Oligo Phenylenevinylene Research Articles

Polaron formation and symmetry breaking

In a molecular semiconductor, a charged molecule experiences a lattice relaxation which reorganizes it into a cation or an anion-radical. This species is not, in general, a polaron. By using calculations of the geometry and the electronic structure both ab initio and at the semi-empirical levels, we have explored the conditions of polaron formation in a molecular model system: oligophenylene–vinylenes, PVs of increasing sizes. The symmetry breaking occurs at sizes larger than five monomers for the anion and six monomers for the cation. The driving force for this process is primarily the charge–lattice coupling through the stretching mode at 1600 cm −1.

Luminescence of Conjugated Molecules Confined in Nanochannels

The optical properties, molecular orientations and host-guest ratios of a series of p,p′-disubstituted oligophenylenevinylenes (OPVs), incorporated in the nanochannels of perhydrotriphenylene, are investigated by polarized fluorescence and UV absorption spectroscopy. The spectral positions and fine-structures of the fluorescence bands are very similar to those obtained in solution, thus indicating only weak interactions within the channels. In three-dimensional arrangements, the spectra are additionally red-shifted due to an increase of intermolecular interactions. Strongly red-shifted emission spectra due to intermolecular vibronic coupling are observed for films and single crystals of p,p′-dicyano-distyrylbenzene with π,π-stacking of the molecules.

A supramolecular oligophenylenevinylene–C60 conjugate

A new methanofullerene derivative with an ammonium subunit has been prepared and its ability to form a supramolecular complex with an oligophenylenevinylene (OPV)–crown ether conjugate evidenced by NMR, electrospray mass spectrometry and luminescence experiments.

Synthesis and Functional Properties of Donor−Acceptor π-Conjugated Oligomers

Novel donor−acceptor oligophenylenevinylenes (OPVs) bearing an electron-donating 2-(2-butoxyethoxy)ethoxy group at one end and various electron-withdrawing groups including alkylsulfonyl, cyano, and nitro functionalities at the other end have been synthesized for investigation of structure−functional property relationships. Depending on the nature of the electron-withdrawing group, the newly synthesized donor−acceptor OPVs can exhibit an efficient light-emitting property or a large photovoltaic effect. The asymmetrically disubstituted OPV bearing 2-(2-butoxy-ethoxy)ethoxy-hexylsulfonyl functionalities possesses superior molecular properties for light-emitting applications than the symmetrically 2-(2-butoxyethoxy)ethoxy-disubstituted counterparts. In addition, our first observation and investigation on the photovoltaic response in polyalkyleneoxy-nitro disubstituted OPV series is reported. The spectral responsivity of the photovoltaic device corresponds to the absorption characteristics of the oligomer. Most importantly, the photocurrent responsivity increases with an extension of the conjugated length of the oligomer.

Alkoxysilyl substituted oligo(phenylenevinylene)s: chromophores with reactive side chains

The synthesis and properties of highly luminescent oligo(phenylenevinylene)s (OPV) with curable alkoxysilyl groups are described. Two diethoxymethylsilane moieties are connected directly or through flexible spacers to monodisperse alkoxy-substituted OPVs via hydrosilylation of alkinyl and allyloxy groups, Heck reaction with silylstyrene or condensation of aldehydes with aminopropyl silanes. Hydrolysis of the alkoxysilanes yields silanols condensing to curable three-dimensional networks, thus allowing the transformation of small molecules to transparent and fluorescent films with well-defined chromophores.

Synthesis of Dumbbell‐Shaped Bis‐(pyrazolino[60]fullerene)‐oligophenylenevinylene Derivatives.

Abstract Symmetrically substituted oligophenylenevinylene (OPV) derivatives bearing terminal p-nitrophenyl-hydrazone groups have been prepared and used for the synthesis of dumbbell-shaped bis-(pyrazolino[60]fullerene)-OPV systems.

Copper(i) complexes of 1,10-phenanthroline–oligophenylenevinylene conjugates

Copper(I) complexes obtained from 2,9-diphenyl-1,10-phenanthroline derivatives substituted with an oligophenylenevinylene (OPV) unit have been prepared. Very strong intramolecular quenching of the lowest OPV excited state by the copper(I) complex has been evidenced in these multicomponent systems. The mechanism of the photoinduced process depends on the length of the conjugated OPV backbone. Upon irradiation of the OPV unit, quantitative sensitization of the Cu(I) complex has been evidenced for the system substituted with trimeric OPV units, but not for those with tetrameric OPV units. Therefore, energy transfer is the sole quenching mechanism for the former complex, whereas electron transfer might play a role in the latter case. This different behaviour is ascribed to the slightly increased electron-accepting character of the OPV tetrameric unit when compared to the corresponding trimer. As far as excited state deactivation in the copper(I) complex is concerned, the hybrid compounds exhibit the characteristic luminescence band attributable to the deactivation of low-lying metal-to-ligand charge transfer (MLCT) excited state(s). As shown by the comparison with a model copper(I) complex, the OPV units have no influence on the MLCT excited state(s) deactivation at room temperature in fluid solutions. In contrast, they are capable of acting as “hooks” when the measurements are performed at low temperature in a rigid matrix, thus reducing the excited state distortion of the copper(I) complex. As a result, at 77 K the MLCT emission spectral shapes and band maxima of the hybrid compounds are no longer identical to those of the corresponding model complex.

Oligo(phenylenevinylene)s end-capped with phenothiazine or triphenylamine

AbstractMonodisperse oligo(phenylenevinylene)s end-capped with arylamines have been prepared via Horner Olefinations from bisphosphonates and arylaminobenzaldehydes. The influences of the conjugation length, different arylamine end groups, and of side chains with various electronic character on the electrical and optical properties of the chromophores are investigated. The elongation of the π-conjugated segment from 3 to 5 rings gives rise to bathochromic shifts of the electronic spectra and a slight increase of the oxidation potential. The same but more pronounced is true when the central electron donating ethers are replaced by the strong acceptor alkylsulfone. The electronic spectra of chromophores with triphenylamine and with N-alkylphenothiazines as end groups are quite similar, but the heterocyclic unit reduces the oxidation potential. The incorporation of a chromophor into a segmented copolymer has only negligible effect on the optical and electrical properties.

Erratum: “Absorption and emission in pinwheel aggregates of oligo-phenylene vinylene molecules” [J. Chem. Phys. 114, 5376 (2001)

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Synthesis of dumbbell-shaped bis-(pyrazolino[60]fullerene)-oligophenylenevinylene derivatives

Symmetrically substituted oligophenylenevinylene (OPV) derivatives bearing terminal p-nitrophenyl-hydrazone groups have been prepared and used for the synthesis of dumbbell-shaped bis-(pyrazolino[60]fullerene)-OPV systems.

Synthesis and Third-Order Nonlinear Optical Properties of End-Functionalized Oligo-Phenylenevinylenes

Novel homologues series of the highly soluble and coplanar oligo-phenylenevinylenes (OPV), containing up to eight phenyl rings symmetrically end-functionalized with multiple polyalkyleneoxy substituents (OPV(n)-OR), and containing up to six phenyl rings, asymmetrically end-functionalized with polyalkyleneoxy and alkylsulfonyl substituents (OPV(n)-ORSO), were synthesized for structure-third-order optical nonlinearities investigation. The theoretical molecular nonlinearities, Acalc at zero frequency calculated by the Finite Field method in MOPAC6 and the time-dependent coupled perturbed Hartree-Fock method within the MOPAC93 package showed a similar trend of the increase with an extension of chain length. However, the predicted Acalc differences between the symmetrically and asymmetrically disubstituted OPVs are relatively minor. The real part (Areal) and the imaginary part (Aimag) of the molecular nonlinearities of the newly synthesized OPVs were determined by the closedand open-aperture Z-scan technique at 800 nm with 100-fs laser pulses in two different solvents. It is evidenced that solvent effect plays an important role in determining thirdorder nonlinearities of molecules in solution. Although the absorption behavior of these OPVs is very similar in chloroform and tetrahydrofuran (THF), the sign reversal of Areal from positive to negative appears earlier in chloroform than in THF. The A enhancement due to asymmetric substitution in lower homologues of these oligomers is significant; however, such contribution becomes less pronounced in the higher homologues. In addition, the asymmetrically disubstituted OPVs show a faster convergence of jAj than the symmetrically disubstituted series. A very large jAj value, up to 2.5 10 -32 esu, was obtained in the symmetrically disubstituted OPVs.

The synthesis and condensation of oligo(phenylenevinylene)s with alkoxysilyl end groups

Monodisperse alkoxylated oligo(phenylenevinylene)s with 3, 4, or 5 benzene rings were connected to reactive di- and triethoxysilanes, either directly or via flexible spacers. Aminopropylsilanes were condensed with stilbenoid aldehydes and subsequently reduced to amines, for the direct, rigid connection, the Heck reaction and also cross-metathesis with vinyl silanes proved to be successful routes. Hydrolysis of the ethoxysilanes leads to polymerisable cyclosiloxanes or curable three-dimensional networks with pendent chromophores.

Absorption and emission in oligo-phenylene vinylene nanoaggregates: The role of disorder and structural defects

The impact of exciton-phonon coupling and defect states on the photophysical properties of p-distyrylbenzene nanoaggregates is studied numerically. Molecular packing within aggregates is based on the known crystal structures of poly-p-phenylene vinylene (Type I) and the five phenyl group oligomer (Type II). Calculations of absorption and emission are conducted using a reduced basis set consisting of all one- and two-particle vibronic states. The calculated spectra are very similar for both aggregate types, the only substantial difference being the polarization directions for the J-band and 0-0 emission line. Under the noninteracting domains approximation the calculated nanoaggregate absorption spectrum is in excellent agreement with experiment, assuming an exciton coherence length of approximately 20 Å. In the calculated emission spectrum the 0-0 emission is uniquely polarized compared with the rest of the vibronic progression, also in agreement with experiment. The 0-0 emission intensity in defect-free Type I and II aggregates is linearly proportional to the total number of molecules, becoming superradiant beyond a certain size threshold. The 0-0 emission is highly sensitive to stacking faults and dislocations. These defects account for the measured Stokes shift, but quench the 0-0 emission (and superradiance) while only slightly affecting the rest of the vibronic progression. Adding orientational point defects to an aggregate with stacking faults and/or dislocations enhances the 0-0 oscillator strength, bringing the 0-0 emission intensity into good agreement with experiment.

Photovoltaic devices from fullerene--oligophenyleneethynylene conjugates.

Exploitation of the particular electronic properties of fullerenes for solar energy conversion has become a field of intensive investigation. The modification of semiconductor or metal electrodes with fullerene thin films has revealed promising photoelectrochemical properties. Good solar energy conversion efficiencies have also been obtained with sandwich-type conjugated polymer/fullerene heterojunctions. As part of this research, we have recently shown that fullerene derivatives, in which an oligophenylenevinylene (OPV) group is attached to C60, can be incorporated into photovoltaic cells. This molecular approach for solar energy conversion appears to be particularly interesting, since the bicontinuous network obtained by chemically linking the hole-conducting OPV moiety to the electron-conducting fullerene subunit prevents any problems arising from bad contacts at the junction, as observed for polymer/C60 blends. Furthermore, this new synthetic approach also offers great versatility for designed tuning of the photovoltaic system. We now report the preparation of plastic solar cells from fullerene ±oligophenyleneethynylene (OPE) derivatives 1 ±4. For compounds 1 and 2, the efficiencies of the resulting photovoltaic devices are similar to those prepared from corresponding fullerene ±OPV conjugates. Interestingly, by increasing the donating ability of the

Oligo(phenylenevinylene)s with reactive side chains: amine- and amide-bound alkoxysilanes

Strongly luminescent oligo(phenylenevinylene) chromophores with monodisperse chain lengths are connected via short spacers containing a secondary amine or amide with di- and tri-ethoxysilane groups. The alkoxysilanes can be hydrolysed and condensed to cyclic and linear oligomers with high film forming capability and are also interesting functional units for hybrid materials for electro-optical applications. The luminescence properties in the solid state are influenced by hydrogen bonding of the amides resulting in strong hypsochromic shifts. The synthesis of the title compounds, their oligomerisation and the electronic spectra in the solution and solid state are presented.

Polarizability effects and energy transfer in quinquethiophene doped bithiophene and OPV films

Oligothiophene films ( nT) and oligophenylenevinylene (OPV) nanoparticles are doped with quinquethiophene (5T) and investigated by steady-state and time-resolved fluorescence spectroscopy. In 2T films and highly ordered nanoparticles of unsubstituted OPVs, the fluorescence excitation spectra of 5T show vibrational structure, indicating a small distribution of ground-state geometries. The anisotropic effective polarizabilities of the host materials are obtained from the spectral positions of the fluorescence maxima of 5T. In the highly disordered nanoparticles of tert-butyl substituted OPVs, the vibrational structure of 5T excitation spectra is lost and the polarizability is isotropic. Efficient host–guest energy transfer is observed upon excitation of the host. The overall fluorescence quantum yield φ F increases fivefold upon doping 2T films at doping levels of x 5T=5×10 −4. In OPV films, φ F is almost independent of the doping level, probably due to the competition of energy and electron transfer between host and dopant.

W(CO) 6-Mediated desulfuroligomerization of bis-dithioacetals. New synthesis of substituted oligo(phenylene–vinylenes)

Treatment of bisdithioacetals of 1,4-diaroylbenzenes ( 4) with W(CO) 6 in refluxing chlorobenzene afforded the corresponding substituted oligophenylenevinylenes (OPVs) ( 5). Average molecular weights determined by GPC indicate that OPVs 5 have 5–13 repetitive substituted phenylenevinylene units with narrow polydispersities. Emission in the blue–green to green region was observed for these OPVs depending on the nature of the substituent. The electron-donating alkoxy substituent shifted the emission to the longer wavelength whereas the electron-withdrawing trifluoromethyl group caused a blue shift in the fluorescence spectra.

Absorption and emission in pinwheel aggregates of oligo-phenylene vinylene molecules

The effects of exciton-vibrational coupling and point defects on the absorption and emission of distyrylbenzene nanoaggregates are treated theoretically. Two aggregate types based on a two-dimensional array of cyclic tetramers (pinwheels) are considered: type A aggregates, composed of chiral pinwheels, and type B aggregates, composed of achiral pinwheels. The low-energy vibronic features in the experimental excitation spectrum arise from vibrationally dressed K=(0,0) excitons, while the more intense blue shifted H-band is due to nearly free K=(0,0) excitons. The K=(0,0) features are polarized primarily along the herringbone plane normal. The lowest Davydov component is polarized in the herringbone plane and is due to the lowest energy K=(π,π) exciton. This state is also responsible for the aggregate emission. The 0-v peaks for v>0 are mainly due to indirect transitions to the ground electronic state containing v phonons, with wave vector sum equal to (π,π). These peaks are largely independent of defect fraction and are polarized primarily along the herringbone plane normal. In stark contrast, the 0–0 emission critically depends on the concentration of point defects and is polarized entirely in the herringbone plane. This wavelength dependent emission polarization is in full agreement with experimental observations. Type A aggregates are weakly emissive, with the 0–0 emission peak vanishing in defect-free aggregates and increasing with defect concentration. The reverse holds for type B aggregates: the 0–0 intensity scales with the number of molecules in the aggregate and decreases with defect concentration. Sufficiently large type B aggregates are superradiant, and may be used to enhance the quantum yield in optical devices such as light-emitting diodes.

Photoconductivity in ultrathin oligo(phenylene vinylene) films during vapor deposition

The photoconductivity (PC) of oligo(phenylene vinylene) (OPV) films during vapor deposition was measured as a function of the chain length of the OPV molecules. The films show PC even in sub nanometer thicknesses immediately after deposition. With short OPVs, the PC vanishes completely within 10 minutes, whereas with longer OPVs, the PC signal keeps rising after deposition. By comparison with optical absorption, luminescence and light scattering experiments, we show that the effects can be ascribed to a transformation from amorphous films to aggregates and microcrystallites.

Calix[4]oligophenylenevinylene: a new rigid core for the design of π-conjugated liquid crystalline derivatives

The synthesis and the liquid crystalline properties of a new class of conjugated derivatives that assembled four oligophenylenevinylene (OPV) moieties arising from a calix[4]arene core are described. Photophysical investigations also revealed strong electronic coupling between the four OPV fragments of the calix[4]OPV derivative.