrelenes

Carbo-mer of Barrelene: A Rigid 3D-Carbon-Expanded Molecular Barrel

After extensive studies of 1D and 2D skeletal carbo-mers based on C₈ π-conjugating dialkynylbutatriene units (DABs: ∼C≡C-(R)C=C=C=C(R)-C≡C∼) bridging sp or sp² centers in carbo-butene, carbo-xylylene or carbo-benzene derivatives, 3D versions are envisaged through carbo-barrelenes and partially reduced derivatives thereof where two or three DAB blades span a bridge between sp³ carbinol vertices or ether thereof. For R=Ph, stable representatives were synthesized through a pivotal [6]pericyclynedione, and extensively characterized by spectroscopic, electrochemical and crystallographic methods. Density functional theory calculations allow detailed analysis of structural and electronic features of the 7 Å high C₂₆ barrel-shaped molecules, and show that they can behave as cages for ionic species. Beyond aesthetical concerns, the results could open prospects of applications in host-guest supramolecular chemistry and single molecule charge transport.

Stereoretentive Ring-Opening Metathesis Polymerization to Access All-cis Poly(p-phenylenevinylene)s with Living Characteristics

Poly(p-phenylenevinylene)s (PPVs), a staple of the conductive polymer family, consist of alternating alkene and phenyl groups in conjugation. The physical properties of this organic material are intimately linked to the cis/trans configuration of the alkene groups. While many synthetic methods afford PPVs with all-trans stereochemistry, very few deliver the all-cis congeners. We report herein a synthesis of all-cis PPVs with living characteristics via stereoretentive ring-opening metathesis polymerization (ROMP). Exquisite catalyst control allows for the preparation of homopolymers or diblock copolymers with perfect stereoselectivity, narrow dispersities, and predictable average molar masses. All-cis PPVs can then serve as light-responsive polymers through clean photoisomerization of the stilbenoid units.

Direct laser writing of poly(phenylene vinylene) on poly(barrelene)

The ring-opening metathesis polymerization of barrelene (bicyclo[2.2.2]octa-2,5,7-triene) is described and well-defined fluorescent patterns with micrometer dimensions were created by direct laser writing on films of poly(barrelene-co-norbornene).

Grubbs-Hoveyda type catalysts bearing a dicationic N-heterocyclic carbene for biphasic olefin metathesis reactions in ionic liquids

The novel dicationic metathesis catalyst [(RuCl₂(H₂ITapMe₂)(=CH–2-(2-PrO)-C₆H₄))²⁺ (OTf⁻)₂] (Ru-2, H₂ITapMe₂ = 1,3-bis(2’,6’-dimethyl-4’-trimethylammoniumphenyl)-4,5-dihydroimidazol-2-ylidene, OTf⁻ = CF₃SO₃⁻) based on a dicationic N-heterocyclic carbene (NHC) ligand was prepared. The reactivity was tested in ring opening metathesis polymerization (ROMP) under biphasic conditions using a nonpolar organic solvent (toluene) and the ionic liquid (IL) 1-butyl-2,3-dimethylimidazolium tetrafluoroborate [BDMIM⁺][BF₄⁻]. The structure of Ru-2 was confirmed by single crystal X-ray analysis.

Poly(ω-bromoalkylnorbornenes-co-norbornene) by ROMP-hydrogenation: a robust support amenable to post-polymerization functionalization

The new polymers described have a saturated backbone and a bromo-substituent as the entry point to other functional groups of choice.

Synthesis of bottlebrush polymers via transfer-to and grafting-through approaches using a RAFT chain transfer agent with a ROMP-active Z-group

A novel dithiocarbamate chain transfer agent for reversible addition–fragmentation chain transfer polymerization with a directly polymerizable Z-group was synthesized and used to make bottlebrush polymers via multiple strategies.

Conjugated polyelectrolytes with pH-dependent conformations and optical properties

We report here the synthesis and characterization of two new conjugated polymers: poly{2,5-bis[3-(N,N-diethylammonium acetate)-1-oxapropyl]-1,4-phenylenevinylene} (P1') and poly{2,5-bis[3-(N,N,N-triethylammonium bromide)-1-oxapropyl]-1,4-phenylenevinylene} (P2). Both polymers exhibit unique pH-dependent optical properties in aqueous solution. These pH-dependent optical properties are attributed to the mutual electrostatic repulsions of positive charges pendent on the benzene rings. This electrostatic repulsion leads to an increased or decreased torsional angle in the conjugated backbone, thus affecting the effective conjugation length of these polymers. The UV-vis spectra of P1 in various pH solutions exhibit a near-isosbestic point, which indicates changes in the composition of the two distinct conformations (the charged and the neutral forms). The transition between the highly charged state and the neutral state was clearly observed in the UV-vis and photoluminescence studies on both P1 and P2. This transition is particularly sensitive in the pH range from 6.2 to 7.0, a range that would allow the detection of minor environmental changes. P2 has a quantum efficiency of 14% in water, which is considered to be relatively high among water-soluble PPVs.

Femtosecond Time Resolved Fluorescence Dynamics of a Cationic Water-Soluble Poly(fluorenevinylene-co-phenylenevinylene)

A recently synthesized cationic water-soluble poly(fluorenevinylene-co-phenylenevinylene) was studied by means of steady state and femtosecond time resolved upconversion spectroscopy in aqueous and EtOH solutions. Steady state spectroscopic measurements showed that the polymer emits at the blue-green spectral region and that aggregates are formed in concentrated polymer solutions. The fluorescence dynamics of the polymer in concentrated solutions, studied at a range of emission wavelengths, exhibited a wavelength dependent and multiexponential decay, indicating the existence of various decay mechanisms. Specifically, a rapid decay at short emission wavelengths and a slow rise at long wavelengths were observed. Both features reveal an energy transfer process from isolated to aggregated chains. The contribution of the energy transfer process as well as of the isolated chains and the aggregates on the overall fluorescence decay of the polymer was determined. The dependence of the energy transfer rate and efficiency on polymer concentration was also examined.

Synthesis of Sugar-Substituted Poly(phenylenevinylene)s

Sugar-containing PPVs, poly{2-[O-(2-acetamido-2-deoxy-beta-D-glucopyranosyl)]-5-methoxy-p-phenylenevinylene-alt-p-phenylenevinylene} (PPV-GlcNAc) and poly{2,5-bis-[O-(beta-d-glucopyranosyl)]-p-phenylenevinylene-alt-p-phenylenevinylene} (PPV-Glc(2)), were synthesized via Heck reaction of p-divinylbenzene (DVB) with O-glycosylated hydroquinones, 2,5-dibromo-4-methoxyphenyl 2-acetamido-3,4,6-tri-O-acetyl-2-deoxy-beta-D-glucopyranoside (3) and 1,4-bis(O-2,3,4,6-tetra-O-acetyl-beta-D-glucopyranosyl)-2,5-dibromobenzene (6), respectively. Acetyl protecting groups of the PPVs are completely removable under mild conditions (yield 69-87%). The structures were confirmed using (1)H NMR and IR spectra. Size exclusion chromatography (SEC) (eluent: DMF, polystyrene standards) measurements indicated that respective M(n) and M(w)/M(n) values of the obtained polymers are 4.49 x 10(3) and 2.3(5) (PPV-GlcNAc) and 3.86 x 10(3) and 1.3(9) (PPV-Glc(2)). These sugar-containing PPVs are soluble in water/DMF (8/2, v/v) and are recognized by Concanavalin A (Con A), D-glucose-binding protein. Blue shift of lambda(max) of the conjugated polymer backbone was confirmed when the glucose-substituted PPV interacts with Con A. Based on those binding properties, these results revealed that the obtained PPVs with pendant sugars have capabilities for detection of biological stimuli.

Synthesis and Hydrolysis Behavior of Side-Chain Functionalized Norbornenes

[reaction: see text] The stabilities of various functionalized norbornenes that are monomers for the ring-opening metathesis polymerization (ROMP) in aqueous solution were evaluated toward hydrolysis under a range of temperatures (37, 60, and 80 degrees C) and pH values (3-9). All monomers contain hydrolyzable linkages to pendant functional groups, and conclusions were drawn relating to how the chemical diversity of these pendant functional groups, in accordance with the pH and temperature variations, affect hydrolysis of the aforementioned linkages. The hydrolysis was monitored by reverse phase HPLC analysis, and/or NMR spectroscopy. As expected, monomers containing ester linkages were fairly labile at higher pH values, while acetal-based linkers were cleaved at lower pH values. Beta-amino ester groups experienced a significant increase in hydrolysis rate, while carboxylic acid-containing monomers did not follow any clear trend. Saccharide-containing monomers exhibited unique behaviors for various pH values and temperature ranges.

Direct synthesis of soluble, end-functionalized polyenes and polyacetylene block copolymers

The ring-opening metathesis polymerization (ROMP) of 1,3,5,7-cyclooctatetraene (COT) in the presence of a chain transfer agent (CTA) with a highly active ruthenium olefin metathesis catalyst resulted in the formation of soluble polyenes. Small molecule CTAs containing an internal olefin and a variety of functional groups resulted in soluble telechelic polyenes with up to 20 double bonds. Use of polymeric CTAs with an olefin terminus resulted in polyacetylene block copolymers. These materials were subjected to a variety of solution and solid phase characterization techniques including (1)H NMR, UV/vis, and FT-IR spectroscopies, as well as MALDI-TOF MS and AFM.

Scope and limitations of a new highly selective synthesis of unsymmetrical monomers for the synthesis of precursors toward poly(arylenevinylene)s

In our laboratory a precursor route to poly(p-phenylenevinylene) derivatives is developed in which unsymmetrically substituted p-xylene derivatives, possessing a benzylic sulfinylalkyl group, are used as monomers. Because of this unsymmetry, we were forced to investigate thoroughly the synthesis of these sulfoxides, as we start from symmetric and readily accessible molecules, namely, bis(halomethyl)-p-xylene derivatives. In a former publication, a new extremely effective route for the production of these unsymmetrically substituted sulfinyl monomers was presented. This paper expands upon these previously reported results. To examine the scope and limitations of this elegant route, this new method was applied to the synthesis of various derivatives not included in the initial work.