Synthesis of Poly(arylenevinylene)s with Fluorinated Vinylene Units

Poly(arylenevinylene) polymers bearing fluorine atoms in the vinylene units were obtained by a Stille cross-coupling reaction of (E)-(1,2-difluoro-1,2-ethenediyl)bis(tributylstannane) with diiodoaryl derivatives. The introduction of fluorine atoms on the double bond of the stannane leads to polymers with relatively high molecular weights. Furthermore, the presence of fluorinated vinylene units changes the optical properties of the polymers and shifts the emission towards the blue region of the visible spectrum. A fluorinated analogue of MEH-PPV was obtained, and it shows photoluminescence that is considerably blueshifted, also in the solid state, relative to that found for nonfluorinated MEH-PPV and to other PPVs with fluorinated double bonds.

European Journal of Organic Chemistry DOI: 10.1002/ejoc.200700815

Catalytic Hunsdiecker Reaction and One-Pot Catalytic Hunsdiecker–Heck Strategy: Synthesis of α,β-Unsaturated Aromatic Halides, α-(Dihalomethyl)benzene

The reaction of α,β-unsaturated aromatic (or heteroaromatic) carboxylic acids with N-halosuccinimides (1 equiv.) and catalytic tetrabutylammonium trifluoroacetate (0.2 equiv.) in dichloroethane results in facile halodecarboxylation affording the corresponding (E)-halides in good to excellent yields. A similar reaction, but with 2 equiv. of N-halosuccinimides in acetonitrile-water (1:1 v/v) results in the exclusive formation of the corresponding α-(dihalomethyl)benzenemethanols. Furthermore, a one-pot strategy has been developed combining catalytic Hunsdiecker reaction (using tetrabutylammonium trifluoroacetate in dichloroethane) and Heck coupling (using palladium acetate/triethylamine/triphenylantimony/dichloroethane) for the synthesis of 5-aryl-2,4-pentadienoic acids, esters and amides in moderate to good yields. The natural product piperine and pipergualamine has been synthesized via the above route. Mechanistic and theoretical studies (via AM1 calculations) provide a useful insight into the mechanism of the present halodecarboxylation reaction, suggesting an ionic pathway involving the attack of the halogenium ion across the carbon–carbon double bond, triggering the elimination of carbon dioxide.

Tetrahedron doi:10.1016/S0040-4020(99)01035-2

Electron and Hole Dynamics on Isolated Chains of a Solution-Processable Poly(thienylenevinylene) Derivative in Dilute Solution

Advanced Materials

10.1002/adma.200400879

External Electric Field Effects on State Energy and Photoexcitation Dynamics of Diphenylpolyenes

External electric field effects on state energy and photoexcitation dynamics have been examined for para-substituted and unsubstituted all-trans-diphenylpolyenes doped in a film, based on the steady-state and picosecond time-resolved measurements of the field effects on absorption and fluorescence. The substitution dependence of the electroabsorption spectra shows that the dipole moment of the substituted stilbene in the Franck-Condon excited state becomes larger with increasing difference between the Hammet constants of the substituents. Fluorescence quantum yields of 4-(dimethylamino)-4'-nitrostilbene and 4-(dimethylamino)-4'-nitrodiphenylbutadiene are markedly reduced by an electric field, suggesting that the rates of the intramolecular charge transfer (CT) from the fluorescent state to the nonradiative CT state are accelerated by an external electric field. The magnitude of the field-induced decrease in fluorescence lifetime has been evaluated. The isomerization of the unsubstituted all-trans-diphenylpolyenes to the cis forms is shown to be a significant nonradiative pathway even in a film. Field-induced quenching of their fluorescence as well as field-induced decrease in fluorescence lifetime suggests that the trans to cis photoisomerization is enhanced by an electric field.

J. Am. Chem. Soc., 127 (19), 7041 -7052, 2005

Synthesis of Regioregular Poly(p-phenylenevinylene)s by Horner Reaction and Their Regioregularity Characterization

A new synthetic route was developed to obtain highly regioregular poly[(2-methoxy-5-alkyloxy)-1,4-phenylenevinylene]s (PPVs) by the Horner reaction using asymmetrically functionalized monomers. The polymers showed good solubility in chlorobenzene at over 100 C. The high regioregularity of the polymers was confirmed by ¹H NMR quantitative analysis using chlorobenzene-d₅ as solvent, which was developed for the first time in this study. Assignment of the ¹H NMR peaks was conducted by synthesizing four novel model compounds for PPV. UV-vis, fluorescence spectra, and XRD data revealed that these regioregular PPVs have higher crystallinity compared to regiorandom PPVs in the solid state.

Macromolecules, 40 (18), 6521 -6528, 2007. 10.1021/ma0628836